{"id":120317,"date":"2022-05-09T17:44:10","date_gmt":"2022-05-09T12:14:10","guid":{"rendered":"https:\/\/www.mapsofindia.com\/my-india\/?p=120317"},"modified":"2022-05-09T17:44:10","modified_gmt":"2022-05-09T12:14:10","slug":"chapter-21-neural-control-and-coordination-questions-and-answers-ncert-solutions-for-class-11-biology","status":"publish","type":"post","link":"https:\/\/www.mapsofindia.com\/my-india\/education\/chapter-21-neural-control-and-coordination-questions-and-answers-ncert-solutions-for-class-11-biology","title":{"rendered":"Chapter 21 – Neural Control and Coordination Questions and Answers: NCERT Solutions for Class 11 Biology"},"content":{"rendered":"

1. Briefly describe the structure of the following:
\n(a) Brain (b) Eye (c) Ear<\/h2>\n

Solution:
\nThe structure is as follows:
\n(a) Structure of the brain<\/h3>\n

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1. The brain is the central information processing organ of the body acting as the \u2018command and control system\u2019. It is protected in the skull.
\n2. It is covered by three membranes known as cranial meninges \u2013 the outer layer is the dura mater which is a fibrous and a tough membrane, the middle layer is the arachnoid, which is delicate and thin, the innermost layer is the pia mater which is an extension of the brain tissue. This layer is extremely vascular and supplied richly with blood
\n3. The three main regions of the brain are:
\n(i) Forebrain
\n(ii) Hindbrain
\n(iii) Midbrain
\nForebrain \u2013 has three main parts \u2013 cerebrum, hypothalamus, thalamus
\n\u2192Cerebrum forms the most important and major part of the entire brain. It is longitudinally segregated into halves by a deep cleft, each half is known as the cerebral hemisphere. Both these hemispheres are linked by the corpus callosum which is a tract of nerve fibers. The cerebral hemispheres are internally hollow and the walls of the cerebrum have an inner medulla and the outer cortex.
\nThe cerebral cortex consists of cell bodies of neurons which imparts the grey appearance; hence it is referred to as grey matter. The grey matter has many grooves (sulci) and folds (gyri). Higher the number of convolutions, greater the intelligence.
\nThe cerebral cortex consists of sensory areas, motor areas and association areas (neither motor nor sensory). These specific areas are responsible for the complex functions namely communication, memory and intersensory associations.
\nThe cerebral medulla is made of axons of nerve fibers, imparts a white appearance, hence it is referred to as white matter. There a group of interrelated deep structures inside the cerebral hemispheres, namely the amygdala and hippocampus which results in the formation of a complicated structure known as the limbic system or the limbic lobe.
\nRole \u2013 The cerebrum is the centre of memory, intelligence, consciousness, voluntary actions and will power
\n\u2192Thalamus
\nIt is made up of grey matter and located superior to the midbrain.
\nRole \u2013 it relays motor and sensory impulses to the cerebrum and also controls the manifestation of emotions, comprehends heat, pain and cold.
\n\u2192Hypothalamus
\nLocated at the base of the thalamus, it consists of the optic chiasma. It is a point wherein the optic nerve fibers cross opposite sides. Behind this structure is the infundibulum, which is a greyish protuberance of the hypothalamus. It contains the pituitary gland.
\nRole \u2013 The hypothalamus has centres responsible in regulating temperature of the body, hemeostasis, blood pressure, centre to control appetite (hunger, sleep, fatigue, thirst, pleasure, anger and penance). The neurosecretory cells of the hypothalamus produce releasing factors or several hormones that are crucial in regulating the activities of the pituitary hormones. Along with the limbic system, the hypothalamus also plays a part in regulating the sexual behavior.
\nMidbrain
\nIt consists of the cerebral peduncles and the corpora quadrigemina
\n\u2192Cerebral Peduncles
\nThey are fibrous thick tracts which connect the cerebrum and the cerebellum.
\nRole \u2013 Relay the sensory and the motor impulses between the hindbrain and the forebrain
\n\u2192Corpora quadrigemina
\nThe dorsal part of the brain has two pairs of solid lobes which are referred to as the corpora quadrigemina where one pair is referred to as the superior colliculi and the other pair is referred to as the inferior colliculi
\nRole \u2013 Corpora quadrigemina controls the visual reflexes and the movement of the eye and head. They also regulate auditory reflexes and movement of the head to identify and detect the source of sound.
\nHindbrain
\nIt consists of the cerebellum, pons varolii and medulla oblongata
\n\u2192Cerebellum
\nPresent behind the top part of the brain stem. The outer cerebellar cortex consists of grey matter and the inner cerebellar medulla consists of white matter. The cerebellum is connected with the medulla oblongata and the cerebrum through the fiber tracts of the white matter.
\nRole \u2013 It coordinates the balance of the body and the muscular activity. The impulse of the performing muscular activity is initiated in the cerebrum. It controls the voluntary movements originating in the cerebrum.
\n\u2192Pons varolii
\nIt is built of a thick bundle of white nerve fibers that is found above the medulla oblongata.
\nRole \u2013 Synchronizes between both the lobes of the cerebellum. It has the center to control breathing which is referred to as the pneumotaxic center.
\n\u2192Medulla oblongata
\nIt is conical in shape and is located at the skull\u2019s base. It runs behind the brain as the spinal cord. Any injury to this site of the brain could be fatal.
\nRole \u2013 serves as a passage to conduct nerve impulses from the spinal cord to the brain. It controls all the activities of the internal organs, breathing and heartbeat.
\n(b) Structure of the Eye \u2013<\/h3>\n

