Muscles, Nerves and Movement Third edition Barbara Tyldesley

Support and Propulsion 143 originates on the shaft of the fibula and inserts into the distal phalanx of the big toe. The extensor digitorum longus has fibres attached to the shafts of the tibia and fibula and the interosseous mem- brane in between. The common tendon passes over the front of the ankle and divides into four, each inserting via an extensor expansion to the toes, in a similar way to the extensors of the fingers. A fifth tendon is sometimes present, which is the tendon of peroneus tertius, inserting into the base of the fifth metatarsal. Two transverse bands of fascia over the anterior side of the leg above the ankle hold the tendons of the dorsiflexors in position during movements of the ankle (Fig. 8.12). Propulsion So far, movements of the lower limb in support and Fig. 8.13 Gluteus maximus, right posterior. swing have been described. This section will look at the muscles of the thigh and leg that exert force are often damaged in athletes in the explosive against the ground to move the body forwards and propulsion movement from the position of leaning upwards. forwards at the starting blocks. Muscle groups used in propulsion movements are: Extensors of the knee The knee extensors are the quadriceps femoris • the hip extensors group, composed of four muscles on the anterior • the knee extensors of the thigh. The individual muscles are: the • The ankle plantar flexors. rectus femoris, the most superficial in the midline; the vastus medialis on the medial side; the Extensors of the hip vastus lateralis on the lateral side; and vastus inter- The main hip extensor is the gluteus maximus (Fig. medius, which lies deep to the rectus femoris. 8.13). The most superficial muscle of the gluteal These muscles can be clearly seen in athletes and group, the gluteus maximus is the largest muscle in footballers, when the vasti in particular become the body. It can be seen when lying prone or stand- enlarged in response to weight training. ing upright, forming the curve of the buttocks. The gluteus maximus extends the hip to lift the body in • SIT on a chair and put your hands on the top of standing up from sitting and in climbing stairs. your thighs. Now stand up slowly and feel the quadriceps in action. Pause in standing and feel the The extensive origin of the gluteus maximus tension decrease. Then sit down slowly to feel the spreads from the posterior corner of the iliac crest quadriceps in action again. The muscle is working across the posterior side of the sacrum and coccyx, concentrically to extend the knee and lift the body with some fibres attached to the fascia of the lower upwards, then working eccentrically against grav- back (thoracolumbar fascia) and to the sacro- ity as the knee flexes and the body lowers to the seat tuberous ligament of the pelvis. All of the fibres of the chair again. pass downwards and laterally over the posterior side of the hip joint. The main insertion of the mus- cle is into the iliotibial tract, with the remaining fibres passing deeply to attach to the gluteal tuberosity on the posterior shaft of the femur. The hamstring muscles (see section on swing) also have an extensor action at the hip, particularly when the trunk is flexed forwards. The hamstrings

144 Muscles, Nerves and Movement The quadriceps group can be seen in anterior view prevent lateral displacement of the patella at the in Figure 8.10, with the exception of the vastus end of knee extension. intermedius which lies deep to the rectus femoris. The quadriceps group is a powerful extensor The rectus femoris is the only part of the quadri- of the knee, and the rectus femoris alone has a ceps that passes over the hip joint. This muscle is weak flexor action on the hip. Acting with the attached by two heads, one from the anterior infe- gluteus maximus, the quadriceps raise the body rior iliac spine and the other from just above the from sitting and squatting. When the knees are acetabulum. The three vastus muscles surround flexed at an angle less than a right angle, the quadri- the shaft of the femur. The vastus medialis begins ceps has to develop a force of 4–5 times body posteriorly on the spiral line and down the medial weight to hold the position. The knees are under side of the linea aspera. The fibres wrap round great stress when the body is raised from a low medially to approach the knee. The vastus lateralis squat position, since the line of body weight is some is attached posteriorly to the lateral side of the linea distance from the knee joint (Fig. 8.15) (see also aspera and wraps round the lateral side of the Chapter 2). femoral shaft. The vastus intermedius originates on the anterior and lateral shaft of the femur. In the When the knee is injured, or after a period of transverse section of the thigh in Figure 8.14, bed rest, the quadriceps wastes very rapidly. The the quadriceps can be seen around three sides of strength of this muscle is restored by lying supine the shaft of the femur. and lifting one leg at a time with the knee held in extension. All four muscles of the quadriceps meet at the patella on the front of the knee, and insert by a Plantar flexors of the ankle common tendon, the ligamentum patellae, to the The ankle plantar flexors raise the heel from the anterior tubercle of the tibia. The ligamentum ground and lift the body upwards or forwards in a patellae provides extra stability for the knee joint ‘push-off’ movement. The calf muscles, attached by on the anterior side where the capsule is absent. the Achilles tendon to the heel, are active in this The lower horizontal fibres of the vastus medialis movement. Fig. 8.14 Relationship of the muscles of the thigh, transverve section of the right thigh at the upper third level.

Support and Propulsion 145 flexors lying underneath the gastrocnemius and soleus. The names of the two long flexors are relat- ed to their action on the toes, and they originate on the posterior shaft of the tibia and fibula (hal- lucis to the fibula, and digitorum to the tibia). The tibialis posterior lies deep to these two and origi- nates on the shaft of both the tibia and the fibula. The tendons of all three muscles pass round the medial side of the ankle to enter the sole of the foot and insert on the plantar surface of the bones of the foot (Fig. 8.16b). Fig. 8.15 Change in the line of gravity in moving from Clinical note-pad 8E: Avulsion of the (a) low squat to (b) high squat. Achilles tendon The Achilles tendon may sustain spontaneous avulsion (severing), with a feeling of being struck just above the heel and an inability to tiptoe. This occurs in tennis players and athletes who rely on thrust at the ankle, and sometimes in middle age when the tendon has degenerated. • STAND on your toes and feel the calf muscles con- FUNCTIONS OF THE FOOT tracting. The muscles are also working eccentrically when you lower your heels to the ground. The foot is a relatively small area that makes con- tact between the body weight and the ground. The When the calf muscles are weak, the spring and lift surface of the ground may be rough, smooth, hard, of the lower limb is lost. soft, level or sloping, and the sole of the foot has to be able to accommodate all of these. The weight The gastrocnemius and soleus, which form the of the body above compresses the parts of the foot calf of the leg, are the superficial muscles active in in different directions and the foot resists this plantar flexion of the ankle (Fig. 8.16a). deformation. The gastrocnemius is attached by two heads to Another feature of the foot is flexibility and the posterior surface of the femur, one above each strength to provide spring and lift during move- femoral condyle. The soleus attaches below the ment. At each step in walking, 60% of the time is knee, across the soleal line on the posterior shaft spent supporting the body weight and providing of the tibia, and to the head and shaft of the fibu- momentum for moving the body forwards. In walk- la. Both muscles join to form the very strong ing up stairs and jumping, strong propulsive forces Achilles tendon attached to the posterior surface must be generated by the ankle and transmitted of the calcaneum. The length of the calcaneum through the foot to lift the body upwards. The behind the axis of the ankle joint gives good lever- skin of the sole of the foot monitors the pressure age to the calf muscles. There is a small muscle, the on it exerted by the position of the upright body plantaris, lying between the gastrocnemius and the above and the variations in the surface of the soleus. The short belly of this muscle originates ground below. This information is transmitted to above the lateral condyle of the femur, near to the the brain via the somatosensory system, and lateral head of the gastrocnemius, and becomes a adjustments to posture are made to keep the body thin tendon just below the knee joint. The tendon in balance. In this way, the foot is one of the fac- passes down the length of the calf to insert on to tors that regulate the posture of the body (see the calcaneum in the Achilles tendon. Chapter 11). The flexor digitorum longus, flexor hallucis longus and tibialis posterior are the deep plantar

146 Muscles, Nerves and Movement Fig. 8.16 Ankle plantar flexors, right posterior: (a) superficial, gastocnemius and soleus; (b) deep muscles. In summary, the functions of the foot are: The ankle joint between the lower end of the tibia and fibula, articulating with the convex trochlear • to accommodate to variations in the supporting surface of the talus, moves the foot in dorsiflexion surface during standing and locomotion and plantar flexion. • to provide spring and lift in body movement There are two important joints between the • to provide sensory information for the regulation tarsal bones that move the foot in other directions. of body posture in standing and moving. The subtalar joint is formed by a concave facet on the undersurface of the talus, articulating with Joints and movements of the foot a convex surface on the upper surface of the cal- caneum. Strong ligaments unite the bones, partic- • LOOK at the bones on the foot seen in lateral and ularly an interosseous ligament that acts as a medial view in Appendix I. fulcrum for movements of the foot on the leg.

Support and Propulsion 147 The midtarsal joint is formed by the arti- The movements of the toes occur at the meta- culations between the talus, calcaneum and navic- tarsophalangeal and the interphalangeal joints. ular medially, together with that between the Movements of flexion, extension, abduction and calcaneum and the cuboid laterally. This forms an adduction occur at the metatarsophalangeal irregular joint extending from one side of the foot joints at the ball of the foot. The abduction to the other. The subtalar and midtarsal joints and adduction movements are seen clearly in the co-operate in the movements of the foot. feet of a baby, but become restricted by wearing shoes later. As in the hand, the interphalangeal The movements of the foot that occur between joints of the toes move in flexion and extension the tarsal bones are known as inversion and only. eversion (Fig. 8.17a, b). Muscles moving the foot In inversion, the foot turns so that the sole faces inwards when the foot is off the ground, the medial The muscles acting on the foot originate in the leg border is raised and the lateral border is depress- and pass around the ankle to insert into the bones ed. This movement shifts the body weight to the of the foot. Like the hand, the foot also has intrin- lateral side of the foot when weight bearing. sic muscles that begin and end in the foot. The arrangement of the intrinsic muscles of the foot is In eversion, the opposite movement occurs. The similar to that in the hand. Children with malfor- sole of the foot faces outwards, with the lateral bor- mation of the upper limb may develop the muscles der raised and the medial border depressed, when of the foot to take over the manipulative functions the foot is off the ground. This movement shifts the of the hand. weight towards the medial side of the foot in weight bearing. The dorsiflexors and plantar flexors of the ankle have already been described. Most of the movement in inversion and eversion occurs at the subtalar joint. This joint also allows Invertors and evertors of the foot the side-to-side adjustment of the line of gravity in The invertors of the foot are the tibialis anterior standing. The midtarsal joint is more important in and tibialis posterior. The tibialis anterior is also anterior to posterior adjustments in the upright one of the dorsiflexors already described (see Fig. posture. Inversion and eversion are important 8.12). The tibialis posterior is the deepest muscle when putting the foot down on sloping ground or of the calf, originating on the posterior shaft of the on an irregular surface. tibia and fibula. The tendon of this muscle passes round the medial side of the ankle and it inserts on • REMEMBER how difficult it is to walk on loose the plantar surface of the navicular and adjacent shingle, on a rocky hillside or down the aisle of a tarsal bones (Fig. 8.18a). The relationship between moving train. the tendons of the tibialis anterior and posterior on the medial side of the foot can be seen in (a) (b) Figure 8.18b. Fig. 8.17 Movements of the foot: (a) inversion; The evertors of the foot are the peroneus longus (b) eversion. and peroneus brevis. These two muscles are attached to the lateral shaft of the fibula and their tendons pass round the lateral side of the ankle. The tendon of the peroneus brevis ends at the base of the fifth metatarsal. The peroneus longus turns under at this point and crosses the sole of the foot in a groove on the cuboid bone, to reach the medi- al cuneiform and the base of the first metatarsal on the medial side of the foot (Fig. 8.19). When the evertors are weak, lateral stability of the ankle is lost and the lateral ligament of the

148 Muscles, Nerves and Movement Fig. 8.18 (a) Tibialis posterior, right leg and foot; (b) tendons of tibialis anterior and posterior, right ankle medial. ankle is often torn. When the foot is in contact with out on the floor: (i) sitting on a chair, i.e. non- an uneven surface, the movements of inversion and weight bearing; (ii) standing upright; and (iii) walk- eversion, together with the actions of the intrinsic ing for several steps. Note the variation in the muscles of the foot, allow the foot to adjust to the pattern of footprints in (i), (ii) and (iii). Compare ground and stabilise the ankle. Shoes reduce your footprints with those of other students and the amount of adaptation required, but the foot note any individual differences. and the shoe still have to accommodate sloping ground and avoid slipping on wet or icy surfaces. The change seen in the footprints shows an increase in the area of foot in contact with the The arches of the foot ground as the force of the body weight on the feet increases in the change from sitting to standing to The bones of the foot form a complex arched walking. In all of the prints, the heel and ball of the mechanism that combines stability with flexibility. foot will be seen. The lateral border of the foot will be present when the foot is weight bearing. The • REVISE the bones of the foot. Place an articulat- medial border of the foot remains absent, except ed skeleton of the foot on a flat surface. Note which when there is abnormal flattening of the foot. bones are in contact with the table, and which bones are wholly or partly raised above the surface. Looking at the bones of the foot and the foot- prints, it can be seen that the foot is arched in dif- • STAND the feet in a tray of water-soluble paint, ferent directions. A longitudinal arch from the heel then make footprints on a sheet of lining paper laid to the ball of the foot is easy to recognise. The foot

Support and Propulsion 149 Fig. 8.20 Arches of the foot, right medial. Fig. 8.19 Peroneus longus and brevis, right leg lateral. and metatarsals 1, 2 and 3. The highest part of the arch is the talus, which sits on the calcaneum is also arched transversely across the distal row of supported by a shelf on the medial side known tarsals and the metatarsals (Fig. 8.20). as the sustentaculum tali. • Lateral longitudinal arch: this arch also begins Ligaments bind the bones of the foot together at the calcaneum and extends along the lateral and provide the main factors supporting the arch- side of the foot to the cuboid and metatarsals es in standing. During movement, it is the muscles 4 and 5. There is considerable stress on this of the leg acting as slings from above, and the arch during running, when the body weight intrinsic muscles of the foot acting as bowstrings is transferred along the lateral border of the across the base of the arches, that maintain the foot and on to the big toe. The shoes of a arches. The height of the arches varies during dif- marathon runner, which are often worn down on ferent phases of locomotor movements, particularly the outer border, show how high this stress the medial part of the longitudinal arch. can be. • Transverse arch: the foot is most arched in the The bony compartments of the arches are as transverse direction across the distal row of follows. tarsals: the three cuneiforms and the cuboid. The metatarsals are also arched transversely, the • Medial longitudinal arch: this arch is formed by region of the heads of the metatarsals is some- the calcaneum, talus, navicular, three cuneiforms times called the anterior arch. When the foot is stressed from above in standing, the anterior arch is flattened as the weight is taken by the heads of the metatarsals. Ligaments bonding the arches • Spring ligament: a tough, fibrous band extends from the sustentaculum tali of the calcaneum to the navicular, and supports the head of the talus. This ligament is very elastic and responds to compression of the medial longitudinal arch (Fig. 8.21a). • Long and short plantar ligaments: these two lig- aments bind the bones of the lateral longitudi- nal arch. The long plantar ligament stretches from the calcaneum to the ridge on the cuboid and the bases of the middle metatarsals. Deep

150 Muscles, Nerves and Movement (a) (b) (c) Fig. 8.21 Plantar surface, right foot: (a) plantar ligaments; (b) plantar aponeurosis; (c) three muscles of the first layer (second and third layers named in brackets).

