Samacheer Kalvi 11th Bio Zoology Solutions Chapter 10 Neural Control and Coordination

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Tamilnadu Samacheer Kalvi 11th Bio Zoology Solutions Chapter 10 Neural Control and Coordination

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Samacheer Kalvi 11th Bio Zoology Neural Control and Coordination Text Book Back Questions and Answers

Textbook Evaluation Solved
Choose The Correct Answer
Question 1.
Which structure in the ear converts pressure waves to action potentials?
(a) Tympanic membrane
(b) Organ of Corti
(c) Oval window
(d) Semicircular canal
Answer:
(b) Organ of Corti

Question 2.
Which of the following pairings is correct?
(a) Sensory nerve – afferent
(b) Motor nerve – afferent
(c) Sensory nerve – ventral
(d) Motor nerve – dorsal
Answer:
(a) Sensory nerve – afferent

Question 3.
During synaptic transmission of nerve impulse, a neurotransmitter (P) is released from synaptic vesicles by the action of ions (Q)? Choose the correct P and Q?
(a) P = Acetylcholine, Q = Ca^+–
(b) P = Acetylcholine, Q = Na⁺
(c) P = GABA, Q = Na⁺
(d) P = Cholinesterase, Q = Ca⁺⁺
Answer:
(a) P = Acetylcholine, Q = Ca^+–

Question 4.
Examine the diagram of the two cell types A and B given below and select the correct option?

(a) Cell-A is the rod cell found evenly all over retina
(b) Cell-A is the cone cell more concentrated in the fovea centralis
(c) Cell-B is concerned with colour vision in bright light
(d) Cell-A is sensitive to bright light intensities
Answer:
(c) Cell-B is concerned with colour vision in bright light

Question 5.
Assertion: The imbalance in the concentration of Na⁺, K⁺ and proteins generates action potential.
Reason: To maintain the unequal distribution of Na⁺ and K⁺, the neurons use electrical energy.
(a) Both Assertion and Reason are true and Reason is the correct explanation of the Assertion.
(b) Both Assertion and Reason are true but the Reason is not the correct explanation of Assertion.
(c) Assertion is true, but Reason is false.
(d) Both Assertion and Reason are false.
Answer:
(a) Both Assertion and Reason are true and Reason ¡s the correct explanation of the Assertion.

Question 6.
Which part of the human brain is concerned with the regulation of body temperature?
(a) Cerebellum
(b) Cerebrum
(c) Medulla oblongata
(d) Hypothalamus
Answer:
(a) Cerebellum

Question 7.
The respiratory centre is present in the …………………..
(a) Medulla oblongata
(b) Hypothalamus
(c) CerebeLlum
(d) Thalamus
Answer:
(a) Medulla oblongata

Question 8.
Match the following human spinal nerves in column-I with their respective number in column-II and choose the correct option?

	Column -1		Column – II
P	Cervical nerves	(i)	5 pairs
Q	Thoracic nerve	(ii)	1 pair
R	Lumbar nerve	(iii)	12 pairs
S	Coccygeal nerve	(iv)	8 pairs

(P – iv), (Q – iii), (R – i), (S – ii)
(b) (P – iii), (Q – i), ( R – ii), (S – iv)
(c) (P – iv), (Q – i), (R – ii), ( S – iii)
(d) (P – ii), (Q – iv), (R – i), (S – iii)
Answer:
(a) (P -iv)
(b) (Q – iii)
(c) (R – i)
(d) (S – ii)

Question 9.
Which of the following cranial nerve controls the movement of eyeball?
(a) Trochlear nerve
(b) Optic nerve
(c) Olfactory nerve
(d) Vagus nerve
Answer:
(a) Trochlear nerve

Question 10.
The abundant intracellular cation is ………………….
(a) H⁺
(b) K⁺
(c) Na⁺
(d) Ca⁺⁺
Answer:
(b) K⁺

Question 11.
Which of the following statement is wrong regarding the conduction of nerve impulses?
(a) In a resting neuron, the axonal membrane is more permeable to K⁺ ions and nearly impermeable to Na⁺ ions.
(b) Fluid outside the axon has a high concentration of Na⁺ ions and a low concentration of K⁺, in a resting neuron.
(c) Ionic gradients are maintained by Na-K pumps across the resting membrane, which transport 3Na⁺ ions outwards for 2K⁺ into the cell.
(d) A neuron is polarized only when the outer surface of the axonal membrane possesses a negative charge and its inner surface is positively charged.
Answer:
(d) A neuron is polarized only when the outer surface of the axonal membrane possesses a negative charge and its inner surface is positively charged.

Question 12.
All of the following are associated with the myelin sheath except ………………….
(a) Faster conduction of nerve impulses
(b) Nodes of Ranvier forming gaps along the axon
(c) Increased energy output for nerve impulse conduction
(d) Saltatory conduction of action potential
Answer:
(c) Increased energy output for nerve impulse conduction

Question 13.
Several statements are given here in reference to cone cells. Which of the following option indicates all correct statements for cone cells?
Statements:
(i) Cone cells are less sensitive in bright light than Rod cells
(ii) They are responsible for colour vision
(iii) Erythropsin is a photo pigment which is sensitive to red colour light
(iv) They are present in fovea of retina
(a) (iii), (ii) and (i)
(b) (ii), (iii) and (iv)
(c) (i), (iii) and (iv)
(d) (i), (ii) and (iv)
Answer:
(b) (ii), (iii) and (iv)

Question 14.
Which of the following statement concerning the somatic division of the peripheral neural system is incorrect?
(a) Its pathways innervate skeletal muscles
(b) Its pathways are usually voluntary
(c) Some of its pathways are referred to as reflex arcs
(d) Its pathways always involve four neurons
Answer:
(d) Its pathways always involve four neurons

Question 15.
When the potential across the axon membrane is more negative than the normal resting potential, the neuron is said to be in a state of …………………
(a) Depolarization
(b) Hyperpolarization
(c) Repolarization
(d) Hypopolarization
Answer:
(b) Hyperpolarization

Question 16.
Why is the blind spot called so?
Answer:
Slightly below the posterior pole of the eye, the optic nerve and the retinal blood vessels enter the eye. This region is devoid of rods and cones. Hence, this region is called a blind spot.

Question 17.
Sam’s optometrist tells him that his intraocular pressure is high. What is this condition called and which fluid does it involve?
Answer:
The aqueous humour present in between iris and lens and the cornea and iris is produced and drained at the same rate, maintaining a constant intraocular pressure of about 16 mm Hg. Any block in the canal of schlemm increases the intraocular pressure of aqueous humour. This condition is called ‘Glaucoma’. Due to pressure, the optic nerve and the retina are compressed. This leads to blindness.

Question 18.
Why are we getting running nose while crying?
Answer:
When we cry, the tears come out of the tear glands under the eyelids and drain through the tear duct that empties into the nose. It mixes with mucus there and the nose runs.

Question 19.
The action potential occurs in response to a threshold stimulus; but not at subthreshold stimuli. What is the name of the principle involved?
Answer:
All or none principle.

Question 20.
Pleasant smell of food urges Ravi to rush into the kitchen. Name the parts of the brain involved in the identification of food and emotional responses to odour?
Answer:
When we cry, the tears come out of the tear glands under the eyelids and drain through the tear duct that empties into the nose. It mixes with mucus there and the nose runs.

Question 21.
Cornea transplant in humans is almost never rejected. State the reason?
Answer:
The cornea does not have blood vessels. Hence there is no possibility of rejection when the cornea is transplanted from one person to another person.

