Question 1

The structural and functional unit of the nervous system is the:

Accepted Answer

Neuron. The neuron (nerve cell) is the basic unit that conducts nerve impulses.

Question 2

The part of a neuron that receives impulses and carries them toward the cell body is the:

Accepted Answer

Dendrite. Dendrites receive signals and carry them toward the cell body; the axon carries impulses away.

Question 3

At rest, the inside of a neuron's membrane is ______ relative to the outside:

Accepted Answer

Negatively charged. The resting membrane potential (~ −70 mV) keeps the axon interior negative relative to the outside.

Question 4

During the generation of an action potential, the membrane suddenly becomes permeable to ______ ions:

Accepted Answer

Sodium (Na⁺). Depolarisation occurs when Na⁺ channels open and Na⁺ rushes in, reversing the membrane polarity.

Question 5

The junction between two neurons across which an impulse passes is the:

Accepted Answer

Synapse. A synapse is the junction between the axon terminal of one neuron and the dendrite of the next.

Question 6

At a chemical synapse, the impulse is transmitted by molecules called:

Accepted Answer

Neurotransmitters. Neurotransmitters (e.g. acetylcholine) diffuse across the synaptic cleft to relay the impulse.

Question 7

The largest and most developed part of the human brain, controlling thought and voluntary actions, is the:

Accepted Answer

Cerebrum. The cerebrum is the seat of intelligence, memory, and voluntary control.

Question 8

The part of the brain that controls balance and coordination of muscular activity is the:

Accepted Answer

Cerebellum. The cerebellum coordinates and maintains posture, balance and precise muscular movement.

Question 9

A rapid, automatic, involuntary response to a stimulus (e.g. knee-jerk) is called a:

Accepted Answer

Reflex action. A reflex action is an involuntary, automatic response mediated by the spinal cord (reflex arc).

Question 10

The light-sensitive layer of the eye that contains the photoreceptor cells is the:

Accepted Answer

Retina. The retina holds the rods and cones (photoreceptors) that detect light.

Question 11

A neuron that has a single axon and two or more dendrites arising from the cell body, typical of most neurons in the vertebrate brain, is classified as a:

Accepted Answer

Multipolar neuron. A multipolar neuron has one axon and several dendrites; these are the commonest neurons, found in the cerebral cortex. Bipolar (one axon + one dendrite) occur in the retina and cochlea, unipolar in embryos.

Question 12

Which one of the following correctly matches a neuron type with its typical location? (i) Bipolar — retina of eye; (ii) Multipolar — cerebral cortex; (iii) Unipolar — embryonic stage.

Accepted Answer

All three matches are correct. Bipolar neurons occur in the retina and olfactory epithelium, multipolar neurons in the cerebral cortex, and unipolar neurons are usually found only in the embryonic stage. All three pairings are correct.

Question 13

In a myelinated nerve fibre of the peripheral nervous system, the myelin sheath is produced by which cells, and the small gaps where the sheath is absent are called:

Accepted Answer

Schwann cells; nodes of Ranvier. In the PNS, Schwann cells wrap around the axon to form the myelin sheath, and the periodic unmyelinated gaps between adjacent Schwann cells are the nodes of Ranvier. (In the CNS, oligodendrocytes make myelin.)

Question 14

The part of a neuron that conducts the nerve impulse away from the cell body and ends in fine branches bearing synaptic knobs is the:

Accepted Answer

Axon. The axon carries impulses away from the cell body toward the axon terminals (synaptic knobs). Dendrites receive impulses and conduct them toward the cyton.

Question 15

In a resting neuron, the concentration gradients maintained across the axonal membrane are:

Accepted Answer

High K⁺ and low Na⁺ inside; low K⁺ and high Na⁺ outside. At rest the axoplasm has high K⁺ and low Na⁺, while the fluid outside has high Na⁺ and low K⁺. This distribution, maintained by the Na⁺/K⁺ pump, underlies the resting potential.

Question 16

The resting membrane is far more permeable to K⁺ than to Na⁺ mainly because of the presence of:

Accepted Answer

Open potassium leak channels in the resting membrane. At rest, K⁺ leak channels remain open, allowing K⁺ to diffuse out, while most Na⁺ channels are closed. This selective K⁺ permeability makes the inside negative (~ -70 mV).

Question 17

During the falling phase (repolarisation) of an action potential, the membrane potential is restored toward its resting value chiefly by the:

Accepted Answer

Efflux of K⁺ through voltage-gated potassium channels. Repolarisation results from opening of voltage-gated K⁺ channels and outflow of K⁺, which restores the negative interior. The Na⁺/K⁺ pump only slowly re-establishes the original ionic gradients afterwards.

Question 18

A stimulus that is below the threshold intensity fails to trigger an action potential. This illustrates that nerve conduction obeys the:

Accepted Answer

All-or-none principle. A neuron fires a full action potential only when the stimulus reaches threshold; below threshold it does not fire at all. This all-or-none behaviour means the impulse amplitude is independent of stimulus strength once threshold is met.

Question 19

At a chemical synapse, the pre-synaptic and post-synaptic membranes are separated by a fluid-filled space called the:

Accepted Answer

Synaptic cleft. The synaptic cleft is the narrow gap between the pre-synaptic and post-synaptic membranes across which the neurotransmitter diffuses at a chemical synapse.

Question 20

The neurotransmitter that is released at cholinergic synapses and at the neuromuscular junction is:

Accepted Answer

Acetylcholine. Acetylcholine is the neurotransmitter released at cholinergic synapses and at the skeletal neuromuscular junction, where it binds receptors on the post-synaptic membrane.

Neural Control and Coordination — NEET Biology MCQs with Solutions

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