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Cranial fossae, Cranial nerves, Cranial meninges & Dural venous sinus Aj. Poonyawee JirarattanawanOverview about scalp, calvaria and cranial meninges Scalp is the skin, connective tissue and muscles that cover the calvaria (skullcap). It is supplied by nerves and blood vessels from face, and composed of 5 layers;skin, connective tissue (dense), aponeurosis, loose connective tissue and pericranium. meningesFigure 1: Layers of scalp, cranium and meninges (Agur, 2013) Meninges is the connective tissue covering and protecting the brain bysurrounding it in fluid-filled space. The meninges also form the supporting frameworkfor arteries, vein, and venous sinus, and the infolding membranes that divide thecranial cavity into compartments Calvaria is the roof of cranial cavity, covering the superior part of brain. Itconsists of 3 layers of bone; compact outer lamina, compact inner lamina, and (middle)diploe which is spongy bone. Within the diploe, there are diploic veins which connectto the veins of scalp and those in cranial cavity. The diploe cannot be found in theparts of temporal bone that covered with temporalis muscles.Gross Anatomy for dental student / 1st semester, 2017 1

Figure 2: diploic veins within diploe (Netter, 2014)The interior surface of calvaria has landmarks due to the structures that press on skull.• Groove for branch (anterior and posterior) of middle meningeal arteries ( ). The groove for anterior branch lies on the pterion.• Granular pits (granular foveola) are the landmarks formed by the compression of arachnoid granulations.Figure 3: Landmarks on interior surface of skull (Netter, 2014) 2 Gross Anatomy for dental student / 1st semester, 2017

Figure 4: Layers of scalp and calvaria (Netter, 2014)Cranial fossa Floor of cranial cavity is the cranial fossa, divided into 3 major fossae. Eachfossa contains different parts of brain.1. Anterior cranial fossa: frontal lobe of cerebrum2. Middle cranial fossa: Temporal lobe of cerebrum3. Posterior cranial fossa: Cerebellum, pons, medulla oblongata(A) (B) 3 Figure 5: (A) Lateral view of cranial cavity with contained brain (B) Superior view of cranial fossae (Marieb et al, 2012) Gross Anatomy for dental student / 1st semester, 2017

Bones of base of skull1. Anterior cranial fossa consist of; ➢ Orbital plate and frontal crest of frontal bone ➢ Crista galli and cribiform plate of ethmoid bone ➢ Body and lesser wing of sphenoid bone2. Middle cranial fossa consist of; ➢ Body and greater wing of sphenoid bone • Sella turcica; tuberculum sellae, hypophysial fossa ➢ Petrous part of temporal bone3. Posterior cranial fossa consist of; ➢ Basilar, condylar and squamous part of occipital bone ➢ Mastoid part of temporal boneFigure 6: interior surface of base of skull (Agur, 2013) 4 Gross Anatomy for dental student / 1st semester, 2017

Figure 7: Landmarks on base of skull (Netter, 2014) 5Gross Anatomy for dental student / 1st semester, 2017

Cranial nerves Figure 8: Cranial nerves arising from brain stem (Agur, 2013)There are 12 pairs of cranial nerve. Each of them has specific function. • CN I and CN II arise above midbrain. • CN III and CN IV arise above the junction between midbrain and pons. • CN V arises at the level of pons. • CN VI, VII and VIII arise at the level of pontomedullary junction. • CN IX, X, XI, and XII arise at the level of medulla oblongata. Gross Anatomy for dental student / 1st semester, 2017 6

Figure 9: Parts of cranial nerves before exiting the opening on base of skull (Agur, 2013)12 pairs of cranial nerve Cranial nerve Opening that it FunctionCN I Olfactory nerve pass through Sensory: smellCN II Optic nerve Sensory: vision Perforations of cribiform plate Optic canalGross Anatomy for dental student / 1st semester, 2017 7

