NCERT Solutions for Class 11 Biology Chapter 18: Neural Control and Coordination (NCERT 2026–27)

Q: What is Class 11 Biology Chapter 18 about?

Chapter 18, Neural Control and Coordination, explains how the neural system coordinates the body's organs. It covers the structure of a neuron, the central and peripheral neural systems, generation and conduction of a nerve impulse, transmission across synapses, and the organisation of the human brain into forebrain, midbrain and hindbrain.

Q: What is the role of Na+ in a nerve impulse?

On stimulation, the membrane becomes freely permeable to Na+. The rapid influx of Na+ reverses the membrane polarity (depolarisation), generating the action potential, which is the nerve impulse.

These Class 11 Biology Chapter 18 solutions cover Neural Control and Coordination with every end-of-chapter NCERT exercise reproduced verbatim and solved in clear, exam-ready prose. The chapter explains how the neural system provides a quick, point-to-point network that coordinates the activities of organs — from the structure of a neuron, the generation and conduction of a nerve impulse, and transmission across a synapse, to the organisation of the human brain and the central and peripheral neural systems.

Class: 11 Subject: Biology Chapter: 18 Title: Neural Control and Coordination Exercises: 10 questions (all solved) Session: 2026–27

On this page

Chapter overview
Key concepts & definitions
NCERT Exercises — solutions (all)
Extra practice questions
MCQs & Assertion–Reason
Common mistakes to avoid
Exam tips
FAQs

Class 11 Biology Chapter 18 Solutions – Overview

Coordination is the process by which two or more organs interact and complement one another’s functions to maintain homeostasis. In the body, this is achieved jointly by the neural system (a rapid, point-to-point network of nerves) and the endocrine system (slower, chemical integration through hormones). The human neural system has two parts: the central neural system (CNS) — the brain and spinal cord, where information is processed and controlled — and the peripheral neural system (PNS), made of afferent and efferent fibres that carry impulses to and from the CNS. The functional unit is the neuron, an excitable cell whose polarised membrane can generate and conduct an action potential. Impulses pass between neurons at synapses, usually by chemical neurotransmitters. The brain — forebrain, midbrain and hindbrain — is the command and control centre for movement, vital functions, behaviour and higher mental processes.

Key Concepts & Definitions

Coordination: the process through which two or more organs interact and complement the functions of one another to maintain homeostasis.

Neuron: a highly specialised, excitable cell — the structural and functional unit of the neural system — made of a cell body (with Nissl’s granules), dendrites, and an axon.

CNS & PNS: the CNS (brain + spinal cord) is the site of information processing and control; the PNS comprises all the nerves linking tissues to the CNS via afferent (sensory) and efferent (motor) fibres.

Resting potential: the electrical potential difference across the resting (polarised) neural membrane, maintained by the Na⁺–K⁺ pump (3 Na⁺ out for 2 K⁺ in) and selective ion permeability.

Action potential (nerve impulse): the rapid reversal of membrane polarity at a stimulated site, caused by a sudden influx of Na⁺; it travels as a wave of depolarisation and repolarisation along the axon.

Synapse: the junction between a pre-synaptic and a post-synaptic neuron; impulses cross electrical synapses directly, or chemical synapses via neurotransmitters released into the synaptic cleft.

Brain regions: forebrain (cerebrum, thalamus, hypothalamus), midbrain (corpora quadrigemina, cerebral aqueduct) and hindbrain (pons, cerebellum, medulla oblongata).

NCERT Exercises — Solutions

All questions below are reproduced verbatim from the NCERT textbook (Reprint 2026–27). The answers are original, exam-ready explanations.

