NCERT Solutions for Class 11 Biology Chapter 18: Neural Control and Coordination – Free PDF Download

Chapter 18, Neural Control and Coordination, explains how the human nervous system detects, processes and responds to stimuli. It covers the structure of a neuron, the generation and conduction of the nerve impulse (resting potential, action potential, saltatory conduction), transmission across a synapse, the organisation of the human neural system into the central and peripheral divisions, and the structure of the human brain.

Last Updated: September 23, 2026

Exercises

Q1. Briefly describe the structure of the brain — The brain is the main coordinating centre of the body. It lies inside the skull and is…

The brain is the main coordinating centre of the body. It lies inside the skull and is protected by three membranes called cranial meninges — the outer dura mater, a thin middle layer called the arachnoid, and an inner layer in direct contact with the brain tissue called the pia mater. The brain is broadly divided into the forebrain, midbrain and hindbrain.

Forebrain: The largest part of the brain. It consists of the cerebrum (divided into left and right cerebral hemispheres joined by a band of fibres called the corpus callosum; the outer cerebral cortex is folded grey matter that contains sensory, motor and association areas, while the inner myelinated white matter connects different regions), the thalamus (the main relay centre for sensory and motor signalling), and the hypothalamus (which controls body temperature, hunger, thirst and several other visceral functions and is linked to the pituitary gland).

Midbrain: A short segment between the thalamus/hypothalamus and the pons, containing the corpora quadrigemina; it relays visual and auditory reflexes.

Hindbrain: Consists of the pons (fibre tracts connecting different parts of the brain), the cerebellum (a highly folded structure that coordinates voluntary movement, posture and balance), and the medulla oblongata, which connects the brain to the spinal cord and contains centres controlling respiration, cardiovascular reflexes and gastric secretions. The midbrain, pons and medulla together form the brain stem.

Q2. Compare the following: (a) Central neural system (CNS) and Peripheral neural system (PNS); (b) Resting potential and action potential — (a) CNS and PNS: The central neural system comprises the brain and the spinal cord; it…

(a) CNS and PNS: The central neural system comprises the brain and the spinal cord; it is the site where information is processed and responses are initiated, and it is protected by the skull and vertebral column. The peripheral neural system comprises all the cranial nerves (arising from the brain) and spinal nerves (arising from the spinal cord) that connect the CNS to the rest of the body; it lacks bony protection. The PNS is further divided into the somatic neural system (relays impulses to and from the CNS to skeletal muscles) and the autonomic neural system (relays impulses to smooth and cardiac muscles and glands, further split into sympathetic and parasympathetic divisions).

(b) Resting potential and action potential: The resting potential is the electrical potential difference across the membrane of a nerve fibre when it is not conducting any impulse; the axoplasm is electronegative with respect to the outside, and the membrane is more permeable to K⁺ than to Na⁺. The action potential is the potential difference generated across the membrane when the nerve fibre is stimulated; here the membrane becomes highly permeable to Na⁺, and the inside of the membrane becomes electropositive while the outside becomes electronegative. The resting potential is maintained by the sodium-potassium pump, which actively pumps 3 Na⁺ out for every 2 K⁺ pumped in.

Q3. Explain the following processes: (a) Polarisation of the membrane of a nerve fibre; (b) Depolarisation of the membrane of a nerve fibre; (c) Transmission of a nerve impulse across a chemical synapse — (a) Polarisation: In the resting nerve fibre, the axoplasm has a higher concentration of…

(a) Polarisation: In the resting nerve fibre, the axoplasm has a higher concentration of K⁺ and negatively charged proteins, while the fluid outside the axon has a higher concentration of Na⁺. Because the resting membrane is comparatively more permeable to K⁺ and nearly impermeable to Na⁺, K⁺ ions diffuse out faster than Na⁺ ions diffuse in. The sodium-potassium pump actively moves 3 Na⁺ out of the axon for every 2 K⁺ moved in. As a result, the outer surface of the membrane accumulates a positive charge and the inner surface a negative charge — the membrane is said to be polarised, and this potential difference (about −70 mV) is the resting potential.