Support and Propulsion 151 to this, the short plantar ligament is attached to flexion at the tarsometatarsal joints, and trans- the anterior end of the calcaneum and to the versely as the shafts of the metatarsals move cuboid (Fig. 8.21a). towards the axis of the foot. • Plantar aponeurosis: a thick sheet of dense fibrous tissue is attached to the tuberosities of the The maintenance of the flexibility of the foot is calcaneum, and passes forwards over the muscles important for mobility, especially in dancers and of the sole, to blend with the ligaments joining gymnasts who need to balance the body on the the heads of the metatarsals (deep transverse whole, or part of, one foot. In the supporting foot metatarsal ligaments). There are five main in walking and running, the body weight is trans- bands in the plantar aponeurosis, and each band mitted from the heel to the big toe at each step. The blends with a fibrous sheath round a flexor ten- big toe takes most of the weight in standing, and don to a toe. The plantar aponeurosis joins the provides the thrust in driving the body forwards in two ends of the medial and lateral longitudinal walking and running. Long-distance runners com- arches (Fig. 8.21b). monly experience pain in the big toe as a result of the great stress on it. Muscles supporting the arches • Muscles of the leg: the medial longitudinal arch Clinical note-pad 8F: Flat foot and hallux valgus is supported by the tibialis anterior lifting the Flat foot is the collapse of the medial arch so that middle of the arch and the tendon of the tibialis the medial border of the foot almost touches the posterior uniting the medial tarsal bones on ground. Predisposing factors are muscle weak- the plantar surface. The tendon of the flexor ness or joint erosion, e.g. rheumatoid arthritis. hallucis longus acts as a bowstring for the arch. Further support for the longitudinal arch is Hallux valgus is the most common deformity provided by the tendons of the flexor digitorum of the foot. The first metatarsal deviates media longus lying along the plantar surface of the foot. lly away from the second metatarsal, and the The chief support for the transverse arch is the big toe slants laterally towards the second toe. peroneus longus, the tendon of which crosses the The head of the metatarsal develops a protec- foot from the lateral border to the medial side. tive bursa where the shoe rubs. There is some • Intrinsic muscles of the foot: the longitudinal evidence for shoes with inadequate support in arches are supported by the three muscles of standing contributing to the condition. It does not the first layer of the foot that originate on the occur in people who have never worn shoes. calcaneum and insert into the toes. Like the plantar aponeurosis, these muscles (abductor In rheumatoid arthritis, pain and swelling hallucis, flexor digitorum brevis and abductor occur in the metatarsophalangeal joints of the digiti minimi) join the two ends of the longitu- foot, which gives a feeling of ‘walking on stones’. dinal arches (Fig. 8.21c). The transverse arch is supported by the transverse head of the adduc- SUMMARY OF THE LOWER LIMB tor hallucis in the third layer of the foot. This MUSCLES muscle crosses the anterior end of the transverse arch, from the heads of metatarsals 3, 4 and 5 to • Muscles of the hip: gluteus maximus, medius and the proximal phalanx of the big toe. The trans- minimus, tensor fascia lata, iliacus and psoas verse arch is also supported by activity in the (ilio-psoas), six lateral rotators. interossei and the flexors that draw the meta- tarsals towards the axis of the foot, the second • Anterior thigh: quadriceps femoris (rectus metatarsal. femoris, vastas medialis, intermedius and lateralis) sartorius. • PLACE the foot flat on the ground while sitting in a chair. Try to pull up the centre of the foot (flex- • Medial thigh: adductor magnus, longus and ion) with the toes kept flat on the ground. Notice brevis, pectineus, gracilis. how the foot arches both longitudinally by some • Posterior thigh: hamstrings (biceps femoris, semitendinosus, semimembranosus).

152 Muscles, Nerves and Movement • Anterior leg: tibialis anterior, extensor hallucis tar flexion gives the ‘push-off’ in walking and lifts longus, extensor digitorum longus. the foot on to the toes. • Posterior leg: gastrocnemius, soleus, (plantaris The muscles of the lower limb can be divided and popliteus), tibialis posterior, flexor hallucis into groups that are active in support, swing and longus, flexor digitorum longus. propulsion. • Lateral leg: peroneus longus and brevis. In double support, the joints of the limb are in • Sole of the foot: close packed position, supported by strong liga- ments and the iliotibial tract on the lateral aspect – first layer: abductor hallucis, flexor digitorum of the thigh. In standing on one leg, the body weight brevis, abductor digiti minimi shifts to a position over the supporting foot by the action of the adductors of the hip. The hip abduc- – second layer: lumbricals, flexor digitorum tors in the supporting leg contract to prevent the accessorius pelvis dropping on the unsupported side. The knee is stabilised by the extensor muscles. – third layer: flexor hallucis brevis, flexor digiti minimi brevis, adductor hallucis In swing, the thigh moves forwards and upwards by the action of the hip flexors. The knee flexors – fourth layer: plantar interossei, dorsal and the ankle dorsiflexors lift the foot to clear the interossei. ground as the leg swings. SUMMARY In propulsion, the ankle plantar flexes to raise the heel. This creates a force that moves the body The lower limbs form the support for the body in upwards or forwards. Propulsive force is also the upright position, with the line of body weight generated by the extensors of the hip and the knee, passing from the trunk through the pelvis at the particularly in lifting the body upwards. sacroiliac joint and on to the hip joints. The pelvic girdle is an irregular ring of bone formed by the The functions of the foot are: to accommodate sacrum and the two innominate bones bound to the variations in the slope and texture of the together by strong ligaments. The tilt of the pelvis ground; to provide spring and lift during move- affects the lumbar curvature and the consequent- ment; and to activate the sensory system from ly the upright posture. receptors in the skin of the sole of the foot in the maintenance of posture and balance. The hip joint is a stable ball and socket joint allowing movements of the thigh in all planes, car- Movements of the foot on the leg occur at the rying the foot in all directions around the body. The ankle, subtalar and midtarsal joints. Inversion and knee joint is a complex synovial joint that moves eversion movements turn the sole of the foot medi- mainly in flexion and extension. Flexion of the knee ally and laterally, respectively. shortens the limb so that the foot can clear the ground. Extension of the knee converts the limb The bones of the foot are arranged in the form into a pillar of support and also lifts the body in ris- of arches directed longitudinally from the heel to ing from sitting to standing and in walking the metatarsal heads, and transversely across the upstairs. base of the metatarsals. The arches are maintained by strong ligaments on the plantar surface of the The ankle joint moves from the neutral stand- foot, and by both extrinsic and intrinsic muscles ing position into dorsiflexion and plantar flexion. of the foot, forming a structure that combines Dorsiflexion lifts the toes clear of the ground. Plan- stability and flexibility.

9 Nerve Supply of the Lower Limb Lumbar plexus: position and formation branches of the plexus may be damaged by Terminal branches of the lumbar plexus enlargement of the pelvic organs compressing the Femoral, lateral cutaneous and obturator nerves as they leave the pelvis to enter the limb. nerves Peripheral nerves in the thigh and leg may be dam- Sacral plexus aged by trauma to the limb, for example stab Position and formation wounds in the thigh or fractures of the tibia and Terminal branches of the sacral plexus fibula in the leg. Superior and inferior gluteal, sciatic, tibial and common peroneal nerves Figure 9.1 shows the position of the lumbar and Nerve supply to the foot sacral plexuses in relation to the lumbar spine, the Spinal segmental innervation of the lower pelvis and the hip. The course of the muscular limb branches of the lumbar and sacral plexus will be described; the cutaneous branches will be men- tioned in outline only. Action and sensation in the lower limb as a whole Fig. 9.1 Lumbar and sacral plexiuses: position and depend on the nerves that originate in the lumbar relations. and sacral spinal segments. The spinal nerve roots branch and join to form the lumbar plexus, which lies in the abdomen, and the sacral plexus, in the pelvis. The terminal branches of the lumbar and the sacral plexuses together form the peripheral nerves of the lower limb. The first four lumbar nerves form the lumbar plexus, which lies embedded in the psoas muscle in the posterior abdominal wall. A second sacral plexus is formed from the fifth lumbar to the fourth sacral spinal nerves. These spinal nerves of the sacral plexus are part of the cauda equina (see Chapter 4, Fig. 4.2) and enter the pelvis through the anterior foramina of the sacrum. The lumbar plexus is less vulnerable to injury than the brachial plexus. Injury to the back, for example a prolapsed intervertebral disc, may compress either the roots of the lumbar nerves (particularly L4 and L5) or the lumbar and sacral spinal nerves of the cauda equina. The terminal

154 Muscles, Nerves and Movement LUMBAR PLEXUS: POSITION AND TERMINAL BRANCHES OF THE FORMATION LUMBAR PLEXUS The upper four lumbar nerves (L1–L4) form the Three important nerves are formed from the lum- lumbar plexus, which lies in the psoas muscle bar plexus: alongside the lumbar vertebrae in the posterior abdominal wall. Branches direct from the plexus • the femoral nerve supplying the anterior muscles supply the hip flexors (psoas and iliacus) and quad- of the thigh ratus lumborum (see posterior abdominal wall in Chapter 10). The branches of the plexus emerge • the lateral cutaneous nerve supplying the skin on from the psoas. Most of the fibres of L4 join the the lateral side of the thigh lumbar plexus, but the remainder join L5 to form the lumbosacral trunk, which is part of the sacral • the obturator nerve supplying the medial mus- plexus. Figure 9.2 shows the roots of the lumbar cles of the thigh. plexus and the formation of the main terminal branches. Figure 9.1 shows the three nerves in relation to the pelvis and the hip. Femoral nerve This is the largest nerve of the lumbar plexus. It lies in the psoas muscle in the pelvis, and then emerges from the lateral border of the muscle to lie between the psoas and iliacus, leaving the pelvis anteriorly under the inguinal ligament. In the thigh, the femoral nerve branches to supply the quadri- ceps group of muscles. The saphenous nerve, a branch of the femoral nerve in the thigh, becomes cutaneous at the medial side of the knee and con- tinues on to the medial side of the ankle (Fig. 9.3). Lateral cutaneous nerve This nerve emerges from the lateral side of the psoas muscle and crosses the iliacus obliquely to the anterior superior spine of the ilium (Fig. 9.4). The nerve passes under the lateral end of the inguinal ligament and becomes cutaneous in the lateral thigh. Pressure on the nerve in the area of the iliac spine causes loss of sensation on the lateral side of the thigh. Obturator nerve This leaves the medial side of the psoas muscle at the brim of the pelvis and passes through the obturator foramen of the hip bone to reach the medial side of the thigh (Fig. 9.4). In the medial compartment of the thigh, the obturator nerve supplies all of the adductor group of muscles. Fig. 9.2 Lumbar plexus: roots and main terminal • LOOK at an articulated skeleton and trace how the branches. three nerves leave the pelvis to enter the thigh.

Nerve Supply of the Lower Limb 155 Sar torius L1 (cut) L2 L3 Rectus L4 femoris L5 S1 Vastus lateralis S2 Vastus medialis S3 S4 S5 Femoral nerve Formed from the posterior divisions of L2, 3, 4, emerges from the lateral border of psoas, passes between it and iliacus under the inginiunal ligament to enter the thigh and form a leash of nerves Deep branches supply quadriceps Superficial branches supply pectineus and sartorius muscles and skin over front of thigh (upper and medial) Saphenous nerve Is a deep branch of the femoral nerve, which passes under sartorius and becomes cutaneous at the medial side of the knee In the leg, the saphenous nerve supplies the skin over the tibia and the medial side of the foot Fig. 9.3 Right femoral and saphenous nerve.

156 Muscles, Nerves and Movement Fig. 9.4 Right obturator nerve and lateral cutaneous nerve. Functional importance of the femoral and obturator damage of the obturator nerve, the leg swings out- nerves wards instead of forwards in the swing phase in The femoral and obturator nerves are both walking. important in walking. The quadriceps, supplied by the femoral nerve, stabilises the knee during Other nerves of the lumbar plexus support. It propels the body upwards in standing Three other cutaneous nerves are formed from the up from sitting. In climbing stairs the quadriceps first two nerves of the lumbar plexus. The first lum- acts concentrically to lift the body on to the bar nerve divides into two, the iliohypogastric and next step, and eccentrically in coming down. the ilioinguinal nerves, which supply the skin of the The hip adductors, supplied by the obturator buttock and groin, respectively. A third cutaneous nerve, are active to shift the body weight over nerve, the genitofemoral, is formed from L1 and the supporting foot when the other leg is off the L2, and supplies a small area of skin on the upper ground. If the adductors are weak owing to front part of the thigh.

