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Answer: (I) (a) Structure of brain. The brain is divided into three regions – Forebrain, Midbrain and Hindbrain. Procencephalon. It is made up of olfactory lobes and the cerebrum. Olafactory lobes are concerned with the sense of smell. Cerebrum is made up of two cerebral hemispheres, which are joined, by band of nerve fibres called corpus callosum. Each hemisphere is divided into lobes viz, Frontal, Parietal, Temporal and Occipital. Diencephalon. The roof of diencephalon is called hypothalamus. The anterior part of hypothalamus is vascular and folded to form the anterior choroid plexus. The hypothalamus gives off a body called the pineal body suspended by the pineal stalk. The sidewalls of the diencephalon are called the thalamus while its floor is called the hypothalamus. The optic nerves coming out of the eyes cross at a point called optic chiasma in front of the hypothalamus. The pituitary gland (hypophysis) is directly attached to the hypothalamus by a stalk called infundibulum. (II) Midbrain. It exists in the form of two pair of round protrusions called coproa quadrigemina. The anterior pair is called superior colliculi and the posterior pair is called inferior colliculi. Two bundles of fibres lie on the lower surface of midbrain and are called cerebral peduncles. (III) Hindbrain. 1. Cerebellum. It consists of two cerebellar hemispheres joined by a central worm- shaped parte, the vermis. It controls muscular activities concerned with maintaining body equilibrium. 2. Pons Varoli. It is situated in front of the cerebellum, below the midbrain and above the medulla oblongata. It consists of nerve fibres connecting the two-cerebellar hemispheres. 3. Medulla Oblongata. It extends from the pons varoli to the spinal cord. It also possesses a non-vascular folded structure called posterior choroid plexus. (b) Structur of eye: It is a hollow spherical structure measuring about 2.5 cm in diameter. Its wall is composed of three coats - Outer fibrous coat made of sclera and cornea. Sclera: It contains many collagen fibres. It functions to protect and maintain the shape of the eyeball. Cornea: It is transparent in nature that helps to admit and focus light. It is a vascular. Middle vascular coat made of chorod, ciliary body and iris. Choroid: It lies adjacent to scleral and is abundant in blood vessels that provide nutrients and oxygen. Ciliary Body: It extends towards the inside of the eye from Choroid. It consists of ciliary muscles and ciliary processes. The ciliary processes secrete aqueous humour. Suspensory ligaments are attached from the ciliary body to the lens and hold the lens in place. Iris: It is the pigmented region that gives eye its colour. It separates the aqueous humour region into anterior and posterior region. It has an opening in the center called the pupil. The iris controls the amount of light entering the eye with the help of muscles. Retina (Inner nervous coat): The retina is the neural and sensory layer of the eye. A small oval yellowish area of the retina lying opposite the centre of the cornea is called Macula lutea or yellow spot, which contains the fovea centralis. The fovea centralis has cone cells only and no rod cells. (c) Structure of ear. Each ear consist of three portions – External Ear. It comprises of a pinna and external auditory meatus. Pinna. The pinna is a projecting elastic cartilage covered with skin. It performs the function of collecting the sound waves. External Auditory Meatus. It is a tubular passage lined by hairy skin and ceruminous glands. The functions of the meatus is to pass on the sound waves and that of ceruminous glands is to secrete cerumen (ear wax) to prevent the entry of foreign bodies into the ear. Middle Ear. It contains the following parts – Tymphanic Membrane. It separates the tymphanic cavity from the external ear. It is thin and semi transparent. Tymphanic cavity. It is the cavity of the middle ear that is connected with the mesopharynx via the eustachian tube that maintains pressure. The tymphanic cavity contains a small flexible chain of three small bones called ear ossicles – the malleus (hammer shaped), the incus (anvil shaped) and the stapes (stirrup shaped). The middle ear is connected to the inner ear through two small openings – (i) Fenestra ovalis (oval window) (ii) Fenestra rotunda (round window) Internal Ear. It consists of the membranous labyrinth. The membranous labyrinth of the middle ear consists of the following parts: Semi Circular Canals: There are three semi circular canals – the anterior, posterior and the lateral semi circular canals which are perpendicular to each other. Utricle, saccus endolymphaticus and saccule. The three semicircular canals are connected to the utricle. The sacculus is joined to the utriculus via an utriculo- saccular duct. From this duct, a long tube called ductus endolymphaticus arises which ends blindly as the saccus endolymphaticus. Cochlea. It is the main hearing organ, which consists of three fluid filled chambers, the upper scala vestibuli, middle scala media and the lower scala tympani. The cochlea contains the organ of corti, which has hair cells that help in hearing.