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Human eye is embedded in a bony socket of the skull and they are spherical. The walls of the eye ball consist of three layers, namely \u2013 The inner neurosensory coat, the middle vascular coat and the outer fibrous coat.
\nOuter fibrous coat \u2013 it is a thick and tough covering protecting the eye ball and helping to maintain its form. It has two regions \u2013 cornea and sclera
\nSclera \u2013 consists of a dense white fibrous connective tissue, where only the white eye is visible, the remaining major part is orbiting. The white of the eye is composed of collagen fibers.
\nRole \u2013 maintaining and protecting the shape of the eyeball.
\nCornea \u2013 It is the non-vascular transparent part of the outer fibrous coat that is visible and is covered by a thin, transparent vascular layer of stratified epithelium known as the conjunctiva. It is in the continuation with the lining of the eyelids.
\nRole \u2013 The cornea refracts light which enters the eye and converges it into the lens.
\nMiddle vascular coat \u2013 it consists of three regions, namely \u2013 choroid, ciliary body, and iris.
\nChoroid \u2013
\nHighly vascular and made of loose fibrous connective tissue. It is in the continuation on the inner portion of the sclera. It finely layers over the posterior two-thirds of the eye ball and tends to turn thicker towards the front, imparting a bluish appearance. It consists of some pigmented cells.
\nRole \u2013 nourishes the retina supplying it with oxygen. The pigmented cells absorb excessive light to avoid reflection in the eye ball.
\nCiliary body \u2013
\nIt is thick and forms the anterior part of the choroid. Comparatively, it is less pigmented and vascular and is composed of ciliary muscles and ciliary processes.
\n\u2192Ciliary muscles \u2013 They are smooth muscles and are of two types \u2013 circular muscles and meridional muscles.
\n\u2192Ciliary processes \u2013 the inner portion of the ciliary body has plenty of folds known as ciliary processes.
\nRole \u2013 secrete aqueous humour.
\nIris \u2013 it is a fine, opaque and a pigmented structure, located at the junction of sclera and cornea. The color of the iris is imparted by the pigmented cells of the choroid. The color varies between black, dark-brown, blue or green. It consists of a pupil centrally, as an aperture. The iris consists of two types of smooth muscles \u2013 circular muscles and the radial muscles.
\nRole \u2013 iris controls the eye size and hence the amount of light that enters. When radial muscles contract, pupil enlarges in dim light. When circular muscles contract, the pupil diminishes in bright light
\nInner neurosensory coat \u2013
\nThe retina forms the innermost, neurosensory fine layer of the eyeball. The outer surface of retina is in contact with the choroid and the inner surface is in contact with the vitreous humor.
\nThe external surface has four layers:
\nPigmented layer \u2013 it is made up of single layer of cells containing dark-brown pigment.
\nThe layer of photoreceptors \u2013 has two types of cells \u2013 rods and cones
\nRods \u2013 it is rod-shaped and elongated containing a purplish-red protein pigment known as rhodopsin or visual purple. It contains vitamin A derivatives. Rods do not respond to colours and are sensitive to dim light. They provide vision in the dark, hence known as twilight vision or scotopic vision
\nCones \u2013 these are sensitive to colors and bright lights, providing daylight or photopic vision. The pigment that is found in the cone cells is known as iodopsin. Three kinds of cone cells respond to green, red and blue light. Other colors are detected by the simultaneous trigger of cone cells of more than one kind. A sensation of white light is generated when all the three types of cells are simultaneously triggered.
\nCone cells are insensitive to the dim light hence in the dark, colour cannot be recognized.
\nLayer of bipolar neurons, layer of ganglionic cells are the two layers. This layer contains the cell bodies of the ganglion cells which forms the optic nerve.
\nBlind spot \u2013 The optic nerve exits the brain, retinal blood vessels enter the brain at a point where the photoreceptor cells are absent, this is the blind spot.
\nMacula lutea \u2013 It is the yellowish pigmented spot that is present lateral to the blind spot. It is located exactly opposite the cornea\u2019s centre. It has a pit located centrally known as the fovea which lacks in rods and blood vessels. It has only cone cells and is the area of most distinct vision.
\nLens \u2013 It is elastic, transparent and biconvex in nature which is located just behind the iris. It is covered by a thin, elastic and transparent membrane known as the lens capsule. The lens is intact in its position due to the suspensory ligaments. These ligaments along with the lens segregates the eye ball into two chambers known as the aqueous chamber and the vitreous chamber.
\nAqueous chamber \u2013 it is the space between the cornea and the lens containing a thin watery fluid known as aqueous humor.
\nVitreous chamber \u2013 it is the space between the lens and the retina which is filled with a transparent gel known as vitreous humor.
\nEar<\/h3>\n