Nerve Supply of the Lower Limb 157 SACRAL PLEXUS: POSITION AND (Remember how the femoral nerve passed anteriorly FORMATION under the inguinal ligament, and the obturator nerve passed medially through the obturator foramen.) The sacral plexus is formed in the pelvis from the joining of the lumbosacral trunk (L4, L5), the first You should now understand the three directions three and part of the fourth sacral nerves. The land- of exit of nerves from the pelvis to the thigh. mark to find the position of the sacral plexus in the pelvis is the piriformis muscle, lying across the pos- TERMINAL BRANCHES OF THE terior aspect of the hip joint. The main part of the SACRAL PLEXUS plexus passes backwards with the piriformis to enter the posterior compartment of the thigh. Three main nerves are formed from the sacral Figure 9.1 shows the emerging sacral nerves lying plexus: the superior and inferor gluteal nerves, and on the anterior surface of the sacrum. Figure 9.5 the sciatic nerve. Figure 9.6 shows the three nerves represents the roots of the sacral plexus and the emerging posteriorly through the greater sciatic main terminal branches. notch of the pelvis. • LOOK at an articulated skeleton and identify the The superior gluteal nerve supplies the abductors greater sciatic notch of the pelvis, which is converted of the hip: the gluteus medius and minimus and the into the greater sciatic foramen by the sacrospinous tensor fascia lata. The inferior gluteal nerve supplies ligament joining the sacrum to the ischial spine. the gluteus maximus. These two nerves are found in relation to the piriformis muscles, one of the lat- • LOOK at the anterior surface of the sacrum to see eral rotators of the hip. The piriformis is attached how spinal nerves originating inside the pelvis from to the anterior aspect of the second, third and fourth the sacral foramina reach the back of the thigh segments of the sacrum, and passes out of the pelvis by passing through the greater sciatic foramen. into the thigh through the greater sciatic notch of the pelvis to attach to the apex of the greater trochanter of the femur. The two nerves leave the pelvis either above (superior) or below (inferior) the piriformis muscle. Figure 9.6 shows a posterior view of piriformis muscle with the nerves emerging pos- teriorly through the greater sciatic notch. Fig. 9.5 Sacral plexus: roots and main terminal branches. Fig. 9.6 Right pelvis and hip, posterior; sciatic nerve and the gluteal nerves emerging through the greater sciatic foramen.

158 Muscles, Nerves and Movement Sciatic nerve L5 and S1–3, and a wide distribution to the pos- terior muscles of the thigh and all the muscles This is the largest nerve in the body, about the same below the knee (Fig. 9.7). This means that pressure size as the thumb or 2 cm in diameter. The nerve on the roots of the sciatic nerve, usually L4 and L5, has extensive roots of origin in the spinal cord, L4, can have widespread effects in the lower limb. Gluteus maximus (cut) Tensor fascia late (cut) Piriformis Biceps long head (cut) Sciatic nerve Popliteal fossa Formed from the lumbosacral trunk L4, 5 and S1, 2, 3. Passes out of the pelvis below piriformis to lie 1. Tibial nerve between the ischial tuberosity and the greater trochanter of the femur. Enters the posterior Passes down the middle of the popliteal fossa thigh deep to the hamstrings. Divides into two at the back of the knee, between the two heads in the thigh: of gastrocnemius, and pierces the origin of soleus, to lie between it and the deep plantar 2. Common peroneal nerve flexors in the calf. At the medial side of the ankle, the tibial nerve divides into the medial and lateral Passes through the popliteal fossa with the plantar nerves tendon of biceps femoris, over the lateral head of gastrocnemius to the head of the fibula. Medial malleolus The nerve winds forwards round the neck of the fibula and pierces peroneus longus, where it Medial plantar nerve divides into two (see 9.7b) Lies between the muscles of the first Lateral malleolus layer of the sole of the foot on the medial side (compare with median Lateral plantar nerve nerve in hand) Crosses to the lateral side of the sole of the (a) foot and supplies all the muscles not supplied by the medial plantar nerve (compare with ulnar nerve in the hand) 1. Superficial peroneal nerve Common peroneal nerve Head of fibula Passes down the lateral side of the leg 2. Deep peroneal nerve between the peronei. The nerve becomes cutaneous at the anterior border of peroneus and supplies the dorsal skin of the foot Lateral malleolus Pierces extensor digitorum to pass down (b) the front of the leg on the interosseous membrane between the tibia and fiblula. At the ankle, it continues into the foot to supply extensior digitorum brevis and gives off cutaneous branches to the lateral side of the great toe and medial side of the second toe Fig. 9.7 Right sciatic nerve and branches; course and distribution: (a) posterior view; (b) lateral view.

Nerve Supply of the Lower Limb 159 There are two divisions of the sciatic nerve that 9.8). A branch of the tibial nerve at the ankle sup- lie together as one nerve, deep to the hamstrings plies the skin of the heel. in the posterior thigh. The nerve divides into its two components above the knee (Fig. 9.7a). Branches The common peroneal nerve (Fig. 9.7b) is the of the sciatic nerve high in the thigh supply the lateral part of the sciatic nerve that forms in hamstring group of muscles. The sciatic nerve also the upper part of the popliteal fossa. It travels supplies the fibres of the adductor magnus that with the biceps femoris of the hamstring group to originate from the ischium. Trauma to the sciatic the lateral side of the knee, where it passes around nerve in the middle of the thigh does not usually the neck of the fibula and into the peroneus longus. affect the hamstrings since the branches to these There it divides into the superficial and deep muscles begin high in the thigh. peroneal nerves. The branches of the sciatic nerve are the tibial The superficial peroneal nerve lies on the later- nerve and the common peroneal nerve. al side of the leg, deep to the peroneus longus, and continues over the front of the ankle to supply the The tibial nerve lies in the popliteal fossa at the skin of the dorsum of the foot. This nerve supplies back of the knee and continues down the posteri- the evertors, the peroneus longus and brevis. or leg between the muscles of the calf. This is the nerve of the posterior muscles of the calf, supply- The deep peroneal nerve passes forwards to the ing all of the plantar flexors: the gastrocnemius, anterior compartment of the leg lying on the soleus, flexor hallucis longus, flexor digitorum interosseous membrane between the tibia and fibu- longus and tibialis posterior (Fig. 9.7a). The sural la. This nerve supplies the dorsiflexors, the tibialis nerve is a cutaneous branch of the tibial nerve in anterior, extensor hallucis longus, extensor digito- the calf that supplies the skin on the lateral side of rum longus and peroneus tertius. The nerve ends the lower calf and the lateral side of the foot (Fig. on the dorsum of the foot, where it supplies the extensor digitorum brevis and the skin over the first and second toes. Functional importance of the tibial and the peroneal nerves The tibial nerve is important for movements that lift the heel to propel the body forwards and upwards in walking, running and jumping. The deep peroneal nerve activates the dorsiflexors of the ankle, which lift the toes clear of the ground when the leg swings forwards in locomotion or when kicking a ball. The superficial peroneal nerve stabilises the ankle joint by counteracting the tendency to twist and turn the foot inwards. Fig. 9.8 Cutaneous nerve supply to the right lower limb: Clinical note-pad 9A: Peroneal nerve lesion (a) posterior view; (b) sole of foot. The common peroneal nerve is vulnerable to damage at the lateral side of the knee, where it is subcutaneous as it winds round the neck of the fibula. The result is loss of dorsiflexion and ever- sion of the ankle, producing ‘foot drop’ when the leg is lifted off the ground. Fracture of the shaft of the fibula, common in skiing and skating falls, may injure the superfi- cial peroneal nerve. The foot then tends to go into inversion and the ankle loses stability.

160 Muscles, Nerves and Movement The muscles of the pelvic floor are supplied by This means that the dermatomes and myotomes lie the pudendal nerve (S2–4), which passes out of the in order down the front, and up the back, of the greater sciatic foramen with the sciatic nerve and lower limb. Look at Chapter 4, Figure 4.4, to see then turns below the ischial spine to supply the how the dermatomes of the upper segments L1–5 levator ani and coccygeus. are in the anterior thigh, knee and leg, while S1–5 are posterior. Nerve supply to the foot The upper lumbar spinal segments supply ante- The nerves of the plantar surface of the foot orig- rior (quadriceps) and medial (adductors) muscles inate from the tibial nerve at the medial side of the of the thigh. The lower lumbar spinal segments sup- ankle (Fig. 9.7a). There are two plantar nerves, ply the muscles of the buttock (glutei) and the pos- which are comparable to the median and ulnar terior thigh (hamstrings). All muscles of the leg and nerves of the hand. foot below the knee are supplied by the fourth and fifth lumbar and the sacral spinal segments. (See The medial plantar nerve supplies the abductor Appendix II, Tables A2.3 and A2.4.) hallucis, flexor hallucis brevis, flexor digitorum bre- vis and the first lumbrical. SUMMARY The lateral plantar nerve supplies the lateral three The nerve supply of the whole of the lower limb is lumbricals, all of the interossei, the abductor digiti derived from segments L1–5 and S1–4 of the spinal minimi, flexor digiti minimi and adductor hallucis. cord. The roots of the spinal nerves emerging from these segments form the lumbar plexus (L1–4) and Summary of the cutaneous supply in the foot the sacral plexus (L4, L5, S1–4). The nerve supply to the skin of the sole of the foot is important for sensory information about the con- The femoral, obturator and lateral cutaneous tact of the foot with the ground during standing and nerves are formed from the lumbar plexus. Direct walking, and the distribution of the body weight branches of the lumbar plexus supply the hip over the feet. The major part of the skin of the sole flexors, which swing the thigh forwards in the of the foot is supplied by the medial and lateral unsupported limb or move the trunk forwards in plantar nerves (Fig. 9.8b). The heel receives a preparation for standing up from sitting. branch of the tibial nerve, and the lateral border of the foot receives branches of the sural nerve. The functional importance of the femoral and obturator nerves is in stabilising the hip and the The dorsal surface of the foot is largely supplied knee in standing and walking. by branches of the superficial peroneal nerve, except for a triangular area over the first and sec- The sacral plexus forms the superior and inferior ond toes which receives branches of the deep per- gluteal nerves and the sciatic nerve. The superior oneal nerve. The saphenous nerve, a branch of the gluteal nerve supplies the abductors of the hip, femoral nerve in the thigh, becomes the cutaneous which are important in locomotion to prevent the nerve to the medial side of the lower leg and con- pelvis from dropping on the unsupported side. The tinues to the medial dorsal surface of the foot. inferior gluteal nerve supplies the large extensor of the hip, the gluteus maximus. This muscle provides SPINAL SEGMENTAL INNERVATION propulsion upwards to lift the body in standing up OF THE LOWER LIMB from sitting, jumping and climbing stairs. In development, the lower limb bud grows out from The sciatic nerve supplies the posterior muscles the side of the embryo. The nerve from the central of the thigh and all the muscles below the knee. Its segment, S1, grows down the limb to end along the branches in the leg and the foot supply the mus- outer side of the foot, in the same way that the mid- cles that move the ankle in dorsiflexion and plan- dle segments of the brachial plexus supply the hand. tar flexion, and the foot in inversion and eversion. The later stage of development differs from the upper limb, when the lower limb rotates medially. The course and distribution of the femoral, obturator and sciatic nerves, together with their branches, are shown in Figures 9.3, 9.4 and 9.7.

10 Upright Posture and Breathing: The Trunk Upright posture pelvis lies in the abdomen. The pelvic part of Joints and movements of the vertebral column the cavity is a bowl formed by the sacrum and the Muscles moving the trunk two innominate bones, with a muscular floor. Muscles moving the head and neck Breathing Joints and movements of the thoracic cage Muscles moving the ribs The diaphragm Pelvic tilt and the pelvic floor Nerve supply of the muscles of the neck and trunk Summary of the muscles of the trunk The trunk is the central axis of the body. The limbs Fig. 10.1 Side view of the trunk: outlines of the thoracic use the trunk as the base on which to move. When and abdominopelvic cavities. the body is upright, the trunk supports the head and maintains the erect posture with minimal effort. The trunk consists of the thorax, abdomen and pelvis, stacked one above the other (Fig. 10.1). These three areas form two enclosed cavities, with bony and muscular walls, separated by the muscu- lar diaphragm. Any change in the pressure inside one of the cavities affects the other. The vertebral column links the two cavities posteriorly. • The thoracic cavity extends from the clavicle and first rib above to the muscular diaphragm below. Its walls are formed by the thoracic ver- tebrae, the ribs and the intercostal muscles in between. • The abdominopelvic cavity has the dome of the diaphragm as the roof and the muscular pelvic floor below. The posterior wall contains the lum- bar vertebrae, with muscle on either side of it. The anterolateral wall is formed by the abdom- inal muscles. The blade of the iliac bone of the

162 Muscles, Nerves and Movement The joints and muscles of the trunk combine to muscle activity when standing still. Any slight form a stable system when standing upright. The sway is counteracted by the tension in the strong muscles act like guy-ropes keeping the balance longitudinal ligaments joining the individual when external forces act on the trunk. If a group vertebrae. of muscles becomes weak, the trunk changes its position, in the same way that a tent will lean to one The vertebral column contains 33 bony seg- side if a guy-rope is loosened. ments. An individual vertebra articulates with the one above and the one below by a cartilaginous The trunk has a protective function for the lungs, joint (intervertebral disc) between the bodies, and heart, digestive tract, kidneys and pelvic organs by four synovial joints between the articular (bladder, rectum and reproductive organs). The processes. The position of the articular processes spinal cord is also protected by being enclosed by in a thoracic vertebra is shown in Appendix I. the bones of the vertebral column, with pairs of spinal nerves emerging between adjacent vertebrae At birth, the vertebral column has a primary to be distributed to all parts of the body. curve, concave forwards. As the baby learns to sup- port the weight of the head and trunk in sitting and Ventilation of the lungs is the result of changes then standing, two secondary curves develop in the in the size of the thoracic cavity. Breathing also neck and lower back. From 2 years onwards, the involves the anterior abdominal wall. Increased vertebral column has four curves as follows: seven abdominal pressure pushes the diaphragm upwards cervical vertebrae, convex forwards, secondary; and expels air from the lungs. Changes in the pres- 12 thoracic vertebrae, concave forwards, primary; sure in the abdominopelvic cavity are used to expel five lumbar vertebrae, convex forwards, secondary; urine or faeces and in childbirth. five sacral vertebrae (fused), concave forwards, primary; and three coccygeal vertebrae. Lifting, carrying, pushing and pulling heavy loads all involve the trunk. The muscles of the trunk coun- The four curves provide an efficient way of teract the forces on the limbs, and adjust the line of combining support with flexibility and resilience gravity over the foot base. Carrying a heavy load of (Fig. 10.2). shopping in one hand requires muscle activity on the opposite side of the trunk to balance the weight. Centre of gravity Increase in pressure in the abdominopelvic cavity, of the body by tensing the anterior abdominal muscles, reduces the stress on the back in lifting loads from the front. In summary, the trunk: • maintains the upright posture • protects the organs of the thorax, abdomen and pelvis • ventilates the lungs in breathing • expels urine, faeces, and also the baby at birth • adapts to changes in the line of gravity as the body moves. • releases pressure on the spine when lifting loads. Most of the movements of the trunk are performed by large muscles arranged in sheets around the axial skeleton. The position of the muscles and direction of the fibres determine the ways in which each contributes to trunk movement. UPRIGHT POSTURE The bones and ligaments of the vertebral column Fig. 10.2 Side view of the vertebral column: cervical, form a stable balanced support that requires little thoracic, lumbar and sacral curves.