Question 22.
At the end of repolarization, the nerve membrane gets hyperpolarized. Why?
Answer:
At the end of repolarization, the membrane potential inside the axolemma becomes negative due to the efflux of K⁺ ions. When it becomes more negative than the resting potential -70 mV to about – 90mV, it becomes hyperpolarised.

Question 23.
Label the parts of the neuron?
Answer:

1. Nucleolus
2. Node of Ranvier
3. Dendrite
4. Myelin sheath
5. Axon
6. Nucleus

Question 24.
The choroid plexus secretes cerebrospinal fluid. List the function of it?
Answer:
Cerebrospinal fluid provides buoyancy to the central nervous system.

1. It acts as a shock absorber for the brain and spinal cord.
2. It nourishes the brain cells by transporting food and oxygen.
3. It carries harmful metabolic wastes from the brain to the blood.
4. It maintains constant pressure inside the cranial vessels.

Question 25.
What is the ANS controlling centre? Name the parts that are supplied by the ANS?
Answer:
Hypothalamus is the ANS controlling centre. The Autonomic neural system innervates smooth muscles, glands, and cardiac muscle.

Question 26.
Why the limbic system is called the emotional brain? Name the parts of it?
Answer:
The limbic system is a set of components located on both sides of the thalamus present in the inner part of the cerebral hemisphere. It includes the olfactory bulbs, cingulate gyrus, mammillary body, amygdala, hippocampus, and hypothalamus. The limbic system plays a primary role in the regulation of pleasure, pain, anger, fear, sexual feeling, affection, and memory. Hence it is called the emotional brain.

Question 27.
Classify receptors based on the type of stimuli?
Answer:

Receptors	Stimulus	Effector organs
Mechano receptors	Pressure and vibration	Mechano receptors are present in the cochlea of the inner ear and the semicircular canal and utriculus
Chemoreceptors	Chemicals	Taste buds in the tongue and nasal epithelium
Thermoreceptors	Temperature	Skin
Photoreceptors	Light	Rod and cone cells of the retina in the eye

Question 28.
Name the first five cranial nerves, their nature, and their functions?
Answer:

	Cranial nerves	Nature of nerve	Function
1.	Olfactory nerve	Sensory	Sense of smell
2.	Optic nerves	Sensory	Sense of sight
3.	Oculomotor nerves	Motor	Movement of the eye
4.	Trochlear nerve	Motor	Rotation of the eye ball
5.	Trigeminal nerve	Sensory and motor (mixed)	Functioning of facial parts

Question 29.
The sense of taste is considered to be the most pleasurable of all senses? Describe the structure of the receptor involved with a diagram?
Answer:
Gustatory receptor: The sense of taste is considered to be the most pleasurable of all senses. The tongue is provided with many small projections called papillae which give the tongue an abrasive feel. Taste buds are located mainly on the papillae which are scattered over the entire tongue surface.

Most taste buds are seen on the tongue few are scattered on the soft palate, the inner surface of the cheeks, pharynx, and epiglottis of the larynx. Taste buds are flask-shaped and consist of 50 – 100 epithelial cells of two major types.

Gustatory epithelial cells (taste cells) and Basal epithelial cells (Repairing cells). Long microvilli called gustatory hairs project from the tip of the gustatory cells and extend through a taste pore to the surface of the epithelium where they are bathed by saliva.

Gustatory hairs are the sensitive portion of the gustatory cells and they have sensory dendrites which send the signal to the brain. The basal cells that act as stem cells, divide and differentiate into new gustatory cells.

Question 30.
Describe the structures of olfactory receptors?
Answer:
The smell receptors are excited by air-borne chemicals that dissolve in fluids. The yellow coloured patches of olfactory epithelium form the olfactory organs that are located on the roof of the nasal cavity.

The olfactory epithelium is covered by a thin coat of mucus layer below and olfactory glands bounded connective tissues, above. It contains three types of cells: supporting cells, Basal cells and millions of pin-shaped olfactory receptor cells (which are unusual bipolar cells).

The olfactory glands and the supporting cells secrete the mucus. The unmyelinated axons of the olfactory receptor cells are gathered to form the filaments of olfactory nerve [cranial nerve-I] which synapse with cells of olfactory bulb.

The impulse, through the olfactory nerves, is transmitted to the frontal lobe of the brain for identification of smell and the limbic system for the emotional responses to odour.

In-Text Questions Solved

Question 1.
Can you state why some areas of the brain and spinal cord are grey and some are white?
Answer:
Some areas of the brain and spinal cord are grey due to the presence of non-myelinated nerve cells. The white matter has myelinated nerve cells with myelin sheath made of fat.

Question 2.
Human brain is formed of a large number of parts like cerebrum, thalamus, hypothalamus, pons, cerebellum and medulla oblongata. Each part performs some specialized function and all the parts are essential for the survival of a person. Discuss the following statements:
(a) Thalami are called relay centres of the brain.
(b) Damage to medulla may cause the death of organism.
Answer:
(a) Thalamus is composed of grey mater which serves as a relay centre for impulses between the spinal cord, brain stem and cerebrum. Thus acting as a major coordinating centre for sensory and motor signaling. Within the thalamus, information is sorted and edited and plays a key role in learning and memory.

(b) Medulla contains vital centres that control cardiovascular reflexes, respiration and gastric secretions. Therefore, damage to medulla may cause the death of an organism.

Question 3.
Your friend is returning home after his visit to USA. All at home are waiting for his arrival. How would you feel? State the division of ANS that predominates and mention few changes that take place in your body?
Answer:
I would feel excited. The sympathetic neural system of the ANS predominates and the various changes taking place inside the body include; excess secretion of “adrenaline” to the bloodstream from the medulla of the adrenal gland. This in turn, dilates pupil, inhibits salivation, accelerates heartbeat, inhibits digestion, etc.

Question 4.
Name the parts of the organ of equilibrium involved in the following functions?
(a) Linear movement of the body.
(b) Changes in the body position.
(c) Rotational movement of the head.
Answer:
(a) The utricle and saccule are two membranous sacs, found nearest the cochlea and contain equilibrium receptor regions called maculae that are involved in detecting the linear movement of the head.

(b) Two fluids, perilymph and endolymph, respond to the mechanical forces, during changes occurring in body position and acceleration.

(c) The anterior, posterior and lateral canals detect the rotational movement of the head.