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the body. It can be divided into three main sections \u2013 inner ear, outer ear, middle ear.
\n\u2192Inner ear \u2013 also known as the labyrinth, it is split into membranous labyrinth and the bony labyrinth. Membranous labyrinth is filled with endolymph while bony labyrinth is filled with perilymph.
\nThe Membranous labyrinth is segregated into two portions \u2013 vestibular apparatus and the cochlea. The vestibular apparatus consists of three semi-circular canals and otolith. Each semi-circular canal lies in a different plane at right angles to each other. The membranous canals are suspended in the bony canals(perilymph). The base of the canals is swollen and is known as ampulla containing crista ampullars \u2013 a projecting ridge which has hair cells.
\nThe utricle and the saccule have a projecting ridge known as macula. The macula and the crista are the particular receptors of the vestibular apparatus that has a role to play in maintaining the posture and body balance.
\nSacculus has a coiled and long outgrowth \u2013 cochlea which is the chief hearing structure consisting of three membranes. A hearing organ, the organ of corti, is situated on the basilar membrane possessing hair cells.
\n\u2192Outer ear \u2013 it has the pinna and the external auditory canal (meatus). The pinna gathers the vibrations in the air that generate sound. The external auditory canal extends up to the ear drum (tympanic membrane). It has very fine hair, wax-secreting glands in the skin of the meatus and the pinna. The tympanic membrane consists of connective tissues covered with mucous membrane inside and with skin on the outside.
\n\u2192Middle ear \u2013 it consists of three ossicles known as the malleus, stapes and incus that are linked to one another in a chain pattern. The malleus is linked to the tympanic membrane and the stapes is linked to the oval window of the cochlea. The ear ossicles increase the efficiency of transmission of sound waves to the inner ear. The middle ear cavity is connected to the pharynx through the Eustachian tube which aids in equalizing the pressure on both sides of the ear drum.<\/h3>\n

2. Compare the following:
\n(a) Central neural system (CNS) and Peripheral neural system (PNS)
\n(b) Resting potential and action potential
\n(c) Choroid and retina<\/h2>\n

Solution:
\nThe comparison is as shown below:
\n(a) Central neural system (CNS) and Peripheral neural system (PNS)
\nCentral neural system (CNS)
\nPeripheral neural system (PNS)
\nConsists of the spinal cord and the brain
\nIt consists of the spinal nerves and the cranial nerves
\nSpinal column is protected by the vertebral column whereas the brain is protected by the skull
\nNo protective structures
\nNo subdivisions
\nIt is divided into autonomic nervous system and the somatic nervous system
\nProcesses information and regulates the responses to impulses.
\nNerves of PNS passes impulses to the CNS and responses from the CNS to various structures of the body
\nGroup of neurons is known as nuclei
\nGroup of neurons is known as ganglia
\n(b) Resting potential and action potential
\nResting potential
\nAction potential
\nWhen the neuron is at the resting phase, it is the potential difference across membrane
\nWhen the neuron is triggered it is the potential difference across the membrane
\nThe exterior side of the neuron is positively charged while the interior side is negatively charged
\nThe exterior side of the neuron is negatively charged and the interior side of the neuron is positively charged
\nPermeability of K+ ions are observed to be more by the plasma membrane of neurons
\nPermeability of Na+ions are observed to be more by the plasma membrane of the neurons
\nTo maintain the resting potential, the sodium-potassium ATPase pump is activated, sending Na+ions outside the neuron
\nIt functions in a reverse pattern wherein the sodium-potassium ATPase pump sends Na+ions to the neuron.
\n(c)Choroid and retina
\nChoroid
\nRetina
\nForms the mid coat of the eyeball
\nForms the inner coat of the eye ball
\nForms the vascular layer of the eyeball
\nForms the neurosensory layer of the eyeball
\nHas no photoreceptor cells
\nHas two kinds of photoreceptors \u2013 rods and cones
\nPrevents reflection of light in the eye and nourishes the retina
\nImparts vision<\/h3>\n

