Biology Question Bank – 34 MCQs on “Nervous System and Sense Organs” – Answered!

(b) shark

(c) bat

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(d) frog.

Answer and Explanation:

1. (a): Bird’s (e.g. vulture) sense of sight has much higher resolution than ours. Their eyes are much larger in proportion to the sizes of their heads than our eyes are.

2. Sensitive pigmented layer of eye is

(a) cornea

(b) retina

(c) sclerotic

(d) iris.

Answer and Explanation:

2. (b): The retina consists of both pigmented layer and the sensory layer. The pigment cells reinforce the light absorbing property of choroid in reducing the scattering of light in the eye. The sensory layer consists of rods and cones required for vision.

3. Which of the following cranial nerves can regulate heart beat?

(a) X

(b) IX

(c) VIII

(d) VII.

Answer and Explanation:

3. (a): X nerve i.e. the vagus nerve (mixed) that arises from the side of medulla controls the visceral sensations and movements of larynx, lungs, heart, stomach and intestines. IX nerve innervates pharynx and tongue. VIII nerve innervates internal ear and VII nerve innervates face, neck, taste buds and salivary glands.

4. One function of parasympathetic nervous system is

(a) contraction of hair muscles

(b) stimulation of sweat glands

(c) acceleration of heart beat

(d) constriction of pupil.

Answer and Explanation:

4. (d): The action of the parasympathetic nervous system is opposite to that of the sympathetic nervous system. If the sympathetic nervous system accelerates an action, the parasympathetic nervous system slows it. However, neither system is exclusively exitatory or inhibitory. The parasympathetic fibres constrict the pupil, decrease the rate and force of heart beat, dilate many blood vessels, lower the arterial blood pressure, quicken the peristaltic movements, and contract the urinary bladder.

5. Third ventricle of brain is also known as

(a) metacoel

(b) rhinocoel

(c) paracoel

(d) diacoel.

Answer and Explanation:

5. (d): The ventricles consist of four hollow, fluid filled spaces inside the brain. The third ventricle is also known as diacoel. The third ventricle consists of a narrow channel between the hemispheres through the area of the thalamus. It is connected by the cerebral aqueduct or aqueduct of Sylvius or iter in the midbrain portion of the brainstem to the fourth ventricle in the pons and medulla. Metacoel is the IV ventricle, rhinocoel is the I ventricle and paracoel are the II ventricles.

6. Vagus nerve is

(a) X

(b) IX

(c) VII

(d) V.

Answer and Explanation:

6. (a): Vagus nerve is X nerve. It arises from the side of medulla oblongata. It innervates the larynx, trachea, oesophagus, stomach, lungs, heart and intestines. It is a mixed nerve. It controls the visceral sensations and visceral movements, i.e., heartbeat, respiratory movements, peristalsis, sound production, etc. Glossopharyngeal is the IX nerve. Facial is the VII nerve and trigeminal is the V nerve.

7. Afferent nerve fibres carry impulses from

(a) effector organs to CNS

(b) receptors to CNS

(c) CNS to receptors

(d) CNS to muscles.

Answer and Explanation:

7. (b): Afferent nerve fibres carry impulses from the receptors to the central nervous system. Efferent nerve fibres conduct nerve impulses from the central nervous system to the effector organs such as muscles and glands.

8. Iris is part of

(a) sclerotic

(b) choroid

(c) choroid and retina

(d) sclerotic and choroid.

Answer and Explanation:

8. (d): At the junction of the sclera and the cornea, the vascular coat sharply bends into the cavity of the eyeball to form a thin, coloured partition. This partition is called iris.

9. Function of iris is to

(a) move lens forward and backward

(b) refract light rays

(c) bring about movements of eye lids

(d) alter the size of pupil.

Answer and Explanation:

9. (d): At the junction of the sclera and the cornea, the vascular coat sharply bends into the cavity of the eyeball to form a thin, coloured partition.