Samacheer Kalvi 11th Bio Zoology Neural Control and Coordination Additional Questions & Answers

I. Choose The Correct Answer

Question 1.
What is the functional unit of the nervous system?
a) Neuroglial cells
b) Neuron
c) Nephron
d) Axon
Answer:
b) Neuron

Question 2.
The granular endoplasmic reticulum of the cell body and dendrites are …………………..
(a) Schwann cells
(b) Myelin sheath
(c) Nissl’s granules
(d) Cytoplasm
Answer:
(c) Nissl’s granules

Question 3.
Name the cell organelle which is not seen in the nerve cell.
a) Mitochondria
b) Golgi apparatus
c) Centrioles
d) Nucleus
Answer:
c) Centrioles

Question 4.
Which of the following is present more in the extracellular fluid found outside the axolemma?
(a) Sodium chloride
(b) Potassium
(c) Magnesium phosphate
(d) Organic molecules
Answer:
(a) Sodium chloride

Question 5.
Name the plasma membrane surrounds the axon?
a) Neurilemma
b) Myalin membrane
c) Sarcolemma
d) Axolemma
Answer:
d) Axolemma

Question 6.
When a nerve fibre is stimulated, the axolemma is permeable to Na⁺ ions in which of the following process?
(a) Opening sodium voltage-gate
(b) Opening potassium voltage-gate
(c) Opening sodium voltage-gated and closing potassium voltage-gate
(d) Opening neurolemma
Answer:
(c) Opening sodium voltage-gated and closing potassium voltage-gate

Question 7.
Name the cell organelle which is not seen in the axons.
a) Mitochondria
b) Golgi apparatus
c) Centriole
d) Endoplasmic reticulum
Answer:
b) Golgi apparatus

Question 8.
When the membrane potential reaches the spike potential, what happens?
(a) The potential again goes to the spike potential
(b) The potential reaches to the threshold potential
(c) The potential falls back towards the resting potential
(d) The potential remains the same
Answer:
(c) The potential falls back towards the resting potential

Question 9.
Which part of the nerve cells do not contain myelin sheath.
a) Axon
b) Cell body
c) Dendrites
d) Axon end plate
Answer:
c) Dendrites

Question 10.
The hormone melatonin which regulates the sleep and wake cycle is secreted by ………………..
(a) Choroid plexus
(b) Pituitary gland
(c) Infundibulum
(d) Pineal body
Answer:
(d) Pineal body

Question 11.
Find out the correct statement
a) The short nerve fibres are called dentrites.
b) The membrane surrounds the neuron is axolemma.
c) The longest sciatic nerve runs from the base of the spine to the big toe of each foot
d) Schwann cell’s do not synthesize myalin sheath
Answer:
c) The longest sciatic nerve runs from the base of the spine to the big toe of each foot

Question 12.
Which of the following controls and coordinates the muscular movements and body equilibrium?
(a) Cerebrum
(b) Cerebellum
(c) Pons
(d) Medulla oblongata
Answer:
(b) Cerebellum

Question 13.
This substance is more in the tissue fluid of cytoplasm of axolemma?
a) Sodium chloride and bicarbonates.
b) Nutritious substances and oxygen.
c) Potassium and magnesium phosphate.
d) All the above.
Answer:
c) Potassium and magnesium phosphate.

Question 14.
The number of lumbar spinal nerves is ………………..
(a) 8
(b) 12
(c) 5
(d) 1
Answer:
(c) 5

Question 15.
Name the gaps in the myelin sheath between adjacent Schwann.
a) Nodes of Ranvier
b) Nodes of axon
c) Nodes of cyton
d) Nodes of dendrites
Answer:
a) Nodes of Ranvier

Question 16.
The eye lens is made up of long ……………….
(a) Ciliated epithelial cells
(b) Squamous epithelial cells
(c) Germinal epithelial cells
(d) Columnar epithelial cells
Answer:
(d) Columnar epithelial cells

Question 17.
Where are Bipolar neurons situated?
a) Spinal cord
b) Retina
c) Inner ear
d) Brain.
Answer:
a) Spinal cord

Question 18.
What of the following does not happen in the bright light?
(a) Size of the pupil increases
(b) Size of the pupil decreases
(c) Lens light enters the eye
(d) The circular muscle of the iris contract
Answer:
(a) Size of the pupil increases

Question 19.
Where are Bipolar neurons meet?
a) Synapses
b) Synaptic cleft
c) Synaptic vesicle
d) Synaptic Knob
Answer:
a) Synapses

Question 20.
Which are the sensory cells in the ear?
(a) Ossicles
(b) Endolymph
(c) Cochlea
(d) Organs of corti
Answer:
(d) Organs of corti

Question 21.
The central nervous system forms from this layer during embryonic development.
a) Endoderm
b) Ectoderm
c) Mesoderm
d) Middle layer.
Answer:
b) Ectoderm

Question 22.
Which of the following is a wrong statement?
(a) Gustatory hairs project from the tip of the gustatory cells.
(b) Gustatory cells are a sensory portion of the taste.
(c) Basal epithelial cells are stem cells which divide and differentiate into new gustatory cells.
(d) Basal epithelial cells are sensitive portions of the taste.
Answer:
(d) Basal epithelial cells are sensitive portions of the taste.

Question 23.
Which is considered as the seat of intelligence.
a) Cerebellum
b) Cerebrum
c) Medulla oblongata
d) Pons.
Answer:
b) Cerebrum

Question 24.
The blind spot is called so because
(a) It has only cones
(b) It has only rods
(c) It has neither rods nor cones
(d) It is present beyond the lens
Answer:
(c) It has neither rods nor cones

Question 25.
Find out the wrong pair
a) Synapses – The junction of two neurons
b) Neurotransmitter – Postsynaptic neuron
c) Synaptic vesicles – A small bag filled with chemicals
d) Piamatter – Membrane which closely adheres to the brain.
Answer:
b) Neurotransmitter – Postsynaptic neuron

II. Fill in the Blanks

Question 1.
The structural and functional unit of the nervous system are ………………..
Answer:
Neurons

Question 2.
……………….. neurons that take sensory impulses from the sense organs to the central nervous system.
Answer:
Afferent

Question 3.
The efferent neurons carry ……………….. impulses from the central nervous system to the effector organs.
Answer:
Motor

Question 4.
The plasma membrane covering the neuron is called ………………..
Answer:
Neurilemma

Question 5.
Myelin sheath acts as an ………………..
Answer:
Insulator

Question 6.
The synaptic vesicles of the synaptic knob are filled with ………………..
Answer:
Neurotransmitters

Question 7.
……………….. neurons are found in the retina of the eye, inner ear, and the olfactory area of the brain.
Answer:
Bipolar

Question 8.
The neurons which have only one process are called ………………..
Answer:
Unipolar

Question 9.
During the resting potential, the interior of the cell is negative due to greater efflux of ……………….. ions outside the cell.
Answer:
potassium

Question 10.
The normal value of resting membrane potential is ………………..
Answer:
-70 mV

Question 11.
Due to the rate of flow of Na⁺ ions into the axoplasm, more than the rate of flow of K⁺ ions to the outside fluid makes the neurilemma ……………….. charged inside.
Answer:
Positively

Question 12.
The threshold potential is ………………..
Answer:
-55 mV

Question 13.
The spike potential is ………………..
Answer:
+45 mV

Question 14.
In the neurilemma, the synaptic vesicles release neurotransmitters into the synaptic cleft by ………………..
Answer:
Exocytosis

Question 15.
……………….. is the layer which is closely adhered to the brain.
Answer:
Pia mater

Question 16.
The folds on the surface of the cerebrum are called
Answer:
Gyri

Question 17.
The grooves between the gyri are called ………………..
Answer:
Sulci

Question 18.
The cerebral hemispheres are connected by a tract of nerve fibres called ………………..
Answer:
Corpus callosum

Question 19.
The medulla acts as a nerve tract between cortex and the ………………..
Answer:
Diencephalon

Question 20.
……………….. forms the roof of the diencephalon.
Answer:
Epithalamus

Question 21.
The pineal body secretes the hormone ……………….. which regulates sleep and wake cycle.
Answer:
Melatonin

Question 22.
……………….. is composed of grey matter which serves as a relay centre for impulses between the spinal cord, brain system and cerebrum.
Answer:
Thalamus

Question 23.
……………….. plays a key role in learning and memory.
Answer:
Thalamus

Question 24.
The downward extension of the hypothalamus, ……………….. connects the hypothalamus with the pituitary gland.
Answer:
Infundibulum