(b) Depolarisation: When a stimulus is applied to a polarised region of the membrane, its permeability to Na⁺ suddenly increases. Na⁺ ions rush into the axoplasm, reversing the charge on the membrane — the inner surface becomes electropositive and the outer surface electronegative. This sudden reversal of the resting potential is called depolarisation, and it generates the action potential (nerve impulse), which travels as a wave of depolarisation along the fibre.

(c) Transmission across a chemical synapse: A chemical synapse has a fluid-filled gap called the synaptic cleft separating the axon terminal of the presynaptic neuron from the dendrite of the postsynaptic neuron. When a nerve impulse reaches the axon terminal, it triggers the release of a stored neurotransmitter (such as acetylcholine) from synaptic vesicles by exocytosis. The neurotransmitter diffuses across the cleft and binds to specific receptors on the postsynaptic membrane, opening ion channels there. This generates a new potential in the postsynaptic neuron, which may be excitatory or inhibitory depending on the neurotransmitter and receptor involved.

Q4. Draw labelled diagrams of the following: (a) Neuron; (b) Brain — (a) Neuron: A neuron consists of a cell body (cyton) containing the nucleus and…

(a) Neuron: A neuron consists of a cell body (cyton) containing the nucleus and cytoplasm with granular Nissl bodies; short, branched dendrites that receive impulses and conduct them towards the cell body; and a single long axon that conducts impulses away from the cell body, ending in branched axon terminals with synaptic knobs. Many axons are wrapped in a fatty, insulating myelin sheath secreted by Schwann cells; the gaps between successive Schwann cells, where the axon is exposed, are called nodes of Ranvier.

(b) Brain: A labelled diagram of the brain should show the cerebrum divided into left and right hemispheres with the corpus callosum beneath, the thalamus and hypothalamus of the diencephalon, the midbrain with the corpora quadrigemina, and the hindbrain structures — pons, cerebellum and medulla oblongata — leading into the spinal cord.

Q5. Write short notes on the following: (a) Neural coordination; (b) Forebrain; (c) Midbrain; (d) Hindbrain; (e) Synapse — (a) Neural coordination: The neural system uses electrical nerve impulses for the rapid…

(a) Neural coordination: The neural system uses electrical nerve impulses for the rapid coordination and integration of all the organs and organ systems of the body. Receptors detect stimuli, and the information travels through afferent pathways to the CNS, which processes it and sends a response through efferent pathways to effector organs (muscles or glands).

(b) Forebrain: Comprises the cerebrum, thalamus and hypothalamus. The cerebrum forms the seat of intelligence, learning and voluntary actions; the thalamus relays sensory and motor signals; the hypothalamus regulates temperature, hunger, thirst and links the nervous and endocrine systems via the pituitary.

(c) Midbrain: A small region connecting the forebrain and hindbrain, containing the corpora quadrigemina which mediate visual and auditory reflexes; the cerebral aqueduct passes through it.

(d) Hindbrain: Comprises the pons (a bridge of fibre tracts), the cerebellum (coordinates muscular activity, posture and balance) and the medulla oblongata (controls respiration, heart rate and gastric secretion; continues as the spinal cord).

(e) Synapse: The point of junction between the axon terminal of one neuron and the dendrite of the next, allowing a nerve impulse to pass from one neuron to another either chemically (via a neurotransmitter, across a synaptic cleft) or electrically (through direct, rapid ionic continuity).

Q6. Give a brief account of the mechanism of synaptic transmission — Synaptic transmission can occur chemically or electrically. In chemical transmission, an…

Synaptic transmission can occur chemically or electrically. In chemical transmission, an arriving nerve impulse causes voltage-gated Ca²⁺ channels to open at the presynaptic axon terminal; the resulting influx of Ca²⁺ causes synaptic vesicles containing a neurotransmitter (commonly acetylcholine) to fuse with the presynaptic membrane and release the neurotransmitter into the synaptic cleft by exocytosis. The neurotransmitter diffuses across the cleft and binds to specific receptor proteins on the postsynaptic membrane, opening ion channels and generating a new potential (excitatory or inhibitory) in the postsynaptic neuron. In electrical transmission, the membranes of the pre- and postsynaptic neurons are in very close proximity, allowing the electrical current itself to spread directly from one neuron to the next; this is much faster than chemical transmission but is comparatively rare in the human nervous system.

