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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, 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?
Samacheer Kalvi 11th Bio Zoology Solutions Chapter 10 Neural Control and Coordination img 1
(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 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 explanations 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 eye ball ?
(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 conduction of nerve impulse?
(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 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 possess 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 possess 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 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 intra ocular pressure of about 16 mm Hg. Any block in the canal of schlemm increases the intra ocular pressure of aqueous humour. This condition is called ‘Glaucoma’. Due to pressure, 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 empty 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:
Olfactory nerve carries the sense of smell to the sensory strip present in the cerebrum. The sensory areas are present in the parietal lobe of the cerebrum. The stimuli of smell reaches the mammillary bodies present in the hypothalamus. This produces olfactory reflexes and emotional responses to odour.

Question 21.
Cornea transplant in humans is almost never rejected. State the reason?
Answer:
Cornea does not have blood vessels. Hence there is no possibility of rejection when 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:
Samacheer Kalvi 11th Bio Zoology Solutions Chapter 10 Neural Control and Coordination img 2

  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:
Cerebro spinal 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 a 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 side 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 emotional brain.

Question 27.
Classify receptors based on 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 semi circular 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

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

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, 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 extends 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.
Samacheer Kalvi 11th Bio Zoology Solutions Chapter 10 Neural Control and Coordination img 2

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 cardio vascular 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. Sympathetic neural system of the ANS predominates and the various changes taking place inside the body includes; excess secretion of “adrenaline” to the blood stream from the medulla of the adrenal gland. This in turn, dilates pupil, inhibits salivation, accelerates heartbeat, inhibites 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 detects 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.
Which of the following acts as a phagocytic cells to engulf the foreign particles at the time of any injury to the brain?
(a) Neuron
(b) Neurilemma
(c) Neuroglia
(d) Axolemma
Answer:
(b) Neurilemma

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.
Which of the following has bipolar neurons?
(a) Intemeurons
(b) Cranial nerves
(c) Spinal nerves
(d) Inner ear
Answer:
(d) Inner ear

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

Question 5.
The interior of the cell of the resting neuron is negative due to ……………….
(a) Greater efflux of Na+ outside the cell than,K+ influx into the cell.
(b) Only greater efflux of Na+ outside the cell.
(c) Greater efflux of K+ outside the cell than Na+ influx into the cell.
(d) Only greater efflux of K+ outside the cell.
Answer:
(c) Greater efflux of K+ outside the cell than Na+ influx into the cell.

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-gate and closing potassium voltage-gate
(d) Opening neurolemma
Answer:
(c) Opening sodium voltage-gate and closing potassium voltage-gate

Question 7.
When the membrane potential shoots.rapidly upto +45 mV, it is called the ………………….
(a) Threshold potential
(b) Spike potential
(c) Repolarization
(d) Hyperpolarization
Answer:
(b) Spike potential

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.
The subarachnoid space is present in between ………………..
(a) Piamater and arachnoid mater
(b) Arachnoid mater and duramater
(c) Brain and Piamater
(d) Spinal cord and duramater
Answer:
(a) Piamater and arachnoid mater

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

Question 11.
Which of the following plays a key role in learning and memory?
(a) Hypothalamus
(b) Pons varolii
(c) Thalamus
(d) Medulla oblongata
Answer:
(c) Thalamus

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.
The reflex action is effected by ……………..
(a) Brain
(b) Medulla oblongata
(c) Effector organs
(d) Spinal cord
Answer:
(d) Spinal cord

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

Question 15.
Which of the following is produced at the terminal ends of the post ganglionic fibres at the effector organs of parasympathetic neural system?
(a) Noradrenaline
(b) Acetylcholine
(c) Adrenalin
(d) Melatonin
Answer:
(b) Acetylcholine

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.
Which of the following absorbs light to prevent internal reflection in the eye?
(a) Sclera
(b) Retina
(c) Chorid
(d) Cornea
Answer:
(c) Chorid

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.
The defect hypermetropia can be overcome by using ……………
(a) Concave lens
(b) Convex lens
(c) Cylindrical glass
(d) Surgical procedures
Answer:
(b) Convex lens