Question 25.
……………….. acts as the satiety centre.
Answer:
Hypothalamus

Question 26.
The ……………….. system is called the emotional brain.
Answer:
Limbic

Question 27.
……………….. is the second largest part of the brain.
Answer:
Cerebellum

Question 28.
……………….. forms the posterior-most part of the brain.
Answer:
Medulla oblongata

Question 29.
……………….. connects the spinal cord with various parts of the brain.
Answer:
Medulla oblongata

Question 30.
……………….. contains vital centres that control cardiovascular reflexes, respiration, and gastric secretions.
Answer:
Medulla oblongata

Question 31.
The ……………….. connects the lateral ventricles with the III ventricle.
Answer:
Foramen of Monro/Interventricular foramen

Question 32.
The choroid plexus found in the roof of the ventricles forms ………………..
Answer:
Cerebrospinal fluid

Question 33.
……………….. provide information about position and movements of the body.
Answer:
Proprioceptors

Question 34.
The receptors of taste and smell are called ………………..
Answer:
Chemoreceptors

Question 35.
The sebaceous glands at the base of eyelashes are called ……………….. glands.
Answer:
Ciliary

Question 36.
……………….. is the outermost layer of the eyeball.
Answer:
Sclera

Question 37.
……………….. is the highly vascularized pigmented layer that nourishes all the eye layers.
Answer:
Choroid

Question 38.
……………….. is the coloured protein of the eye lying between the cornea and lens.
Answer:
Iris

Question 39.
The aperture at the centre of the iris is the ………………..
Answer:
Pupil

Question 40.
The ……………….. muscle alters the convexity of the eye lens.
Answer:
Ciliary

Question 41.
The ……………….. optic nerve arises from the
Answer:
Blindspot

Question 42.
The protein part of the photopigment is ………………..
Answer:
Opsin

Question 43.
Myopia can be corrected by using ……………….. lens.
Answer:
Concave

Question 44.
……………….. is the defect of the eye due to a shortened eyeball or thin lens.
Answer:
Hypermetropia

Question 45.
……………….. is due to the rough curvature of the cornea or lens.
Answer:
Astigmatism

Question 46.
The opaqueness of the lens is called ………………..
Answer:
Cataract

Question 47.
……………….. connects the middle ear cavity with the pharynx.
Answer:
Eustachian tube

Question 48.
The scala vestibuli and scala media are separated by a membrane called ………………..
Answer:
Reisner’s membrane

Question 49.
Protruding from the apical part of each hair cell is hair-like structures known as ………………..
Answer:
Stereocilia

Question 50.
The hair cells are embedded in a gelatinous otolithic membrane that contains small calcareous particles called ………………..
Answer:
Otoliths

Question 51.
The swollen area of each semicircular canal is called ………………..
Answer:
Ampulla

Question 52.
The tongue has many small projections called ………………..
Answer:
Papillae

Question 53.
……………….. is the largest sense organ.
Answer:
Skin

Question 54.
……………….. are numerous in hairless skin areas such as fingertips and soles of the feet.
Answer:
Meissner’s corpuscles

Question 55.
……………….. detect different textures, temperature, hardness, and pain.
Answer:
Pacinian corpuscles

Question 56.
……………….. which lie in the dermis respond to continuous pressure.
Answer:
Ruffini endings

Question 57.
……………….. are thermoreceptors that sense temperature.
Answer:
Krause end bulbs

Question 58.
Melanocytes are the cells responsible for producing the skin pigment called ………………..
Answer:
Melanin

Question 59.
……………….. is a condition in which the melanin pigment is lost from areas of the skin, causing white patches.
Answer:
Vitiligo (Leucoderma)

Question 60.
The sense of taste is recognized by the ………………..
Answer:
Gustatory receptor

III. Short Answer Questions

Question 1.

What are the two branches of the human nervous system?
Answer:

1. Central nervous system
2. Peripheral nervous system

Question 2.
What are neuroglia?
Answer:
The non-nervous special supporting cells of the nervous tissue are called neuroglia.

Question 3.
Differentiate between afferent neurons and efferent neurons?
Answer:

Afferent Neurons	Efferent Neurons
1. These take sensory impulses to the central nervous system from the sense organs.	1. These carry motor impulses from the central nervous system to the effectors.

Question 4.
Give notes on

1. Synaptic Knob
2. Neurotransmitters
3. Inter neural space.

Answer:

1. Synaptic Knob: Distant end of the axon terminates into a bulb
2. Synaptic vesicles: Vesicles filled with neurotransmitters
3. Inter neural space – The space between presynaptic and postsynaptic neurons.

Question 5.
Distinguish between Axon and Dendrites?
Answer:

	Axon	Dendrites
1.	An axon is a long fibre that arises from a cone shaped area of the cell body called the Axon hillock and ends at the branched distal end.	1. Dendrites are the repeatedly branched short fibres coming out of the cell body.
2.	It does not have Nissl’s granules and Golgi apparatus.	2. It has Nissl’s granules and Golgi apparatus.
3.	It is myelinated.	3. It is non-myelinated.

Question 6.
What is meant by resting potential?
Answer:
The electrical potential difference across the plasma membrane of a resting neuron is called the resting potential.

Question 7.
What is axolemma?
Answer:
The plasma membrane covering the axon is the axolemma.

Question 8.
What is threshold stimulus?
Answer:
The particular stimulus which is able to bring the membrane potential to the threshold is called the threshold stimulus.

Question 9.
What is Synapse?
Answer:
The junction between two neurons is called a Synapse through which a nerve impulse is transmitted.

Question 10.
What is the cause of brain tumours?
Answer:

• Glial cells: Nerve cells do not divide but glial cells do not lose the ability to undergo cell division.
• So most brain tumours of neural origin consist of glial cells.

Question 11.
What are meninges?
Answer:
The brain is covered by the outer Dura mater, the median Arachnoid mater, and the inner Pia mater. These membranes are called meninges.

Question 12.
What is subdural space?
Answer:
The space between the dura mater and arachnoid mater is called subdural space.

Question 13.
What is spike potential?
Answer:
Due to the rapid influx of Na⁺ ions, the membrane potential shoots rapidly up +45 mV which is called the spike potential.

Question 14.
What is corpus callosum?
Answer:
The cerebral hemispheres are connected by a tract of nerve fibres called the corpus callosum.

Question 15.
What is Hyper polarisation?
Answer:
If repolarisation becomes more negative than the resting potential -70 mV to about -90 mV it is called hyper polarisation.

Question 16.
What are corpora quadrigemina?
Answer:
The dorsal portion of the midbrain consists of four rounded bodies called corpora quadrigemina. It acts as a reflex centre for vision and hearing.

Question 17.
What is septum pellucidum?
Answer:
A thin membrane which separates the lateral ventricles I and II are called the septum pellucid.

Question 18.
What is foramen of Monro?
Answer:
The lateral ventricle communicates with the III ventricle in the diencephalon through an opening called interventricular foramen or foramen of Monro.

Question 19.
What is cerebral aqueduct or aqueduct of Sylvius?
Answer:
The ventricle III is continuous with the ventricle IV in the hindbrain through a canal called the aqueduct of Sylvius or cerebral aqueduct.

Question 20.
Name the lobes of the cerebrum?
Answer:

1. Pair of frontal
2. Pair of parietal
3. Pair of temporal
4. Occipital

Question 21.
What is cauda equina?
Answer:
The thick bundle of elongated nerve roots within the lower vertebral canal is called the cauda equina.

