Neural Control and Coordination 157 — When an impulse (action potential) arrives at the axon terminal, it stimulates the movement of the synaptic vesicles towards the membrane, where they fuse with the plasma membrane and release their neurotransmitter in the synaptic cleft. — The released neurotransmitter binds to specific receptors, present on the post synaptic membrane. — Their binding opens ion channels and allow the entry of ions which generate new potential in post synaptic neuron. — The new potential may be either excitatory or inhibitory. Central Neural System (CNS) The central neural system includes the brain and the spinal cord. Human brain — The brain is the central information processing organ of the body and acts as the command and control system. — It controls the following activities/functions of the body (i) Voluntary movements (ii) Balance of the body (iii) Functioning of vital involuntary organs (like lungs, heart, kidneys, etc.) (iv) Thermoregulation (v) Hunger and thirst (vi) Circadian (24 hours) rhythms of our body (vii) Activities of several endocrine glands (viii) Human behaviour — It is also the site for processing of : (i) vision, (ii) hearing, (iii) speech, (iv) memory, (v) intelligence, (vi) emotions and (vii) thoughts. — The human brain remains within the cranium. — It is covered by the cranial meninges, which consists of (i) an outer duramater (ii) a thin middle layer called arachnoid and (iii) an inner layer called pia mater. Parts of Brain — The human brain has the following parts:
158 Biology-XI Diagram showing sagital section of the human brain 1. Fore brain (i) Cerebrum — Cerebrum forms the major part of the brain. — A deep cleft/longitudinal fissure divides the cerebrum into two halves, called left and right hemispheres. — The two cerebral hemispheres are joined together by a bundle of densely packed nerve fibres, called corpus callosum. — The outer region of the cerebral hemisphere has prominent folds and is called cerebral cortex or grey matter due to its greyish appearance; the cell bodies of the neurons are concentrated in this region. — It contains motor areas, sensory areas and association areas (areas of intersensory associations, memory and communication). — Inner to the cortex is the white matter, consisting of myelinated nerve fibres in the form of nerve fibre tracts. — The cerebrum is the centre of intelligence, memory, imagination, reasoning, judgement and expression of will power. (ii) Thalamus — Thalamus lies below the cerebrum and is the major coordinating centre for sensory and motor signals i.e. relay centre to receive and transmit sensory and motor signals. (iii) Hypothalamus — Hypothalamus lies at the base of thalamus. — It contains a number of centres which control body temperature (thermoregulation), and urge for eating and drinking. — It also contains several groups of neurosecretory cells which secrete hormones called hypothalamic hormones.
Neural Control and Coordination 159 The inner part of the cerebral hemispheres and a group of associated deep structures like amygdala, hippocampus etc. form a complex structure called lymbic lobe or lymbic system. A long with the hypothalamus, the lymbic system is involved in the regulation of (a) sexual behaviour (b) expression of emotional reactions (e.g., excitement, pleasure, rage and fear), and (c) motivation. 2. Mid brain Mid brain is located between the hypothalamus of the forebrain and pons of hind brain. A canal called cerebral aqueduct passes through the mid brain. The dorsal portion of the mid brain consists of four small lobes called corpora quadrigamina. It is responsible for coordination visual reflexes and auditory reflexes. 3. Hind brain Hind brain consists of cerebellum, pons and medulla. (i) Cerebellum — It controls rapid muscular activities such as running, talking, writing etc. and maintains posture and equilibrium. (ii) Pons — It consists of fibre tracts that interconnect different regions of brain. — It relays impulses between medulla and cerebral hemisphere and between the hemispheres of cerebrum and cerebellum. (iii) Medulla/Medulla oblongata — The medulla is connected to the spinal cord. — It contains centres which control respiration, cardiovascular reflexes and gastric secretions. Very Short Answer Type Questions 1. What is coordination? Ans. Coordination is the process through which two or more organs interact and complement the functions of one another. 2. Name the two systems of the body that jointly coordinate and integrate all the activities of body’s organs. Ans. Neural system and endocrine system. 3. What is the structural and functional unit of neural system. Ans. Neuron. 4. What are neurons? Ans. Neurons are specialised cells, which can detect, receive and transmit different kinds of stimuli.