1. Briefly describe the structure of the brain.

ANSWER The human brain is the central information-processing organ and acts as the ‘command and control system’ of the body. It is well protected inside the skull and is wrapped by three cranial meninges — the outer dura mater, the thin middle arachnoid, and the inner pia mater in contact with brain tissue. The brain is divided into three major parts: (i) Forebrain — consists of the cerebrum, thalamus and hypothalamus. The cerebrum is the largest part, divided into left and right hemispheres joined by the corpus callosum; its outer cerebral cortex (grey matter) contains motor, sensory and association areas, while the inner white matter is made of myelinated fibres. The thalamus is a major relay centre for sensory and motor signalling, and the hypothalamus controls body temperature, hunger and thirst and secretes hypothalamic hormones. The limbic system (with amygdala, hippocampus, etc.) governs emotions, sexual behaviour and motivation. (ii) Midbrain — lies between the thalamus/hypothalamus and the pons; the cerebral aqueduct passes through it, and its dorsal part bears four lobes called corpora quadrigemina. (iii) Hindbrain — comprises the pons (fibre tracts interconnecting brain regions), the cerebellum (a highly convoluted surface that coordinates balance and movement), and the medulla oblongata, which connects to the spinal cord and controls respiration, cardiovascular reflexes and gastric secretions. The midbrain, pons and medulla together form the brain stem.

2. Compare the following: (a) Central neural system (CNS) and Peripheral neural system (PNS) (b) Resting potential and action potential

ANSWER (a) CNS vs PNS

Central neural system (CNS)	Peripheral neural system (PNS)
Includes the brain and the spinal cord.	Comprises all the nerves of the body associated with the CNS.
Is the site of information processing and control.	Carries information to and from the CNS.
Receives impulses and issues commands.	Made of afferent (sensory) and efferent (motor) nerve fibres.
Centrally located and well protected by the skull and vertebral column.	Spread throughout the body; divided into somatic and autonomic neural systems.

(b) Resting potential vs action potential

Resting potential	Action potential
The potential difference across the membrane when the neuron is not conducting any impulse.	The potential difference at a site when the membrane is stimulated and conducting an impulse (a nerve impulse).
Membrane is polarised: outer surface positive, inner surface negative.	Membrane is depolarised: polarity reversed — outer surface negative, inner positive.
Membrane is more permeable to K⁺ and nearly impermeable to Na⁺.	Membrane at the stimulated site becomes freely permeable to Na⁺, causing a rapid Na⁺ influx.
Maintained by the Na⁺–K⁺ pump (3 Na⁺ out, 2 K⁺ in).	Generated on stimulation and is self-propagating along the axon.

3. 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

ANSWER (a) Polarisation: In a resting neuron, the axonal membrane is comparatively more permeable to K⁺ and nearly impermeable to Na⁺ and to the negatively charged proteins in the axoplasm. The Na⁺–K⁺ pump actively transports 3 Na⁺ out for every 2 K⁺ in. As a result, the axoplasm holds a high K⁺ and protein concentration while the outside has high Na⁺. This makes the outer surface of the membrane positively charged and the inner surface negatively charged — the membrane is said to be polarised, and this potential difference is the resting potential. (b) Depolarisation: When a stimulus is applied at a site, that part of the membrane suddenly becomes freely permeable to Na⁺. A rapid influx of Na⁺ follows, reversing the polarity — the outer surface becomes negatively charged and the inner surface positively charged. This reversal of charge is depolarisation, and the resulting potential difference is the action potential (nerve impulse). (c) Transmission across a chemical synapse: At a chemical synapse, the pre- and post-synaptic neurons are separated by a fluid-filled synaptic cleft. When an action potential reaches the axon terminal, it triggers the synaptic vesicles to move towards the pre-synaptic membrane, fuse with it, and release neurotransmitters into the cleft. These neurotransmitters diffuse across and bind to specific receptors on the post-synaptic membrane. This binding opens ion channels, allowing ions to enter and generate a new potential in the post-synaptic neuron, which may be excitatory or inhibitory.