Upright Posture and Breathing 163 • OBSERVE a partner standing upright. Look first There are two series of joints between adjacent from the side to imagine a line from the ear through vertebrae in the column: anterior and posterior. the vertebral column to the hip and knee, ending just in front of the ankle. Move the trunk until the Anterior joints between the bodies of the verte- position looks balanced. Notice the curves of the brae: these articulations are secondary cartilagi- back. Refer to an articulated skeleton to see the nous joints, the intervertebral discs. They increase curves more easily. Next, look at your partner from in thickness from the upper cervical vertebrae down the front to see whether the shoulders and hips are to the lumbar vertebrae. In the fibrocartilaginous level, i.e. no lateral curves. discs, which form about a quarter of the total length of the vertebral column, the collagen fibres are • WATCH a person sitting at a keyboard and notice arranged in concentric layers, the annulus fibrosus. the shape of the back in relation to the shape of the The semifluid central mass of the disc is the nucleus back of the chair. Try raising and lowering the key- pulposus. During movements of the trunk, the board to see the effect on the working posture. cartilaginous discs are compressed on one side (see Chapter 1, Fig. 1.6b). • LOOK at elderly people sitting in easy chairs. Think where a cushion should be placed to support the Posterior joints between articular processes on lumbar curve of the back. the vertebral arch of bone which surrounds the spinal cord: these are synovial plane joints. A thin If an abnormal posture is adopted over long peri- capsule surrounds the adjacent articular surfaces ods, the normal relaxed position is progressively and allows gliding movements between adjacent lost and muscle activity must be used to a greater vertebrae. extent. Examples of abnormal posture are: kypho- sis, standing with rounded shoulders; lordosis, All of the vertebrae are joined together by ante- standing with a hollow back; and scoliosis, lateral rior and posterior longitudinal ligaments that curvature to the spine, and tilting of the shoulders. extend along the whole length of the vertebral col- umn joining the respective surfaces of the vertebral Shoes with high heels throw the body weight for- bodies. Other ligaments join all of the spines and wards and the vertebral column adapts by increas- transverse processes of the vertebrae. ing the lumbar curvature (lordosis). Problems with breathing may develop in scoliosis owing to the Clinical note-pad 10A: Prolapsed effect on the shape of the thorax. Poor working pos- intervertebral disc ture increases the possibility of lower back pain, A movement that involves a sudden compression even in the young. In the elderly, degenerative of the intervertebral disc may result in tearing of changes in the vertebrae and discs due to disease the annulus fibrosus, and this allows the nucleus or ageing, coupled with the loss of the need and pulposus to protrude and press on the spinal cord motivation to move about during the day, give or the roots of a spinal nerve. Severe pain then general loss of mobility, and deformity develops radiates down the path of the affected nerve. which may become permanent. The movements of the trunk, shown in Fig. 10.3, Joints and movements of the vertebral are described as follows. column • Flexion occurs in bending forwards, or sitting up When the trunk moves in different directions, the from lying. The thorax moves towards thepelvis. movement between adjacent vertebrae is small, but the result of combined movement of vertebrae at all • Extension straightens the trunk from flexion and levels results in a considerable range of movement. the trunk can bend backwards from the upright position. The thorax moves away from the Joints of the vertebral column pelvis. • LOOK at the structure of a vertebra, seen from • Lateral flexion bends the trunk to the side. The above and from the side, in Appendix I and in an ribs move towards the pelvis on one side only. articulated skeleton. • Rotation twists the trunk to the right or the left. The head and shoulders are turned so that the eyes can look to the side or behind, either to the right or left.

164 Muscles, Nerves and Movement Fig. 10.3 Movements of the trunk: (a) flexion (forwards) and extension (backwards); (b) lateral flexion; (c) rotation; (d) circumduction. The trunk-rolling exercise shown in Figure Deep posterior muscles of the back 10.3d is a combination of all of these movements. The posterior aspect of the vertebral column, from the sacrum to the skull, provides a long line of The range of the individual movements varies in bony processes for the attachment of muscle different parts of the vertebral column, depending fibres. Some of these muscles fibres are long, on the thickness of the intervertebral discs, the extending from the sacrum to the thorax, while direction of the articular facets of the synovial others are short and only span one, two or three joints, and the length and angulation of the spines. vertebrae. The vertical fibres pull the column into The regions with secondary curves have the great- extension, those arranged obliquely can rotate one est mobility. Movements of the cervical region are vertebra on the next, and the lateral fibres which important for the eyes to scan a large area. are attached to the angles of the ribs can assist Reversing a car becomes difficult when there is loss lateral flexion. of mobility in the neck. The lumbar region has the greatest range for flexion and extension move- The largest muscle in this group of deep back ments. The extreme bending movements of the muscles is the erector spinae (also known as the acrobat and gymnast are achieved by continual sacrospinalis), which originates from the sacrum by exercises to stretch the intervertebral ligaments and a thick broad tendon. In the lumbar region, this increase the separation of the lumbar vertebrae. muscle is thick and can be palpated in the lower Conversely, the fusion of the lumbar vertebrae in back. Continuing upwards, the muscle is in three some pathological changes of the spine will bands in the thoracic region, attached to the spines reduce the overall mobility of the trunk by a sig- of the vertebrae, the transverse processes and the nificant amount. ribs. The uppermost fibres in the cervical region end on the base of the skull. Muscles moving the trunk The muscles connecting the trunk to the upper Two systems of muscles collectively perform all limb, for example the latissimus dorsi and trapez- movements of the trunk: the deep posterior mus- ius (described in Chapter 5), are separated from cles of the back and the abdominal muscles. the deep muscles of the back by a layer of deep fascia.

Upright Posture and Breathing 165 Fig. 10.4 Erector spinae (right); semispinalis and quad- obliquely from the transverse process of one ratus lumborum (left), posterior view of the trunk. vertebra to the spine of the vertebra above, or they may span three or four vertebrae. The parts Figure 10.4 follows the line of erector spinae found in the thorax and neck are known as on the right-hand side of the vertebral column. semispinalis. Note how the muscle starts at the sacrum and climbs up the back to the head. Deep to the In movements of the trunk, the erector spinae erector spinae another group of muscles is found acts strongly to raise the body from forward flex- (Fig. 10.4, left-hand side of the vertebral column). ion to an upright position. The erector spinae coun- Most of the fibres in this deeper group lie teracts both the tendency to sway forwards in standing and the force of loads carried in front of the body. Lifting loads placed in front of the body may cause considerable stress on the lower back. In rais- ing the trunk and the load, the pull of the erector spinae muscle compresses the lumbar interverte- bral discs, which may prolapse (see Clinical note- pad 10A). The aim of good lifting practice is to reduce the compression force on the lumbar discs. Figure 10.5 shows the application of the principle of levers (see Chapter 2) in three positions for lifting a child. In lifting with straight legs, the starting position is forward flexion (Fig. 10.5a). From this position, the line of weight of the trunk plus the child (1) is some distance from the fulcrum in the lower back, so that the load arm (2) is long. The erector spinae, acting on a short lever arm, must develop consid- erable effort force (3) to overcome the moment of force of the trunk. In lifting from the sitting position (Fig. 10.5b), the line of weight (1) is even further from the 1 1 1 2 2 2 3 3 3 Fig. 10.5 Lifting: (a) straight legs; (b) sitting; (c) knees bent. 1 = line of gravity, 2 = load arm; 3 = effort force.

166 Muscles, Nerves and Movement fulcrum and the load arm (2) is longer. The trunk by pulling the sternum towards the pelvis, so compression load on the discs is therefore much acting strongly in sitting up from lying. When the greater as the erector spinae extends the spine. body is lifted off the ground, as in running and People in wheelchairs should avoid lifting heavy jumping, the rectus abdominis supports the front loads, since the stress on the back will be greater of the pelvis. than the same load lifted by someone who can stand close to the load. The external oblique abdominal muscle is attached to the outer surfaces of the lower eight In lifting with the knees bent and with the load ribs. The posterior fibres pass vertically to insert on as close to the body as possible, the line of weight the anterior part of the iliac crest of the pelvis. All (1) is moved nearer to the body, and the load arm of the other fibres lie in a direction downwards and of the trunk plus the child (2) is short. This means forwards, i.e. like hands in a side-pocket, to attach that the effort force (3) exerted by erector spinae to the wide central aponeurosis (Fig. 10.6c). to counteract the load is reduced. In addition, it The lower margin of the muscle and aponeurosis allows the extensors of the hip and the knee to con- is thickened to form the inguinal ligament, which tribute most of the effort force for the lift. This extends from the anterior superior iliac spine to explains how bending the knees and keeping the the pubic crest (see Chapter 8, Fig. 8.10). The trunk as upright as possible puts less stress on inguinal ligament acts as a retinaculum forming the the back in lifting. division between the trunk and the thigh. Anterior abdominal wall The internal oblique abdominal muscle is The anterior abdominal wall consists of flat sheets attached to the fascia of the lower back (thora- of muscle forming a four-way corset or girdle columbar fascia), the anterior iliac crest (deep to between the ribs and the pelvis. The position of the external oblique) and the inguinal ligament. the individual muscles is as follows. The rectus The muscle fibres pass upwards and inwards, to abdominis lies down the centre of the abdomen, attach to the lower ribs, and become a wide one on either side of the midline. The muscle aponeurosis as far as the midline (Fig. 10.6d). The fibres are in the vertical direction. The external and aponeuroses of the right and left obliques meet in internal oblique abdominal muscles are two the midline at the linea alba, a strip of fascia sheets of muscle around the anterior and lateral from the lower end of the sternum to the pubic walls of the abdomen. The muscle fibres are symphysis. arranged diagonally. The transversus abdominis is a muscle lying deep to the obliques which has The muscle fibres of the two oblique abdominal horizontal fibres forming a band wrapping round muscles lie at right angles to each other. The ways the abdomen. in which the two layers of oblique abdominal mus- cles work in combination to produce movements of Figure 10.6a shows the direction of the fibres of the trunk will now be considered. the abdominal muscles seen from the side. The fibres of the two oblique muscles and transversus • Flexion of the trunk involves the external and abdominis blend into an aponeurosis (dense fibrous internal obliques on both sides together. tissue) towards the midline, connecting with those from the opposite side to form a sheath around the • Lateral flexion involves the external and inter- rectus abdominis. nal oblique on one side only. The rectus abdominis (Fig. 10.6b) is a strap-like • Rotation of the trunk involves the external muscle extending from the lower end of the ster- oblique on one side working with the internal num and the costal cartilages of the fifth, sixth and oblique on the opposite side. The trunk then seventh ribs to the pubis below. The muscle fibres rotates towards the side of the internal oblique are usually interrupted at three intervals by trans- (Fig. 10.6e). verse bands of fibrous tissue, known as tendinous intersections. The four bulges of muscle fibres in In standing and sitting, the oblique abdominals between can be seen clearly in men who have done work with the neck muscles in turning to look weight training. The rectus abdominis flexes the to the side and behind. In walking, the pelvis is carried forwards on the side of the leading leg and the trunk rotates to keep the eyes looking forwards.

Upright Posture and Breathing 167 Fig. 10.6 Muscles of the anterior abdominal wall: (a) direction of the muscle fibres; (b) rectus abdominis, anterior view; (c) right external oblique abdominal, side view; (d) right internal oblique abdominal, side view; (e) oblique abdom- inals working togerher; (f) right transversus abdominis, side view.

168 Muscles, Nerves and Movement • LIE down supine and feel the abdominal muscles on the intervertebral discs of the lumbar region set working in: up by the back muscles. Weight-lifters learn to use (1) sitting up from lying; the abdominal muscles to reduce the stress on the (2) lifting the head from lying. Feel the rectus abdo- back. A sudden or unexpected demand for lifting minis working statically to fix the thorax so that can produce back strain. Even simple everyday the neck muscles can act on the head; tasks, such as making a bed, can cause back injury. (3) sitting up from lying while turning the trunk to Some of the lifting tasks used in the care of the dis- the left at the same time. Think which abdo- abled have been replaced by the use of hoists, but minal muscles are working. it is still important to be aware that contraction of the abdominal muscles can relieve stress on the It should now be clear why it is difficult to sit up back when lifting a patient. from lying if the abdominal muscles are weak, for example after abdominal surgery, with fractured The function of the anterior abdominal muscles ribs or in the late stages of pregnancy. In these in breathing will be described later in this chapter instances sitting up can be performed by turning on with the action of the diaphragm. to one side and pushing up with the opposite arm to raise the trunk. The legs can then be swung The posterior abdominal wall between the 12 rib round to the sitting position (see Chapter 13). and the posterior part of the iliac crest is formed by the quadratus lumborum. This muscle lies The transversus abdominis is the deepest abdomi- lateral to the psoas and deep to the origin of the nal muscle, originating from the inner aspect of the transversus abdominis (Fig. 10.4). Contraction of costal margin, the thoracolumbar fascia, iliac crest the quadratus lumborum on one side only assists and inguinal ligament. From this extensive posteri- lateral flexion of the trunk. Acting in reverse, the or origin, the fibres pass transversely round the muscle can lift the pelvic brim on the same side, abdomen to form a central aponeurosis anteriorly. which prevents the pelvis dropping down on the The muscles from each side meet in the midline at unsupported side in standing on one leg. The quad- the linea alba. Figure 10.6f shows the right trans- ratus lumborum on both sides together stabilise the versus viewed from the side. The transversus has no lumbar vertebrae and the pelvis during movements action in moving the trunk. The tension in the trans- of the upper trunk and upper limb. versus supports the abdominal organs and contrac- tion increases the pressure inside the abdomen. This Muscles moving the head and neck rise in pressure aids the expulsion of air from the lungs in breathing. The two main functions of the muscles of the head and neck are to hold the head upright on the trunk, The functions of the anterior abdominal wall and to allow the eyes to focus over a wide field of are: support and protection of the abdominal vision by turning the head. organs; expulsion of the contents of the pelvic organs in micturition, defecation and parturition; Two of the muscles supporting the head on the increase in the depth of expiration in breathing; and trunk are the upper fibres of the trapezius relief of pressure on the lower back in lifting. (described in Chapter 5) and the upper part of the erector spinae. Lying in between these two muscles The organs of the digestive system lie in the at the back of the neck is another pair of muscles, abdomen. Contraction of the muscles of the ante- the splenius capitis and splenius cervicis (Fig. rior abdominal wall improves the circulation of 10.7). Holding down the deep muscles of the neck blood and aids digestion. The pelvic organs (the in this region, the splenius capitis has been called bladder, rectum and uterus) are protected by the the ‘bandage muscle’. The splenius muscles are bony pelvis. In straining movements, the muscles attached to the lower part of the ligament in the of the anterior abdominal wall contract and raise midline of the neck (ligamentum nuchae) and to the pressure inside the abdomen to expel the urine the spines of the upper four thoracic vertebrae. and faeces. When lifting loads with the back, con- Passing upwards and laterally, the capitis is insert- traction of the abdominal muscles raises the intra- ed on the base of the skull, to the mastoid process abdominal pressure. This pressure is distributed of the temporal bone and adjacent occipital bone. upwards and downwards, and reduces the pressure