Question 22.
What is meant by a blood-brain barrier?
Answer:
It protects the brain by preventing many foreign substances in our vascular system from reaching the brain.

Question 23.
What are spinal nerves?
Answer:
The 31 pairs of nerves which emerge out from the spinal cord through spaces called the intervertebral foramina found between the adjacent vertebrae are the spinal nerves.

Question 24.
What is meant by motor area?
Answer:

• The area which controls the voluntary muscular movements lies in the posterior part of the frontal lobes.
• Functions They receive and interpret the sensory impulses.

Question 25.
What is the function of the association area?
Answer:
They deal with memory communications learning and reasoning.

Question 26.
What are Interoceptors?
Answer:
Interoceptors are located in the visceral organs and blood vessels. These are sensitive to internal stimuli.

Question 27.
For a man to live all parts of the brain is important. How is the brain divided into?
Answer:

• Cerebrum
• Thalamus
• Hypothalamus
• Pons
• Cerebellum
• Medulla oblongata

Question 28.
What is Lysozyme?
Answer:
The enzyme present in tears that destroy bacteria is lysozyme.

Question 29.
What is the canal of schlemm?
Answer:
At the junction of the sclera and the cornea, there is a channel called ‘canal of schlemm’. It continuously drains out the excess of aqueous humour.

Question 30.
What is the accommodation?
Answer:
The ability of the eyes to focus on objects at varying distances is called accommodation.

Question 31.
What is meant by reflex arc?
Answer:

• It is a fast involuntary unplanned sequence of actions that occurs in response to a particular stimulus.
• The nervous elements involved in carrying out reflex action constitute reflex arc.

Question 32.
What is fovea centralis?
Answer:
A small depression present in the centre of the yellow spot is called fovea centralis.

Question 33.
Write the difference between Rod cells and Cone cells.
Answer:

Rod cells	Cone cells
1. Rods are responsible for vision in dim light.	1. The cones are responsible for colour vision and work best in bright light.
2. The pigment present in the rods is rhodopsin, formed of a protein scotopsin and retinal (an aldehyde of vitamin A).	2. The pigment present in the cones is photopsin, formed of opsin protein and retinal.
3. There are about 120 million rod cells.	3. There may be 6-7 million cone cells.
4. Rods are predominant in the extra fovea region.	4. Cones are concentrated in the fovea region.

Question 34.
What are ceruminous glands?
Answer:
The wax-producing sebaceous glands in the external auditory meatus are ceruminous glands.

Question 35.
What is the Eustachian tube?
Answer:
A tube called the Eustachian tube connects the middle ear cavity with the pharynx. It helps in equalizing the pressure of air on either side of the eardrum.

Question 36.
What are mammillary bodies? What are its functions?
Answer:

• The hypothalamus contains a pair of small rounded body called mammillary bodies.
• Functions: It is involved in olfactory reflexes and emotional responses to odour.

Question 37.
What are Meissner’s corpuscles?
Answer:
Meissner’s corpuscles are small light pressure receptors found just beneath the epidermis in the dermal papillae.

Question 38.
What are Pacinian corpuscles?
Answer:
Pacinian corpuscles are the large egg-shaped receptors found scattered deep in the dermis and monitoring vibration due to pressure.

Question 39.
What is cauda equina?
Answer:

• After the 2nd lumbar vertebra, the spinal nerves are greatly elongated
• The thick bundle of elongated nerve roots appears as a horse’s tail called cauda equina.

Question 40.
What is Tactile Merkel disc?
Answer:
Tactile Merkel disc is a light touch receptor lying in the deeper layer of the epidermis.

IV. Long Answer Questions

Question 1.
Explain the structure of neurons?
Answer:
A neuron is a microscopic structure composed of three major parts namely cell body (soma), dendrites, and axon. The cell body is the spherical part of the neuron that contains all the cellular organelles as a typical cell (except centriole). The plasma membrane covering the neuron is called the neurilemma and the axon is axolemma.

The repeatedly branched short fibres coming out of the cell body are called dendrites, which transmit impulses towards the cell body. The cell body and the dendrites contain cytoplasm and granulated endoplasmic reticulum called Nissl’s granules.

An axon is a long fibre that arises from a cone-shaped area of the cell body called the Axon hillock and ends at the branched distal end. Axon hillock is the place where the nerve impulse is generated in the motor neurons.

The axon of one neuron branches and forms connections with many other neurons. An axon contains the same organelles found in the dendrites and cell body but lacks Nissl’s granules and Golgi apparatus.

The axon, particularly of peripheral nerves is surrounded by Schwann cells (a type of glial cell) to form a myelin sheath, which act as an insulator. Myelin sheath is associated only with the axon; dendrites are always non-myelinated.

Schwann cells are not continuous along the axon; so there are gaps in the myelin sheath between adjacent Schwann cells. These gaps are called Nodes of Ranvier.

Large myelinated nerve fibres conduct impulses rapidly, whereas non-myelinated fibres conduct impulses quite slowly. Each branch at the distal end of the axon terminates into a bulb-like structure called a synaptic knob which possesses synaptic vesicles filled with neurotransmitters. The axon transmits nerve impulses away from the cell body to interneural space or to a neuromuscular junction.

Question 2.
Classify neurons on the basis of a number of axons and dendrites?
Answer:
The neurons are divided into three types based on number of axon and dendrites they possess:

• Multipolar neurons have many processes with one axon and two or more dendrites. They j are mostly intemeurons.
• Bipolar neurons have two processes with one axon and one dendrite. These are found in the retina of the eye, inner ear and the olfactory area of the brain.
• Unipolar neurons have a single short process and one axon. Unipolar neurons are located in the ganglia of cranial and spinal nerves.

Question 3.
Tabulate the ionic channels in the axolemma?
Answer:

Question 4.

Give an account of resting potential?
Answer:

• The electrical potential difference across the plasma membrane of a resting neuron is called the resting potential.
• More potassium is getting out of the neurilemma rather than sodium which is getting into.
• Hence the interior of the cell becomes negative.
• In resting condition the axon membrane is more permeable to K⁺ and less permeable to Na⁺ cons whereas it remains impermeable to negatively charge protein icons.
• On the outer side of axon there is low concentration of K⁺ and high concentration of Na⁺ ions.
• This difference can be maintained by ATP – driven sodium-potassium pump. This exchange 3 Na⁺ outwards for 2K⁺ in the cells.
• In neurons, the resting membrane potential ranges from 40mv to 90mv. And its normal value is 70mv.

Question 5.
Explain the Synaptic transmission?
Answer:
The junction between two neurons is called a Synapse through which a nerve impulse is transmitted. The first neuron involved in the synapse forms the pre-synaptic neuron and the second neuron is the post-synaptic neuron.

A small gap between the pre-and postsynaptic membranes is called Synaptic Cleft that forms a structural gap and a functional bridge between neurons. The axon terminals contain synaptic vesicles filled with neurotransmitters.

When an impulse [action potential] arrives at the axon terminals, it depolarizes the presynaptic membrane, opening the voltage-gated calcium channels. The influx of calcium ions stimulates the synaptic vesicles towards the pre-synaptic membrane and fuses with it.

In the neurilemma, the vesicles release their neurotransmitters into the synaptic cleft by exocytosis. The released neurotransmitters bind to their specific receptors on the post-synaptic membrane, responding to chemical signals.