4. Draw labelled diagrams of the following: (a) Neuron (b) Brain

ANSWER (Diagram-based question — described in words; draw and label in your answer book.) (a) Neuron: Draw an enlarged nerve cell. Label the rounded cell body (cyton) containing the nucleus and Nissl’s granules; the short, branched dendrites projecting from the cell body (carrying impulses towards it); the long single axon; the myelin sheath covering the axon; the Schwann cells; the nodes of Ranvier (gaps between adjacent myelin sheaths); and the terminal synaptic knobs with synaptic vesicles at the branched distal end. (b) Brain: Draw a sagittal section of the human brain. Label the cerebrum (with cerebral cortex and corpus callosum), thalamus and hypothalamus in the forebrain; the midbrain with corpora quadrigemina; and the pons, cerebellum and medulla oblongata in the hindbrain, with the medulla continuing as the spinal cord.

5. Write short notes on the following: (a) Neural coordination (b) Forebrain (c) Midbrain (d) Hindbrain (e) Synapse

ANSWER (a) Neural coordination: The neural system provides an organised network of point-to-point connections for quick coordination of the body’s organs. Using electrical impulses carried by neurons, it rapidly relays sensory information to the CNS and motor commands back to muscles and glands, working alongside the endocrine system to integrate all activities and maintain homeostasis. (b) Forebrain: Consists of the cerebrum, thalamus and hypothalamus. The cerebrum (two hemispheres joined by the corpus callosum) controls voluntary actions, sensation, memory and intelligence; the thalamus relays sensory and motor signals; the hypothalamus regulates temperature, hunger, thirst and secretes hormones; the limbic system controls emotions and behaviour. (c) Midbrain: Located between the forebrain’s thalamus/hypothalamus and the pons of the hindbrain. The cerebral aqueduct passes through it, and its dorsal portion has four lobes (corpora quadrigemina). It receives and integrates visual, tactile and auditory inputs. (d) Hindbrain: Comprises the pons (fibre tracts interconnecting brain regions), the cerebellum (coordinates balance and precise movement, integrating inputs from the ear’s semicircular canals and the auditory system), and the medulla oblongata (controls respiration, cardiovascular reflexes and gastric secretions). (e) Synapse: A junction formed by the membranes of a pre-synaptic and a post-synaptic neuron, which may or may not be separated by a synaptic cleft. At electrical synapses, current flows directly and transmission is faster; at the more common chemical synapses, neurotransmitters carry the signal across the cleft.

6. Give a brief account of mechanism of synaptic transmission.

ANSWER A nerve impulse passes from one neuron to the next at junctions called synapses. There are two types — electrical and chemical. Electrical synapses: The pre- and post-synaptic membranes lie in very close proximity, so electrical current flows directly from one neuron to the other. Transmission resembles impulse conduction along a single axon and is faster than at chemical synapses, but such synapses are rare in our system. Chemical synapses: Here the two membranes are separated by a fluid-filled synaptic cleft. When an action potential arrives at the axon terminal, it stimulates the synaptic vesicles to move towards and fuse with the pre-synaptic membrane, releasing neurotransmitters into the cleft. The neurotransmitters diffuse across and bind to specific receptors on the post-synaptic membrane. This opens ion channels, allowing ions to enter and generate a fresh potential in the post-synaptic neuron, which may be excitatory or inhibitory.

7. Explain the role of Na⁺ in the generation of action potential.

ANSWER In a resting neuron the membrane is nearly impermeable to Na⁺, so most sodium ions stay outside the axon, helping keep the membrane polarised (outer surface positive). When a stimulus is applied, the membrane at that site becomes freely permeable to Na⁺. Sodium ions rush in rapidly (influx of Na⁺), and this reverses the polarity — the inner surface now becomes positive and the outer surface negative. This reversal (depolarisation) is the action potential, i.e. the nerve impulse. The increased permeability to Na⁺ is very short-lived; it is quickly followed by a rise in K⁺ permeability, K⁺ diffuses out, and the resting potential is restored. Thus, the inward movement of Na⁺ is the key event that generates the action potential.