Q7. Explain the role of Na⁺ in the generation of the action potential — In a resting nerve fibre, the Na⁺ channels are closed and the membrane is far less…

In a resting nerve fibre, the Na⁺ channels are closed and the membrane is far less permeable to Na⁺ than to K⁺. When a stimulus reaches threshold, voltage-gated Na⁺ channels open rapidly, and Na⁺ ions rush into the axoplasm along their electrochemical gradient. This sudden inward movement of positively charged Na⁺ ions makes the inside of the membrane electropositive with respect to the outside, reversing (depolarising) the resting potential and generating the action potential. The Na⁺ channels then close and voltage-gated K⁺ channels open, allowing K⁺ to flow out and repolarise the membrane, after which the sodium-potassium pump restores the original ionic distribution so the fibre returns to its resting state.

Q8. Differentiate between: (a) Myelinated and non-myelinated axons; (b) Dendrites and axons; (c) Thalamus and hypothalamus; (d) Cerebrum and cerebellum — (a) Myelinated vs non-myelinated axons: Myelinated axons are covered by a fatty myelin…

(a) Myelinated vs non-myelinated axons: Myelinated axons are covered by a fatty myelin sheath deposited by Schwann cells, interrupted at nodes of Ranvier; because ion exchange occurs only at these nodes, the impulse “jumps” from node to node (saltatory conduction), making conduction fast and energy-efficient. Non-myelinated axons lack this sheath, so ion exchange occurs continuously along the entire length of the fibre, making conduction comparatively slow.

(b) Dendrites vs axons: Dendrites are short, branched extensions of the cell body that receive impulses and conduct them towards the cell body; they generally lack a myelin sheath. The axon is typically a single, long process that conducts impulses away from the cell body to another neuron or effector; axons may or may not be myelinated and end in branched terminals.

(c) Thalamus vs hypothalamus: The thalamus is the main relay centre for sensory and motor signals travelling to and from the cerebral cortex. The hypothalamus lies below the thalamus and contains centres that regulate body temperature, hunger, thirst and several other visceral functions, besides secreting hormones that control the pituitary gland.

(d) Cerebrum vs cerebellum: The cerebrum is the largest part of the forebrain, responsible for voluntary actions, intelligence, memory and consciousness, and is divided into two hemispheres joined by the corpus callosum. The cerebellum is part of the hindbrain, has a highly convoluted surface to accommodate more neurons, and its main function is coordinating muscular activity, maintaining posture and balance rather than initiating voluntary movement.

Q9. Answer the following: (a) Which part of the human brain is the most developed? (b) Which part of our central neural system acts as a master clock? — (a) The cerebrum is the most highly developed part of the human brain, responsible for…

(a) The cerebrum is the most highly developed part of the human brain, responsible for higher functions such as reasoning, memory, language and voluntary control.

(b) The hypothalamus acts as the master clock of the body, since it contains centres that regulate many circadian (24-hour) rhythms, including body temperature and other physiological cycles.

Q10. Distinguish between: (a) Afferent neurons and efferent neurons; (b) Impulse conduction in a myelinated nerve fibre and an unmyelinated nerve fibre; (c) Cranial nerves and spinal nerves — (a) Afferent vs efferent neurons: Afferent (sensory) neurons carry impulses from…

(a) Afferent vs efferent neurons: Afferent (sensory) neurons carry impulses from receptors towards the central neural system. Efferent (motor) neurons carry impulses from the central neural system towards effector organs such as muscles and glands.