This partition is called iris. It is perforated at the middle by an aperture called pupil. The iris contains two sets of smooth muscles: sphincters and dilators. These muscles regulate the amount of light entering the eyeball by varying the size of the pupil.

The sphincter muscles are arranged in rings. Their contraction makes the pupil smaller in bright light so that less light enters the eye. The dilator muscles are arranged in a radial manner. Their contraction widens the pupil in dim light to let in more light. Iris, by regulating the size of the pupil, allows light to pass only through the centre of the lens, which is optically the most effective part.

10. Retina is most sensitive at

(a) optic disc

(b) periphery

(c) macula lutea

(d) fovea centralis.

Answer and Explanation:

10. (d): A small area of the optical part of the retina lying exactly opposite to the centre of the cornea is called the macula lutea, or yellow spot which has a yellow pigment (xanthophyll). The macula lutea has at its middle a shallow depression, the fovea centralis. The fovea has cone cells only, and is the place of most distinct vision. Away from the fovea, the rod and cone cells occur in equal numbers, and at the periphery of the retina, the rods are more numerous than the cones.

This is why we see better in dim light by looking out of the corner of the eye. The point on the retina from where the optic nerve starts is called the blind spot, or optic disc, as it lacks the receptor cells and is insensitive to light.

11. Light rays entering the eye is controlled by

(a) pupil

(b) iris

(c) cornea

(d) lens.

Answer and Explanation:

11. (a): Pupil is the opening which controls the amount of light entering in eye. When light intensity is high, it decrease in size and when light intensity is low it dilates to allow more light in the eye to make eye enable to see the object.

12. Ivan Pavlov performed experiments on

(a) simple reflexes

(b) conditioned reflexes

(c) cardiac reflexes

(d) origin of life.

Answer and Explanation:

12. (b): By training, a particular response can be obtained to a stimulus other than the one which normally evokes that response. Such a reflex is known as the conditioned reflex.

The conditioned reflexes were first demonstrated in 1920’s by the Russian physiologist I.P. Pavlov. He found that the “sight and smell of food reflexly cause flow of saliva in hungry animals. He rang a bell every time he offered food to a dog. The bell did not induce salivation by itself in the beginning of the experiment. Gradually, the dog learnt to associate the bell with food. Eventually, mere ringing of bell, without presenting food, induced salivation in the dog.

Thus, ringing of bell can substitute sight of food to cause salivation. Pavlov called sound of the bell as ‘ conditioned stimulus, salivation in response to bell a conditioned response, food itself as unconditioned stimulus, and salivation in response to food an unconditioned response. A conditioned reflex is established when a new sensory clue (the bell) becomes associated with an inborn reflex (salivation).

13. By which nervous system and of what type, the blood is supplied into visceral organs?

(a) both SNS and PNS, involuntary

(b) para-sympathetic nervous system, involuntary

(c) sympathetic nervous system, involuntary

(d) sympathetic nervous system, voluntary.

Answer and Explanation:

13. (a): The blood is supplied into visceral organs by both SNS (sympathetic nervous system) and PNS (parasympathetic nervous system) involuntarily. The sympathetic fibres increase the rate and force of heart beat, constrict most blood vessels and raise the arterial blood pressure. The parasympathetic fibres decrease the rate and force of heart beat, dilate many blood vessels and lower the arterial blood pressure.

14. The vagus nerve is the cranial nerve numbering

(a) 7

(b) 5

(c) 10

(d) 9.

Answer and Explanation:

14. (c): Vagus nerve is the tenth cranial nerve. It arises from the side of medulla oblongata. It innervates the larynx, trachea, oesophagus, stomach, lungs, heart and intestines. It is a mixed nerve. It controls the visceral sensations and visceral movements, i.e., heartbeat, respiratory movements, peristalsis, sound production, etc.

15. In the chemistry of vision in mammals, the photosensitive substance is called

(a) rhodopsin

(b) melanin

(c) sclerotin

(d) retinol.