8. Differentiate between: (a) Myelinated and non-myelinated axons (b) Dendrites and axons (c) Thalamus and Hypothalamus (d) Cerebrum and Cerebellum

ANSWER (a) Myelinated vs non-myelinated axons

Myelinated axon	Non-myelinated axon
Schwann cells form a myelin sheath around the axon.	Schwann cell encloses the axon but does not form a myelin sheath.
Nodes of Ranvier (gaps in the sheath) are present.	Nodes of Ranvier are absent.
Found in spinal and cranial nerves; conduct impulses faster.	Found in autonomous and somatic neural systems; conduct impulses slower.

(b) Dendrites vs axons

Dendrites	Axon
Short fibres that branch repeatedly from the cell body.	A single long fibre with a branched distal end.
Contain Nissl’s granules.	Lacks Nissl’s granules.
Transmit impulses towards the cell body.	Transmits impulses away from the cell body to a synapse or neuro-muscular junction.

(c) Thalamus vs Hypothalamus

Thalamus	Hypothalamus
The structure around which the cerebrum wraps.	Lies at the base of the thalamus.
A major coordinating centre for sensory and motor signalling.	Controls body temperature, hunger and thirst.
Mainly a relay centre.	Contains neurosecretory cells that secrete hypothalamic hormones.

(d) Cerebrum vs Cerebellum

Cerebrum	Cerebellum
Part of the forebrain; the largest part of the brain.	Part of the hindbrain.
Divided into two hemispheres joined by the corpus callosum.	Has a very convoluted surface for extra neurons.
Controls voluntary movement, sensation, memory, intelligence and emotions.	Coordinates balance and precise movement, integrating inputs from the semicircular canals and auditory system.

9. 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?

ANSWER (a) The cerebrum (specifically the cerebral cortex of the forebrain) is the most developed part of the human brain. It forms the major part of the brain and controls higher functions such as voluntary movement, intelligence, memory, speech and emotions. (b) The hypothalamus acts as the master clock, controlling the circadian (24-hour) rhythms of the body. (The suprachiasmatic nucleus within the hypothalamus is the body’s internal pacemaker.)

10. Distinguish between: (a) afferent neurons and efferent neurons (b) impulse conduction in a myelinated nerve fibre and unmyelinated nerve fibre (c) cranial nerves and spinal nerves.

ANSWER (Question numbering follows the textbook; sub-parts shown as printed.) (a) Afferent vs efferent neurons

Afferent neurons	Efferent neurons
Also called sensory neurons.	Also called motor neurons.
Transmit impulses from tissues/organs (receptors) to the CNS.	Transmit regulatory impulses from the CNS to the concerned peripheral tissues/organs.
Carry sensory (incoming) information.	Carry motor (outgoing) commands.

(b) Conduction in myelinated vs unmyelinated fibres

Myelinated nerve fibre	Unmyelinated nerve fibre
Has a myelin sheath with nodes of Ranvier.	Has no myelin sheath and no nodes of Ranvier.
The impulse appears to jump from node to node, so conduction is fast.	The impulse travels continuously along the membrane, so conduction is slow.
Found in spinal and cranial nerves.	Found in the autonomous and somatic neural systems.

(c) Cranial nerves vs spinal nerves

Cranial nerves	Spinal nerves
Arise from the brain.	Arise from the spinal cord.
Mainly supply the head, neck and sense organs.	Mainly supply the trunk and the limbs.
Twelve pairs in humans.	Thirty-one pairs in humans.

Extra Practice Questions

Short Answer Type Questions

Q1. What are Nissl’s granules and where are they found?

ANSWERNissl’s granules are granular bodies present in the cytoplasm of the cell body of a neuron and in its dendrites. They are involved in protein synthesis for the neuron.

Q2. Name the three types of neurons based on the number of axons and dendrites, with one location of each.

ANSWERMultipolar (one axon, two or more dendrites; cerebral cortex), bipolar (one axon, one dendrite; retina of the eye) and unipolar (cell body with one axon only; embryonic stage).

Q3. What is the synaptic cleft and what crosses it?

ANSWERThe synaptic cleft is the fluid-filled space separating the membranes of the pre- and post-synaptic neurons at a chemical synapse. Neurotransmitters released from the axon terminal cross it to carry the impulse forward.