Question 2.
Answer: (a) Differences between central neural system and peripheral neural system
(b) Differences between resting potential and action potential
(c) Differences between choroid and retina.
Question 3.
Answer: (a) Polarisation of the membrane of a nerve fibre: The neurons exist in a state of excitability called the polarised state. This is a state of rest when the neuron is not conducting an impulse. At this point, the neurilemma (plasma membrane of a nerve fibre) is more permeable to potassium ions and nearly impermeable to sodium ions. As a result of this, the axoplasm has high concentration of K+ and negatively charged proteins and low concentration of Na+. In contrast, the fluid outside the axon contains low concentration of K+, high concentration of Na+ leading to existence of a concentration gradient. Such a state of the fibre where there exists an electrical potential difference across the resting plasma membrane is the state of depolarisation and the potential is called the resting membrane potential. (b) Depolarisation of the membrane of a nerve fibre:The impulse spreads through the length of the nerve fibre in the form of a wave of depolarisation. Depolarisation is a state of reverse polariy. Depolarisation occurs as a result of the opening of Na+ channels whereas K+ channels remain closed. As a result there is an entry Na+ ions into the neuroplasm which leads to reversed potential difference as inside of the membrane starts turning positive i.e. from – 70 mV towards zero. At zero mV, the membrane is said to be depolarized (c) Conduction of a nerve impulse alone a nerve fibre:Electrical events in the nerve conduction. The electrical events involve the following changes in the electrical potential of nerve fibre. Resting potential state. The nerve cells remain bathed in a fluid called interstitial fluid. In this fluid remain dissolved sodium (Na+) and potassium (K+). During the resting phase, the neurilemma is comparatively 30 times more permeable to potassium ions (K+) than to sodium ions (Na+). As a result Na+ ions are present in high concentration outside the membrane and in low concentration on the inner side. Thus other surface whose (+ve) electric charge and inner surface (-ve) charge due to organic anions. The membrane at this state is said to be in polarised state and the resting potential remains at a value of 70 mm. Depolarization and action potential. When a stimulus of any kind is applied to the nerve, it disturbs the set up. There is marked change in the potential and it is called action potential. The polarity of membrane gets reversed after excitation because the Na+ ions move inward and K+ ions move outward. Thus the membrane is said to be depolarised. It is termed active phase, during which the inner surface is positively charged and outer surface is negatively charged. Conduction of impulse. The electrochemical changes are conducted up to synapses as the electric wave of change of potential progresses forward along the fibre. Repolarization. In the recovery phase, the axon again restores the original +ve concentration by the outside of movement of Na+ ions from the inner side of membrane. The process of change requires something during which nerve cannot be stimulated again. It is of the duration 1/ 1000 second and called refractory period. (d) Transmission of nerve impulses across a chemical synapseSynapse. Synapse is the close proximity of terminal branch of the axon of one neuron with dendrites of the next neuron in a chain without actual contact. There are two types of synapses i.e. electrical and chemical depending upon the nature of transfer of information across the synapse. In transmission of nerve impulse across a synapse the impulse reaches the end knob, a neurotransmitter called acetylcholine is released from the synaptic vesicles present in the end knob of axon. It results in depolarization of dendrite membrane initiating a new impulse (action potential- passes along the next neuron). The neurotransmitter is released by synaptic membrane and received by post – synaptic membrane and received by post-synaptic membrane of dendrite of next neuron. To check continued stimulation of dendrite membrane an enzyme acetylcholinestrase inactivates the acetylcholine. Some sympathetic fibres norepinephrine as neurotransmitter. It is inactivated by enzyme monoamino oxidase to prevent continued stimulation of muscle. It involves two processes neurosecretion by axon endings and chemoreception by dendrites and get into state of excitation.
Question 4.
