Question

Receptor sites for neurotransmitters are present on [NEET 2017]

(a) membrances of synaptic vesicles

(b) pre-synaptic membrane

(c) tips of axons

(d) post-synaptic membrane

Answer/Explanation

Ans. (d)

The post-synaptic membrane of the synapse of a neuron contains the receptors for neurotransmitters.

Question

Myelin sheath is produced by [NEET 2017]

(a) Schwann cells and Oligodendrocytes

(b) Astrocytes and Schwann cells

(c) Oligodendrocytes and Osteoclasts

(d) Osteoclasts and Astrocytes

Answer/Explanation

Ans. (a)
The myelin sheath is a greatly extended and modified plasma membrane wrapped around the nerve axon in a spiral fashion. It is originated from Schwann cells in the peripheral nervous system and oligodendroglial cells in the central nervous system.

Question

Destruction of the anterior horn cells of the spinal cord would result in loss of [CBSE AIPMT 2015]

(a) sensory impulses

(b) voluntary motor impulses

(c) commissural impulses

(d) integrating impulses

Answer/Explanation

Ans. (b)

Destruction of the anterior horn cells of the spinal cord would result in loss of voluntary motor impulses. It is because the anterior horn cells (also called anterior grey column), which is the front column of grey matter in the spinal cord contains motor neurons that affect the axial muscles.

Question

 How do parasympathetic neural signals affect the working of the heart? [CBSE AIPMT 2014]

(a) Reduce both heart rate and cardiac output

(b) Heart rate is increased without affecting the cardiac output

(c) Both heart rate and cardiac output increase

(d) Heart rate decreases but cardiac output increases

Answer/Explanation

Ans. (a)
Parasympathetic neural signal reduces both heart rate and cardiac output, through the post ganglionic fibres. These fibres are very short, and are cholinergic in nature.

Question

 When a neuron is in resting state, i.e. not conducting any impulse, the axonal membrane is [CBSE AIPMT 2011]

(a) equally permeable to both $\mathrm{Na}^{+}$and $\mathrm{K}^{+}$ ions

(b) impermeable to both $\mathrm{Na}^{+}$and $\mathrm{K}^{+}$ions

(c) comparatively more permeable to $\mathrm{K}^{+}$ ions and nearly impermeable to $\mathrm{Na}^{+}$ions

(d) comparatively more permeable to $\mathrm{Na}^{+}$ ions and nearly impermeable to $\mathrm{K}^{+}$ions

Answer/Explanation

Ans. (c)

Neurons are excitable cells because their membrane are in a polarised state. Different types of selectively permeable channels are present on the neural membrane. When a neuron is not conducting any impulse, or in the resting stage, the axonal membrane is comparatively more permeable to potassium ion $\left(\mathrm{K}^{+}\right)$and nearly impermeable to sodium ion $\left(\mathrm{Na}^{+}\right)$.

Question

 During the propagation of a nerve impulse, the action potential results from the movement of [CBSE AIPMT 2008]

(a) $\mathrm{K}^{+}$ions from extracellular fluid to intracellular fluid

(b) $\mathrm{Na}^{+}$ions from intracellular fluid to extracellular fluid

(c) $\mathrm{K}^{+}$ions from intracellular fluid to extracellular fluid

(d) $\mathrm{Na}^{+}$ions from extracellular fluid to intracellular fluid

Answer/Explanation

Ans. (a)
During the nerve impulse when a stimulus of adequate strength is applied to a polarised membrane, the permeability of the membrane to $\mathrm{Na}^{+}$is increased at the point of stimulation. As a result the sodium ion channels permit the influx of $\mathrm{Na}^{+}$by diffusion into the intracellular fluid from extracellular fluid.

Question

Which one of the following pairs of structures distinguishes a nerve cell from other types of cell? [CBSE AIPMT 2007]

(a) Perikaryon and dendrites

(b) Vacuoles and fibres

(c) Flagellum and medullary sheath

(d) Nucleus and mitochondria

Answer/Explanation

Ans. (a)

A nerve cell consists of cell body (perikaryon) containing the nucleus, Nissl granules, dendrites and an axon. These are specialised cells.