The entry of the ions can generate a new potential in the post-synaptic neuron, which may be either excitatory or inhibitory. Excitatory post-synaptic potential causes depolarization whereas inhibitory post-synaptic potential causes hyperpolarization of the postsynaptic membrane.

Question 6.
Write a short note on meninges?
Answer:
Brain is covered by three cranial meninges. The outer thick layer is Duramater which lines the inner surface of the cranial cavity; the median thin layer is the Arachnoid mater which is separated from the dura mater by a narrow subdural space. The innermost layer is Piamater which is closely adhered to the brain but separated from the arachnoid mater by the subarachnoid space.

Question 7.
Describe the structure of hindbrain?
Answer:
Rhombencephalon forms the hindbrain.
It comprises of cerebellum pons varolii and medulla oblongata.

Cerebellum:
It is the second-largest part of the brain. It consists of two cerebellar hemisphere and central worm-shaped part the vermis.

Function:
It controls and coordinates muscular movements and body equilibrium.
Any damage to cerebellum results in uncoordinated voluntary muscle movements.

Pons varoli:
It lies in between the midbrain and the medulla oblongata.
This form a bridge between the two cerebellar hemisphere and connect the medulla oblongata with the other region of the brain.

Medulla oblongata:
This forms the posterior-most part of the brain. It connects the spinal cord with various parts of the brain.
It receives and integrates signals from spinal cord and sends it to the cerebellum and thalamus.

Function:
It controls cardiovascular reflexes respiration and gastric secretions.

Question 8.
Explain the mid-brain?
Answer:
The midbrain is located between the diencephalon and the pons. The lower portion of the midbrain consists of a pair of longitudinal bands of nervous tissue called cerebral peduncles which relay impulses back and forth between the cerebrum, cerebellum; pons, and medulla. The dorsal portion of the midbrain consists of four rounded bodies called corpora quadrigemina which acts as a reflex centre for vision and hearing.

Question 9.
Give an account of the ventricles of the brain.
Answer:

• The brain has four hollow fluid-filled spaces.
• The c – shaped space found inside each cerebral hemisphere forms the lateral ventricles I and II which are separated by a thin membrane called the septum pellucidum.
• Each lateral ventricle communicates with the III ventricle through an opening called the foramen of the metro.
• The III ventricle opens into the IVth ventricle through a canal called the aqueduct of Sylvius. The choroid plexus is a network of blood capillaries found in the root of the ventricles and forms cerebrospinal fluid.

Functions:

• CSF provides buoyancy to the CNS.
• It acts as a shock absorber.
• It nourishes the brain by supplying food and oxygen.
• It carries harmful metabolic wastes from the brain to the blood.
• It maintains a constant pressure inside the cranial vessels

Question 10.
Explain the Ventricles of the brain?
Answer:
The brain has four hollow, fluid-filled spaces. The C- shaped space found inside each cerebral hemisphere forms the lateral ventricles I and II which are separated from each other by a thin membrane called the septum pellucidum. Each lateral .ventricle communicates with the narrow III ventricle in the diencephalon through an opening called interventricular foramen (foramen of Monro).

The ventricle III is continuous with the ventricle IV in the hindbrain through a canal called the aqueduct of Sylvius (cerebral aqueduct). Choroid plexus is a network of blood capillaries found in the roof of the ventricles and forms cerebrospinal fluid (CSF) from the blood. CSF provides buoyancy to the CNS structures; CSF acts as a shock absorber for the brain and spinal cord; it nourishes the brain cells by transporting a constant supply of food and oxygen; it carries harmful metabolic wastes from the brain to the blood, and maintains a constant pressure inside the cranial vessels.

Question 11.
Explain the structure of Spinal cord?
Answer:
The spinal cord is a long, slender, cylindrical nervous tissue. It is protected by the vertebral column and surrounded by the three membranes as in the brain. The spinal cord that extends from the brain stem into-the vertebral canal of the vertebral column up to the level of 1st or 2nd lumbar vertebra. So the nerve roots of the remaining nerves are greatly elongated to exit the vertebral column at their appropriate space. The thick bundle of elongated nerve roots within the lower vertebral canal is called the cauda equina (horse’s tail) because of its appearance.

In the cross section of spinal cord, there are two indentations: the posterior median sulcus and the anterior median fissure. Although there might be slight variations, the cross section of spinal cord is generally the same throughout its length. In contrast to the brain, the grey matter in the spinal cord forms an inner butterfly shaped region surrounded by the outer white matter.

The grey matter consists of neuronal cell bodies and their dendrites, intemeurons and glial cells. White matter consists of bundles of nerve fibres. In the center of the grey matter there is a central canal which is filled with CSF. Each half of the grey matter is divided into a dorsal horn, a ventral horn and a lateral hom.

The dorsal hom contains cell bodies of intemeurons on which afferent neurons terminate. The ventral hom contains cell bodies of the efferent motor neurons supplying the skeletal muscle.

Autonomic nerve fibres, supplying cardiac and smooth muscles and exocrine glands, originate from the cell bodies found in the lateral horn. In the white matter, the bundles of nerve fibres form two types of tracts namely ascending tracts which carry sensory impulses to the brain and descending tracts which carry motor impulses from the brain to the spinal nerves at various levels of the spinal cord.

The spinal cord shows two enlargements, one in the cervical region and another one in the lumbosacral region. The cervical enlargement serves the upper limb and lumbar enlargement serves the lower limbs.

Question 12.
Write a short note on Reflex action and Reflex arc?
Answer:
Reflex action is a fast, involuntary unplanned sequence of actions that occurs in response to a particular stimulus, e.g., closing the eyelids when dust falls in the eyes, withdrawing hand on touching a hot pan. It is brought about by the spinal cord. The nervous elements involved in carrying out the reflex actions constitute a reflex arc.

Reflex arc-has:-

1. Sensory receptors: It is a sensory structure that responds to a specific stimulus.
2. Sensory neuron: This neuron takes sensory impulse to the grey matter of the spinal cord through the dorsal root of the spinal cord.
3. Interneurons: one or two intemeurons serve to transmit impulses from the sensory neuron to the motor neuron.
4. Motor neuron: It transmits impulse from the central nervous system to the effector organ.
5. Effector organs: It may be a muscle or gland which responds to the impulse received.

Question 13.
Explain the type of reflexes?
Answer:
There are two types of reflexes. They are:

1. Unconditional reflex is an inborn reflex for an unconditioned stimulus. It does not need any past experience, knowledge or training to occur; Ex: blinking of an eye when a dust particle is about to fall into it, sneezing and coughing due to foreign particle entering the nose or larynx.

2. Conditioned reflex is a respone to a stimulus that has been acquired by learning. This does not naturally exists in animals. Only an experience makes it a part of the behaviour. Example: excitement of salivary gland on seeing and smelling food. The conditioned reflex was first demonstrated by the Russian physiologist Pavlov in his classical conditioning experiment in a dog. The cerebral cortex controls the conditioned reflex.