Upright Posture and Breathing 169 or, medius and posterior (Fig. 10.7). Attached centrally to the transverse processes of the cervi- cal vertebrae, the scalenes pass downwards and laterally to the first and second ribs. These muscles are an important landmark in the location of the brachial plexus, which passes between the scalenus anterior and scalenus medius in its course towards the first rib. The scalenes flex the cervical spine if both sides contract, or produce lat- eral flexion if one side only is active. The muscles are also used to fix the first two ribs in deep inspi- ration before a powerful or long exhalation as when singing or playing a wind instrument. Fig. 10.7 Sternomastoid: scalenus anterior, medius and • LIE SUPINE and lift the head. Feel the ster- posterior; right side view of the neck. nomastoid and scalenes in action. Turn the head to the right and feel the left sternomastoid in action. The splenius cervicis inserts on to the transverse BREATHING processes of cervical vertebrae 1–4. Working stat- ically, the splenius muscles prevent the head from The action of the muscles moving the ribs, and the falling forwards. Both sides working together pull muscle dividing the thorax and abdomen (the the head backwards in extension. If one side only diaphragm), combine to change the size of the contracts, the head is rotated to turn the face to the thoracic cavity and to ventilate the lungs. The same side. abdominal muscles are also involved in breathing, since their activity affects the position of the The most superficial muscle on the front of the diaphragm. neck, clearly visible in action, is the sternocleido- matoid, often shortened to sternomastoid (Fig. The two lungs fill the thoracic cavity, apart from 10.7). This strap-like muscle crosses the neck diag- the space occupied by the heart and major blood onally, and combines with other muscles to perform vessels. Shaped like two cones, the base of each all of the movements of the head. Its name indi- lung sits on the diaphragm and the apex of each lies cates the attachments of this muscle. From the above the clavicle. Each lung is surrounded by a upper end of the sternum and the medial end of narrow, airtight space called the pleural cavity. The the clavicle, the sternocleidomastoid crosses up- pleural membranes which form this cavity are wards and outwards to end on the mastoid process attached to the outer surface of the lungs and the of the temporal bone of the skull, extending medi- inner wall of the thorax. The cavity between the ally to meet the upper fibres of the trapezius. Both membranes is a completely enclosed space in which sides of the sternomastoid working together draw the pressure is lower than the pressure of the air the head forwards and act strongly to lift the head outside the thorax. As the thorax expands as a up when lying supine. One side contracting pro- result of muscle contraction, the lowered pressure duces lateral flexion and rotation to the opposite in the pleural cavity causes the lungs to be side. These movements are important in looking expanded also. The two layers of pleura remain in from side to side to scan the visual field. The ster- contact like the sides of a new plastic bag when one nomastoid and the splenius muscles combine to tries to separate them. produce most of the turning movements of the head. When the head is tilted backwards beyond When the lungs expand, the air pressure within the vertical, the sternomastoid can act as a neck the air sacs is reduced and atmospheric air is drawn extensor. in through the nose and trachea to equalise the pressure inside the lungs. Relaxation of the A group of three muscles in the lateral part of muscles reduces the size of the thorax to the resting the neck comprises the scalenes: scalenus anteri-

170 Muscles, Nerves and Movement volume and the pressure in the air sacs rises, there- of the vertebra, one between the tubercle of the rib fore air passes out into the atmosphere. and the transverse process. Anteriorly, the first to seventh ribs join with the sternum by the costal The exact amount of air entering and leaving the cartilages. lungs at any one time depends on the amount of movement of the thorax. Other factors that influ- Note two things about the general direction of ence the volume of air breathed are the elasticity ribs 2–7: (i) the anterior end is lower than the and inertia of the lung tissue, and the resistance vertebral articulations; and (ii) when viewed from offered by the airways in the lungs. the side, the central part of each rib is lower than both the anterior and the posterior ends. In quiet breathing, active expansion of the tho- rax occurs in inspiration, while expiration is passive. Movements at all of the joints provides the mobil- Additional muscle activity is recruited during ity of the ribs required to ventilate the lungs. Ribs deep inspiration, and expiration becomes active. 2–7 move about two axes simultaneously (Fig. 10.8): Clinical note-pad 10B: Pneumothorax • axis (A–A′) passes through the neck of each rib. If the pleural membranes are punctured by a stab When the rib moves about this axis, the sternum wound, or as a result of infection, then air can is raised upwards and forwards to increase the enter the pleural cavity and the pressure rises. anterior to posterior diameter of the thorax; This reduces tension on the elasticity of the lung and it collapses. Once the pleural membrane • axis (B–B′) passes through the angle of the ribs heals, the excess air is slowly absorbed into posteriorly and the sternocostal joints anterior- the bloodstream and the lung reinflates. This ly. Movement about this axis lifts the middle of process can be used clinically to allow lung tissue the rib upwards and outwards to increase the to rest and repair. transverse diameter of the thorax. Joints and movements of the thoracic The eight, ninth and tenth ribs have no sternocostal cage joints and therefore only move about one axis (A–A′). Articulations Posteriorly, the 12 ribs articulate with the thoracic • PLACE your hands on the thorax of a partner, first vertebrae at the costovertebral joints. These are at the sides over the lower rib cage. Ask your part- formed between facets on the head of the rib and ner to breathe in deeply and watch how your hands those on the sides of the bodies of two adjacent ver- move further apart, i.e. the thorax becomes wider. tebrae and the transverse process of the corre- Next, stand at the side and place one hand flat sponding vertebra. The costovertebral joints are on the sternum, the other hand flat on the thoracic synovial of the plane type. vertebrae. Again ask your partner to breathe in deeply, and notice how the hand on the sternum Anteriorly, the sternocostal joints are formed by moves forwards and upwards. the costal cartilages of the second to the seventh These two movements occur together each time ribs articulating directly with the sternum by syn- the ribs move. ovial joints, each with a capsule and ligaments. The first sternocostal joint is a primary cartilaginous Muscles moving the ribs joint. The eigth, ninth and tenth ribs link indirect- ly to the sternum by their costal cartilages. The 11th The external and internal intercostal muscles, and 12th ribs, which are small and free anteriorly, which form two layers in the space between adja- play little part in breathing. cent ribs, move the ribs in quiet breathing. • LOOK at the position of the ribs on an articulat- The fibres of the external intercostal muscles ed skeleton. pass obliquely from the lower border of one rib to Posteriorly, identify the position of two synovial the upper border of the rib below. At the anterior joints, one between the head of the rib and the body end of each intercostal space, the muscle is replaced by membrane. The posterior fibres pass downwards and laterally, and the more anterior

Upright Posture and Breathing 171 Fig. 10.8 Movement of a rib in side view and plan view: A–A′ axis through the neck of the rib; B–B′ axis through the vertebral and sternal ends of the rib. fibres lie downwards and medially, i.e. in the same muscles that are recruited to increase the depth of direction as the external oblique abdominal mus- inspiration are the sternomastoid, the scalenes (Fig. cles. The first rib does not move in quiet breath- 10.7) and the pectoralis minor (see Chapter 5, Fig. ing. Figure 10.9 shows the position of the external 5.6). These muscles pull the clavicle and first two intercostal muscles in the spaces between ribs 1–6. ribs upwards when their upper attachments are Contraction of the external intercostals lifts the ribs fixed. The result is that the other ribs can move up about the two axes described. The thorax increas- further. es in size by expanding in a forwards and sideways • WATCH the neck of a person breathing deeply to direction, and air is drawn into the lungs. see the activity in neck muscles. The internal intercostal muscles lie deep to the external intercostals, and their fibres are at right In deep expiration, the latissimus dorsi (see Chap- angles, downwards and backwards from one rib to ter 5, Fig. 5.11a), which wraps round the rib cage the one below. The muscle fibres are replaced by membrane at the posterior end of the intercostal Sternum space, between the angle and head of each rib. Fig- ure 10.9 shows the position of the internal inter- External costal muscles in the spaces between ribs 6–10. intercostals There is conflicting evidence about the action of the internal intercostals. It has been shown that the Internal anterior fibres between the costal cartilages are intercostals active in inspiration. Other studies have shown activity during speech, which is expiratory. The con- Fig. 10.9 Intercostal muscles: external intercostals tribution of the internal intercostals to rib move- shown in the upper five intercostal spaces; internal inter- ments probably depends on which fibres are costals (deep to the external) shown in the lower six active, and on the level of inflation of the lungs. spaces. Relaxation of the intercostal muscles lowers the ribs to their resting position, and air leaves the lungs. Expiration in quiet breathing is therefore passive. In deep breathing, the muscles in the neck that elevate the shoulder girdle and upper ribs allow the thorax to expand further in inspiration. The main

172 Muscles, Nerves and Movement heart lies immediately above the central tendon with the pericardium, the membrane round the heart, attached to it. • LOOK at an umbrella (with a very curved shape if possible). The ribs of the umbrella are in the direction of the muscles fibres of the dome of the diaphragm. Imagine the point of the umbrella com- pressed into a flat trefoil shape to understand the position of the central tendon. Fig. 10.10 Diaphragm viewed from below. Figure 10.10 is a view of the diaphragm from below (i.e. in the abdomen looking up to the under- from the lower back to the shoulder, can compress surface of the muscle). The muscle fibres of the the ribs further if the humerus is fixed. The abdom- diaphragm originate all round the lower margin of inal muscles are also involved in deep expiration, the thorax. Beginning anteriorly, fibres originate see later in this chapter. from the xiphoid process of the sternum. Next, ribs 7–12 and their costal cartilages form the largest sur- Clinical note-pad 10C: Asthma and chronic face for the attachment of fibres. Posteriorly, the obstructive airways disease (COAD) origin from the 12th rib is interrupted by the mus- Asthma occurs in children and adults. Attacks of cles of the posterior abdominal wall, the quadra- breathing difficulty occur in response to certain tus lumborum and psoas. These two muscles are protein substances, such as pollen or animal pro- bridged by fibrous bands, known as the lateral and tein, which release allergens within the body. The medial arcuate ligaments, which provide a base for muscular walls of the narrow airways in the lungs the attachment of the diaphragm. The most pos- constrict. Inspiration that is initiated by muscle terior fibres originate from the sides of the lumbar activity can take place, but passive expiration vertebrae by two bands, the right crus (from L1, L2 becomes difficult. Expiratory muscles have to be and L3) and the left crus (from L1 and L2), used to try to force the air out of the lungs. which arch over the aorta in the midline. The right crus is longer to overcome the resistance of COAD occurs in the elderly. There is a chron- the larger liver lying below the diaphragm on the ic inflammation of the lining of the airways right side. (chronic bronchitis) and the air sacs become dis- tended (emphysema). The thorax and the lungs Figure 10.10 follows the complete circle that become less elastic. The muscles of the neck and forms the origin of the diaphragm, which can be shoulders, normally used in deep inspiration, are summarised as follows: sternal fibres from the used for quiet breathing, and diaphragmatic xiphoid process of the sternum; costal fibres from breathing becomes more important. inner surfaces of the seventh to 12th ribs; lumbar fibres from the arcuate ligaments over the muscles The diaphragm of the posterior abdominal wall, and from lumbar vertebrae by two crura. The diaphragm is a dome-shaped muscle that forms the floor of the thoracic cavity. At rest, the Figure 10.11 shows how the sternal origin is high- fibres of the peripheral part of the dome are almost er than the lumbar origin. The inferior vena cava vertical. Converging inwards, the muscle fibres end passes through the central tendon, and the in a central tendon, a strong flat aponeurosis oesophagus passes through the muscular part just shaped like a trefoil or clover leaf. The central ten- towards the left of the midline. The aorta lies pos- don is nearer to the front of the thorax than the teriorly against the vertebral column. back, so that the posterior fibres are longer. The The action of the diaphragm can be understood by focusing on the shape of the dome. When the diaphragm is active, the contractile muscle fibres pull the central tendon downwards and the dome

Upright Posture and Breathing 173 Fig. 10.11 Diaphragm viewed from the side. limbs. Muscles of the trunk that are attached to the pelvis are the rectus abdominis, oblique becomes flatter. When the diaphragm relaxes, the abdominals, erector spinae and quadratus lumbo- muscle fibres return to their resting length and rum. Muscles of the lower limb attached to the the central tendon moves upwards. Remember: pelvis are the iliopsoas, gluteus maximus, medius contract – down; relax – up. and minimus, hamstrings, hip adductors, rectus femoris, tensor fascia lata and sartorius (see The muscles of the anterior abdominal wall can Chapter 8). actively participate in breathing out. Contraction of the abdominal muscles raises the pressure inside The tilt of the pelvis in relaxed standing largely the abdomen and the diaphragm is pushed upwards. depends on the weight of the trunk above, that The vertical diameter of the thorax is decreased tends to tilt the upper end of the sacrum forwards and air is expelled from the lungs in expiration. The and the lower end backwards. This tendency for diaphragm and abdominal muscles co-operate in rotation of the sacrum is prevented by the breathing movements. sacrospinous and sacrotuberous ligaments, two strong bands that bind the sacrum to the hip bone • PLACE your hands on your anterior abdominal (Fig. 10.12). Pelvic tilt is affected by the opposing wall. tension in the rectus abdominis pulling the pubis Breathe in deeply, lifting the ribs, and feel the up towards the ribs, and the gluteus maximus abdominals relax as the diaphragm moves down. pulling on the posterior surface of the sacrum in Breathe out deeply, contracting the abdominals to the opposite direction. Wearing shoes with high expel as much air as possible. heels tilts the pelvis anteriorly and the lumbar lor- dosis increases to compensate. Posterior or back- ward tilting occurs when sitting in low chairs with poor back support. In this sitting position the lum- bar curvature of the spine is lost. Lateral tilting of the pelvis when one leg is lift- ed off the ground is counteracted by contraction of the gluteus medius and minimus on the supported During quiet breathing, the contribution of the abdominal muscles to the ventilation of the lungs varies in different individuals. In deep breathing, the contraction of the abdominal mus- cles increases the depth of expiration. The ability to control the muscle work of the abdominals is important in singing and in some relaxation techniques. PELVIC TILT AND THE PELVIC FLOOR Fig. 10.12 Pelvic tilting. Arrows indicate the direction of pull of the rectus abdominis and gluteus maximus. Right The pelvis is a staging post for muscles passing innominate bone and sacrum viewed from the inside of upwards to the trunk or downwards to the lower the pelvis.

