BiologyICSE Class 10 · Nervous System and Sense Organs

Brain, Spinal Cord, Reflex Arc and Autonomic Nervous System (ICSE Class 10 Biology)

Updated 16 October 2026 · Fact-checked

The brain, protected by the meninges and cerebrospinal fluid, has the cerebrum for thought and voluntary actions, the cerebellum for balance and coordination, and the medulla oblongata for involuntary actions such as heartbeat and breathing. The spinal cord handles reflexes. The autonomic system's sympathetic part prepares for emergencies; the parasympathetic part restores rest.

Understand The Brain and Autonomic Nervous System

Divisions of the nervous system.

Central nervous system (CNS): brain and spinal cord.
Peripheral nervous system (PNS): cranial nerves (12 pairs) and spinal nerves (31 pairs, all mixed, carrying both sensory and motor fibres).
Autonomic nervous system (ANS): controls involuntary organs (heart, glands, gut, blood vessels); has sympathetic and parasympathetic parts.

Protection of the brain. The brain lies in the cranium, wrapped in three membranes, the meninges: dura mater (outer, tough), arachnoid (middle) and pia mater (inner, thin, with blood vessels). Cerebrospinal fluid between them cushions the brain against shocks and supplies nutrients. The meninges protect; they do not speed up impulses (that is the myelin sheath).

Parts of the brain and their functions.

Part	Position	Functions
Cerebrum	largest; two hemispheres with folded surface	thinking, intelligence, memory, will; voluntary actions; centres of sight, hearing, speech, touch
Cerebellum	below the back of the cerebrum	balance, posture and coordination of muscular movements
Medulla oblongata	lowest part, joins the spinal cord	involuntary actions: heartbeat, breathing, swallowing, coughing, sneezing, vomiting
Thalamus	deep, below the cerebrum	relays sensory impulses (pain, touch, temperature) to the cerebrum
Hypothalamus	below the thalamus	body temperature, hunger, thirst, sleep, emotions; controls the pituitary
Pons	above the medulla	relays impulses between brain parts; helps regulate breathing

Grey and white matter. Grey matter = cell bodies; white matter = myelinated axons. Brain: grey outside (cortex), white inside. Spinal cord: white outside, grey inside (butterfly or H-shaped).

Spinal cord. Runs inside the vertebral column from the medulla. It conducts impulses to and from the brain and is the centre for spinal reflexes.

Voluntary, involuntary and reflex actions.

Voluntary: under our will; cerebrum (writing, kicking a ball).
Involuntary: not under our will; medulla and ANS (heartbeat, peristalsis).
Reflex: quick, automatic response to a stimulus without thinking. Spinal reflexes (knee jerk, withdrawing from a hot object); cranial reflexes (blinking, pupil changes, sneezing).
Natural reflexes are inborn (blinking); acquired reflexes are learnt by repetition (braking when cycling, typing without looking).

Reflex arc. Receptor (skin) → sensory neuron (enters spinal cord by the dorsal root) → relay neuron (grey matter) → motor neuron (leaves by the ventral root) → effector (muscle or gland). The response happens before the brain is aware; the sensation of pain arrives a moment later.

Sympathetic versus parasympathetic.

Effect on	Sympathetic (emergency, 'fight or flight')	Parasympathetic (rest, 'rest and digest')
Heartbeat	faster	slower
Breathing	faster	slower
Pupils	dilate	constrict
Digestion	slowed	active
Blood to muscles	increased	normal

The sympathetic system works together with adrenaline from the adrenal medulla.

Flow chart: reflex. Stimulus → receptor → sensory neuron → spinal cord (relay neuron) → motor neuron → effector → response.

Draw-and-label checklist: reflex arc. T.S. of spinal cord with inner grey matter and outer white matter; dorsal root with a ganglion; sensory neuron from a receptor in the skin; relay neuron in the grey matter; motor neuron leaving by the ventral root to a muscle (effector). Arrows show the one-way path.