160 Biology-XI 5. Name the two parts of the human neural system. Ans. (i) The central neural system (CNS), and (ii) The peripheral neural system (PNS). 6. What are Schwann Cells? Ans. Schwann cells are specialised cells that form an envelope around the axon/nerve fibre. 7. What are unipolar neurons and where do they occur? Ans. The neuron in which cell body has no dendrite and one axon only; they are found in the embryonic stage. 8. Rearrange the following in the correct order of involvement in electrical impulse movement: Synaptic knob, dendrites, cell body, axon terminal, axon. Ans. Dendrites → cell body → axon → axon terminal → synaptic knob. 9. What are nodes of Ranvier? Ans. The gaps in the myelin sheath of a myelinated nerve fibre are called nodes of Ranvier. 10. Why are neurons are excitable? Ans. Neurons are excitable because their membranes are in a polarised state. 11. What is resting potential? Ans. The electrical potential difference across the resting plasma membrane (axon membrane) is called resting potential. 12. What is action potential/nerve impulse? Ans. It is the electrical potential difference across the plasma membrane (axon membrane) when stimulated with a stimulus of threshold value. 13. What is a synapse? Ans. A synapse is a junction formed by the membranes of a pre-synaptic neuron and a post synaptic neuron with or without a gap between them. 14. What is a synaptic cleft? Ans. The synaptic cleft is the gap between the membranes of pre-synaptic and post synaptic neurons at the synapse. 15. What are neurotransmitters? Ans. Neurotransmitter are the chemicals involved in the transmission of impulses at the chemical synapses. 16. Why can impulses flow only in one direction? Ans. Because each synapse allow impulse to cross it in a single direction. 17. Name the structure involved in the protection of the brain. Ans. Cranium and cranial meninges. 18. Name the innermost meninges of the brain. Ans. Pia mater.
Neural Control and Coordination 161 19. Name the bundle of fibres that connect two cerebral hemisphere in human being. Ans. Corpus callosum. 20. Which part of the human brain is the most developed? Ans. Cerebrum. 21. What do the grey and white matter in the brain represent? Ans. Grey matter–the cell bodies of neurons. White matter–the fibres of neurons. 22. Name the structure that cerebrum wraps around. Ans. Thalamus. 23. Where is hypothalamus located in the brain? Ans. At the base of thalamus. 24. Our reactions like aggressive behaviour, use of abusive words, restlessness etc. are regulated by brain. Name the part involved. Ans. Lymbic system with hypothalamus. 25. What is cerebral aqueduct? Ans. It is a central canal that passes through the mid brain. 26. Mention the component parts of brain stem. Ans. Mid brain and hind brain (pons, cerebellum and medulla). Short Answer Type-I Questions 1. What are the roles of the neural system and endocrine system in coordination? Ans. — The neural system provides an organised network of point to point connections for a quick coordination. — The endocrine system provides chemical integration through hormones. 2. Compare the central neural system (CNS) and peripheral neural system (PNS)? Ans. Central neural system (CNS) Peripheral neural system (PNS) — It consists of brain and spinal — It consists of all the nerves of the cord. body associated with CNS (brain and spinal cord). — In CNS, the groups of neurons — In PNS, the groups of neurons are are called nuclei. called ganglia. — It is the site of information — It transmit impulses from peripheral processing and control. tissues/organs to CNS and vice versa.
162 Biology-XI 3. Distinguish between somatic neural system and autonomic neural system. Ans. Somatic neural system Autonomic neural system — It relays impulses from — It relays impulses from the CNS to the the CNS to the skeletal involuntary organs and smooth muscles muscles. of the body. 4. Distinguish between afferent neurons and efferent neurons. Ans. Afferent/Sensory neurons Efferent/Motor neurons — They conduct impulses from — They conduct impulses from CNS to the receptors to CNS. the effectors. — The terminals of dendrites — The axon terminals come in contact become modified to form with the motor end plate to form receptors. neuro muscular junction. — They are sensory in nature. — They are motor in nature. 5. Differentiate between dendrites and axons. Ans. Dendrites Axon — These are short processes — Axon is a single long process projecting out from the cell body (fibre) arising from the cell body and are branched all along their and are branched at the distal length. end. — Their branches do not have — Its branches terminate into synaptic knob. bulb like synaptic knobs. — Their neuroplasm contains Nissl’s — Its neuroplasm lacks Nissl’s granules. granules. — They transmit impulses towards — It transmit impulses away from the cell body. the cell body. 6. Differentiate between myelinated and non-myelinated nerve fibres? Ans. Myelinated nerve fibres Non-myelinated nerve fibres — The nerve fibre (axon) is covered — The nerve fibre (axon) is covered by a lipid rich myelin sheath and a by only neurilemma made of outer thin neurilemma made up of Schwann’s cells, myelin sheath Schwann’s cells. is absent. — They appear white in fresh state. — They appear grey in fresh state. — They occur in white matter of CNS — They occur in somatic and (brain and spinal cord). autonomic nerves. — The action potential occurs only at — The action potential propagates the nodes of Ranvier i.e. the action all along the nerve fibre (axon). potential jumps from nodes to node. — They transmit nerve impulses with — They conduct nerve impulse faster speed. with slow speed.