3. Explain the following processes:
\n(a) Polarisation of the membrane of a nerve fibre
\n(b) Depolarisation of the membrane of a nerve fibre
\n(c) Conduction of a nerve impulse along a nerve fibre
\n(d) Transmission of a nerve impulse across a chemical synapse<\/h2>\n

Solution:
\n(a)Polarisation of the membrane of a nerve fiber:<\/h3>\n

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Impulse conduction through an axon
\nA nerve fiber is said to be in a polarized state when it is at a resting phase. In this polarized state, the membrane of the nerve fibers undergo a resting potential. Listed below are the steps that occur during the process of polarization of the membrane of a nerve fiber:
\n1. Initially, when a depolarized region of a nerve fiber becomes polarized, the count of K+ions outside the nerve fibers is more while the axon membrane has an excessive number of Na+ions.
\n2. When the membrane starts to turn into a polarized state, it turns more permeable to the K+ions and impermeable to the negatively charged proteins and the Na+ions
\n3. The 2 K+ions are passed to the axon by a sodium-potassium pump through active transport while the 3 Na+ions are passed outside the axon
\n4. The outer side turns electropositive while the inner side of the membrane turns electronegative due to the movement of potassium and sodium ions which causes the nerve fiber to be polarized.
\n(b) Depolarisation of the membrane of a nerve fibre<\/h3>\n

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1. A nerve fiber is said to be in a depolarized state when it is triggered
\n2. In this state, action potential is experienced by the membrane of the nerve fiber
\n3. During the process of depolarization of the membrane of the nerve fiber, the following steps take place:
\n(i) Axon has more concentration of K+ions in a polarized state and outside the axon, the Na+concentration is more.
\n(ii) The permeability of the membranes of Na+and K+ions is reversed when the nerve fiber is triggered by the stimulus.
\n(iii) The permeability for Na+ions by the membrane increases
\n(iv) A rapid influx of Na+ions into the axon are observed
\n(v) Hence, the inner side of the membrane turns positively charged while the outer side of the membrane turns negatively charged
\n(vi) This causes depolarization of the membrane of the nerve fiber, resulting it to experience an action potential
\n(c) Conduction of a nerve impulse along a nerve fibre
\n1. When a nerve impulse is conducted across the nerve fiber, it takes place in an organized manner
\n2. During the conduction of an impulse on the nerve fiber, a portion is depolarized always while the adjacent region is polarized. In order for the impulse to advance, repolarization of the depolarization area occurs while the polarized area depolarizes which continues across the entire length of the nerve fiber helping in the impulse conduction.
\n3. It takes place in the following stages:
\n(i) Let A be a site on the depolarized region, where the inner surface of the membrane is positively charged while the outer surface of the membrane is negatively charged
\n(ii) At site B, the adjacent region is polarized, where the outer surface is positively charged while the inner surface of the membrane is negatively charged
\n(iii) Therefore, the flow of current at site A is on the inner surface of the membrane from A to B and at the site B, the flow of current is on the outer surface from B to A. This completes the circuit of current flow.
\n(iv) This causes the site B to depolarize so as to conduct the impulse at site B
\n(v) Site A gets repolarized as soon as the impulse is conducted to site B
\n(vi) Assume a site C adjacent to site B which will be polarized when the site B is in a depolarized state.<\/h3>\n

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(d) Transmission of a nerve impulse across a chemical synapse<\/h3>\n

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1. The membranes of the pre-synaptic neuron and the post-synaptic neuron form a synapse
\n2. A synaptic cleft is a synapse which may or may not be segregated by a gap
\n3. The pre-synaptic neuron and the post-synaptic neuron at a chemical synapse are separated by the synaptic cleft
\n4. The calcium ions present at the synaptic cleft enters the synaptic knobs located at the axon terminal of the pre-synaptic neuron when an impulse reaches the axon terminal
\n5. The synaptic knobs have the synaptic vesicles of the pre-synaptic neuron which advance towards the plasma membrane to fuse with it
\n6. In the synaptic cleft, the vesicles release the neurotransmitter acetylcholine
\n7. The acetylcholine molecules tend to bind to the protein receptors located on the plasma membrane of the post-synaptic neurons
\n8. The binding opens up channels for sodium ions to enter the post-synaptic neuron. Simultaneously, the potassium ions exit the post-synaptic membrane
\n9. This causes an action potential in the post-synaptic neuron membrane. Thus, the impulse is conveyed to the post-synaptic neuron.<\/h3>\n