12 pairs of cranial nerve (cont.) Cranial nerve Opening that it Function pass throughCN III Oculomotor nerve Motor: all intrinsic muscles of eyes except those supplied by CN Superior orbital IV and VI, cililary muscles, fissure sphichcter pupillaeCN IV Trochleae nerve Motor: superior oblique muscle of eye • Ophthalmic Superior orbital Sensory root: face, sinus, teeth nerve (V1) fissure • Maxillary Foramen nerve (V2) rotundum • Mandibular Foramen ovale nerve (V3)CN VI Abducent nerve Superior orbital Motor: lateral rectus muscle of fissure eyesCN VII Facial nerve Motor: muscles of facialCN VIII expression, submandibular & Vestibulocochlear Internal acoustic nerve meatus sublingual glands Sensory: taste from anterior two third of tongue, soft palate Sensory (vestibular nerve): orientation, motion (involves in equilibrium) Sensory (cochlear nerve): hearing Gross Anatomy for dental student / 1st semester, 2017 8

12 pairs of cranial nerve (cont.) Cranial nerve Opening that it FunctionCN IX Glossopharyngeal pass through Motor: stylopharyngeus, parotid nerve Jugular foramen glandCN X Vagus nerve Jugular foramen Sensory: taste from posterior Foramen third of tongue, generalCN XI Accessory nerve magnum • Cranial part Hypoglossal sensation from pharynx, tonsillar • Spinal part canal sinus, pharyngotympanic tube,CN XII Hypoglossal nerve middle ear cavity Motor: palate, pharynx, larynx, trachea, bronchial tree, heart, GI tract to left colic flexure Sensory: pharynx, larynx (reflex sensory from tracheobronchial tree, lungs, heart, GI tract to left colic flexure Motor: sternocleidomastoid, trapezius Motor: all intrinsic and extrinsic muscles of tongue (except palatoglossus)** Motor = send the orders from brain to peripheral structures such as muscles and glands Sensory = receive information from receptors and send it to brainGross Anatomy for dental student / 1st semester, 2017 9

Figure 10: Opening in the base of skull and the structures that pass through them (Netter, 2014)Gross Anatomy for dental student / 1st semester, 2017 10

Cranial meninges The cranial meninges are the protection structures of the brain. It consists of 3 major layers; dura mater, arachnoid mater and pia mater. 1. Dura mater (dura) is the outer layer which consist of two layers of tough and thick membrane, endosteal (periosteal) layer and meningeal layer. I. The endosteal layer is the outermost layer, which formed by periosteum. It attaches to the internal surface of the skull II. The meningeal layer is the inner layer of dura, continuous from the dura of the spinal meninges at the foramen magnum. In some area, the meningeal layer extends and reflects to form the partition, separating the cranial cavity into compartments, and lies between parts of brain, called dural infolding (also called dural fold, dural partition or dural reflection in some textbooks) The two layers of dura are normally fused together expect in the area that they enclose dural venous sinus (blood filled spaces) and the dural infolding. Figure 11: Layers of meninges and meningeal space 11with blood vessels and dural venous sinuses (Netter, 2014) Gross Anatomy for dental student / 1st semester, 2017

2. Arachniod mater (arachnoid) is the intermediate layer of the meninges, separating from pia by subarachnoid space which contains blood vessels that supply the brain. The subarachnoid space is filled with cerebrospinal fluid (CSF) which is the clear fluid similar in constitution to blood, providing the nutrient for the brain. The CSF is produced by the choroid plexuses within the ventricles. The arachnoid is enclosed with the meningeal layer of dura. The arachnoid gives some parts to be the structures supporting the brain and ventricular system; I. Arachnoid trabeculae is the web-liked fiber in the subarachnoid space, connecting arachnoid with pia. II. Arachnoid granulations are the tufted prolongation of arachnoid that protrude through the meningeal layer of dura into dural venous sinus and lateral venous lacunae. Each arachnoid granulation is a group arachnoid villi. They transfer CSF from subarachnoid space to the venous sinus.3. Pia mater (pia) is the inner most layer that closely cover each gyrus and in each sulcus of cerebral cortex. It cannot be separated from brain.Figure 12: Superior sagittal sinus and lateral venous lacuna 12 with arachnoid granulations (Moore et al, 2015) Gross Anatomy for dental student / 1st semester, 2017