174 Muscles, Nerves and Movement Clinical note-pad 10D: Stress incontinence Stretching of the muscles of the pelvic floor in childbirth may affect the action of the levator ani on the control of the bladder and the rectum. This leads to incontinence, particularly at times when there is a sharp rise in intra-abdominal pressure such as coughing, sneezing and laughing. NERVE SUPPLY OF THE MUSCLES OF THE NECK AND TRUNK Fig. 10.13 Levator ani of the pelvic floor. Right innom- The muscles of the trunk are supplied by branch- inate bone viewed from the inside of the pelvis. es of spinal nerves at the cervical, thoracic and sacral levels. side (see Chapter 8). When the glutei and the knee flexors are weak, the toes of the swinging leg in In the neck, the spinal accessory (cranial) walking drag on the ground. In this case, the drop- nerve, together with branches of C2 and C3, sup- ping of the pelvis to the unsupported side can be ply the sternomastoid muscles. Branches of C6, C7 conteracted by the contraction of the quadratus and C8 supply the scalene muscles. lumborum and the latissimus dorsi on that side; this is known as ‘hip hitching’. In the thorax, the phrenic nerves supply the two sides of the diaphragm. They are formed from Pelvic floor branches of the third, fourth and fifth cervical nerves in the neck. Each nerve passes down the neck deep The muscles of the floor of the pelvis are suspended to the sternomastoid and enters the thorax. The from the bony walls of the pelvis, and from a fibrous right phrenic nerve lies on the pericardium cover- arch, a thickened band in the pelvic fascia. This ing the right atrium and pierces the central tendon fibrous arch extends from the pubis anteriorly to of the diaphragm with the inferior vena cava. The the spine of the ischium posteriorly. The main mus- left phrenic nerve lies on the pericardium over the cle of the pelvic floor, the levator ani, is attached left ventricle and pierces the diaphragm in front of to this band of fascia (Fig. 10.13). The fibres of the the central tendon (Fig. 10.14). Each phrenic nerve levator ani descend and then turn inwards to meet is the motor and sensory supply to the corres- those from the opposite side in the midline. Pos- ponding side of the diaphragm. teriorly to the levator ani, the pelvic floor is com- pleted by the coccygeus muscle, which extends from Fig. 10.14 Phrenic nerve: position and relations in the the spine of the ischium to the lower part of the thorax. sacrum and the coccyx. The functions of the pelvic floor are to support the pelvic organs, and to withstand any increase in pressure in the abdominopelvic cavity, for example in lifting, coughing and sneezing. In women, the levator ani surrounds the vagina and supports the uterus.

Upright Posture and Breathing 175 • Muscles moving the thorax in the ventilation of the lungs: external and internal intercostals; diaphragm. • Deep posterior muscles of the back: erector spinae (sacrospinalis). • Abdominal muscles: – anterior abdominal wall: rectus abdominis, external oblique, internal oblique, transversus abdominis; – posterior abdominal wall: quadratus lumbo- rum. • Pelvic floor: levator ani and coccygeus. Fig. 10.15 Transverse section of the thorax through an SUMMARY intercostal space showing one pair of intercostal nerves. The trunk consists of the thoracic and the Clinical note-pad 10E: Cervical spine abdominopelvic cavities, bounded by bony and injuries muscular walls, and separated by the muscular Injuries to the neck may occur by falls from a diaphragm. The functions of the trunk can be sum- height, a blow on the head, or violent free move- marised as: maintenance of the upright posture; ments of the neck. If there is damage to the roots protection of the thoracic and abdominal organs; of the phrenic nerves (C3–5), a loss of the action ventilation of the lungs; and expulsion of urine and of the diaphragm in breathing occurs and a faeces. The trunk supports the head and provides ventilator must be used. a base for the movements of the limbs. The thoracic spinal nerves form the intercostal The bones of the vertebral column, which sup- nerves, which supply the intercostal muscles. ports the trunk and the head, are arranged as four Intercostal nerves 1–6 run parallel to the corre- curves, forming a strong and resilient unit of struc- sponding rib and deep to the internal intercostal ture. Seven cervical vertebrae form a secondary muscles (Fig. 10.15). Branches of the intercostal curve that supports the head above. A primary curve, nerves 7–12 continue forwards from the intercostal concave forwards, is formed by 12 thoracic vertebrae spaces to the muscles of the anterior abdominal that articulate with the ribs. The five large lumbar wall. Each layer of the anterior abdominal wall (the vertebrae combine strength with mobility for the rectus abdominis, the oblique abdominals and movements of the trunk. The five sacral vertebrae transversus) receives branches of the thoracic are fused to form the sacrum, which anchors the two nerves 7–12 from above downwards. Thoracic innominate bones in the pelvic girdle. nerve 12 branches to supply the quadratus lumbo- rum in the posterior abdominal wall. Movements between adjacent vertebrae occur at anterior secondary cartilaginous joints between the The muscles of the pelvic floor are supplied by bodies of the vertebrae, and posterior synovial branches of the third and fourth sacral spinal nerves. plane joints between the articular processes. Movements of the vertebral column as a whole pro- SUMMARY OF THE MUSCLES OF duce flexion, extension, lateral flexion and rotation THE TRUNK of the trunk. • Muscles moving the head and neck: sterno- The deep posterior muscle of the back (erector cleidomastoid; scalenus anterior, medius and spinae) performs extension movements of the posterior; splenius capitis and cervicis. trunk, and counteracts both forward sway in standing and the force exerted by loads carried in front of the body. The anterior abdominal wall is composed of four layers of muscles which, com- bining in different ways, produce flexion, lateral

176 Muscles, Nerves and Movement flexion and rotation of the trunk. The anterior SECTION II FURTHER READING abdominal wall supports the digestive organs and assists in expiratory movements in breathing. Agur A. & Lee M. (1999) Grant’s Atlas of Anatomy. Lippincott, Williams & Wilkins, In lifting loads, contraction of the anterior Philadelphia, PA. abdominal wall raises the intra-abdominal pressure and relieves the pressure on the lower back. The Apley A.G. & Solomon L. (1994) Concise System load force of the body plus a load is counteracted of Orthopaedics and Fractures. Arnold, London. by the effort force exerted by the erector spinae. The effort required is least when the load is placed Caillet R. (1994) Hand Pain and Impairment. F.A. near to the body. Davis, Philadephia, PA. Ventilation of the lungs is achieved by move- Lehmkulh L.D., Smith L.K. & Weiss E.L. (1995) ments of the ribs, which change the size of the tho- Brunnstrom’s Clinical Kinesiology. F.A. Davis, racic cavity. In inspiration, the thoracic cage is Philadelphia, PA. enlarged by the action of the intercostal muscles and the diaphragm. The action of the muscles of Palastanga N., Field D. & Soames R. (2002) the neck increases the depth of inspiration. The Anatomy and Human Movement. Butterworth depth of expiration is increased by contraction of Heinemann, Oxford. the anterior abdominal wall which pushes the diaphragm up further. Stone R. & Stone J. (1999) Atlas of Skeletal Muscles. McGraw-Hill, New York. The pelvis forms a bowl, with a bony wall and a muscular floor, at the inferior end of the abdomi- Thompson C. & Floyd R.T. (2000) Manual of nopelvic cavity. In upright standing the pelvis can Structural Kinesiology. McGraw-Hill, London. tilt forwards and backwards, and in standing on one leg the pelvis tends to drop on the unsupported Trew M. & Everett T. (2001) Human Movement. side. Forward tilting is resisted by the action of Churchill Livingstone, Edinburgh. the rectus abdominis and the gluteus maximus. Lateral tilting is counteracted by gluteus medius Wirhed R. (1997) Athletic Ability and the Anatomy and minimus on the supported side. The muscles of Human Motion. Mosby, St Louis, MO. of the pelvic floor support the pelvic organs.

Section III Sensorimotor control of movement • Sensory background to movement • Motor control



11 Sensory Background to Movement Somatosensory system duck the head when a bird flies towards the wind- Posterior (dorsal) column, anterolateral screen when driving in a car along the road. If there pathway is a deficit in the processing of sensory information Interpretation of pain due to neural damage or disease, the motor per- Vestibular system formance that is dependent on it cannot proceed Visual system normally. Regulation of posture Sensory processing is organised in a series of All movement starts with a background of operations whereby information is transmitted sensory information about the surrounding space from peripheral receptors to a neural network and about the position of the body entering the and on to another network in a sensory pathway central nervous system. As movement proceeds, in the central nervous system. One centre this sensory activity changes from moment to in the pathway may alter the resting level of moment. excitability of the neurones at another level, making the input either more effective or less effec- • THINK about the origin of incoming information tive. This is known as modulation. Examples of to the brain as you walk along a path towards a modulation are experiences of cold or pain that are gate: from the eyes scanning the visual field, affected by the perception of these sensations at anticipating obstructions to be avoided; from the the time. skin of the soles of the feet, detecting the roughness of the path; from the attitude and movement of the The sensory system is composed of subsystems, head in relation to the body to keep in balance; each transmitting specific information to the cen- from the joints and the muscles in the moving body tral nervous system. Activity in the subsystems is parts. integrated in association areas of the brain. In this chapter, three subsystems will be considered, We are aware of some of the changes, but many of with emphasis on their role in movement. The the motor responses to the changing input are somatosensory system is the body sensation. It entirely automatic. Obstacles in the way can be monitors a wide variety of stimuli from all over recognised and avoided by changing direction. In the body from the activity in receptors found in the the absence of information from the eyes, there skin, and proprioceptors in the muscles and is more reliance on information from the other the joints. The vestibular system is concerned with senses, including sound and smell. Some of the sensation originating in the inner ear about the automatic responses to the changing input are basic position and movements of the head. The visual protective reflexes, which may occur even when system processes information about the features of there is no threat. For example, we may blink and the external environment and about the position of objects within it. The chapter ends with a summa- ry of the contribution of these three systems to the regulation of posture during movement.

180 Muscles, Nerves and Movement SOMATOSENSORY SYSTEM body parts are represented in a particular topo- graphical arrangement (see Chapter 3). The functions of the somatosensory system are: • REVISE the composition of a spinal nerve from Chapter 4, and the position of ascending tracts of • to monitor the contact of objects and surfaces the spinal cord described in Chapter 3. with the skin, particularly the hands and feet • LOOK at Fig. 11.1 to follow the general plan of • to report the position of body segments in space these two pathways. and in relation to each other (body scheme) Fig. 11.1 Ascending pathways to the somatosensory • to initiate sensory activity for the interpretation cortex, general plan. Frontal section of the brain with of harmful stimuli. spinal cord. From this system, one knows where the arms are in space, the pressure of a pencil held in the fin- gers, and how cold the wind is on the face. The skin is not only a simple sense organ for touch, but responds to the particular pressure and temperature of surfaces. In gripping, the feedback from all the receptors of the skin in contact with the object guides the muscle force that is requir- ed. Pressure receptors in the skin of the soles of the feet monitor the distribution of body weight over the feet, and therefore assist balance reactions. In reaching out to grasp an object, the proprio- ceptors in the upper limb monitor the changing angulation of the joints as the movement proceeds. We can judge the weight of an object held in the hand from activity in the proprioceptors of the elbow flexors and the mechanoreceptors in the skin of the palm of the hand. The sensory information from the somatosenso- ry system forms the body scheme and regulates pos- ture during movement. We are unaware of a large amount of the activity of the somatosensory system and its role in movement is often underestimated. Somatosensory information is transmitted in two main ascending pathways in the spinal cord and the brain, known as the posterior (dorsal) column pathway and the anterolateral pathway. Alterna- tive names are the medial lemniscus pathway and the spinothalamic tracts, respectively. Both systems link the receptors on one side of the body with the somatosensory area in the opposite parietal lobe. The anterolateral pathway crosses at the spinal level, while the posterior column crosses in the sensory decussation in the medulla of the brain. The pathways converge in the brain stem, and both synapse in the thalamus. All fibres from both the anterolateral and posterior column pathways pass through the internal capsule to end in the somatosensory area of the parietal lobe, where the

Sensory Background to Movement 181 The function of each of the two sensory pathways route. The anterolateral pathway conducts the is different, even though some of the sensation reponses from stimuli, such as temperature, that transmitted appears to be the same. The posterior are neither urgent nor require precise location. column pathway is concerned with fast-acting information that has a high degree of discrimina- Posterior (dorsal) column tion. For example, changes in joint position occur rapidly during movement. The changing activity The posterior column pathway provides the route in the joint proprioceptors is conducted via this for touch and proprioception. This ascending Fig. 11.2 Posterior (dorsal) column pathway seen in a frontal section of the brain with spinal cord, and its position in a transverse section of the spinal cord.