4. Draw labelled diagrams of the following:
\n(a) Neuron (b) Brain (c) Eye (d) Ear<\/h2>\n

Solution:
\nThe diagrams are as follows:
\n(a)Neuron<\/h3>\n

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(b) Brain<\/h3>\n

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(c) Eye<\/h3>\n

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d)Ear<\/h3>\n

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5. Write short notes on the following:
\n(a) Neural coordination
\n(b) Forebrain
\n(c) Midbrain
\n(d) Hindbrain
\n(e) Retina
\n(f) Ear ossicles
\n(g) Cochlea
\n(h) Organ of Corti
\n(i) Synapse<\/h2>\n

Solution:
\n(a) Neural coordination \u2013It is a phenomena through which two or more organs interact and complement functionalities of each other through the neural system of the body. The various physiological processes that take place in the body are interlinked with each other. The neural and the endocrine system jointly are responsible to coordinate and integrate all the actions and activities of the organs such that they function in a synchronized manner. This neural system renders a systematic and organized network for a point-to-point connection for a prompt coordination. The endocrine system renders chemical integration through the hormones.
\n(b) Forebrain \u2013
\nForebrain\u2013 has three main parts \u2013 cerebrum, hypothalamus, thalamus
\n\u2192Cerebrum forms the most important and major part of the entire brain. It is longitudinally segregated into halves by a deep cleft, each half is known as the cerebral hemisphere. Both these hemispheres are linked by the corpus callosum which is a tract of nerve fibers. The cerebral hemispheres are internally hollow and the walls of the cerebrum have an inner medulla and the outer cortex.
\nThe cerebral cortex consists of cell bodies of neurons which imparts the grey appearance; hence it is referred to as grey matter. The grey matter has many grooves (sulci) and folds (gyri). Higher the number of convolutions, greater the intelligence.
\nThe cerebral cortex consists of sensory areas, motor areas and association areas (neither motor nor sensory). These specific areas are responsible for the complex functions namely communication, memory and intersensory associations.
\nThe cerebral medulla is made of axons of nerve fibers, imparts a white appearance, hence it is referred to as white matter. There are a group of interrelated deep structures inside the cerebral hemispheres, namely the amygdala and hippocampus which results in the formation of a complicated structure known as the limbic system or the limbic lobe.
\nRole \u2013 The cerebrum is the centre of memory, intelligence, consciousness, voluntary actions and will power
\n\u2192Thalamus
\nIt is made up of grey matter and located superior to the midbrain.
\nRole \u2013 it relays motor and sensory impulses to the cerebrum and also controls the manifestation of emotions, comprehends heat, pain and cold.
\n\u2192Hypothalamus
\nLocated at the base of the thalamus, it consists of the optic chiasma. It is a point wherein the optic nerve fibers cross opposite sides. Behind this structure is the infundibulum, which is a greyish protuberance of the hypothalamus. It contains the pituitary gland.
\nRole \u2013 The hypothalamus has centres responsible in regulating temperature of the body, hemeostasis, blood pressure, centre to control appetite (hunger, sleep, fatigue, thirst, pleasure, anger and penance). The neurosecretory cells of the hypothalamus produce releasing factors or several hormones that are crucial in regulating the activities of the pituitary hormones. Along with the limbic system, the hypothalamus also plays a part in regulating the sexual behavior.
\n(c) Midbrain
\nIt consists of the cerebral peduncles and the corpora quadrigemina
\n\u2192Cerebral Peduncles
\nThey are fibrous thick tracts which connect the cerebrum and the cerebellum.
\nRole \u2013 Relay the sensory and the motor impulses between the hindbrain and the forebrain
\n\u2192Corpora quadrigemina
\nThe dorsal part of the brain has two pairs of solid lobes which are referred to as the corpora quadrigemina where one pair is referred to as the superior colliculi and the other pair is referred to as the inferior colliculi
\nRole \u2013 Corpora quadrigemina controls the visual reflexes and the movement of the eye and head. They also regulate auditory reflexes and movement of the head to identify and detect the source of sound.
\n(d) Hindbrain
\nIt consists of the cerebellum, pons varolii and medulla oblongata
\n\u2192Cerebellum
\nPresent behind the top part of the brain stem. The outer cerebellar cortex consists of grey matter and the inner cerebellar medulla consists of white matter. The cerebellum is connected with the medulla oblongata and the cerebrum through the fiber tracts of the white matter.
\nRole \u2013 It coordinates the balance of the body and the muscular activity. The impulse of the performing muscular activity is initiated in the cerebrum. It controls the voluntary movements originating in the cerebrum.
\n\u2192Pons varolii
\nIt is built of a thick bundle of white nerve fibers that is found above the medulla oblongata.
\nRole \u2013 Synchronizes between both the lobes of the cerebellum. It has the center to control breathing which is referred to as the pneumotaxic center.
\n\u2192Medulla oblongata
\nIt is conical in shape and is located at the skull\u2019s base. It runs behind the brain as the spinal cord. Any injury to this site of the brain could be fatal.
\nRole \u2013 serves as a passage to conduct nerve impulses from the spinal cord to the brain. It controls all the activities of the internal organs, breathing and heartbeat.
\n(e) Retina
\nIt is the innermost layer containing layers of neural cells, namely \u2013 ganglion cells, bipolar cells and photoreceptor cells (mentioned in order from inside to the outside). The photoreceptor cells are of two types \u2013 cones and rods. Cones are responsible to impart daylight vision or colour vision whereas rods impart twilight vision. Image of an object is formed on the retina when light enters through the cornea, the lens.
\n(f) Ear ossicles
\nThe middle ear possesses three ear ossicles known as malleus, incus and stapes that are interlinked to one another in a chain-like pattern. The malleus is in contact with the tympanic membrane, the incus with stapes and stapes inturn with the oval window of the cochlea. The ear ossicles promote and cause an increase in the efficiency of sound wave transmission to the inner ear.
\n(g) Cochlea
\nIt is the coiled portion of the labyrinth. The membranes constituting cochlea, the basilar and reissner\u2019s segregate the enveloping perilymph that is filled with the bony labyrinth into an upper scala vestibule and a lower scala tympani. The scala media (space within cochlea) is filled with endolymph and at the base of the cochlea, the scala vestibule terminates at the oval window whereas the scala tympani ends at the round window that opens to the middle ear.<\/h3>\n