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 olfactory impulses are transmitted to the ……………….. lobe of the brain.
(a) Parietal
(b) Temporal
(c) Occipital
(d) Frontal
Answer:
(d) Frontal

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 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 of the following are present in the finger tips and soles of the feet?
(a) Pacinian corpuscles
(b) Meissner’s corpuscles
(c) Ruffini endings
(d) Krause end bulbs
Answer:
(b) Meissner’s corpuscles

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 lens
Answer:
(c) It has neither rods nor cones

Question 25.
The protein part of the photo pigment is ………………..
(a) Retinal
(b) Opsin
(c) Macula lutea
(d) Fovea centralis
Answer:
(A) Opsin

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:
Piamater

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:
Hpothalamus

Question 26.
The ……………….. system is called 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:
Cerebro spinal 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:
Blind spot

Question 42.
The protein part of the photo pigment 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 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 finger tips 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 neurons? What are their functions?
Answer:
The structural and functional unit of the nervous system is neurons. They detect, receive, process and transmit different kinds of stimuli. They are sensory, motor and autonomic in functions.

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.
What are the functions of neuroglia?
Answer:

  1. They provide nourishment to the surrounding neurons.
  2. They involve in the memory process.
  3. They repair the injured tissue due to their dividing and regenerating capacity.
  4. They engulf the foreign particles at the time of any injury to the brain.

 

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 neurilemma?
Answer:
The plasma membrane covering the neuron is the neurilemma.

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

Question 8.
What are Nodes of Ranvier?
Answer:
The Schwann cells covering the axon are not continuous. There are gaps in the myelin sheath between adjacent Schwann cells. These gaps are called Nodes of Ranvier.

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 Synaptic Cleft?
Answer:
A small gap between the pre and post synaptic membranes is called Synaptic Cleft. It forms a structural gap and a functional bridge between neurons.

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

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

Question 13.
What is subarachnoid space?
Answer:
The space between the piamater and arachnoid mater is called subarachnoid space.

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

Question 15.
What are mammillary bodies?
Answer:
A pair of small rounded body in the hypothalamus is called mammillary bodies. These are involved in olfactory reflexes and emotional response to odour.

Question 16.
What are corpora quadrigemina?
Answer:
The dorsal portion of the mid brain 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 is called the septum pellucidum.

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 hind brain through a canal called aqueduct of Sylvius or cerebral aqueduct.

Question 20.
What is Choroid plexus?
Answer:
Choroid plexus is a network of blood capillaries found in the roof of the ventricles. This forms cerebro spinal fluid from the blood.

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 are Cranial nerves?
Answer:
The 12 pairs of nerves which arise from the brain are called cranial nerves.

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 a mixed nerve?
Answer:
A nerve which contains both sensory (afferent) and motor (efferent) fibres is called a mixed nerve.

Question 25.
What are Exteroceptors?
Answer:
Exteroceptors are located at or near the surface of the body. These are sensitive to external stimuli and receive sensory impulses for hearing, vision, touch, taste and smell.

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

Question 27.
What are Lacrymal glands?
Answer:
Tears secreting glands located in the upper lateral region of each orbit are called Lacrymal glands.

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

Question 29.
What is 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 accommodation?
Answer:
The ability of the eyes to focus objects at varying distances is called accommodation.

Question 31.
What is macula lutea?
Answer:
The yellow flat spot at the centre of the posterior region of the retina is called macula lutea. It is responsible for sharp detailed vision.

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 works 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 Eustachian tube?
Answer:
A tube called Eustachian tube connects the middle ear cavity with the pharynx. It helps in equalizing the pressure of air on either sides of the ear drum.

Question 36.
What is crista ampullaris?
Answer:
The lower end of each semicircular canal is swollen and it is called ampulla. Each ampulla has a sensory area known as crista ampullaris.

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 are Krause end bulbs?
Answer:
These are thermoreceptors of the skin that sense temperature.

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

IV. Long Answer Questions

Question 1.
Explain the structure of neuron?
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 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 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 synaptic knob which possesses synaptic vesicles filled with neurotransmitters. The axon transmits nerve impulses away from the cell body to inter neural space or to a neuro-muscular junction.