Answer and Explanation:

15. (a): Photosensitive means sensitive to light. The rod cells of retina contain a purplish pigment called rhodopsin. They function in dim light and at night. Rhodopsin consists of a protein component, opsin, linked to a nonprotein chromophore, retinal (or retinene), a derivative of vitamin A, Light falling on the rod is absorbed by the retinal, which changes its form and separates from the opsin component.

This initiates the transmission of a nerve impulse to the brain. Retinol is the another name of vitamin A. Deficiency of this affects the eyes, causing night blindness and xerophthalmia. Melanin is a pigment that gives colour to the eyes, skin and hair in vertebrates.

16. The Nissl’s granules of nerves cell are made up of

(a) DNA

(b) RNA

(c) ribosome

(d) protein.

Answer and Explanation:

16. (c): Cell body of a nerve cell contains basophilic granules called Nissl’s granules. These granules appear to be cisternae of rough endoplasmic reticulum with numerous attached and free ribosomes. They probably synthesize proteins for the cell.

17. Which of the following is regarded as a unit of nervous tissue?

(a) neurons

(b) myelin sheath

(c) axons

(d) dendrites.

Answer and Explanation:

17. (a): Neurons or nerve cells are the structural and functional unit of nervous system. These have a special structure but vary greatly in size and shape. Each neuron has a cell body which encloses cytoplasm and has a nucleus. A number of processes arise from the cell body. There is usually a single axon and a variable number of dendrites.

The medullated nerve a fibre is composed of a shining, white, fatty substance called myelin.

18. The junction between the axon of one neuron and the dendrite of the next is called

(a) constant bridge

(b) junction point

(c) a joint

(d) a synapse.

Answer and Explanation:

18. (d): Synapse is the close proximity of the axon of one neuron and the dendrite or cyton of another neuron with a gap of just about 200 A in between. A nerve impulse is transmitted across the synapse by the release from the presynaptic membrane of neurotransmitter, which diffuses across the synaptic cleft to the post synaptic membrane. This triggers the propagation of the impulse from the dendrite along the length of the post synaptic neuron.

19. Sympathetic nervous system induces

(a) secretion of digestive juices

(b) heart beat

(c) secretion of saliva

(d) all of these.

Answer and Explanation:

19. (b): Sympathetic nervous system is a component of autonomic nervous system consisting of a pair of sympathetic trunks, preganglionic sympathetic fibres, postganglionic sympathetic fibres and collateral ganglia. It quickens rate and force of heart beat while it inhibits secretion of saliva and gastric juice.

20. Which cranial nerve has the highest number of branches?

(a) vagus nerve

(b) trigeminal nerve

(c) facial nerve

(d) none of these.

Answer and Explanation:

20. (b): Trigeminal nerve is the largest 5th cranial nerve. It has 3 branches –

(i) Ophthalamic, a sensory branch from skin of the nose, eyelids, forehead and scalp, and from the conjunctiva and lacrimal glands.

(ii) Maxillary, also sensory branch from skin and mucous membrane of cheeks and upper lip, and from lower eyelids.

(iii) Mandibular, a mixed branch innervating the lower jaw, lower lip, pinna and tongue.

Vagus nerve is the 10th cranial nerve and innervates larynx, trachea, oesophagus, stomach, lungs, heart and intestines. Facial nerve is the 7th cranial nerve and innervates muscles of face and back, taste buds and salivary glands.

21. Depolarization of axolema during nerve conduction takes place because of

(a) equal amount of Na+ and K+ move out across axolema

(b) Na+ move inside and K+ move more outside.

(c) more Na+ outside

(d) none of the above

Answer and Explanation:

21. (b): Depolarization of a nerve cell membrane occurs during the passage of an action potential along the axon where the nerve is transmitting an impulse. During depolarization, the activation gates of Na channels open, and the K channels remain closed. Na+ rush into the axon. Entry of sodium ions leads to depolarization (reversal of polarity) of the nerve membrane, so that the nerve fibre contents become electropositive with respect to the extracellular fluid.

22. Which of the following statements is the characteristic of human cornea?

(a) secreted by conjuctiva and glandular layer

(b) it is a lacrimal gland which secrete tears

(c) blood circulation is absent in cornea

(d) in old age it becomes the cause of cataract.