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(h) Organ of Corti
\nSituated in the basilar membrane of the inner ear, the organ of corti is the organ of hearing. It contains hair cells that has auditory receptor cells which are inturn found in rows on the internal side of the organ. Stereo cilia are the processes that are found on the apical ends of the hair cells whereas the basal sections of the hair cells consist of synaptic contacts with afferent nerve fibers. Just above the rows of these hair cells, a smooth gelatinous layer known as the tectorial membrane is found.
\n(i) Synapse \u2013It is formed by the membranes of a pre-synaptic and a post-synaptic neuron, that may or may not be segregated by a gap known as the synaptic cleft. There are two types of synapses namely chemical synapses and electrical synapses.<\/h3>\n

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6. Give a brief account of:
\n(a) Mechanism of synaptic transmission
\n(b) Mechanism of vision
\n(c) Mechanism of hearing<\/h2>\n

Solution:
\n(a) Mechanism of synaptic transmission:<\/h3>\n

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Synapses are the junctions where the nerve impulses are transmitted from one neuron to another. These are formed by the membranes of a pre-synaptic and a post-synaptic neuron, that may or may not be segregated by a gap known as the synaptic cleft. There are two types of synapses namely chemical synapses and electrical synapses.
\nThe membranes of a pre-synaptic and a post-synaptic neuron at the electrical synapses are in close proximity so that electrical current can directly flow from one neuron to the other across these particular synapses. The transmission of an impulse across an electrical synapses is similar to conduction of an impulse along a single axon where the transmission is always quicker than that across a chemical synapse which is not commonly observed in the human body.
\nThe membranes of a pre-synaptic and a post-synaptic neuron at the chemical synapses are segregated by a synaptic cleft (fluid-filled space). The chemicals known as neurotransmitters are involved in the impulse-transmission at these particular synapses.
\n(b) Mechanism of vision:
\nThe passage of light rays is as follows \u2013 pupil, lens, aqueous humour, vitreous humour and finally retina. This light causes the dissociation of the photo-pigment rhodopsin to retinal and opsin. The structure of opsin is subjected to changes due to the dissociation of opsin from the retinal which generates an action potential in the cones and rods of the retina. Furthermore, the action potential is transmitted to the ganglion cells via the bipolar neurons and ultimately transmitted to the visual cortex of the brain through the optic nerve. Analysis of impulses take place at the visual cortex; responses are sent back in order to form images on the retina.
\n(c) Mechanism of hearing:
\nThe pinna of the external ear collects sound waves which pass through the external auditory meatus all the way to the eardrum. This causes the eardrum to vibrate. These vibrations are passed from the eardrum to the malleus, incuse and stapes of the middle ear which causes an increase in the frequency of the vibrations. The vibrations furthermore are passed to the cochlea of the inner ear through the oval window. These vibrations in the endolymph of the cochlea cause vibrations to be induced in the basilar membrane, which inturn cause sensory hair of the organ of corti to vibrate.
\nThe receptor hair cells force themselves against the tectorial membrane converting sound energy to a nerve impulse or action potential. This nerve impulse is transmitted to the auditory cortex of the brain, where the impulse is evaluated and analyzed causing the sound to be recognized.<\/h3>\n