Draw-and-label checklist: brain (L.S.). Cerebrum (large, folded), cerebellum (behind and below), pons, medulla oblongata continuing into the spinal cord, thalamus and hypothalamus deep inside, pituitary below the hypothalamus.

The Brain and Autonomic Nervous System: key facts

Brain parts: Cerebrum thinking, voluntary actions
Cerebellum balance, coordination
Medulla heartbeat, breathing, swallowing
Thalamus sensory relay
Hypothalamus temperature, hunger, thirst
Pons relay, breathing; Cerebrum thinks; cerebellum balances.
Reflex arc: Receptor
Sensory neuron
Relay neuron in spinal cord
Motor neuron
Effector; One-way path.
Autonomic system: Sympathetic: faster heart, dilated pupils, slower digestion | Parasympathetic: slower heart, constricted pupils, active digestion; Opposite effects on the same organs.

Cerebrum	thinking, voluntary actions
Cerebellum	balance, coordination
Medulla	heartbeat, breathing, swallowing
Thalamus	sensory relay
Hypothalamus	temperature, hunger, thirst
Pons	relay, breathing

How to answer The Brain and Autonomic Nervous System questions

ICSE gives a case (a basketball player, a cup of coffee, a hot pan) and asks you to name the brain part, the membranes, the nervous system division, or to trace a reflex.

1Thinking, deciding, aiming = cerebrum; balance and smooth movement = cerebellum; heartbeat and breathing = medulla.
2For protective layers, give the collective term meninges first, then the three names if asked.
3For emergency responses, name the sympathetic nervous system.
4For reflexes, list all five parts of the arc in order.
5Read assertion-reason statements word by word for wrong scientific terms.

The Brain and Autonomic Nervous System in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Touching a hot pan

Suppose while cooking you touch a hot pan handle and jerk your hand away before you even feel the pain.

Explain why the hand moves before you feel pain.

Try it first, then show the solutionSolution

Heat receptors in the skin start impulses in a sensory neuron.
In the spinal cord, a relay neuron passes the impulse straight to a motor neuron.
The motor neuron makes the arm muscles contract and the hand is withdrawn.
The impulse also travels up to the cerebrum, which registers pain slightly later.

Answer: It is a spinal reflex; the spinal cord triggers the response before the message reaches the brain.

Memory hook: Spinal cord acts first; the brain hears later.

Before a board exam

Suppose just before your board exam your heart races, your mouth is dry and you have 'butterflies' in your stomach.

Which part of the nervous system is responsible, and what is it doing?

Try it first, then show the solutionSolution

Stress is treated by the body like an emergency.
The sympathetic nervous system, with adrenaline, increases heartbeat and breathing.
It slows digestion and saliva flow, causing the dry mouth and stomach feelings.
After the exam the parasympathetic system restores calm.

Answer: The sympathetic nervous system prepares the body for an emergency.

Memory hook: Sympathetic = Stress; Parasympathetic = Peace.

Tricks to remember The Brain and Autonomic Nervous System

Short memory aids. Say each one aloud once, then use it on a question the same day.

Cerebellum = Balance-bellum
The little brain at the back keeps you balanced like a tightrope walker.
Use it when: Not confusing cerebrum and cerebellum.
DAP for meninges
Dura, Arachnoid, Pia: 'Do Ants Play?', outer to inner.
Use it when: Order of meninges.
Grey is Guarded in the cord
In the spinal cord, grey matter is inside, guarded by white.
Use it when: Distribution of grey and white matter.

The Brain and Autonomic Nervous System: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Control of breathing · 1 mark · MCQBoard level

The part of the brain that controls heartbeat, breathing and swallowing is the:
(a) cerebrum (b) cerebellum (c) medulla oblongata (d) thalamus

Try it first, then show the solutionSolution

Involuntary vital actions are controlled by the medulla oblongata.

Answer: (c) medulla oblongata.

Example 2: Mixed nerve · 2 marks · Short answerBoard level

A nerve carries both sensory fibres from the skin and motor fibres to muscles. (a) What is such a nerve called? (b) Give an example of nerves of this type.

