The Nervous System
ICSE Class 10 · Biology · Chapter 10
What this chapter covers
- Coordination and the nervous system
- Structure of a neuron
- The central nervous system and its protection
- The brain and its parts
- The spinal cord
- White and grey matter in the brain and spinal cord
- The peripheral nervous system
- The autonomic nervous system
- Voluntary and involuntary actions
- Reflex action
- The reflex arc
- Natural and acquired reflexes
Key points
- The nervous system coordinates the body by quick electrical impulses; receptors detect stimuli and effectors (muscles and glands) respond.
- The neuron is the structural and functional unit of the nervous system: dendrites bring impulses to the cyton, and the axon carries them away.
- The myelin sheath, made by Schwann cells and broken at the nodes of Ranvier, insulates the axon and speeds up conduction.
- A synapse is a junction between neurons, crossed by a neurotransmitter, so impulses pass in one direction only.
- The central nervous system is the brain and spinal cord, protected by the skull, vertebral column, three meninges and cerebrospinal fluid.
- Cerebrum: intelligence, memory, voluntary actions and senses. Cerebellum: balance and coordination. Medulla oblongata: heartbeat, breathing and other vital involuntary actions.
- Thalamus relays sensory impulses to the cerebrum; hypothalamus controls temperature, hunger, thirst, water balance and the pituitary; pons is a bridge and helps regulate breathing.
- Grey matter (cell bodies) is outside in the brain and inside, H-shaped, in the spinal cord; white matter (myelinated axons) has the opposite position.
- The peripheral nervous system has 12 pairs of cranial nerves and 31 pairs of spinal nerves; every spinal nerve is mixed.
- The autonomic nervous system, the third division of the nervous system beside the CNS and the PNS, controls internal organs automatically; its sympathetic part prepares for emergencies and its parasympathetic part restores calm.
- Voluntary actions are controlled by the cerebrum and the will; involuntary actions happen automatically.
- A reflex action is a quick, automatic response, usually controlled by the spinal cord, following the reflex arc: receptor, sensory neuron, relay neuron, motor neuron, effector.
- Natural reflexes are inborn and inherited; acquired reflexes are learnt through practice and are not inherited.
Questions answered
Define a neuron and name its three main parts.
A neuron is a nerve cell, the structural and functional unit of the nervous system, specialised to receive, conduct and pass on nerve impulses. Its three main parts are the cyton (cell body), the dendrites and the axon.
State one function each of the myelin sheath and the nodes of Ranvier.
The myelin sheath insulates the axon and speeds up the conduction of impulses. The nodes of Ranvier are gaps in the sheath at which the impulse jumps from node to node, which makes conduction faster.
Why does a nerve impulse pass across a synapse in one direction only?
Only the axon terminals release the neurotransmitter. The dendrites or cell body of the next neuron receive it, so the impulse can pass only from axon to dendrite, never the other way.
Distinguish between a neuron and a nerve.
A neuron is a single nerve cell, seen only under a microscope. A nerve is a bundle of axons of many neurons wrapped in connective tissue, visible as a white thread.
Name the three meninges from outside inwards and give two functions of cerebrospinal fluid.
Dura mater, arachnoid and pia mater. Cerebrospinal fluid acts as a shock absorber protecting the brain and spinal cord, and supplies them with nutrients and oxygen while removing wastes.
Name the part of the brain that: (a) controls heartbeat and breathing, (b) maintains balance, (c) controls body temperature and thirst, (d) relays sensory impulses to the cerebrum, (e) is the seat of memory and intelligence, (f) forms a bridge between the cerebrum and cerebellum.
(a) Medulla oblongata, (b) cerebellum, (c) hypothalamus, (d) thalamus, (e) cerebrum, (f) pons.
Give the location of grey matter and white matter in the cerebrum and in the spinal cord.
In the cerebrum, grey matter lies outside, as the cortex, and white matter lies inside. In the spinal cord, grey matter lies inside in an H-shape around the central canal and white matter lies outside.
How many pairs of cranial and spinal nerves do humans have? Why is every spinal nerve called a mixed nerve?
12 pairs of cranial nerves and 31 pairs of spinal nerves. Each spinal nerve carries sensory fibres through its dorsal root and motor fibres through its ventral root, so it carries both kinds.
Past board exam questions
ICSE 2027 sample paper · 1 mark
As the school bell rang for the lunch break, Tina’s mouth started watering thinking of her favourite food in the lunch box. This is a/an:
- voluntary action
- somatic reflex
- acquired reflex
- natural reflex
Show answer
acquired reflex
ICSE 2026 board paper · 1 mark
Bharat woke up late in the morning and missed the school bus. This situation stimulated the nerves of the sympathetic system which resulted in:
- Constriction of Coronary arteries
- Muscle relaxation
- Decrease in Respiration rate
- Bronchodilation
Show answer
Bronchodilation
ICSE 2026 sample paper · 1 mark
Reflex actions provide a survival advantage because they:
- are controlled by the cerebrum.
- are controlled by the medulla oblongata.
- require no conscious thought, allowing rapid responses.
- always involve the spinal cord.
Show answer
require no conscious thought, allowing rapid responses.
ICSE 2026 board paper · 1 mark
Karan was standing on a high stool and cleaning the ceiling fan. He suddenly loses balance and sustains a head injury. An examination reveals that his pupils have lost the capacity to constrict in bright light. Which structure has been damaged?
- Suspensory ligaments
- Medulla oblongata
- Eye lens
- Eye lid
Show answer
Medulla oblongata
ICSE 2026 sample paper · 2 marks
Ayush was in the final round of a carrom match. He was focussing intently on the strokes of the opponent player. (a) Which part of the brain helps Ayush to focus on the game? (b) Name the part of the brain that co-ordinates his muscles while using the striker.
Show answer
(a) Cerebrum
(b) Cerebellum
ICSE 2026 board paper · 2 marks
How are the Cytons and Axons of neurons arranged in the following? (a) Cerebrum (b) Spinal Cord
Show answer
(a) Cerebrum: the cytons (cell bodies) lie in the outer region, the cortex (grey matter), and the axons lie in the inner region (white matter).
(b) Spinal cord: the arrangement is reversed — the cytons lie in the inner, H-shaped grey matter, and the axons lie in the outer white matter.
ICSE 2026 sample paper · 2 marks
Mention the number of cranial nerves and spinal nerves in a human being.
Show answer
Cranial nerves – 12 pairs
Spinal nerves – 31 pairs
ICSE 2026 sample paper · 2 marks
Distinguish between Sympathetic system and Parasympathetic system on the basis of heartbeat.
Show answer
Sympathetic system – increases (accelerates) the heartbeat.
Parasympathetic system – decreases (slows) the heartbeat, bringing it back to normal.