182 Muscles, Nerves and Movement route also plays a part in the interpretation of pain. Spinocerebellar Posterior column The important role of this ascending system is in tract Fasciculus gracilis the combination of input from more than one Fasciculus cuneatus modality to interpret complex sensations. For example, both touch and proprioception are Anterolateral tract ANTERIOR involved in the ability to distinguish the size and the (spinothalamic) shape of an object without vision. Fig. 11.3 Position of the ascending tracts at the cervical The activity in the posterior column route is ini- level. tiated by receptors that are fast adapting with large- diameter axons. These receptors are found in the Anterolateral pathway (spinothalamic skin and also lying in muscles, tendons and joints tract) (proprioceptors). The sensory neurones enter the posterior horn of the spinal cord, and then pass into This pathway is primarily concerned with temper- the posterior (dorsal) column of white matter of ature and nociceptive sensations. The spinothala- the same side. Many of the first-order neurones mic tracts play a supplementary role for touch branch to synapse with interneurones in the pos- sensation, but probably only become important terior horn at the spinal level of entry. The poste- when the posterior column is damaged. rior column of white matter, lying underneath the lamina of each vertebra, becomes larger as it Activity in the anterolateral pathway originates ascends the spinal cord, collecting sensory fibres in sensory neurones with slowly adapting receptors from each spinal nerve. In the medulla of the brain, in the skin. The sensory neurones have small- the neurones end in the gracile and cuneate nuclei. diameter axons with slow conduction velocity. At this level, the second-order neurones cross to These sensory neurones enter the spinal cord the opposite side and pass through the brain stem and synapse in the posterior horn before crossing in the medial lemniscus to the thalamus. The third- to the opposite side to enter the spinothalamic order neurones project to the somatosensory tract. The fibres of the spinothalamic tract lie cortex. in the anterolateral white matter of the spinal cord. This route has been divided into anterior • LOOK at Fig. 11.2 to trace the route followed and lateral spinothalamic tracts, but more recent by the posterior column pathway in the central work has shown no difference in the spread of nervous system. Identify the three orders of fibre types across the pathway. There is a topo- neurone. graphical arrangement of the fibres in the antero- lateral pathway, with those from distal body The fibres in the posterior columns are ipsilat- segments more lateral, and proximal areas more eral, i.e. they carry sensation from the same side of medial. the body. Fibres from the lower limbs are most medial and form the fasciculus gracilis. As more The anterolateral route continues in the brain fibres enter the spinal cord from sacral to cervical stem, to end in the thalamus. The third-order segments they are added laterally. In this way, the neurones project from the thalamus to the fibres from the upper limb form the fasciculus somatosensory area in the parietal lobe. cuneatus. Figure 11.3 shows the position of the main ascending tracts in position in the spinal cord at the level of the cervical segments. A similar section at the level of the lumbar segments would have a smaller posterior column with no fasciculus cuneatus. The posterior spinocerebellar tract is formed by some of the fibres from proprioceptors that enter the lateral white matter and reach the ipsilateral cerebellum.

Sensory Background to Movement 183 • LOOK at Figure 11.4 to trace the route followed In the brain stem, some of the second-order neu- by the anterolateral pathway in the central nervous rones branch to link with the reticular formation. system. Identify the three orders of neurone in the pathway. Sensory information from the face Return to Figure 11.1 to find the fibres from both Receptors in the skin and the muscles of the face the ascending pathways lying in parallel in the brain and in the mouth enter the brain stem mainly in the stem. trigeminal (fifth cranial) nerve and synapse in Fig. 11.4 Anterolateral (spinothalamic) pathway seen in a frontal section of the brain with spinal cord, and its position in the transverse section of the spinal cord.

184 Muscles, Nerves and Movement the sensory nuclei of this nerve. Second-order going tissue damage, and it is inferred that the pain neurones cross to the opposite side and lie the person reports is imaginary. alongside the medial lemniscus to reach the thalamus. Third-order fibres end in the region rep- It is now well recognised, especially by people resenting the face in the somatosensory cortex in who experience pain, that tissue healing after dam- the parietal lobe. Input from this trigeminal system age does not always stop pain. The current view of is important for the sensory background to the neural mechanisms responsible for the transmission movements of facial expression, swallowing and of pain is that they have a dynamic/plastic nature speaking. with the capacity to change. The formulation and continuation of pain is a multidimensional experi- Clinical note-pad 11A: Sensory loss in ence that incorporates sensory, emotional, affective, spinal cord damage cognitive and behavioural elements. The interaction Sensory loss occurs when the posterior roots of between people and the environment is also the spinal nerves and/or the posterior column of affected. Individuals may report spontaneous white matter are damaged in the following ways: ongoing pain, pain during occupations that would not be expected to provoke it, and chronic pain over • degeneration of myelin in the spinal cord in many years despite the absence of tissue damage. multiple sclerosis In other words, the extent and severity of pain appear to be disproportionate to the original dam- • infection, e.g. acquired immunodeficiency aging stimulus. This is because pain is a perception syndrome (AIDS) that is the sum of many individual mechanisms occurring in the central nervous system and there- • diseases involving the vertebral column fore is reported to be multidimensional in nature. and/or intervertebral discs, e.g. ankylosing spondylitis and prolapsed discs. In summary, there is no single route from noci- ceptors to the somatosensory cortex or other areas The outcome depends on the segmental level of the brain that can explain how pain is experi- and the extent of the spinal cord damage. Sen- enced at any one time. Pain is a subjective per- sory loss occurs on the same side of the body ception and different individuals may interpret the below the spinal level affected, so that cervical same damaging (noxious) stimulus in different ways damage affects upper and lower limb function. at different times. Loss of position and movement sense in the lower limbs gives a poor prospect for walking. In order to understand more fully why this is the The overall sensory loss is severe in bilateral case, the different types of pain that individuals can lesion of the posterior columns. perceive must be appreciated. Interpretation of pain Transient pain is usually brief in duration and is of little consequence, because tissue damage is min- In the past, pain was thought to be a unidimen- imal. Accidentally sticking a pin into the finger, sional sensory experience. There was a belief that would be an example of this type of pain. The sen- neural mechanisms responsible for the transmis- sation is usually sharp and then a dull sensation is sion of pain were solely ‘hard-wired’, and sensory experienced, which usually subsides quickly. A nerves carried ‘damage information’ to a single function of this type of pain is to prevent further pain centre in the brain. This single pathway repro- damage by initiating escape from the stimulus and duced a pain sensation in proportion to the origi- protection of the body. nal damage. In other words, the more damage done, the more pain was felt, and when the dam- Acute pain describes pain of recent onset and is age ‘healed’, the pain would stop. The return of probably time limited. It is usually associated function would automatically follow. This account with disease or injury that takes longer for the body of the experience of pain leads to frustration when to repair than transient pain. Acute pain that lasts individuals still report pain, in the absence of on- for more than 3 months may be classified as chronic. Chronic pain lasts for long periods, for example years, and persists beyond tissue healing. This may occur in chronic conditions such as joint disease,

Sensory Background to Movement 185 nerve damage or cancer. However, chronic pain with the transmission (T) cells, the fibres of which may also be experienced in the absence of tissue link with the ascending pathways to the brain. This damage. It is now thought that pain mechanisms pain gate mechanism in the spinal cord integrates and neural pathways can become dysfunctional and the incoming information so that onward trans- undergo plastic changes leading to maladaptive mission of information towards the cortex depends responses. Chronic pain by definition is more than on the balance between noxious and non-noxious a sensation and is multidimensional in nature. input. Figure 11.5 shows the SG and T cells in the gate control system, which will be considered fur- Neural mechanisms of transient and acute pain ther under modulation. Peripheral and central mechanisms have been studied to understand the perception of pain. Once The ascending pathways include the spinothal- understood, the plastic changes that can take place amic tract (STT) and the spinoreticular tract in the nervous system contributing to the per- (SRT). ception of chronic pain can be appreciated. • The STT is a direct nociceptive pathway that The mechanisms in the ‘normal state’ of tran- ascends in the cord, synapses in the thalamus and sient and acute pain are presented as transduction, then goes on to the somatosensory strip of the transmission, perception and modulation. cortex (see Fig. 11.4). Transduction: this is the process of converting • The SRT is a less direct nociceptive, multiple the energy content of a stimulus applied to a recep- pathway that ascends the cord and synapses in tor into action potentials in sensory nerve fibres. the medial aspect of the thalamus and then to Nociceptors are activated by noxious stimuli, multiple regions of the brain. which may be mechanical, thermal or chemical (released from damaged tissues), or any combina- Perception: pain is not perceived as ‘pain’ until tion. The energy of the stimulus is converted into it is interpreted within various structures and areas electrochemical impulses in the sensory neurones of the cerebral cortex. This implies that pain is not with small-diameter nerve fibres transmitting merely a sensation but a perceptual experience. noxious information from the periphery to the Nociceptive information via the STT is projected spinal cord (see Chapter 1, the neurone and from the thalamus to the primary somatosensory receptors). Nociceptors are normally only activated cortex, where the pure sensory component of pain transiently by intense levels of stimulation. Long- is registered and discriminated in terms of quality, term stimulation by locally released endogenous intensity, localisation and duration. The STT is pain-producing chemicals associated with tissue responsible for the primary processing of pain, damage can result in changes in receptor sensitiv- which centres on identification of stimuli. Some ity. If the receptors become more sensitive information is also transmitted to the brain stem, (hyperalgesia), the experience of pain is exagger- where the reticular formation influences the state ated. Pain may also be felt from a stimulus that of arousal of the cortex. would not normally cause pain (allodynia). Nociceptive information via the SRT is project- Remember there are other types of receptor in ed diffusely and bilaterally to many other areas the skin, joints and muscles responding to non-nox- of the brain. This secondary processing of pain, ious tactile and proprioceptive stimuli. When acti- related to recognition and meaning, is dependent vated, this information is transmitted towards the on the association areas of the brain that form part spinal cord in large-diameter fibres. of the cognitive control system (Fig. 11.5). The pre- frontal lobe initiates the cognitive evaluation of Transmission: noxious information in small- pain and the development of coping strategies. The diameter fibres and non-noxious information in hypothalamus and the limbic system are involved large-diameter fibres is transmitted to the spinal in the development of pain behaviours. The cord and directed to the posterior horns. In the pos- hypothalamus regulates autonomic responses, e.g. terior horn there is a layer known as the substantia blood pressure and breathing; and the limbic gelatinosa (SG cells), owing to its appearance, com- system is concerned with mood and emotional posed of interneurones with short axons. The sen- responses. The individual may exhibit holding and sory neurones synapse with the SG cells and in turn

186 Muscles, Nerves and Movement Cognitive control system Descending inhibitory control system Large SG Action T system Small Gate control system Excitation Inhibition Fig. 11.5 Gate control theory based on Melzack & Wall (1983). SG = cells in substantia gelatinosa; T = transmis- sion cells. (Redrawn from Main C.J. & Spanswick C.C. (2000) Pain Management – An Interdisciplinary Approach, Churchill Livingstone, Edinburgh, with kind permission.) guarding a limb, adopting awkward postures, in the posterior horn. Impulses then enter the facial grimacing and wincing, vocalising pain, and anterolateral system ascending to the somato- feeling nauseous, sweaty and light-headed. The sensory cortex and pain is perceived. The pain construction of the perception of pain relates both gate is open, and increased noxious traffic is to volition and mood (motivational–affective ascending to the cortex. components) and to the future implications of • Activity in the large-diameter fibres stimulates pain in the individual’s life (cognitive–evaluative the interneurones of the SG cells and these, in components). turn, inhibit the transmission cells. This prevents information from entering the anterolateral Modulation: this is the process by which the level pathway and no pain is perceived. The gate is of excitability of a group of neurones is altered. closed, and less noxious traffic is ascending to the Modulatory influences can raise the base level of cortex. excitability or lower it. In the interpretation of pain, modulation balances noxious and non-noxious The prediction from the pain gate theory is that information within the nervous system. This ulti- large-diameter fibre activity in spinal nerves can mately defines the quality of the perception of pain block the transmission of noxious information at the cortical level. arriving in the small-diameter fibres by the action of interneurones in the substansia gelatinosa in the Two control systems of neural mechanisms that posterior horn of the grey matter. The ultimate are linked together are implicated in the modula- transmission of noxious impulses depends on the tion of pain. These are the pain gate system and the balance of activity in the large- and small-diameter descending inhibitory system. sensory neurones entering the spinal cord. The pain gate control system (see Fig. 11.5) is The pain gate theory explains how rubbing the explained as follows. skin over a painful area often reduces the percep- • Activity in the small-diameter fibres, originating in nociceptors, stimulates the transmission cells

Sensory Background to Movement 187 tion of pain. Tactile stimulation increases activity Clinical note-pad 11B: Chronic pain in the large-diameter fibres and helps to close the Chronic pain occurs in joint disease, cancer and gate. The effectiveness of acupuncture in the relief nerve damage resulting from trauma. Damage to of pain may be partly explained by the stimulation the low back is particularly implicated. The per- of large-diameter fibres. Electrodes implanted in sistence of pain, after tissue healing or outlasting the posterior column of the spinal cord, which can the pathological condition, suggests that struc- be switched on by the subject, have been used to tural neuroplastic changes occur that increase the relieve chronic pain. A less invasive approach for sensitivity of neurones at both the receptor and the management of chronic pain is to use transcu- transmission levels. Action potentials may be taneous electrical neural stimulation (TENS), evoked by innocuous pressure and temperature which activates the large-diameter axons through changes at the receptor level. Neurones at the the skin. Patients can then control the stimulation spinal level become excitable by low-threshold of large-diameter fibres and close the gate. inputs and the pain gate mechanism is opened. The result is an increase in the noxious The descending inhibitory control system orig- information transmitted to the cerebral cortex. inates in the cerebral cortex, the midbrain and Another factor may be a decrease in the modu- medullary reticular formation. The neurones of latory effects of the descending pathway to the these descending pathways use endorphins, which spinal cord. These changes in the processing of are natural painkillers, as a neurotransmitter. noxious information result in abnormal postures, They lie in the spinal cord white matter and and autonomic effects such as sweating and terminate on the SG cells at all levels (Fig. 11.5, nausea. Negative perceptions continuing after descending inhibitory control). Large numbers of the tissues have healed and cognitive evaluation corticospinal fibres also terminate in the same area of the consequences for the future lead to of the posterior horn. The SG cells, in turn, inhib- depression and decreased engagement in it the transmission cells (T cells) and close the gate, occupations. thus reducing noxious activity in the ascending anterolateral pain pathway. In this way, descend- systems which influence the transduction, trans- ing inhibitory pathways from the brain stem mission, perception and modulation of sensory modulate the activity of the ascending systems. information. The descending inhibitory control system may VESTIBULAR SYSTEM explain how the pain from an injury may not be felt by a footballer or an athlete during the match or The functions of the vestibular system are: race. A high level of activity in this descending path- way may also account for the absence of pain often • to monitor the position of the head in space reported by victims of severe trauma at the time of • to co-ordinate head and body movements to injury. keep the body balanced The descending pathways are positively or neg- • to stabilise the gaze when the head is moving. atively influenced by cortical perceptual mecha- nisms. This means that the way in which pain is The receptors lie in the vestibule of the inner ear, perceived can be changed by focusing on the pos- adjacent to the hearing organ (the cochlear). In the itive rather than negative emotions and attitudes, vestibule there are five fluid-filled sacs communi- and maintaining emotional stability by avoiding cating with each other, arranged in the form of: (i) excess anger and fear. Engaging in occupations that two oval bulbs, about 5 mm in diameter, known as distract attention from cognitive processing of pain the utricle and saccule; and (ii) three semicircular towards attending to external stimuli, for example canals, about 1 mm in diameter, lying above and involvement in leisure activities, may energise behind the utricle and saccule. One canal lies in the descending system and have an effect on the each of the three planes of the head: superior, pain gate. posterior and lateral (Fig. 11.6). In conclusion, the interpretation of noxious stimuli depends on activity in three control