Try it first, then show the solutionSolution

(a) Mixed nerve (1 mark).
(b) Spinal nerves (all 31 pairs) (1 mark).

Answer: (a) Mixed nerve (b) Spinal nerves.

Example 3: Archer at the target · 3 marks · Short answerHarder board level

Suppose an archer aims, keeps her stance steady on uneven ground and releases the arrow. Name the brain part that (a) decides when to release, (b) keeps her steady and her movements smooth, (c) keeps her breathing going without thought.

Try it first, then show the solutionSolution

(a) Cerebrum (voluntary action, decision) (1 mark).
(b) Cerebellum (balance and coordination) (1 mark).
(c) Medulla oblongata (1 mark).

Answer: (a) Cerebrum (b) Cerebellum (c) Medulla oblongata.

Example 4: Two responses to one stimulus · 3 marks · Short answerHarder board level

Suppose a mosquito bites your arm while you are writing. Your arm twitches at once; a moment later you decide to slap the mosquito. (a) Classify each response. (b) Name the main control centre of each. (c) Give one reason why the first response is faster.

Try it first, then show the solutionSolution

(a) The twitch is a reflex action; the slap is a voluntary action (1 mark).
(b) Reflex: spinal cord; voluntary: cerebrum (1 mark).
(c) The reflex impulse takes a short path through the spinal cord without waiting for the brain to think and decide (1 mark).

Answer: (a) Twitch: reflex; slap: voluntary. (b) Spinal cord; cerebrum. (c) Short spinal path with no decision-making.

Example 5: Myelin and speed · 3 marks · Case-basedHOTS / competency

Suppose an impulse must travel 1.5 m from a toe to the spinal cord. In a myelinated nerve it travels at 100 m/s, and in an unmyelinated one at 2 m/s. (a) Find the time taken in each, in milliseconds. (b) Which structure explains the difference? (c) Why does this matter for reflexes?

Try it first, then show the solutionSolution

(a) 1.5 ÷ 100 = 0.015 s = 15 ms; 1.5 ÷ 2 = 0.75 s = 750 ms (1 mark).
(b) The myelin sheath, which insulates the axon and speeds conduction (1 mark).
(c) Faster impulses give quicker reflexes, protecting the body from harm sooner (1 mark).

Answer: (a) 15 ms and 750 ms. (b) Myelin sheath. (c) Quicker protective reflexes.

Example 6: Facing a penalty kick · 3 marks · Case-basedHOTS / competency

Suppose a goalkeeper waits for a penalty kick in a final; his heart pounds and his pupils widen. After the match he relaxes and feels hungry. (a) Which division of the ANS acts during the kick? (b) Give two of its effects other than those described. (c) Which division acts after the match, and which brain part, just below the thalamus, coordinates both?

Try it first, then show the solutionSolution

(a) Sympathetic nervous system, working with adrenaline (1 mark).
(b) Faster breathing, slowed digestion (or more blood to the muscles) (1 mark).
(c) Parasympathetic nervous system; hypothalamus (1 mark).

Answer: (a) Sympathetic. (b) Faster breathing and slowed digestion. (c) Parasympathetic; hypothalamus.

Where students lose marks in The Brain and Autonomic Nervous System

The slips examiners see most often, and what to write instead.

Mistake: Cerebrum and cerebellum confused
CISCE examiners' comments (2024): in a basketball case, candidates confused the cerebrum and cerebellum.
Do this: Cerebrum decides and aims; cerebellum balances and coordinates.
Usually costs: 1 mark.
Mistake: Wrong organ, layers or system in a coffee case
CISCE examiners' comments (2025): candidates wrote adrenal gland, heart or nervous system instead of brain, listed the three layers instead of the term meninges, and confused the sympathetic system with the parasympathetic or wrote CNS, PNS or ANS.
Do this: Brain; meninges; sympathetic nervous system.
Usually costs: 1-3 marks.
Mistake: Association neuron for mixed nerve
CISCE examiners' comments (2024): for a nerve with both sensory and motor fibres, candidates wrote association neuron or spinal nerve instead of mixed nerve.
Do this: A nerve with both fibre types is a mixed nerve.
Usually costs: 1 mark.
Mistake: Missing wrong terms in assertion-reason
CISCE examiners' comments (2025): candidates did not notice incorrect scientific statements (such as the arachnoid layer speeding up impulses).
Do this: Myelin speeds impulses; meninges only protect.
Usually costs: 1 mark.