7. Answer briefly:
\n(a) How do you perceive the colour of an object?
\n(b) Which part of our body helps us in maintaining the body balance?
\n(c) How does the eye regulate the amount of light that falls on the retina?<\/h2>\n

Solution:
\n(a) Colour vision is imparted by the cone cells that are found in the retina of the eye. Cone cells are of three types which respond to red, green and blue light respectively. At different wavelengths of light, different cone cells get triggered. Simultaneous stimulation of more than one kind of cone cells, causes the other colours to be detected. A sensation of white light is observed when all the three types of cone cells are triggered at the same time. This is how colour is perceived.
\n(b) The part of the body that helps in maintaining the body balance is the crista ampullaris which is located in the three semicircular canals, the macula sacculi found in the saccule of the inner ear and the macular utriculi found in the utricle.
\n(c) Pupil is an aperture located in the centre of the iris. Light enters the eye through this aperture.
\nThe iris has two types of muscles, namely the radial smooth muscles and circular smooth muscles that check the amount of light falling on the retina. The pupil diminishes in size when the smooth circular muscles contract in bright light. Therefore, less amount of light falls on the retina. The pupil widens, when the light is dim, due to the contraction of the radial smooth muscles such that enough light is incident on the retina.<\/h3>\n

8. Explain the following:
\n(a) Role of Na+ in the generation of action potential.
\n(b) Mechanism of generation of light-induced impulse in the retina.
\n(c) Mechanism through which a sound produces a nerve impulse in the inner ear.<\/h2>\n

Solution:
\n(a) Role of Na+ in the generation of action potential
\nWhen a nerve fiber is triggered, the sodium channels of the neurilemma is open and activated. From the outside, the sodium ions diffuse to the intracellular fluid due to the electrochemical gradient that is established. The membrane gets charged negatively from outside as the potassium ions move out and positively charged from inside. The immediate change that occurs in the membrane is known as action potential causing the membrane to get depolarized.
\n(b) Mechanism of generation of light-induced impulse in the retina
\nHuman eye consists of photo pigments known as retinal and opsin. These are dissociated when light induces bringing about a change in the structure of opsin, causing an action potential to generate in the bipolar neurons. These action potential or impulses are conveyed to the visual cortex of the brain by the optic nerves where these impulses are read to analyze, recognizing an erect image.
\n(c) Mechanism through which a sound produces a nerve impulse in the inner ear
\nVibrations are received through the membrane layering the fenestra ovalis by the perilymph of the internal ear. From here (the perilymph), vibrations are conveyed to the scala vestibule of the cochlea and furthermore to the scala media via the Reissner\u2019s membrane, triggering the sensory hair of the organ of corti, which is the organ of hearing. These hair cells receive impulse to carry it to the brain through the auditory nerve, where the sense of hearing is felt.<\/h3>\n

9. Differentiate between:
\n(a) Myelinated and non-myelinated axons
\n(b) Dendrites and axons
\n(c) Rods and cones
\n(d) Thalamus and Hypothalamus
\n(e) Cerebrum and Cerebellum<\/h2>\n

Solution:
\nListed below are the differences:
\n(a) Myelinated and non-myelinated axons
\nCharacteristics\/Features
\nMyelinated axons
\nNon-myelinated axons
\nMyelin sheath
\nPresent
\nAbsent
\nNodes of Ranvier
\nPresent
\nAbsent
\nLocation
\nFound in grey matter of the brain, autonomous nervous system, spinal cord
\nSpinal cord, white matter of the brain, autonomous nervous system
\nConduction of nerve impulse
\nNode to node
\nSmooth
\nSpeed of impulse-conduction
\n50 times faster than non-myelinated axon
\nComparatively lower
\n(b) Dendrites and axons
\nDendrites
\nAxons
\nDendrites are short processes
\nThey are long processes
\nThey carry impulse towards the cell body of the neuron
\nThey carry impulse away from the cell body to the neuron
\nThey are branched, always
\nAxons may or may not be branched
\nNissl\u2019s granules are found in neuroplasm
\nNissl\u2019s granules are absent in neuroplasm
\n(c) Rods and cones
\nRods
\nCones
\nSensitive to dim light
\nSensitive to bright light
\nContains rhodopsin pigment
\nContains iodopsin pigment
\nNot involved in colour vision
\nCrucial in imparting colour vision
\nRods are of one kind only
\nThree kinds of cones exist sensing \u2013 red, blue, green lights
\n(d) Thalamus and Hypothalamus
\nThalamus
\nHypothalamus
\nConsists of grey matter only
\nConsists of white and grey matter
\nDoes not secrete hormones
\nSecretes several hormones that control the activity of pituitary gland
\nLocated above the midbrain
\nLocated at the base of the thalamus
\nHas the centre for sensations namely \u2013 cold, pain, heat
\nHas the centre for sensations namely \u2013 regulating body temperature, homeostasis, blood pressure
\n(e) Cerebrum and cerebellum
\nCerebrum
\nCerebellum
\nBrain is majorly covered by the cerebrum
\nSecond largest part of the brain after cerebrum
\nIt is portion of forebrain
\nIt is part of hindbrain
\nIt is divided into two cerebral hemispheres
\nIt is divided into three lobes namely \u2013 central vermis, two lateral cerebral hemispheres
\nIt is the centre for intelligence and memory
\nIt is the centre for posture and body equilibrium<\/h3>\n