Q4. How is the resting potential maintained across a neural membrane?

ANSWERIt is maintained by selective ion permeability (more permeable to K⁺, nearly impermeable to Na⁺) and by the Na⁺–K⁺ pump, which actively transports 3 Na⁺ out for every 2 K⁺ in, keeping the outer surface positive.

Q5. Why is the cerebral cortex called grey matter and the inner region white matter?

ANSWERThe cortex appears greyish because neuron cell bodies are concentrated there, while the inner region is white because its myelinated nerve fibres give an opaque white appearance.

Long Answer Type Questions

Q1. Describe the generation and conduction of a nerve impulse along an axon.

ANSWERIn a resting neuron the membrane is polarised — the outer surface is positive and the inner negative — giving the resting potential. When a stimulus is applied at a site (say point A), that membrane becomes freely permeable to Na⁺; a rapid influx of Na⁺ reverses the polarity there, producing the action potential. The site immediately ahead (point B) is still polarised, so a current flows on the inner surface from A to B and on the outer surface from B to A, completing the circuit. This depolarises B and generates an action potential there. The sequence repeats along the axon, conducting the impulse forward. Meanwhile, the brief rise in Na⁺ permeability is quickly followed by a rise in K⁺ permeability; K⁺ diffuses out and the resting potential is restored, making the fibre responsive to fresh stimulation.

Q2. Explain the organisation of the peripheral neural system.

ANSWERThe PNS comprises all the nerves of the body associated with the CNS. Its nerve fibres are of two types: afferent fibres, which carry impulses from tissues/organs to the CNS, and efferent fibres, which carry regulatory impulses from the CNS to peripheral tissues/organs. The PNS has two divisions — the somatic neural system, which relays impulses from the CNS to skeletal muscles, and the autonomic neural system, which transmits impulses from the CNS to involuntary organs and smooth muscles. The autonomic system is further divided into the sympathetic and parasympathetic neural systems. The visceral nervous system, a part of the PNS, carries impulses between the CNS and the viscera.

Q3. Compare electrical and chemical synapses and explain why chemical transmission is more common.

ANSWERAt an electrical synapse the pre- and post-synaptic membranes lie in very close proximity, so electrical current passes directly from one neuron to the next; transmission resembles conduction along a single axon and is faster, but such synapses are rare in our system. At a chemical synapse the membranes are separated by a synaptic cleft. An arriving action potential causes synaptic vesicles to release neurotransmitters, which diffuse across the cleft, bind to specific receptors on the post-synaptic membrane, open ion channels, and generate a new excitatory or inhibitory potential. Chemical synapses dominate because they allow the signal to be modulated — it can be made excitatory or inhibitory and finely regulated — giving the nervous system far greater flexibility than the simple all-or-none, one-way conduction of electrical synapses.

MCQs & Assertion–Reason

1. The structural and functional unit of the neural system is the:

(a) nephron (b) neuron (c) Schwann cell (d) synapse

2. The gaps between two adjacent myelin sheaths along an axon are called:

(a) synaptic clefts (b) Nissl’s granules (c) nodes of Ranvier (d) dendrites

3. The resting potential of a neuron is mainly maintained by the:

(a) calcium pump (b) sodium–potassium pump (c) proton pump (d) chloride pump

4. During the generation of an action potential, the membrane suddenly becomes freely permeable to:

(a) K⁺ (b) Cl⁻ (c) Na⁺ (d) proteins

5. Afferent nerve fibres carry impulses:

(a) from the CNS to muscles (b) from tissues/organs to the CNS (c) only within the brain (d) from gland to gland

6. The corpus callosum connects:

(a) the two cerebral hemispheres (b) the brain and spinal cord (c) the thalamus and pons (d) the cerebellum and medulla