Neural Control and Coordination 163 7. Differentiate between resting membrane potential and action potential. Ans. Resting Membrane potential Action potential — It is the electrical potential — It is the electrical potential difference across a resting axon difference across a stimulated axon membrane. membrane. — The interior or axoplasm — The interior of axoplasm is is electronegative and the electropositive and the exterior is exterior is electropositive. electronegative. — The membrane is more — The membrane is more permeable permeable to K+ ions than to to Na+ ions than to K+ ions. Na+ ions. — An active sodium-potassium — The sodium-potassium pump is pump is operative. non-operative. 8. The membrane of a resting nerve fibre is said to be in a polarised state. What is meant by this statement? Ans. — W hen a neuron is not conducting any impulse i.e. resting, an electrical potential difference exists across the resting membrane. — The outer surface has a high concentration of Na+ ions and is positively charged. — The inner surface has low concentrations of Na+ ions but have negatively charged proteins, and is negatively charged. — Such a membrane is called polarised. 9. Explain the role of Na+ in the generation of action potential. Ans. — When a stimulus is applied to the resting/polarised membrane, the membrane becomes freely permeable to Na+ at the point of stimulation. — This leads to a rapid influx of Na+ followed by the reversal of the polarity at that site, and the membrane at this site is depolarised. — The positive ions travel from the depolarised region to the next polarised region through the axoplasm and from the polarised segment to the depolarised region through ECF (extra cellular fluid) to complete the circuit of current flow. 10. Distinguish between impulse conduction in a myelinated nerve fibre and in an unmyelinated nerve fibre. Ans. Conduction of impulse in Conduction of impulse in non- myelinated nerve fibre myelinated nerve fibre — The depolarisation of axon — The depolarisation occurs all membrane occurs only in the along the length of the nerve nodes of Ranvier where myelin fibre. sheath is absent. — Action potential jumps from one — Action potential travels along the entire length of the fibre. node of Ranvier to another and is called saltatory conduction. — The conduction of the nerve — The conduction of the nerve impulse is much faster. impulse is slow.
164 Biology-XI 11. Complete the statement by choosing appropriate match among the following. (a) Resting potential (i) Chemical involved in the transmission of impulses at synapses. (b) Nerve impulse (ii) G ap between pre-synaptic and post-synaptic neurons. (c) Synaptic cleft (iii) Electrical potential differences across the resting neural membrane. (d) Neurotransmitters (iv) An electrical wave-like response of a neuron to a stimulation. Ans. (a)–(iii), (b)–(iv), (c)–(ii), (d)–(i). 12. What are neurotransmitters? What is their role in transmission of nerve impulses? Ans. — Neurotransmitters are the chemicals involved in the transmission of nerve impulses across a chemical synapse. — When an impulse (action potential) arrive at the axon terminal, it stimulates the movement of synaptic vesicles containing neurotransmitters towards the membrane, where they fuse with the plasma membrane and release their neurotransmitters in the synaptic cleft. — The released neurotransmitters bind to their specific receptors on the post synaptic membrane to generate a new potential in the post synaptic neuron. Short Answer Type-II Questions 1. Describe the three types of neurons based on the number of axon and dendrites. Also mention their locations in human body. Ans. (i) Multipolar neuron—They possess one axon and two or more dendrites. — They are found in cerebral cortex. (ii) Bipolar neuron—They possess one axon and one dendrite. — They are found in the retina of eye. (iii) Unipolar neuron—Their cell body is with one axon only. — They are found usually in the embryonic state. 2. Explain the polarisation of the membrane of a nerve fibre. Ans. — When a neuron is not conducting any impulse i.e. resting, the axonal membrane is more permeable to potassium (K+) ions and nearly impermeable to sodium (Na+) ions. — It is also impermeable to negatively charged proteins present in the axoplasm.