Figure 13: Lateral view of dura covering the brain with middle meningeal artery (Netter, 2014)Figure 14: Arachnoid covering the brain and blood vessels of the brain (Netter, 2014) 13 Gross Anatomy for dental student / 1st semester, 2017

Clinical correlation The trauma may cause intracranial hematoma, depending on the area ofinjury. The extradural or epidural hemorrhage causes by torn middle meningeal arterybetween the skull and endosteal layer of dura, resulting in extradural or epiduralhematoma. Figure 15: Intracranial hematoma (Moore et al, 2015) Normally, the potential space between dura and arachnoid called subduralspace is not the natural space. The space may develop as a result of trauma causingtorn bridging vein that pass at the area. The event cause subdural hemorrhage andforms subdural hematoma. Whereas the subarachnoid hemorrhage is caused by tornblood vessels within the subarachnoid space, resulting in subarachnoid hematoma.Gross Anatomy for dental student / 1st semester, 2017 14

Dural infolding The dural infolding is formed by refection of meningeal layer of dura into two-fused membrane. It separates cranial cavity into compartments and supports parts ofbrain.1. Falx cerebri is the largest dural infolding in a sickle-shape. It lies in the longitudinal fissure, separating between 2 cerebral hemispheres. It attaches anteriorly at frontal crest and crista galli, and continues posteriorly with tentorium cerebelli.2. Tentorium cerebelli is a wide crescentic septum that separate the occipital lobe of cerebrum from cerebellum. The fixed border of tentorium cerebelli attaches at the anterior and posterior clinoid processes, superior border of petrous part of temporal bone and occipital bone, and form the roof of the posterior cranial fossa (covering the cerebellum like a tent). The free border surrounds brain stem that lies in the midline of posterior cranial fossa.3. Falx cerebelli continues inferiorly with tentorium cerebelli and lies between 2 cerebellar hemispheres, separating posterior cranial fossa into 2 compartments.4. Diaphragmatic sellae is a circular extension of dura that is suspended between clinoid processes forming a partial roof over hypophysis fossa. It covers pituitary gland and allow aperture for infundibulum (pituitary stalk). Falx cerebri 15 Anterior cranial fossa Diaphragmatic sellae Tentorium cerebelli Middle cranial fossa Falx cerebelli Posterior cranial fossaFigure 16: Posterolateral view of dural infolding Gross Anatomy for dental student / 1st semester, 2017

Figure 17: Lateral view of dural infolding (Agur, 2013)Dural venous sinus The dural venous sinuses are endothelial-lined spaces between 2 layers ofdura, filled with low oxygen blood. The venous sinuses lie along the attachment ofdural infolding and are divided into paired and unpaired venous sinus.Unpaired dural venous sinus1. Superior sagittal sinus lies at the superior border of falx cerebri. It receives blood from upper part of cerebral cortex.2. Inferior sagittal sinus lies at the inferior border of falx cerebri. It receives blood from upper part of cerebral cortex.3. Straight sinus is the union of great cerebral vein (which receives blood from deep parts of brain) and inferior sagittal sinus. It lies at the junction between falx cerebri and tentorium cerebelli and join confluence of sinuses.Gross Anatomy for dental student / 1st semester, 2017 16

4. Occipital sinus lies along the fixed border of falx cerebelli. It receives blood from small venous channel around foramen magnum and join confluence of sinus.5. Confluence of sinuses is the enlarge parts anterior to internal occipital protuberance. It drains blood from superior sagittal sinus, straight sinus and occipital sinus to left and right transvers sinus Figure 18: Dural infolding anddural venous sinuses (Moore et al, 2015)Paired dural venous sinus (left and right)1. Transverse sinuses lie long the fixed border of tentorium cerebelli on occipital bone, they laterally continue from confluence of sinus.2. Sigmoid sinuses are s-shape sinuses that lie downward medially on parietal bone, mastoid part of temporal bone, and occipital bone. They drain blood from transvers sinuses to internal jugular veins.Gross Anatomy for dental student / 1st semester, 2017 17