Question 14.
Tabulate the Cranial nerves and their function?
Answer:

	Cranial nerves	Nature of nerve	Function
1.	Olfactory nerve	Sensory	Sense of smell
2.	Optic nerves	Sensory	Sense of sight
3.	Oculomotor nerves	Motor	Movement of the eye
4.	Trochlear nerve	Motor	Rotation of the eye ball
5.	Trigeminal nerve	Sensory and motor (mixed)	Functioning of facial parts
6.	Abducens nerve	Motor	Rotation of the eye ball
7.	Facial nerve	Mixed	Functioning of facial parts
8.	Auditory/ Vestibulocochlear nerve	Sensory	Maintains the equilibrium of the body /Auditory function
9.	Glossopharyngeal nerve	Mixed	Taste and touch
10.	Vagus	Mixed	Regulation of the visceral organs
11.	Spinal accessory	Motor	Muscular movement of Pharynx, larynx, neck and shoulder
12.	Hypoglossal	Motor	Speech and swallowing

Question 15.
Explain the peripheral nervous system?
Answer:
Peripheral Neural System (PNS) consists of all nervous tissue outside the CNS. Components of PNS include nerves, ganglia, enteric plexuses and sensory receptors. A nerve is a chord like structure that encloses several neurons inside. Ganglia (singular-ganglion) are small masses of nervous tissue, consisting primarily of neuron cell bodies and are located outside the brain and spinal cord.

Enteric plexuses are extensive networks of neurons located in the walls of organs of the gastrointestinal tract. The neurons of these plexuses help in regulating the digestive system. The specialized structure that helps to respond to changes in the environment i.e. stimuli are called sensory receptor which triggers nerve impulses along the afferent fibres to CNS. PNS comprises of cranial nerves arising from the brain and spinal nerves arising from the spinal cord.

(a) Cranial nerves:
There are 12 pairs of cranial nerves, of which the first two pairs arise from the fore brain and the remaining 10 pairs from the midbrain. Other than the Vagus nerve, which extends into the abdomen, all cranial nerves serve the head and face.

(b) Spinal nerves:
31 pairs of spinal nerves emerge out from the spinal cord through spaces called the intervertebral foramina found between the adjacent vertebrae. The spinal nerves are named according to the region of vertebral column from which they originate

1. Cervical nerves (8 pairs)
2. Thoracic nerves (12 pairs)
3. Lumbar nerves (5 pairs)
4. Sacral nerves (5 pairs)
5. Coccygeal nerves (1 pair)

Each spinal nerve is a mixed nerve containing both afferent (sensory) and efferent (motor) fibres. It originates as two roots: 1) a posterior dorsal root with a ganglion outside the spinal cord and 2) an anterior ventral root with no external ganglion.

Somatic neural system (SNS) or voluntary neural system is the part of the peripheral neural system associated with the voluntary control of body movements via skeletal muscles. The sensory and motor nerves that innervate striated muscles form the somatic neural system. Major functions of the somatic neural system include voluntary movement of the muscles and organs, and reflex movements.

Question 16.
Describe the structure of an eye.
Answer:

• The eye is located in the orbit of the skull and held in its position with the help of six extrinsic muscles.
• Eyelashes and eyebrows help to protect the eyeballs.
• Anteriorly the choroid thickens to form the ciliary body and coloured portion of the iris.
• The aperture at the centre of the iris is the pupil through which the light enters.
• The ability of the eyes to focus objects at varying distances is called accommodation which is achieved by suspensory ligament ciliary muscle and ciliary body.

Retina

• It contains two regions.
• A sheet of the non-visual pigmented part neural visual region.
• The yellow spot is called fovea centralis which contains only cones.
• The optic nerves and the retinal blood vessels enter the eye slightly below the posterior pole which is devoid of photoreceptors called the blind spot.

Question 17.
Tabulate the differences between sympathetic and parasympathetic neural systems?
Answer:

	Sympathetic Neural system (SNS)	Parasympathetic Neural system (PNS)
1.	SNS originates in the thoracic and lumbar region of the spinal cord.	PNS originates in the cranial region of the brain and the sacral region of the spinal cord.
2.	Sympathetic ganglia are linked up to form a chain.	Its ganglia remain isolated.
3.	Preganglionic fibres are short and the postganglionic fibres are long.	Preganglionic fibres are long and the postganglionic fibres are short.
4.	Noradrenaline is produced at the terminal ends of the postganglionic fibres at the effector organs. Hence the system is adrenergic.	Acetylcholine is produced at the terminal ends of the postganglionic fibres at the effector organs. Hence the system is cholinergic.
5.	Active during stressful conditions preparing the body to face them.	Active during relaxing times restoring normal activity after a stress.
6.	The overall effect is excitatory and stimulating.	The overall effect is inhibitory.
7.	It is considered as the flight or fight system.	It is considered as ‘The Rest and Digest System’ or ‘The Feed and Breed System’.

Question 18.
Explain the structure of the Photoreceptor?
Answer:
The eye is the organ of vision; located in the orbit of the skull and held in its position with the help of six extrinsic muscles. They are superior, inferior, lateral, medial rectus muscles, superior oblique and inferior oblique muscles.

These muscles aid in the movement of the eyes and they receive their nerve innervation from III, IV and VI cranial nerves. Eyelids, eyelashes, and eyebrows are the accessory structures useful in protecting the eyes.

The eyelids protect the eyes from excessive light and foreign objects and spread lubricating secretions over the eyeballs. Eyelashes and eyebrows help to protect the eyeballs from foreign objects, perspiration and also from the direct rays of sunlight.

Sebaceous glands at the base of the eyelashes are called ciliary glands which secrete a lubricating fluid into the hair follicles. Lacrymal glands, located in the upper lateral region of each orbit, secrete tears. Tears are secreted at the rate of 1 ml/day and it contains salts, mucus, and lysozyme enzyme to destroy bacteria.

The conjunctiva is a thin, protective mucous membrane found lining the outer surface of the eyeball. The eye has two compartments, the anterior and posterior compartments. The anterior compartment has two chambers, the first one lies between the cornea and iris and the second one lies between the iris and lens.

These two chambers are filled with a watery fluid called aqueous humor. The posterior compartment lies between the lens and retina and it is filled with a jelly-like fluid called vitreous humor that helps to retain the spherical nature of the eye. The eye lens is transparent and biconvex, made up of long columnar epithelial cells called lens fibers. These cells are accumulated with the proteins called crystalline.

The eyeball is spherical in nature. The anterior one- sixth of the eyeball is exposed; the remaining region is fitted well into the orbit. The wall of the eyeball consists of three layers: fibrous Sclera, vascular Choroid, and sensory Retina.

The outer coat is composed of dense non-vascular connective tissue. It has two regions: the anterior cornea and the posterior sclera. The cornea is a non-vascular transparent coat formed of stratified squamous epithelium which helps the cornea to renew continuously as it is very vulnerable to damage from dust.

Sclera forms the white of the eye and protects the eyeball. Posteriorly the sclera is innervated by the optic nerve. At the junction of the sclera and the cornea, is a channel called the ‘canal of schlemm’ which continuously drains out the excess of aqueous humor.

Choroid is highly vascularized pigmented layer that nourishes all the eye layers and its pigments absorb light to prevent internal reflection. Anteriorly the choroid thickens to form the ciliary body and iris. Iris is the coloured portion of the eye lying between the cornea and lens. The aperture at the centre of the iris is the pupil through which the light enters the inner chamber. Iris is made of two types of muscles the dilator papillae (the radial muscle) and the sphincter papillae (the circular muscle).

In the bright light, the circular muscle in the iris contract; so that the size of pupil decreases and less light enters the eye. In dim light, the radial muscle in the iris contract; so that the pupil size increases and more light enters the eye. Smooth muscle present in the ciliary body is called the ciliary muscle which alters the convexity of the lens for near and far vision.