Question 2.
Classify neurons on the basis of number of axon 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.

Samacheer Kalvi 11th Bio Zoology Solutions Chapter 10 Neural Control and Coordination img 4

Question 3.
Tabulate the ionic channels in the axolemma?
Answer:
Samacheer Kalvi 11th Bio Zoology Solutions Chapter 10 Neural Control and Coordination img 5

Question 4.
Explain the transmission of nerve impulses?
Answer:
The transmission of impulse involves two main phases; Resting membrane potential and Action membrane potential. Resting membrane Potential: The electrical potential difference across the plasma membrane of a resting neuron is called the resting potential during which the interior of the cell is negative due to greater efflux of K+ outside the cell than Na+
influx into the cell.

When the axon is not conducting any impulses i.e. in resting condition, the axon membrane is more permeable to K+ and less permeable to Na+ ions, whereas it remains impermeable to negatively charged protein ions. The axoplasm contains high concentration of K+ and negatively charged proteins and low concentration of Na+ ions.

In contrast, fluid outside the axon (ECF) contains low concentration of K+ and high concentration of Na+, and this forms a concentration gradient. This ionic gradient across the resting membrane is maintained by ATP driven Sodium-Potassium pump, which exchanges 3Na+ outwards for 2K+ into the cells.

In this state, the cell membrane is said to be polarized. In neuron, the resting membrane potential ranges from -40 mV to -90 mV, and its normal value is -70 mV. The minus sign indicates that the inside of the cell is negative with respect to the outside.

Action membrane potential:
An action potential occurs when a neuron sends information down an axon, away from the cell body. It includes following phases, depolarization, repolarisation and hypopolarization.

Depolarization – Reversal of polarity:
When a nerve fibre is stimulated, sodium voltage-gate opens and makes the axolemma permeable to Na+ ions; meanwhile the potassium voltage-gate closes. As a result, the rate of flow of Na+ ions into the axoplasm exceeds the rate of flow of K+ ions to the outside fluid [ECF]. Therefore, the axolemma becomes positively charged inside and negatively charged outside.

This reversal of electrical charge is called Depolarization. During depolarization, when enough Na+ ions enter the cell, the action potential reaches a certain level, called threshold potential [-55 mV], The particular stimulus which is able to bring the membrane potential to threshold is called threshold stimulus.

The action potential occurs in response to a threshold stimulus but does not occur at subthreshold stimuli. This is called all or none principle. Due to the rapid influx of Na+ ions, the membrane potential shoots rapidly up to + 45 mV which is called the Spike potential.

Repolarisation [Falling Phase]: When the membrane reaches the spike potential, the sodium voltage-gate closes and potassium voltage-gate opens. It checks influx of Na+ ions and initiates the efflux of K+ ions which lowers the number of positive ions within the cell.’Thus, .the potential falls back towards the resting potential. The reversal of membrane potential inside the axolemma to negative occurs due to the efflux of K+ ions. This is called Repolarisation.

Hyperpolarization:
If repolarization becomes more negative than the resting potential -70 mV to about -90 mV, it is called Hyperpolarization. During this, K+ ion gates are more permeable to K+ even after reaching the threshold level as it closes slowly; hence called Lazy gates. The membrane potential returns to its original resting state when K+ ion channels close completely. During hyperpolarization the Na+ voltage gate remains closed.

Conduction Speed of a nerve impulse: The conduction speed of a nerve impulse depends on the diameter of axon. The greater the axon’s diameter, the faster is the conduction.. The myelinated axon conducts the impulse faster than the non-myelinated axon.

The voltage-gated Na+ and K+ channels are concentrated at the nodes of Ranvier. As a result, the impulse jumps node to node, rather than travelling the entire length of the nerve fibre. This mechanism of conduction is called Saltatory Conduction. Nerve impulses travel at the speed of 1-300 m/s.