Answer and Explanation:

22. (c): Cornea forms the anterior one-sixth of the fibrous coat. It is transparent, circular and fully visible from in front. It is composed of a peculiar variety of connective tissue covered externally by stratified non- keratinized squamous epithelium and internally by simple squamous epithelium. It lacks blood vessels. It is nourished by lymph from adjacent area.

23. When we migrate from dark to light, we fail to see for sometime but after a time visibility becomes normal. It is example of

(a) accommodation

(b) adaptation

(c) mutation

(d) photoperiodism.

Answer and Explanation:

23. (b): The rod cells of eye contain a purplish pigment called visual purple, or rhodopsin. They function in dim light and at night. Bright light splits rhodopsin into a lipoprotein scotopsin and a carotenoid pigment retinene. The splitting of rhodopsin depolarizes the rod cell. In the dark, rhodopsin is resynthesized from scotopsin and retinene.

This process is called “dark adaptation.” It makes the rods functional. It takes some time for rhodopsin to be reformed. This is why on entering a dark room at daytime or on coming out of a well lighted room at night, we feel blind for a while. When we go from darkness into bright light, we feel difficulty in seeing properly for a moment till rhodopsin is bleached and cones become functional.

Accommodation is the reflex mechanism by which the focus of the eye changes to make the images of distant and near objects sharp on the retina. Mutation is a change in the genetic material (DNA) of a cell, or the change in a characteristic of an individual, which is not caused by normal genetic processes. Photoperiodism is the response of an organism to the day length.

24. Which of the following statement is correct for node of Ranvier of nerve?

(a) neurilemma is discontinuous

(b) myelin sheath is discontinuous

(c) both neurilemma and myelin sheath are discontinuous

(d) covered by myelin sheath.

Answer and Explanation:

24. (b): At the level of node of Ranvier the myelin sheath is discontinuous but not the neurilemma lining. Actually myelin sheath is an integral part of Schwann’s cell – which forms a continuous neurilemmal covering. Each Schwann’s cell wrap-around the neurite to form concentric layers of plasma membrane. But at the level of junction between two Schwann’s cells myelin cannot be formed and thus a gap appears.

25. What used to be described as Nissl’s granules in a nerve cell are now identified as?

(a) cell metabolites

(b) fat granules

(c) ribosomes

(d) mitochondria

Answer and Explanation:

25. (c): Refer answer 16.

26. Injury to vagus nerve in humans is not likely to affect

(a) tongue movements

(b) gastrointestinal movements

(c) pancreatic secretion

(d) cardiac movements.

Answer and Explanation:

26. (a): Vagus nerve arises from the side of medulla oblongata. It innervates the larynx, trachea, oesophagus, stomach, lungs, heart and intestines. It is a mixed nerve. It controls the visceral sensations and visceral movements, i.e., heartbeat, respiratory movements, peristalsis, sound production, etc. Movement of the tongue is controlled by hypoglossal nerve as it innervates the muscles of the tongue.

27. In the resting state of the neural membrane, diffusion due to concentration gradients, if allowed, would drive

(a) K+ into the cell

(b) K+ and Na+ out of the cell

(c) Na+ into the cell

(d) Na+ out of the cell.

Answer and Explanation:

27. (c): In the resting nerve fibre, in the external medium (tissue fluid), sodium ions (Na4) predominate, whereas within the fibre (intracellular fluid) potassium ions (K) predominate. Due to different concentrations of ions on the two sides of the membrane, sodium ions tend to passively diffuse into the nerve fibre and potassium ions tend to diffuse out of the nerve fibre down their electrochemical gradients.

The membrane of a resting nerve fibre is, however, more permeable to potassium than to sodium. Because of this selective permeability of the membrane, potassium leaves the nerve fibre faster than sodium enters it. This makes the membrane of the resting nerve fibre polarized, extracellular fluid outside it being electropositive (positively charged) with respect to the cell contents inside it.