The ability of the eyes to focus objects at varying distances is called accommodation which is achieved by suspensory ligament, ciliary muscle and ciliary body. The suspensory ligament extends from the ciliary body and helps to hold the lens in its upright position. The ciliary body is provided with blood capillaries that secrete a watery fluid called aqueous humor that fills the anterior chamber.

Retina forms the innermost layer of the eye and it contains two regions:-

• A sheet of pigmented epithelium (non visual part) and neural visual regions.
• The neural retina layer contains three types of cells:-
• photoreceptor cells – cones and rods, bipolar cells and ganglion cells.
• The yellow flat spot at the centre of the posterior region of the retina is called macula lutea which is responsible for sharp detailed Vision.

A small depression present in the centre of the yellow spot is called fovea centralis which contains only cones. The optic nerves and the retinal blood vessels enter the eye slightly below the posterior pole, which is devoid of photoreceptors; hence this region is called blind spot.

Question 19.
Explain the mechanism of vision?
Answer:
When light enters the eyes, it gets refracted by the cornea, aqueous humor and lens and it is focused on the retina and excites the rod and cone cells. The photopigment consists of Opsin, the protein part and Retinal, a derivative of vitamin A. Light induces dissociation of retinal from opsin and causes the structural changes in opsin.

This generates an action potential in the photoreceptor cells and is transmitted by the optic nerves to the visual cortex of the brain, via bipolar cells, ganglia, and optic nerves, for the perception of vision.

Question 20.
a) What is meant by proprioception?
b) Give an account of organs of equilibrium?
Answer:
The ability to sense the position orientation and movement of the body is called proprioception.
Vestibular system: This is the organ of balance.
It is composed of a series of fluid-filled sacs that contain endolymph and are kept in the surrounding peri lymph.

Semicircular canals

• The canals that lie posterior and lateral to the vestibule are semicircular canals.
• At each end of the semicircular canal has a swollen area called the ampulla.
• Each ampulla has a sensory area known as crista ampullar.
• It detects the rotational movement of the head.

Question 21.
Explain the structure of human ear or Phonoreceptor?
Answer:
The ear is the site of reception of two senses namely hearing and equilibrium. Anatomically, the ear is divided into three regions: the external ear, the middle ear, and the internal ear.

The external ear consists of pinna, external auditory meatus, and eardrum. The pinna is flap of elastic cartilage covered by skin. It collects the sound waves. The external auditory meatus is a curved tube that extends up to the tympanic membrane [the ear drum].

The tympapic membrane is composed of connective tissues covered with skin outside and with mucus membrane inside. There are very fine hairs and wax producing sebaceous glands called ceruminous glands in the external auditory meatus. The combination of hair and the ear wax [cerunien] helps in preventing dust and foreign particles from entering the ear.

The middle ear is a small air-filled cavity in the temporal bone. It is separated from the external ear by the eardrum and from the internal ear by a thin bony partition; the bony partition contains two small membrane covered openings called the oval window and the round window.

The middle ear contains three ossicles: malleus [hammer bone], incus [anyil bone] and stapes [stirrup bone] which are attached to one another. The malleus is attached to the tympanic membrane and its head articulates with the incus which is the intermediate bone lying between the malleus and stapes.

The stapes is attached to the oval window in the inner ear. The ear ossicles transmit sound waves to the inner ear. A tube called Eustachian tube connects the middle ear cavity with the pharynx. This tube helps in equalizing the pressure of air on either sides of the ear drum.

Inner ear is the fluid filled cavity consisting of two parts, the bony labyrinth and the membranous labyrinths. The bony labyrinth consists of three areas: cochlea, vestibule and semicircular canals.

The cochlea is a coiled portion consisting of 3 chambers namely: scala vestibuli and scala tympani- these two are filled with perilymph; and the scala media is filled with endolymph. At the base of the cochlea, the scala vestibule ends at the ‘oval window’ whereas the scala tympani ends at the ‘round window’ of the middle ear.

The chambers scala vestibuli and scala media are separated by a membrane called Reisner’s membrane whereas the scala media and scala tympani are separated by a membrane called Basilar membrane. Organ of Corti.

The organ of corti is a sensory ridge located on the top of the Basilar membrane and it contains numerous hair cells that are arranged in four rows along the length of the basilar membrane. Protruding from the apical part of each hair cell is hair-like structures known as stereocilia. During the conduction of sound waves, stereocilia makes a contact with the stiff gel membrane called the tectorial membrane, a roof-like structure overhanging the organ of Corti throughout its length.

Question 22.
Explain the mechanism of hearing?
Answer:
Sound waves entering the external auditory meatus fall on the tympanic membrane. This causes the eardrum to vibrate, and these vibrations are transmitted to the oval window through the three auditory ossicles. Since the tympanic membrane is 17-20 times larger than the oval window, the pressure exerted on the oval window is about 20 times more than that on the tympanic membrane.

This increased pressure generates pressure waves in the fluid of perilymph. This pressure causes the round window to alternately bulge outward and inward meanwhile the basilar membrane along with the organ of Corti move up and down. These movements of the hair alternately open and close the mechanically gated ion channels in the base of hair cells and the action potential is propagated to the brain as sound sensation through the cochlear nerve.

Question 23.
Write a short note on defects of ear?
Answer:
Deafness may be temporary or permanent. It can be further classified into conductive deafness and sensory-neural deafness. Possible causes for conductive deafness may be due to

1. Blockage of ear canal with earwax
2. Rupture of eardrum
3. Middle ear infection with fluid accumulation
4. Restriction of ossicular movement.

In sensory-neural deafness, the defect may be in the organ of Corti or the auditory nerve or in the ascending auditory pathways or auditory cortex.

Question 24.
Explain the organ of equilibrium of proprioception?
Answer:
Balance is part of a sense called proprioception, which is the ability to sense the position, orientation, and movement of the body. The organ of balance is known as the vestibular system which is located in the inner ear next to the cochlea.

The vestibular system is composed of a series of fluid filled sacs and tubules. These sacs and tubules contain endolymph and are kept in the surrounding perilymph. These two fluids, perilymph and endolymph, respond to the mechanical forces, during changes occurring in body position and acceleration.

The utricle and saccule are two membraiious sacs, found nearest the cochlea and contain equilibrium receptor regions called maculae that are involved in detecting the linear movement of the head.

The maculae contain the hair cells that act as mechanoreceptors. These hair cells are embedded in a gelatinous otolithic membrane that contains small calcareous particles called otoliths. This membrane adds weight to the top of the hair cells and increase the inertia.

The canals that lie posterior and lateral to the vestibule are semicircular canals; they are anterior, posterior, and lateral canals oriented at right angles to each other.

At one end of each semicircular canal, at its lower end has a swollen area called ampulla. Each ampulla has a sensory area known as crista ampullar which is formed of sensory hair cells and supporting cells. The function of these canals is to detect rotational movement of the head.

Question 25.
Give notes on Gustatory receptors?
Answer:

• The sense of taste is considered to be the most pleasurable of all senses.
• The tongue is provided with many small projections called papillae which gives the tongue an abrasive feel.
• Most taste buds are located on the tongue few are scattered on the soft palate inner surface of the cheeks.

Structure
Taste buds are flask-shaped and consist of 50-100 epithelial cells of two major types.

1. ustatory epithelial cells: Taste cells.
2. Basal epithelial cells

Gustatory epithelial cells:

• Long gustatory hairs project from the tip of the gustatory cells and extend through a taste pore to sense the taste.
• The sensory dendrites send signals to the brain and sense the taste.
• The basal cells differentiate into new gustatory cells.

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