Answer: (a) Mechanism of synaptic transmission is a device of synaptic transmission. Synapse is the close proximity of terminal branch of the axon of one neuron with dendrites of the next neuron in a chain. As the impulse reaches the end knob, a neurotransmitter e.g. acetylcholine is released from synaptic vesicles present in the end knob. This results in depolarisation of dendrite membrane initiating a new impulse in it. The neurotransmitter is released by syanptic membrane and received by postsynaptic membrane of dendrite of next neuron. To check continues stimulation of dendrite membrane; an enzyme acetyl cholinesterase in activates acetylcholine. (b) Mechanism of VisionFormation of Inverted Image on Retina. The rays of light coming from an object pass through cornea, aqueous humor, pupil, lens, vitreous humor and then fall on retina and a small inverted image of the object is formed. Accomodation. The ability to the eye to focus objects at various distances is know as accommodation. Changing the convexity of the lens and size of pupil does this. Photoreception. Light splits rhodopsin pigment into retinene (an aldehyde derivative of Vitamin A) and a protein opsin. This depolarises the rod cells to release a neutotransmitter, transmitting the nerve impulse to different cells and then to optic nerve fibres. Eye to Brain. Nerve impulses are then transmitted from the optic nerve to the brain. The centre for sight is in the occipital lobe of the cerebral hemisphere where an erect image is formed and perceived. (c) Mechanism of hearing: The phonoreceptors of organ of Corti of cochlea are sensitive to sound waves of frequency ranging from 20 to 20000 cycles / second or Hertz (Hz) (Maximum sensitive to 1000 cycles per second). In hearing, different parts of ear perform different functions: Internal ear (i) Vibrations of fenestra ovalis cause pressure changes in perilymph of scala vestibuli, vibration in Reissner’s membrane, pressure changes in endolymph of scala media, vibrations in basilar membrane and pressure changes in perilymph of scala tympani. (ii) Due to vibration of basilr membrane auditory hair phonoreceptors are distorted in the tectonial membrane and are stimulated. The phonoreceptoors initiated nerve impulses, which are conducted to the auditory area of cerebral cortex of occipital part of cerebral hemisphere. Auditory area interprets the nerve impulses. (iii) Fenestra rotunda membrane acts as a pressure relief valve in hearing. Its movements are always in opposite direction to that of fenestra ovalis membrane. (iv) Human ear can differentiate quality as well as quantity of sound waves. Sound waves depends the area in maximum displacement e.g. sound waves of high frequencies (high notes) cause maximum displacement at the base of basilar membrane. Quantity of sound waves depends upon the number of phonoreceptors stimulated in a particular area.
Question 5.
Answer: (a) The colour of an object is under the control of the pigment visual violet that is Rodopsin that works in daylight and is sensitive to bright light and colours. There are three different types of pigments under the catogory of Rodopsin: (i) Erythrolable. It is most sensitive to red light. (ii) Chlordolable. It is most sensitive to green light. (iii) Cyanolable. It is sensitive to blue light. The combination of these three pigments produces all the colours that we can see. (b) Equilibrium. It is the controlled by statoreceptors present in the cristae ampullaes or semicircular ducts and the maculae of vestibule. Cristae control the dynamic equilibrium (when in motion) and equilibrium during angular head). As three semicircular ducts are in three different directions so these can detect the disturbances in position in different directions. Maculae control the static equilibrium (tilting of head or body at rest) and linear acceleration (rapid forward movements). (c) The amount of light entering the retina is under the control of two types of muscles present in the iris (sphincters) and radial muscles (dilators). The iris controls the amount of light falling over the retina by the radial muscles contracting in dim light and the circular muscles contracting in bright light.
Question 6.