Neural Control and Coordination 165 — Consequently, the axoplasm inside the axon contains high concentration of K+ and negatively charged proteins and low concentration of Na+. — In contrast, the fluid outside the axon contains a low concentration of K+ and high concentration of Na+ and thus form a concentration gradient. — Thus, the outer surface of the axonal membrane is positively charged and the inner surface is negatively charged. — The potential difference across the membrane is called resting potential and the membrane is said to be polarised. 3. Explain depolarisation of the membrane of a nerve fibre. Ans. — The electrical potential difference that occurs across the axonal membrane, when stimulated by threshold stimulus is called depolarisation. — When a stimulus is applied, the membrane becomes more permeable to sodium (Na+) ions. — This leads to a rapid influx of Na+ ions, followed by the reversal of the polarity of the membrane at the site of stimulation. — The electrical potential difference across the axonal membrane is called action potential and the membrane is called depolarised. 4. Write short notes on hind brain. Ans. — The hind brain consists of pons, cerebellum and medulla. — Pons consists of fibre tracts that interconnect different regions of the brain. — Cerebellum has very convoluted surface; It controls rapid muscular activities and maintains posture and equilibrium. — The medulla is connected to the spinal cord. It contains centres which control respiration, cardiovascular reflexes and gastric secretions. 5. Give the function of the following. (i) Cerebrum (ii) Hypothalamus (iii) Mid brain. Ans. (i) C erebrum—It contains motor areas sensory areas and association areas for complex functions like intersensory association, memory and communication. (ii) H ypothalamus—It has centres which controls body temperature, urge for eating and drinking. (iii) M id brain—It controls and coordinates the movement of head and eyes, receive sensory impulses from ear and relay impulses between cerebrum and cerebellum. Long Answer Type Questions 1. Explain the conduction of a nerve impulse along a nerve fibre. Ans. — I n a resting nerve fibre (i.e. when a neuron is not conducting any impulse), the axoplasm is electronegative and the exterior (ECF) is electropositive. — This state of the resting membrane is called polarised state.
166 Biology-XI — When a stimulus is applied, the axonal membrane become freely permeable to Na+ ions, causing the reversal of the polarity i.e. the axoplasm becomes electropositive and the exterior (ECF) is electronegative. — This state of the membrane is called depolarised state, and the electrical potential difference across the membrane is called action potential, which is in fact termed as a nerve impulse. 2. Explain the transmission of a nerve impulse across a chemical synapse. Ans. — At a chemical synapse, the membranes of the pre and post synaptic neurons are separated by a fluid filled space called synaptic cleft. — Certain chemicals called neurotransmitters are involved in the transmission of impulses at these synapses. — The axon terminals contain vesicles filled with the neurotransmitters. — When an impulse (action potential) arrives at the axonal terminals, it stimulates the movement of the synaptic vesicles towards the membrane, where they fuse with the plasma membrane and release their neurotransmitters in the synaptic cleft. — The released neurotransmitters bind to their specific receptors present on the post synaptic membrane. — This generates a new potential in the post synaptic neuron. 3. Write short note on fore brain. Ans. — F ore brain consists of cerebrum, thalamus and hypothalamus. — Cerebrum forms the major part of the human brain, and consists of two halves called cerebral hemispheres. — The two hemispheres are joined together by a tract of nerve fibres called corpus callosum. — The outer surface of cerebrum (called cerebral cortex) has grey matter and inner to the cortex is white matter. — The cerebral cortex is thrown into prominent folds. — Thalamus lies just under the cerebrum and hypothalamus lies at the base of the thalamus. — Hypothalamus has a number of centres which control body temperature, urge for eating and drinking. — It also contains neurosecretory cells that secrete hormones. — The inner parts of cerebral hemispheres has structures like amygdala, hippocampus etc., to form complex structure called limbic lobe or limbic system. Along with hypothalamus, limbic system is involved in the regulation of sexual behaviour, expression of emotions and motivation.
Neural Control and Coordination 167 4. (a) Distinguish between electrical synapse and chemical synapse. (b) What are cranial menings? Name their constituent layers. Ans. (a) Electrical synapse Chemical synapse — In electrical synapse, the — Inchemicalsynapse,themembranes membranes of pre-synaptic and of pre-synaptic and post-synaptic post-synaptic neurons are in neurons are separated by a fluid close proximity and there is no filled space called synaptic cleft. synaptic cleft. — The transmission of impulse occurs — The electrical current can flow with the help of neurotransmitter. directly from one neuron to the other. — They are slower in transmission of — They are faster in transmission impulse. of an impulse. — They are the most common type of — They are rare in our system. synapse. (b) — The membranes that covers the brain are called cranial meninges. — The cranial meninges consists of an outer layer called duramater, a very thin middle layer called arachnoid and an inner layer called pia mater. 5. (a) Differentiate between thalamus and hypothalamus. (b) Differentiate between cerebrum and cerebellum. Ans. (a) Thalamus Hypothalamus — It lies below the cerebrum. — It lies below the thalamus. — It is the major coordinating — It is the major centre for regulation centre for sensory and motor of body temperature, thirst and signalling. hunger etc. — It does not secrete hormone. — It secretes hormones. (b) Cerebrum Cerebellum — It is a part of fore brain. — It is a part of hind brain. — It is the largest part of the — It is the second largest part of the brain. brain. — It is the seat of highest — It control and coordinate voluntary mental faculties and governs movements and helps in maintaining reasoning learning, memory balance and posture of the body. and intelligence.