28. Parkinson’s disease (characterized by tremors and progressive rigidity of limbs) is caused by degeneration of brain neurons that are involved in movement control and make use of neurotransmitter

(a) acetylcholine

(b) norepinephrine

(c) dopamine

(d) GABA.

Answer and Explanation:

28. (c): Parkinsonism is caused by degenerations of neurons in Substantia Nigra tract which are essentially dopaminergic. This striatum controls muscle tones and coordinates movements. An imbalance is caused by deficiency of dopamine (an inhibitory neurotransmitter) vis a vis. Epinephrine (cholinergic which is an excitatory neurotransmitter) results in motor deficits.

Hence to restore a balance central anticholinergics are given. Parkinson’s disease is a clinical picture characterized by tremor, rigidity, slowness of movement, and postural instability. The commonest symptom is tremor, which often affects one hand, spreading first to the leg on the same side and then to the other limbs.

The patient has an expressionless face, an unmodulated voice, an increasing tendency to stoop, and a shuffling walk.

29. In a man, abducens nerve is injured. Which one of the following functions will be affected?

(a) movement of the eyeball

(b) movement of the tongue

(c) swallowing

(d) movement of the neck.

Answer and Explanation:

29. (a): Abducens is the sixth cranial nerve which innervates the external rectus muscle of the eye ball. It is responsible for turning the eye outwards. Movement of the tongue is controlled by the hypoglossal nerve. Neck movements are controlled by the facial nerve. Swallowing is by glossopharyngeal.

30. Which one of the following is the example of the action of the autonomous nervous system?

(a) swallowing of food

(b) pupillary reflex

(c) peristalsis of the intestine

(d) knee-jerk response.

Answer and Explanation:

30. (c): Options (a), (b) and (d) are reflex actions. Autonomic nervous system is involved in peristalsis of “tine which is affected through mysentric plexus, pathetic fibres decrease peristaltic movements while sympathetic fibres increase these movements.

31. Which one of the following does not act as a neurotransmitter?

(a) cortisone

(b) acetylcholine

(c) epinephrine

(d) norepinephrine

Answer and Explanation:

31. (a): Neurotransmitters are chemicals that are used lorelay, amplify and modulate electrical signals between a neuron and another cell. Substances that act as leurotransmitters can be categorized into three major groups: (1) amino acids (primarily glutamic acid, GABA, aspartic acid & glycine), (2) peptides (vasopressin, somatostatin, neurotensin, etc.), and (3) monoamines (norepinephrine, dopamine & serotonin) plus acetylcholine. Cortisone is a glucocorticoid steroid (hormone, produced by the adrenal glands and has anti-inflammatory and immune-system suppressing Properties.

32. Bowman’s glands are found in

(a) juxtamedullary nephrons

(b) olfactory epithelium

(c) external auditory canal

(d) cortical nephrons only

Answer and Explanation:

32. (b): Bowman’s gland, also called olfactory gland is any of the branched tubuloalveolar glands situated in the mucous membrane of the olfactory region of the nasal cavity that produce mucus to moisten the olfactory epithelium and dissolve odour-containing gases.

33. Bowman’s glands are located in the

(a) anterior pituitary

(b) female reproductive system of cockroach

(c) olfactory epithelium of our nose

(d) proximal end of uriniferous tubules.

Answer and Explanation:

33. (c): Refer answer 32.

34. 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 change?

(a) first positive, then negative and continue to be negative

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

(c) first positive, then negative and again back to positive

(d) first negative, then positive and again back to negative.

Answer and Explanation:

34. (d): Nerve is a strand of tissue comprising many nerve fibres plus supporting tissue enclosed in a connective tissue sheath. The signal that travels along the length of a nerve fibre and is the means by which information is transmitted through the nervous system is called nerve impulse.

It is marked by the flow of ions across the membrane of the axon caused by changes in the permeability of the membrane, producing a reduction in potential difference that can be detected as the action potential. The strength of the impulse produced in any nerve fibre is constant.

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