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 post-synaptic 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 pre-synaptic membrane, opening the voltage-gated calcium channels. 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 post- synaptic 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 Arachnoid mater which is separated from the duramater 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.
Explain the structure of fore brain?
Answer:
Fore brain comprises the following regions: Cerebrum and Diencephalon. Cerebrum is the ‘seat of intelligence’ and forms the major part of the brain. The cerebrum consists of an outer cortex, inner medulla and basal nuclei.

The superficial region of the cerebrum is.called cerebral cortex, which looks grey due to the presence of unmyelinated nerve cells. Cerebral cortex – consists of neuronal cell body, dendrites, associated glial and blood vessels.

The surface of the cerebrum’shows many convolutions (folds) and grooves. The folds are called gyri, the shallow grooves between the gyri are called sulci and deep grooves are called fissures. These sulci and gyri increase the surface area of the cerebral cortex. Several sulci divide the cerebrum into eight lobes; a pair of frontals, parietals, temporals and occipital lobes.

A median longitudinal fissure divides the cerebrum longitudinally into two cerebral hemispheres. A transverse fissure separates the cerebral hemispheres from the cerebellum.

The hemispheres are connected by a tract of nerve fibres called corpus callosum. Cerebral cortex has three functional areas namely sensory areas occur in the parietal, temporal and occipital lobes of the cortex. They receive and interpret the sensory impulses.

Motor area of the cortex which controls voluntary muscular movements lies in the posterior part of the frontal lobes. The areas other than sensory and motor areas are called Association areas that deal with integrative functions such as memory, communications, learning and reasoning. Inner to the cortex is medulla which is white in colour and acts as a nerve tract between the cortex and the diencephalon.

Diencephalon consists largely of following three paired structures. Epithalamus forms the roof of the diencephalon and it is a non-nervous tissue. The anterior part of epithalamus is vascular and folded to form the choroid plexus. Just behind the choroid plexus, the epithalamus forms a short stalk which ends in a rounded body called pineal body which secretes the hormone, melatonin which regulates sleep and wake cycle.

Thalamus is composed of grey mater which serves as a relay centre for impulses between the spinal cord, brain stem and cerebrum. Within the thalamus, information is sorted and edited and plays a key role in learning and memory. It is a major coordinating centre for sensory and motor signalling.

Hypothalamus forms the floor of the diencephalon. The downward extension of the hypothalamus, the infundibulum connects the hypothalamus with the pituitary gland. The hypothalamus contains a pair of small rounded body called mammillary bodies that are involved in olfactory reflexes and emotional responses to odour.

Hypothalamus maintains homeostasis and has many centres which control the body temperature, urge for eating and drinking. It also contains a group of neurosecretory cells which secrete the hypothalamic hormones. Hypothalamus also acts as the satiety centre.

Limbic system: The inner part of the cerebral hemisphere constitutes the limbic system. The main components of limbic system are olfactory bulbs, cingulate gyrus, mammillary body, amygdala, hippocampus and hypothalamus.

The limbic system is called ‘emotional brain’ because it plays a primary role in the regulation of pleasure, pain, anger, fear, sexual feeling and affection. The hippocampus and amygdala also play a role in memory. Brain stem is the part of the brain between the spinal cord and the diencephalon. It consists of mid brain, pons varolii and medulla oblongata.

Question 8.
Explain the mid brain?
Answer:
The mid brain 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 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.
Explain the structure of Hind brain?
Answer:
Rhombencephalon forms the hind brain. It comprises of cerebellum, pons varolii and medulla oblongata. Cerebellum is the second largest part of the brain. It consists of two cerebellar hemispheres and central worm shaped part, the vermis. The cerebellum controls and coordinates muscular movements and body equilibrium. Any damage to cerebellum often results in uncoordinated voluntary muScle movements.

Pons varoli lies infront of the cerebellum between the midbrain and the medulla oblongata. The nerve fibres in the pons varolii form a bridge between the two cerebellar hemispheres and connect the medulla oblongata with the other region of the brain. The respiratory nuclei found in the pons cooperate with the medulla to control respiration.

Medulla oblongata 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. Medulla contains vital centres that control cardio vascular reflexes, respiration and gastric secretions.

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 hind brain through a canal called aqueduct of Sylvius (cerebral aqueduct). Choroid plexus is a network of blood capillaries found in the roof of the ventricles and forms cerebro spinal 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 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.