7. The centres controlling respiration, cardiovascular reflexes and gastric secretions lie in the:

(a) cerebrum (b) cerebellum (c) medulla oblongata (d) thalamus

8. The four round swellings (lobes) on the dorsal portion of the midbrain are called:

(a) corpus callosum (b) corpora quadrigemina (c) cranial meninges (d) limbic lobe

9. Bipolar neurons (one axon and one dendrite) are typically found in the:

(a) cerebral cortex (b) retina of the eye (c) embryonic stage (d) spinal cord

10. The outermost of the three cranial meninges covering the brain is the:

(a) pia mater (b) arachnoid (c) dura mater (d) cerebral cortex

Answer key: 1-(b), 2-(c), 3-(b), 4-(c), 5-(b), 6-(a), 7-(c), 8-(b), 9-(b), 10-(c).

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: The resting membrane of a neuron is polarised.

Reason: The Na⁺–K⁺ pump keeps the outer surface positive and the inner surface negative.

A-R 2. Assertion: An influx of Na⁺ reverses the polarity of the membrane at the stimulated site.

Reason: On stimulation the membrane becomes freely permeable to Na⁺.

A-R 3. Assertion: Impulse transmission across an electrical synapse is faster than across a chemical synapse.

Reason: At electrical synapses the pre- and post-synaptic membranes are in very close proximity, allowing current to flow directly.

A-R 4. Assertion: The cerebellum controls body temperature and thirst.

Reason: The cerebellum contains neurosecretory cells that secrete hypothalamic hormones.

A-R 5. Assertion: Dendrites transmit impulses towards the cell body.

Reason: Dendrites are short, repeatedly branched fibres that contain Nissl’s granules.

Answer key: 1-(A), 2-(A), 3-(A), 4-(D), 5-(B).

Common Mistakes to Avoid

Watch out for these

Confusing the directions of fibres — afferent carry impulses to the CNS, efferent carry them away from the CNS.
Mixing up dendrites (towards cell body) and axon (away from cell body).
Stating the wrong pump ratio — the Na⁺–K⁺ pump moves 3 Na⁺ out for 2 K⁺ in.
Saying the resting membrane is freely permeable to Na⁺ — it is more permeable to K⁺ and nearly impermeable to Na⁺.
Placing temperature/hunger/thirst control in the thalamus — these are functions of the hypothalamus.
Confusing cerebrum (forebrain, voluntary actions/intelligence) with cerebellum (hindbrain, balance and coordination).
Forgetting that neurotransmitters cross only at chemical synapses, not electrical ones.

How to score full marks in this chapter

For impulse questions, always describe events in order — polarisation (resting), depolarisation (Na⁺ influx), then repolarisation (K⁺ efflux). Use the exact terms resting potential, action potential and synaptic cleft. For “differentiate” questions, answer in a neat two-column table with three clear points. In diagram questions (neuron, brain), label every part precisely — nodes of Ranvier, myelin sheath, synaptic knob, corpus callosum, corpora quadrigemina. Link structure to function (e.g. cerebellum → balance, medulla → respiration) to earn full marks.

Frequently Asked Questions

What is Class 11 Biology Chapter 18 about?

Chapter 18, Neural Control and Coordination, explains how the neural system coordinates the body’s organs. It covers the structure of a neuron, the central and peripheral neural systems, generation and conduction of a nerve impulse, transmission across synapses, and the organisation of the human brain into forebrain, midbrain and hindbrain.

How many exercises are solved in these Class 11 Biology Chapter 18 solutions?

All 10 end-of-chapter NCERT exercise questions are reproduced verbatim and solved in detail, along with extra short and long questions, 10 MCQs and 5 Assertion–Reason questions with answer keys.

What is the role of Na⁺ in a nerve impulse?

On stimulation, the membrane becomes freely permeable to Na⁺. The rapid influx of Na⁺ reverses the membrane polarity (depolarisation), generating the action potential, which is the nerve impulse.

Are these Class 11 Biology Chapter 18 solutions free?

Yes. All ClearStudy NCERT Solutions for Class 11 Biology are free and follow the official NCERT textbook for session 2026–27.

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