Answer: (a) Role of Na+ in the generation of action potential. The action potential is determined by Na+ ions. The Na+ channels which are closed in the resting state, open and cause the inflow of Na+ ions by diffusion into the inside of axoplasm. The electrical potential of the membrane changes from 70 mV towards zero and then the membrane is siad to be depolarised. (b) Role of Ca++ ions in the release of neurotransmitters at a synapse. When an impulse arrived at presynaptic cell, Ca++ ions from the synaptic cleft enter the presynaptic cell. The Ca2+ ions cause the movement of the synaptic + vesicles to the surface of the cell and then get fused with the membrane. Rupturing of the vesicles and release of neurotransmitters of exocytosis follow this into the synaptic cleft. (c) Mechanism of generation of light induced impulse in the retina. The photopigments of the retina are photosensitive compounds in the eye that are composed of retinal (an aldehyde of vitamin A) and opsin (a protein). Light induces dissociation of retinal from opsin that leads to a change in membrane permeability. Consequently membrane potential differences are generated producing a signal that generates action potentials in the ganglion cells through the bipolar cells. These action potentials (impulses) are transmitted by the optic nerves to the visual cortex areas of the brain where neural impulses are analysed and image is recognised based on earlier memory and experience. (d) Mechanism through which a sound produces a nerve impulse in the inner ear. When sound falls over the ear drum, it is then transmitted to the inner ear by ear ossicles. The vibrations are passed through the oval window onto the fluid of the cochlea, where they generate waves in the lymphs. The waves induce a ripple in the basilar membrane that bend the hair cells, pressing them against the techtonial membrane. As a result nerve impulses are generated in the associated afferent neurons and transmitted to auditory cortex of brain via auditory nerves, where the impulses are analysed and the sound is recognised.
Question 7.
Answer: (a) Differences between myelinated axon non myelinated axon.
(b) Differences between dendrites and axons.
(c) Differences between rods and cones
(d) Differences between thalamus and hypothalamus.
(e) Differences between cerebrum and cerebellum.
Question 8.
Answer: (a) Cochlea, -receptor cells in the organ of corti(b) cerebrum, (c) Brain.
Question 9.
Answer: (c) blind spot.
Question 10.
Answer: (a) Differences between Afferent neuron and Efferent neuron.
(b) Conduction of nerve impulse in myelinated and non- myelinated nerve fibre.
(c) Differences between vitreous humor and aqueous humor. 
(d) Difference between yellow spot and blind spot
Difference between cranial nerves and spinal nerves.
Neural Control And Coordination
Class 11th Biology CBSE Solution
Ncert Questions
- Briefly describe the structure of the following:(a) Brain(b) Eye(c) Ear.…
- Compare the following-(a) Central neural system and peripheral neural system(b) Resting…
- Explain the following processes.(a) Polarisation of the membrane of a nerve fibre.(b)…
- Give a brief account of (a) Mechanism of synaptic transmission(b) Mechanism of vision(c)…
- Answer briefly -(a) How do you perceive the colour of an object?(b) Which part of our body…
- Explain the following:(a) Role of Na+ in the generation of action potential.(b) Role of…
- Differentiate between(a) Myelinated and Non Myelinated axons(b) Dendrites and axons(c)…
- Answer the following(a) Which part of the ear determines the pitch of a sound?(b) Which…
- The region of the vertebrate eye where the optic nerve passes out the retina, is called…
- Distinguish between - (a) Afferent neurons and efferent neurons (b) Impulse conduction in…
Ncert Questions
Question 1.Briefly describe the structure of the following:(a) Brain (b) Eye (c) Ear.
Answer: (I) (a) Structure of brain. The brain is divided into three regions – Forebrain, Midbrain and Hindbrain. Procencephalon. It is made up of olfactory lobes and the cerebrum. Olafactory lobes are concerned with the sense of smell. Cerebrum is made up of two cerebral hemispheres, which are joined, by band of nerve fibres called corpus callosum. Each hemisphere is divided into lobes viz, Frontal, Parietal, Temporal and Occipital. Diencephalon. The roof of diencephalon is called hypothalamus. The anterior part of hypothalamus is vascular and folded to form the anterior choroid plexus. The hypothalamus gives off a body called the pineal body suspended by the pineal stalk. The sidewalls of the diencephalon are called the thalamus while its floor is called the hypothalamus. The optic nerves coming out of the eyes cross at a point called optic chiasma in front of the hypothalamus. The pituitary gland (hypophysis) is directly attached to the hypothalamus by a stalk called infundibulum. (II) Midbrain. It exists in the form of two pair of round protrusions called coproa quadrigemina. The anterior pair is called superior colliculi and the posterior pair is called inferior colliculi. Two bundles of fibres lie on the lower surface of midbrain and are called cerebral peduncles. (III) Hindbrain. 