10. Answer the following:
\n(a) Which part of the ear determines the pitch of a sound?
\n(b) Which part of the human brain is the most developed?
\n(c) Which part of our central neural system acts as a master clock?<\/h2>\n

Solution:
\n(a) The part of the ear that determines the pitch of a sound is cochlea
\n(b) The part of the human brain that is the most developed is the cerebrum
\n(c) The part of the central neural system that acts as a master clock is the hypothalamus<\/h3>\n

11. The region of the vertebrate eye, where the optic nerve passes out of the retina, is called the
\n(a) fovea
\n(b) iris
\n(c) blind spot
\n(d) optic chaisma<\/h2>\n

Solution:
\nThe region of the vertebrate eye, where the optic nerve passes out of the retina, is called the
\n(c) Blind spot
\nThe optic nerves exit the eye and the retinal blood vessels enter it at a point medial to and slightly above the posterior pole of the eye ball. Here, photoreceptor cells are absent and hence it is referred to as the blind spot.<\/h3>\n

12. Distinguish between:
\n(a) afferent neurons and efferent neurons
\n(b) impulse conduction in a myelinated nerve fibre and unmyelinated nerve fibre
\n(c) aqueous humor and vitreous humor
\n(d) blind spot and yellow spot
\n(e) cranial nerves and spinal nerves.<\/h2>\n

Solution:
\nThe differences are as follows:
\n(a) Afferent neurons and efferent neurons
\nAfferent neurons
\nEfferent neurons
\nAfferent neurons are sensory neurons
\nEfferent neurons are motor neurons
\nConduction of sensory impulses from the receptors towards the central nervous system
\nConduction of motor impulses from the central nervous system to the responsive or effector organs
\nLocated in sense organs
\nFound in the brain and the spinal cord
\n(b) Impulse conduction in a myelinated nerve fibre and unmyelinated nerve fibre
\nImpulse conduction in a myelinated nerve fibre
\nImpulse conduction in an unmyelinated nerve fibre
\nImpulse is transmitted from node to node
\nImpulse travels across the length of the nerve fiber
\nSpeed of impulse-conduction is 50 times faster than non-myelinated axon
\nComparatively lower
\nLess amount of energy is expended during the transmission of an impulse
\nExcess energy is expended during the transmission of an impulse
\n(c) Aqueous humor and vitreous humor
\nAqueous humor
\nVitreous humor
\nFound in the aqueous chamber between the cornea and lens
\nFound in the vitreous chamber between the retina and lens
\nProduced by ciliary processes
\nProduced by the retina of the eye
\nHas a jelly-like consistency
\nHas a watery consistency
\nProvides support to the lens
\nRenders support to the lens and retina
\n(d) Blind spot and yellow spot
\nBlind spot
\nYellow spot
\nIt is a point on the retina where the optic nerve exits the eye while the retinal blood vessels enter the eye
\nIt is a point on the retina which is found exactly opposite to the center of the cornea
\nIt does not contain photoreceptor cells
\nIt contains two kinds of photoreceptor cells \u2013 rods and cones
\nThey are not sensitive to light
\nThey are light-sensitive
\nIt is not functional in vision
\nThe yellow spot is the region that has the most distinct vision
\n(e) Cranial nerves and spinal nerves
\nCranial nerves
\nSpinal nerves
\nHuman body has 12 pairs of cranial nerves
\nWe have 31 pairs of spinal nerves
\nCranial nerves emerge from the brain and extend to other parts of the body
\nThey originate from the spinal cord, extending to other parts of the body
\nCranial nerves can be mixed, motor or sensory
\nSpinal nerves are mixed nerves<\/h3>\n","protected":false},"excerpt":{"rendered":"

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