Exam tips

Cerebrum: voluntary; cerebellum: balance; medulla: vital involuntary acts.
Meninges: dura, arachnoid, pia.
Reflex arc: five links, receptor to effector.
Emergency = sympathetic.

Practice questions on The Brain and Autonomic Nervous System

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The membranes covering the brain are together called:
(a) pericardium (b) pleura (c) meninges (d) peritoneum
Hint
Three layers.
Answer
(c) meninges.
Q2 · 1 mark · Very short answerBoard level
Name the brain part that lies just below the thalamus and controls the pituitary gland.
Hint
Hypo- means below.
Answer
Hypothalamus.
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Digestion slows down when a person is running away from danger.
Reason (R): The sympathetic nervous system diverts blood away from the gut to the skeletal muscles.
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(d) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
Hint
Fight or flight, not rest and digest.
Answer
(c).
Q4 · 2 marks · Short answerHarder board level
A fresh, unstained slice of the cerebrum has a darker outer layer and a pale core, while a slice of the spinal cord has a pale outer zone around a darker H-shaped core. Name the matter forming the darker and pale regions in each organ.
Hint
Cell bodies look greyish; myelinated axons look white.
Answer
Darker regions are grey matter (cell bodies); pale regions are white matter (myelinated axons). Cerebrum: grey outside (cortex), white inside. Spinal cord: white outside, grey inside (H-shaped).
Q5 · 2 marks · Short answerHarder board level
Classify as natural or acquired reflex: (a) blinking when dust approaches; (b) a pianist's fingers finding keys without looking.
Hint
Inborn or learnt.
Answer
(a) Natural (inborn). (b) Acquired (learnt by practice).
Q6 · 2 marks · Short answerHarder board level
Name the three meninges from outside inwards and state one function of cerebrospinal fluid.
Hint
DAP.
Answer
Dura mater, arachnoid, pia mater; cerebrospinal fluid acts as a shock absorber (and supplies nutrients) to the brain.
Q7 · 2 marks · Short answerHarder board level
Give two effects of the parasympathetic nervous system.
Hint
Rest and digest.
Answer
Slows the heartbeat; constricts the pupils (also promotes digestion and saliva flow).
Q8 · 3 marks · Case-basedHOTS / competency
Read and answer.
Suppose after a fall a cyclist can think and speak normally but sways and staggers when he tries to walk, and cannot touch his nose accurately.
(a) Which brain part is likely injured? (1)
(b) Why are his thinking and speech unaffected? (1)
(c) Which inner-ear structures send balance information to this part? (1)
Hint
Coordination centre.
Answer
(a) Cerebellum. (b) Thinking and speech are controlled by the cerebrum, which is unharmed. (c) Semicircular canals and the utriculus and sacculus.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Which part of the brain controls body temperature?Show answer
Hypothalamus.
2.What is the innermost meninx?Show answer
Pia mater.
3.How many pairs of spinal nerves are there?Show answer
31 pairs.
4.Which neuron connects sensory and motor neurons in the spinal cord?Show answer
Relay (association) neuron.
5.Which ANS division slows the heart?Show answer
Parasympathetic.

The Brain and Autonomic Nervous System: frequently asked questions

Is the medulla part of the brain or spinal cord?

It is the lowest part of the brain; it continues into the spinal cord.

Are all reflexes spinal?

No. Blinking, sneezing and pupil changes are cranial reflexes controlled by the brain.

How much ANS detail is needed?

A brief idea: what it controls and a few opposite effects of the sympathetic and parasympathetic parts.

Is a nerve the same as a neuron?

No. A neuron is a single cell; a nerve is a bundle of axons wrapped together.