168 Biology-XI Case Study Based MCQs Passage I Read the passage given below and answer the questions that follows. The neural system consists of highly specialised cells called neurons. The neurons detect and receive information from different sense organs (receptors) in the form of stimuli and transmit the stimuli to the central neural system (CNS) i.e., brain and spinal cord through sensory nerve fibres. The received inputs are processed in the central neural system which analyses and integrates all these inputs and then transmits appropriate neural signals to the concerned organs through motor nerve fibres for a proper response. Thus, the neural system of higher organisms performs three basic functions— (i) receiving sensory input from internal and external environment by nerves and passing it to the brain. (ii) processing the input information by the central processor, the brain, and (iii) responding to stimuli, transmitting motor commands from the brain to determine the response of the body parts or cells. 1. Sympathetic nerve fibres in mammals arise from (a) Thoracolumbar nerves (b) (iii), (iv), (x), cranial nerves (c) Sacral nerves (d) Cervical nerves Ans. (a) 2. Anaesthetics reduce pain by blocking the transmission of nerve impulses. The kind of chemical working as anaesthetics are those that block (a) Voltage-gated sodium and potassium channels and neurotransmitter receptors (b) Only the voltage-gated sodium channels in membranes (c) Only the voltage-gated potassium channels in membranes (d) Only the neurotransmitter receptors Ans. (a) (b) Olfactory 3. The largest cranial nerve is (a) Vagus (c) Hypoglossal (d) Glossopharyngeal Ans. (a) 4. What used to be described as Nissl’s granules in a nerve cell are now identified as (a) Fat granules (b) Ribosomes (c) Mitochondria (d) Cell metabolites Ans. (b) 5. In the resting state of the neural membrane, diffusion due to concentration gradients, if allowed, would drive (a) K+ and Na+ out of the cell (b) Na+ into the cell (c) Na+ out of the cell (d) K+ into the cell Ans. (b)
Neural Control and Coordination 169 Passage II Read the passage given below and answer the questions that follows. Brain is the anterior most part of the central neural system which is situated in the cranial cavity of the skull. The cranial bones protect it from mechanical injury. Human brain weighs about 1.2 to 1.4 kg, and form about 98 per cent of the weight of the whole CNS. Human neural system has about 100 billion neuron, majority of them lie in the brain. The brain is covered by three protective coverings called cranial meninges (sing. meninx)—duramater, archnoid and piamater. (i) Duramater is the outer tuogh fibrous layer adhering closely to the inside of the cranium. (ii) Archnoid also called arachnoid mater is a thin, spider webby’ middle layer, and (iii) Piamater is the inner thin, very delicate vascular layer which is in contact of brain tissue. The space between archnoid membrane and piamater is called sub-archnoid space, while the space between the archnoid and duramater is termed as sub-dural space. The sub-archnoid space is filled with cerebrospinal fluid. The latter serves as cushion to protect the brain from shock, provides a medium for exchange of materials. 1. Synapse is a close proximity of (b) Two arteries (a) Two veins (c) Two neurons (d) Two lymphatics Ans. (c) 2. Membrane covering the brain and spinal cord is called (a) White matter (b) Arachnoid layer (c) Meninges (d) Grey matter Ans. (c) 3. Which part of the brain controls emotions like love, anger and pleasure? (a) Medulla oblongata (b) Hypothalamus (c) Cerebrum (d) Cerebellum Ans. (b) 4. The appetite and satiety centres in the brain are located in (a) Hypothalamus (b) Cerebral hemispheres (c) Cerebellum (d) Medulla oblongata Ans. (a) 5. Which of the nerves function more like a tract of brain than a nerve? (a) Trigeminal (b) Abducens (c) Glossopharyngeal (d) Vagus Ans. (d)
ISBN: 978-93-93738-11-0 789393 738110 T11-8895-249-COMP.CBSE QB BIO T-II XI
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