Samacheer Kalvi 11th Bio Zoology Solutions Chapter 10 Neural Control and Coordination img 6

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 a food. Thb 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 its 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 mid brain. 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.
Explain the Autonomic Neural System?
Answer:
The autonomic neural system is auto functioning and self governed. It is a part of peripheral neural system that innervates smooth muscles, glands and cardiac muscle. This system controls and coordinates the involuntary activities of various organs. ANS controlling centre is in the hypothalamus.

Autonomic neural system comprises the following components:

  1. Preganglionic neuron whose cell body is in the brain or spinal cord; its myelinated axon exits the CNS as part of cranial or spinal nerve and ends in an autonomic ganglion.
  2. Autonomic ganglion consists of axon of preganglionic neuron and cell bodies of postganglionic neuron.
  3. Postganglionic neuron conveys nerve impulses from autonomic ganglia to visceral effector organs.
  4. The autonomic neural system consists of Sympathetic neural system and Parasympathetic neural system.

Question 17.
Tabulate the differences between sympathetic and parasympathetic neural system?
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 Photoreceptor?
Answer:
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, median rectus muscles, superior oblique and inferior oblique muscles.

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

The eye lids protect the eyes from excessive light and foreign objects and spread lubricating secretions over the eyeballs. Eyelashes and the 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, first one lies between the cornea and iris and the second one lies between the iris and lens.

These two chambers are filled with 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. Eye lens is transparent and biconvex, made up of long columnar epithelial cells called lens fibres. These cells are accumulated with the proteins called crystalline.

The eye ball 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 eye ball 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. 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 ‘canal of schlemm’ which continuously drains out the excess of aqueous humor.

Samacheer Kalvi 11th Bio Zoology Solutions Chapter 10 Neural Control and Coordination img 7

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 inner most 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 photo receptors; 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 photo pigment 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.
Explain the Refractive errors of eye or defects of human eye?
Answer:
Myopia (near sightedness): The affected person can see the nearby objects but not the distant objects. This condition may result due to an elongated eyeball or thickened lens; so that the image of distant object is formed in front of the yellow spot. This error can be corrected using concave lens that diverge the entering light rays and focuses it on the retina.

Hypermetropia (long sightedness): the affected person can see only the distant objects clearly but not the objects nearby. This condition results due to a shortened eyeball and thin lens; so the image of closest object is converged behind the retina. This defect can be overcome by using convex lens that converge the entering light rays on the retina.

Presbyopia:
Due to aging, the lens loses elasticity and the power of accommodation. Convex lenses are used to correct this defect. Astigmatism is due to the rough (irregular) curvature of cornea or lens. Cylindrical glasses are used to correct this error.

Cataract:
Due to the changes in nature of protein, the lens becomes opaque. It can be corrected by surgical procedures.

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 internal ear.

The external ear consists of pinna, external auditory meatus and ear drum. 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 wave, stereocilia makes a contact with the stiff gel membrane called 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 ear drum 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 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 or 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 embeded 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 ampullaris 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.
Explain the sensory function of skin?
Answer:
Skin is the sensory organ of touch and is also the largest sense organ. This sensation conies from millions of microscopic sensory receptors located all over the skin and associated with the general sensations of contact, pressure, heat, cold and pain. Some parts of the body, such as the finger tips have a large number of these receptors, making them more sensitive. Some of the sensory receptors present in the skin are:

  • Tactile merkel disc is light touch receptor lying in the deeper layer of epidermis.
  • Hair follicle receptors are light touch receptors lying around the hair follicles.
  • Meissner’s corpuscles are small light pressure receptors found just beneath the epidermis in the dermal papillae. They are numerous in hairless skin areas such as finger tips and soles of the feet.
  • Pacinian corpuscles are the large egg shaped receptors found scattered deep in the dermis and monitoring vibration due.to pressure. It allows to detect different textures, temperature, hardness and pain.
  • Ruffini endings which lie in the dermis responds to continuous pressure.
  • Krause end bulbs are thermoreceptors that sense temperature.

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