188 Muscles, Nerves and Movement Fig. 11.6 The vestibule in the inner ear (utricle, saccule and semicircular canals): position in the head. The proprioceptors found in the walls of these train moving forwards, the otoconia lag behind the sacs respond to movement of the fluid in the sacs movement of the wall of the sac, the cilia are again as the head moves in space and in relation to bent and the sensory cells stimulated (Fig. 11.7c). gravity. Each receptor responds to a particular direction and velocity of head movement. People A simple way to try to understand the mechanism are not generally aware of vestibular activity, so it of the utricle or saccule is to imagine a football filled may be difficult at first to appreciate its importance with fluid. If the football is tilted or moved steadi- in everyday movement. ly in a horizontal direction, there is always a delay in the movement of the fluid inside the football. The receptor areas that lie in the walls of the utri- This moment of delay would be signalled by flexi- cle and saccule are called otoliths or maculae. The ble pins projecting from the inner side. receptor cells have projecting cilia embedded in a jelly-like mass, which contains particles of calcium Receptor areas in the semicircular canals are called otoconia (Fig. 11.7a). If the head tilts, the found in the ampulla, a swelling at the base of each fluid in the sacs lags behind the movement of the canal. Sensory cells in the ampulla also have cilia walls of the utricle and saccule, the cilia are bent embedded in a jelly-like structure called the cupu- and the sensory cells are stimulated (Fig. 11.7b). la, but there are no calcium particles (Fig. 11.8a). Sideways tilting of the head results in increased The cupula forms a flap like a swing-door, moving firing of impulses from one saccule and less from backwards and forwards in response to movement the opposite saccule. The otoliths on the base of the of the fluid along the canal as the head moves. As utricle signal when the head is bent forwards and the cupula bends, the cilia move and the hair cells backwards. In horizontal movement of the head are stimulated. and body, for example when sitting in a car or a Rotation of the head affects the canal lying in the same plane of movement. Figure 11.8 shows the Fig. 11.7 Otolith receptors in the utricle and saccule: (a) head upright; (b) head tilted; (c) head movement.

Sensory Background to Movement 189 Cupula Clinical note-pad 11C: Vertigo Vertigo is a sense of rotation together with a sense Ampulia of imbalance of the head, which occurs in many disorders of the vestibule. Ménière’s disease Receptor cell (which has an unknown cause and occurs main- ly in men aged over 40 years), motion sickness (a) Vestibular nerve and viral infection all produce vertigo. Nausea and dizziness accompany the instability. VISUAL SYSTEM (b) Yes (c) No (d) Maybe The visual system plays an important role in movement for the: Fig. 11.8 Semicircular canals: (a) cupula receptor in the ampulla of a canal; (b–d) stimulation of each canal on the • detection of the features of the environment, left side of the head. their location and movement direction of head movement that stimulates each • maintenance of a stable gaze when the head of the canals on the left side of the head. moves Although individual receptors may respond to a • recognition of the objects used in task per- greater extent in particular movements of the head, formance it is the combined effect of movement of the fluid in all the cavities that is integrated in the vestibu- • maintenance of the balance of the body. lar nucleus. Light entering the eyes passes through several The output from the vestibular nucleus is to the transparent layers of cells and blood vessels to spinal cord, the cerebellum and to the nuclei of reach the rods and cones, the primary receptor the cranial nerves supplying the muscles that move cells. The retina is like a ‘mini-brain’ and some pro- the eyes. Information about the orientation of the cessing occurs in its layers of cells before trans- head with respect to gravity is relayed directly to the mission along the fibres of the optic nerve to the spinal cord, while changes in the head and body posi- brain. An area of the retina opposite the pupil and tion during movement reach the spinal cord via the the lens is densely packed with rods and cones. This cerebellum. The body balance is then maintained by area is the macula lutea, which is best adapted for activity in the contralateral muscles of the neck and the discrimination of form and colour. the ipsilateral extensors of the trunk and lower limbs. The descending spinal pathways, the vestibu- The visual pathway extends from the retina to lospinal tracts, will be described in Chapter 12. the striate cortex in the occipital lobes of the cere- bral hemispheres (Fig. 11.9), where the processing The vestibular system plays a role in the move- for visual identification begins. Further processing ments of the eyes. The detection of head move- for meaning occurs in the prestriate cortex, and ments by the vestibule activates the cranial nerve finally in the temporal and parietal lobes for object nuclei of the eye muscles via the brain stem. If the and face recognition. head turns to one side, the eyes move in the oppo- site direction. This means that when the head Vision can be divided into central and peri- moves, the visual field remains stable and images pheral, relating to the area of the retina involved. are focused on the macula of the retina, which has the greatest visual acuity (see the next section: the Central vision is centred on the macula lutea, visual system). where visual acuity is greatest. The output from this area is processed in the brain for the perception of the shape, distance and size of objects. Further pro- cessing leads to object recognition and to praxis, which is the activation of the movements associat- ed with the functional use of objects. These are

190 Muscles, Nerves and Movement Fig. 11.9 The visual system. When the head turns to one side, the eyes move in the opposite direction to maintain a constant gaze. If the head continues to turn, a rapid eye movement occurs in the same direction as the head to focus on a new fixed point. The rapid eye movements are known as saccades. These eye movements are controlled by co-operation of the vestibular and visual system in the vestibulo-ocular reflex (see Chapter 4, Fig. 4.8). A different type of eye movement occurs when the eyes track a moving object, known as pursuit eye movements. The manipulation of objects in many kitchen tasks involves tracking movements of the eyes. In all reaching and locomotor movements vision becomes more important at the stage when the target is approached. In reaching out to grasp a glass of water, or starting to ascend and descend stairs, visual information is crucial in the stage just before gripping the glass or negotiating the step. essential components for the planning and execu- Clinical note-pad 11D: Visual impairment tion of the movements in task performance. The visually impaired person has to rely on alter- native input for detecting the presence of obsta- Vision from the receptors in the periphery of the cles, the nature of supporting surfaces and the retina detects the features of the environment as form of objects to be manipulated. Touch, pres- an individual moves around. The location, orien- sure, sound, smell and proprioception all help to tation and movement in the environment are compensate for loss of vision. Perceptual and signalled by the peripheral receptors. This aspect cognitive functions such as spatial awareness, of vision is important for functional mobility, visual imagery and memory are also important. enabling a person to react to obstacles in the way by changing direction. Peripheral vision is involv- REGULATION OF POSTURE ed in keeping the body balanced by monitoring the verticality of the features of the environment. The static posture of the body depends on the pos- Vertical and horizontal structures, such as walls, tural tone in the muscles that support the body doors and furniture, are used to align the position against gravity, together with muscle activity of the body. When the eyes are closed, postural required to keep the body balanced over its base sway increases. The contribution of vision to our of support. As the body segments move from one sense of balance can be demonstrated as follows. position to another during movement, the line of gravity of the whole body is constantly shifting. • STAND on one leg with the eyes open, and then Muscles all over the body can be involved in auto- with the eyes closed. Notice how much you sway, matic postural adjustments to maintain balance. and you may fall over when the eyes are closed. Quiet standing requires remarkably little muscle The visual system controls the movements of the activity, but the situation changes when there is an eyes. The visual pathway branches in the midbrain added weight. For example, a shopping bag held in just before the lateral geniculate nucleus (Fig. the hand moves the centre of gravity horizontally 11.9). These fibres, which synapse in the superior to the side of the body with the extra load. If this colliculus of the midbrain, link with the nuclei of movement is great enough, balance will be lost. The the cranial nerves supplying the eye muscles. The postural reflex response moves the centre of grav- position of the eyes keeps the centre of gaze direct- ed on to the central macular area of the retina.

Sensory Background to Movement 191 ity back again by contraction of the neck and trunk Disturbance of balance also occurs during muscles on the opposite side to the load, which active movements of the body, for example when keeps the head and trunk in line over the feet. At kicking a ball or reaching for an item on a shelf. the same time postural tone is increased in the mus- The movements of the head and the limbs shift the cles of the lower limbs. line of weight on the base of support. This recruits the postural support necessary for that movement. The response to postural disturbance depends on It has been proposed that the central motor the direction of the force causing the imbalance commands for voluntary movement include output and the strategy adopted by the postural system to to the postural muscles as well as those to the prime maintain balance. For example, the force on the movers. In this way, the disturbances of posture body when standing on a braking train is counter- that the prime movers will produce are anticipated acted by grabbing a handrail. In lifting a heavy load and the likelihood of imbalance is reduced to a that might topple the body, the position of the feet minimum. This is known as feedforward. The anti- is changed to increase the base of support. cipatory mechanism improves with practice, so that movements are performed with greater smoothness The postural disturbances are detected by the and stability. This is a major component in the somatosensory, vestibular and visual systems. The acquisition of motor skills in sport. The loss of proprioceptors in the somatosensory system are anticipatory postural control is one of reasons for sensitive to changes in the position of the body. The instability in patients with neurological impair- skin is stimulated by a change in the contact of the ments such as stroke and Parkinson’s disease. foot with the ground and by any object interacting with the body. The visual system detects changes If a postural disturbance occurs during the in the orientation of the environment. The vesti- progress of the movement, due to body sway or bular system responds to any movements of the changes in external conditions, further adjustments head that have occurred. The same postural reflex are made in response to feedback. A model of pos- response can be produced by changes in any one tural control during the performance of voluntary of the three sensory systems. movement showing feedback and feedforward is presented in Figure 11.10. The relative contribution of each of the three systems has been studied by neurophysiologists. A The overall ability to maintain balance during patient with no vestibular function and with sensory movement depends on a background of normal loss below the knees was reported. He relied on muscle tone, anticipatory motor commands to pos- visual information to maintain balance and he tural muscles and the response to feedback from could only stand for one second if he closed his the sensory systems. eyes. With his eyes open he could walk but he required great concentration. Removal of all SUMMARY three inputs makes it impossible to stand unaided. The contribution of the somatosensory and visual The wide variety of sensory information entering inputs can be experienced as follows. the central nervous system during movement can be divided into visual, vestibular and somatosen- • STAND on a piece of foam rubber with your eyes sory. The visual system is not only a monitor of closed and hold the position for a minute or two. visual changes in the external environment, but also Change to eyes open and hold that position. Note reinforces proprioceptive information about the whether you feel any difference with respect to bal- movement of body parts, and co-operates with the ance in the two conditions. vestibular system in maintaining balance. The foam-rubber mat reduces the somatosensory The somatosensory system is concerned with input from the feet. In the first condition, you were body sensation. Two ascending pathways in the relying on vestibular input for balance. Patients central nervous system carry information from with no vestibular function would fall over in this the skin, muscles and joints to the somatosensory situation. Studies of balance have shown that at cortex in the parietal lobe. Tactile and proprio- least one of the three main sources of sensory input ceptive information is transmitted in the posterior is necessary for balance.

192 Muscles, Nerves and Movement Motor commands Feed forward Limb movements Postural adjustments Postural disturbance Movement performance Feed Fig. 11.10 Model of the regulation of posture during movement. back (dorsal) column pathway. Sensation from receptors The visual system orientates the upright body in responding to thermal and nociceptive stimuli fol- relation to vertical and horizontal lines in the envi- lows the anterolateral pathway to the cortex. ronment. During manipulative movements, the visual system is important for the perception of dis- The interpretation of pain involves modulation tance and depth in reaching and grasping, and also at the spinal level of the activity originating in for the recognition of objects and the tracking of nociceptors. The pain gate theory proposes their movements during task performance. that large-diameter sensory neurones can block the transmission of nociceptive input from small- The regulation of posture involves feedback diameter axons, via the action of interneurones from the three sensory systems about the position in the posterior horn of the spinal cord. Activity of the body and the features of the environment as in a descending inhibitory pathway from the the movement proceeds. At the same time, a feed- cortex to the spinal level provides another forward system issues motor commands to the pos- modulatory influence. The influence of these two tural muscles as well as the prime movers to mechanisms together with a cognitive evaluation anticipate any adjustments required. determine the experience of nociceptive activity in the individual. The importance of the integration of all of the sensory input entering the nervous system at any one The vestibular system monitors the position of time was identified by Jean Ayres, who observed chil- the head in space via receptors in the inner ear. dren with problems in learning movement and Processing in the brain stem of this information behaviour. By facilitating sensory integration she was about the orientation and the dynamic movements able to improve their ability to interact with the envi- of the head results in output to the muscles of the ronment effectively and to experience satisfaction. neck and the extensors of the trunk and lower Like a radio receiver with an infinite number of limbs. The vestibular system also initiates reflex channels, the integrating centres of the brain are movements of the eyes to keep the image of an tuned to ‘listen’ to particular combinations of signals object centred on the macula of the retina of the so that they can be recognised and acted on. Other eyes during movements of the head. signals may be ignored to reduce irrelevant activity.