(b) Impulse conduction — myelinated vs unmyelinated fibres: In a myelinated fibre, the myelin sheath acts as an insulator, so depolarisation occurs only at the nodes of Ranvier, and the impulse jumps rapidly from node to node — this is called saltatory conduction and is fast and energy-efficient. In an unmyelinated fibre, there is no insulating sheath, so the impulse must depolarise the membrane continuously along its entire length, which is comparatively slow and requires more energy.

(c) Cranial vs spinal nerves: Humans have 12 pairs of cranial nerves that arise directly from the brain and mainly supply structures of the head and neck (some are purely sensory, some purely motor, and some mixed). Humans have 31 pairs of spinal nerves that arise from the spinal cord and are all mixed nerves, carrying both sensory and motor fibres to the rest of the body.

Class 11 Biology Chapter 18 – Notes and Extra Questions

The current (2023-rationalised, 2026-27 session) exercise for Chapter 18 has 10 questions, several of which carry two to five lettered sub-parts (compare, differentiate, short-notes and distinguish-type questions), for a total of roughly 28 gradable parts. When revising, focus first on the ionic basis of the resting and action potential (Q2b, Q3, Q7) and saltatory conduction (Q8a, Q10b), since these are asked repeatedly in both board exams and competitive tests; then consolidate the brain’s three-part organisation (Q1, Q5) and the CNS–PNS–synapse framework (Q2a, Q6, Q10a, Q10c). Students should also be able to reproduce simple labelled diagrams of a neuron and the brain (Q4) from memory, since diagram-based questions are common in the CBSE exam. Older (pre-2023) editions of this chapter carried 12 exercise questions with several additional sub-parts on the detailed structure and mechanism of the eye and ear — including labelled diagrams of the eye and ear, short notes on the retina, cochlea, ear ossicles and organ of Corti, the mechanisms of vision and hearing, and differentiation questions on rods/cones and aqueous/vitreous humour. These detailed sensory-organ sub-questions have been trimmed from the current rationalised exercise, so students should rely on the present 10-question set rather than older solution guides that still reproduce the pre-2023 12-question list.

Frequently Asked Questions

How many questions are there in the NCERT Class 11 Biology Chapter 18 exercise?

The current, rationalised NCERT exercise for Neural Control and Coordination has 10 main questions, several with multiple lettered sub-parts (for example, compare, differentiate and short-notes style questions). This is fewer than the 12-question exercise found in older, pre-2023 editions of the chapter.

What is saltatory conduction and why is it faster than conduction in an unmyelinated fibre?

Saltatory conduction is the “jumping” of the nerve impulse from one node of Ranvier to the next along a myelinated axon. Because the myelin sheath insulates the axon between nodes, ion exchange (and therefore depolarisation) can occur only at the exposed nodes, so the impulse effectively skips the insulated stretches. This makes conduction much faster and more energy-efficient than in an unmyelinated fibre, where the membrane must depolarise continuously along its entire length.

Was Chapter 18 renumbered, and what changed from the older edition?

Yes. Under the pre-2023 numbering this chapter was Chapter 21; after the 2023 NCERT syllabus rationalisation it became Chapter 18 in the current 19-chapter Class 11 Biology textbook. Along with the renumbering, the detailed structural and mechanistic content on the eye and ear (and the corresponding exercise sub-questions on the retina, cochlea, organ of Corti, vision and hearing mechanisms) was trimmed from the main exercise, so the chapter now focuses more tightly on the neuron, nerve impulse, synapse, and the organisation of the CNS and PNS.

What is the key difference between resting potential and action potential?

The resting potential is the stable electrical potential difference (about −70 mV, inside negative) across a nerve fibre’s membrane when it is not conducting an impulse, maintained mainly by the sodium-potassium pump and the membrane’s greater permeability to K⁺. The action potential is the brief, rapid reversal of this potential (inside becomes positive) that occurs when the membrane is stimulated and becomes highly permeable to Na⁺; it is this travelling reversal of potential that constitutes the nerve impulse.

Written by Satish

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