Question

 During the transmission of nerve impulse through a nerve fibre, the potential on the inner side of the plasma membrane has which type of electric charge? [CBSE AIPMT 2007]

(a) First negative, then positive and again back to negative

(b) First positive, then negative and continue to be negative

(c) First negative, then positive and continue to be positive

(d) First positive, then negative and again back to positive

Answer/Explanation

Ans. (a)

During the transmission of nerve impulse through a nerve fibre, the potential on the inner side of the plasma membrane has first become negative charged, then positive and again negative by repolarisation.

Question

 Which of the following statements is correct about node of Ranvier? [CBSE AIPMT 2002]

(a) Axolemma is discontinuous

(b) Myelin sheath is discontinuous

(c) Both neurilemma and myelin sheath are discontinuous

(d) Covered by myelin sheath

Answer/Explanation

Ans. (b)
Neurons are the chief functional units of the nervous system. An ordinary neuron has a soma or cyton and a long thread and, called as axon which is enclosed in a multilayered myelin sheath. The myelin sheath is interrupted at the spaces between Schwann cells to form gaps. These gaps are called nodes of Ranvier. These nodes and the myelin sheath create condition that speed up the nerve impulses.

Question

Which of the following is regarded as a unit of nervous tissue? [CBSE AIPMT 1999]

(a) Myelin sheath

(b) Axons

(c) Dendrites

(d) Neurons

Answer/Explanation

Ans. (d)

The nervous tissue is made up of nerve cells (the repeating units) also called neurons. Each neuron has a cell body or cyton and two kinds of cell processes
(a) Dendrons, come out from cyton.
(b) Axon, an elongated nerve fibre.

Question

The junction between the axon of one neuron and the dendrite of the next is called [CBSE AIPMT 1999]

(a) junction point

(b) a synapse

(c) a joint

(d) constant bridge

Answer/Explanation

Ans. (b)

The end to end position of the axon of one neuron and the dendrites of another neuron is called the synapse.
Most of the neurons do not actually touch other neurons with which they communicate, instead there is a minute space. This separating gap is called the synaptic cleft.

Question

 Sympathetic nervous system induces [CBSE AIPMT 1997]

(a) heartbeat

(b) secretion of digestive juices

(c) secretion of saliva

(d) All of the above

Answer/Explanation

Ans. (a)
Medulla of brain has two regions affecting heart rate (a) cardiac inhibitory centre, (b) cardiac accelerator centre. Sensory nerves originating from the accelerator centre run parallel to the spinal cord and enter the sino-atrial node. Stimulation by these nerves, which are part of sympathetic nervous system cause an increase in heartbeat.

Question

 In humans, visceral organs are innervated by [CBSE AIPMT 1996]

(a) sympathetic nerves and are under conscious control

(b) parasympathetic nerves and are under conscious control

(c) Both (a) and (b)

(d)both sympathetic and parasympathetic nerves but are not under conscious control

Answer/Explanation

Ans. (d)

Both sympathetic and parasympathetic nerve fibres innervate visceral organs and coordinate their activity antagonistically, but this is not under body’s conscious control.

Question

 Afferent nerve fibres carry impulses from [CBSE AIPMT 1992]

(a) effector argans to CNS

(b) receptors to CNS

(c) CNS to receptors

(d) CNS to muscles

Answer/Explanation

Ans. (b)

Afferent nerve fibres are formed of only sensory nerve fibres, conduct nerve impulses from sensory organs or receptors to central nervous system to produce sensation, e-g. optic nerve.

Question

 One function of parasympathetic nervous system is [CBSE AIPMT 1990]

(a) contraction of hair muscles

(b) stimulation of sweat glands

(c) acceleration of heartbeat

(d) constriction af pupil

Answer/Explanation

Ans. (d)
Parasympathetic nervous system involves conservation of energy and brings about relaxation, comfort, pleasure etc, at the time of rest. Another function of this system is that during emergency or stress while SNS dilates pupil for more light, PNS constricts the pupil to its normal condition.
Whereas, sympathetic nervous system involves expenditure of energy and increases the defence system of body against adverse conditions, so, it operates during stress, pain, fear and anger.

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