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Neural Control and Coordination – Class 11 Biology notes, important questions and MCQs

NCERT Class 11 Biology, chapter 18. Notes, key terms, important questions with answers and MCQs.

Chapter overview

The nervous system coordinates body activities through neurons that carry electrical impulses. The brain, spinal cord and sense organs work together for control and response.

Neuron and impulse

Neuron: dendrites, cell body (cyton), axon; myelinated fibres conduct faster (saltatory conduction at nodes of Ranvier).
Resting potential ≈ −70 mV maintained by the Na⁺/K⁺ pump; action potential due to Na⁺ influx.
Synapse: electrical or chemical; neurotransmitters like acetylcholine cross the synaptic cleft.

CNS and reflex

Forebrain (cerebrum, thalamus, hypothalamus), midbrain, hindbrain (pons, cerebellum, medulla).
Cerebellum maintains balance; medulla controls breathing and heartbeat; hypothalamus controls temperature, hunger, thirst.
Reflex arc: receptor → sensory neuron → spinal cord → motor neuron → effector (e.g. knee-jerk).

Key terms

Synapse: junction between two neurons
Reflex action: rapid, automatic response to a stimulus
Neurotransmitter: chemical released at a synapse that carries the signal to the next neuron or muscle, e.g. acetylcholine

Important questions with answers

What is the function of the corpus callosum?2 marks

It is a thick band of nerve fibres connecting the left and right cerebral hemispheres so they can share information.

Describe the structure of the human eye in brief.3 marks

Three layers: sclera (outer, with transparent cornea in front), choroid (middle, with blood vessels; forms the iris and ciliary body in front), and retina (inner, with rods for dim light and cones for colour). The lens behind the pupil focuses light on the retina; the fovea in the yellow spot has only cones for sharpest vision; the blind spot has no photoreceptors where the optic nerve leaves.

Explain how a nerve impulse is generated and conducted along an axon, and how it is transmitted across a chemical synapse.5 marks

At rest, the axon membrane is polarised (inside negative, about −70 mV) because the Na⁺/K⁺ pump keeps Na⁺ outside and K⁺ inside and the membrane is more permeable to K⁺. A stimulus opens Na⁺ channels; Na⁺ rushes in and the inside becomes positive (depolarisation, action potential). The adjacent region is then depolarised, so the impulse travels along the axon; behind it, K⁺ channels open and K⁺ moves out, restoring the negative inside (repolarisation). In myelinated axons the impulse jumps from node to node (saltatory conduction), which is faster. At a chemical synapse, the impulse makes synaptic vesicles release neurotransmitter (e.g. acetylcholine) into the cleft; it binds to receptors on the postsynaptic membrane, opening ion channels and starting a new impulse; enzymes then remove the transmitter.

Quick revision

Cerebellum = balance.
Medulla = breathing and heartbeat.
Myelin speeds conduction.

Exam tips

In the resting state the axon membrane is more permeable to K⁺ than Na⁺.
Remember the ion movements: depolarisation = Na⁺ in; repolarisation = K⁺ out; resting potential restored by the Na⁺/K⁺ pump (3 Na⁺ out, 2 K⁺ in).

Practice MCQs

Balance of the body is maintained by the
1. cerebellum
2. cerebrum
3. medulla
4. pons
Show answer
Answer: (a) cerebellum. Cerebellum.
Junction between two neurons is a
1. dendrite
2. synapse
3. axon
4. node
Show answer
Answer: (b) synapse. Synapse.
Resting membrane potential of a neuron is about
1. +70 mV
2. 0 mV
3. −70 mV
4. −30 mV
Show answer
Answer: (c) −70 mV. Inside negative.
Body temperature, hunger and thirst are controlled by the
1. cerebellum
2. medulla
3. hypothalamus
4. thalamus
Show answer
Answer: (c) hypothalamus. Hypothalamus.
The part of the brain that controls body temperature, hunger and thirst is
1. hypothalamus
2. medulla
3. cerebellum
4. pons
Show answer
Answer: (a) hypothalamus. Also links to pituitary.
Saltatory conduction occurs in
1. non-myelinated fibres
2. dendrites only
3. myelinated fibres
4. synapses
Show answer
Answer: (c) myelinated fibres. Nodes of Ranvier.
Action potential begins mainly due to
1. K⁺ influx
2. Na⁺ influx
3. Cl⁻ efflux
4. Ca²⁺ efflux
Show answer
Answer: (b) Na⁺ influx. Depolarisation.
Transmission across a chemical synapse is one-way because
1. the axon is myelinated
2. neurotransmitters are present only in the presynaptic knob and receptors only on the postsynaptic membrane
3. dendrites cannot conduct
4. Ca²⁺ is absent
Show answer
Answer: (b) neurotransmitters are present only in the presynaptic knob and receptors only on the postsynaptic membrane. Structural polarity.

All chapters of Class 11 Biology

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.