3. Cavernous sinuses lie on both sides of body of sphenoid bone and sellaturcica. The carvernous sinuses have clinical importance due to the connectionto other sinuses and veins from extracranial site, and the structures passthrough the area. The structures passing through cavernous sinuses Figure 19: Coronal section of cavernous sinusshows the structures passing through the area (Netter, 2014).Figure 20: Superior view of dural venous sinus (Netter, 2014) 18 Gross Anatomy for dental student / 1st semester, 2017

Figure 21: Posterior view of dural venous sinuses (Marieb et al, 2012)4. Intercavernous sinuses lie anterior and posterior to infundibulum (pituitary stalk), connecting between 2 cavernous sinuses.5. Sphenoparietal sinuses lie on lesser wing of sphenoid bone. It drain blood to cavernous sinuses.6. Superior petrosal sinuses lie along fixed border of tentorium cerebelli on superior border of petrous part of temporal bone. They connect to posterior end of cavernous sinuses and lateral end of transvers sinuses.7. Inferior petrosal sinuses lie posteroinferiorly on the groove between petrous part of temporal bone and basilar part of occipital bone. They drain blood from cavernous sinus, labyrinthine vein, cerebellar vein, veins from pons, and medulla oblongata to internal jugular veins8. Basilar sinuses and basilar venous plexus lie on basilar part of occipital bone, posterior to sella turcica. The basilar sinuses connect inferior petrosal sinuses to anterior vertebral venous plexus.Figure 22: venous system of head and neck (Moore et al, 2015) 19 Gross Anatomy for dental student / 1st semester, 2017

Direction of venous drainageFigure 23: Superior view (A) and lateral view (B) of dural venous sinuses with some parts of dural infolding (Moore et al, 2015)References• คณาจารยภ์ าควชิ ากายวภิ าคศาสตร์ คณะแพทยศาสตร์ศิริราชพยาบาล มหาวทิ ยาลยั มหิดล. (2556). Reginal Anatomy for Medical Student volume II 3rd edition. กรงุ เทพฯ: โรงพมิ พศ์ ุภวนิชการ พมิ พ.์• คณาจารยภ์ าควชิ ากายวภิ าคศาสตร์ คณะแพทยศาสตร์ศิริราชพยาบาล มหาวทิ ยาลยั มหิดล. (2555). ตาราประสาทกายวภิ าคศาสตร์ พิมพค์ ร้ังท่ี 3. กรงุ เทพฯ: โรงพมิ พศ์ ุภวนิชการพมิ พ.์• Tortora, G.J. & Derrickson, B. (2014) Principal of Anatomy and Physiology 14th edition. Messachusetts: John Wiley & Sons, Inc.• Marieb, E.N. , Wilhelm, P.B. & Mallatt J. (2012). Human Anatomy 6th edition. California: Pearson Benjamin Cummings, an imprint of Pearson Education, Inc.• Agur, A.M.R. & Dalley, A.F. (2013). Grant’s Atlas of Anatomy 13th edition. China: Lippincott Williams & Wilkins, a Wolters Kluwer business.• Hansen, J.T. (2014). Netter’s clinical anatomy 2nd edition. Pennsylvania: Saunders, an imprint of Elsevier Inc.• Snell, R.S. (2015). Clinical anatomy by regions 9th edition. China: Lippincott Williams & Wilkins, a Wolters Kluwer business.• Moore, K.L., Agur, A.M.R. & Dalley, A.F. (2015). Essential Clinical Anatomy 5th edition. China: Lippincott Williams & Wilkins, a Wolters Kluwer business.Gross Anatomy for dental student / 1st semester, 2017 20