1. Cerebellum. It consists of two cerebellar hemispheres joined by a central worm- shaped parte, the vermis. It controls muscular activities concerned with maintaining body equilibrium. 2. Pons Varoli. It is situated in front of the cerebellum, below the midbrain and above the medulla oblongata. It consists of nerve fibres connecting the two-cerebellar hemispheres. 3. Medulla Oblongata. It extends from the pons varoli to the spinal cord. It also possesses a non-vascular folded structure called posterior choroid plexus. (b) Structur of eye: It is a hollow spherical structure measuring about 2.5 cm in diameter. Its wall is composed of three coats - Outer fibrous coat made of sclera and cornea. Sclera: It contains many collagen fibres. It functions to protect and maintain the shape of the eyeball. Cornea: It is transparent in nature that helps to admit and focus light. It is a vascular. Middle vascular coat made of chorod, ciliary body and iris. Choroid: It lies adjacent to scleral and is abundant in blood vessels that provide nutrients and oxygen. Ciliary Body: It extends towards the inside of the eye from Choroid. It consists of ciliary muscles and ciliary processes. The ciliary processes secrete aqueous humour. Suspensory ligaments are attached from the ciliary body to the lens and hold the lens in place. Iris: It is the pigmented region that gives eye its colour. It separates the aqueous humour region into anterior and posterior region. It has an opening in the center called the pupil. The iris controls the amount of light entering the eye with the help of muscles. Retina (Inner nervous coat): The retina is the neural and sensory layer of the eye. A small oval yellowish area of the retina lying opposite the centre of the cornea is called Macula lutea or yellow spot, which contains the fovea centralis. The fovea centralis has cone cells only and no rod cells. (c) Structure of ear. Each ear consist of three portions – External Ear. It comprises of a pinna and external auditory meatus. Pinna. The pinna is a projecting elastic cartilage covered with skin. It performs the function of collecting the sound waves. External Auditory Meatus. It is a tubular passage lined by hairy skin and ceruminous glands. The functions of the meatus is to pass on the sound waves and that of ceruminous glands is to secrete cerumen (ear wax) to prevent the entry of foreign bodies into the ear. Middle Ear. It contains the following parts – Tymphanic Membrane. It separates the tymphanic cavity from the external ear. It is thin and semi transparent. Tymphanic cavity. It is the cavity of the middle ear that is connected with the mesopharynx via the eustachian tube that maintains pressure. The tymphanic cavity contains a small flexible chain of three small bones called ear ossicles – the malleus (hammer shaped), the incus (anvil shaped) and the stapes (stirrup shaped). The middle ear is connected to the inner ear through two small openings – (i) Fenestra ovalis (oval window) (ii) Fenestra rotunda (round window) Internal Ear. It consists of the membranous labyrinth. The membranous labyrinth of the middle ear consists of the following parts: Semi Circular Canals: There are three semi circular canals – the anterior, posterior and the lateral semi circular canals which are perpendicular to each other. Utricle, saccus endolymphaticus and saccule. The three semicircular canals are connected to the utricle. The sacculus is joined to the utriculus via an utriculo- saccular duct. From this duct, a long tube called ductus endolymphaticus arises which ends blindly as the saccus endolymphaticus. Cochlea. It is the main hearing organ, which consists of three fluid filled chambers, the upper scala vestibuli, middle scala media and the lower scala tympani. The cochlea contains the organ of corti, which has hair cells that help in hearing.
Question 2.
Compare the following-(a) Central neural system and peripheral neural system(b) Resting potential and action potential(c) Choroid and retina.
Answer: (a) Differences between central neural system and peripheral neural system
(b) Differences between resting potential and action potential (c) Differences between choroid and retina.
Question 3.
Explain the following processes.(a) Polarisation of the membrane of a nerve fibre.(b) Depolarisation of the membrane of a nerve fibre.(c) Conduction of a nerve impulse along a nerve fibre.(d) Transmission of a nerve impulse across a chemical synapse.
Answer: (a) Polarisation of the membrane of a nerve fibre: The neurons exist in a state of excitability called the polarised state. This is a state of rest when the neuron is not conducting an impulse. At this point, the neurilemma (plasma membrane of a nerve fibre) is more permeable to potassium ions and nearly impermeable to sodium ions. As a result of this, the axoplasm has high concentration of K+ and negatively charged proteins and low concentration of Na+. In contrast, the fluid outside the axon contains low concentration of K+, high concentration of Na+ leading to existence of a concentration gradient. Such a state of the fibre where there exists an electrical potential difference across the resting plasma membrane is the state of depolarisation and the potential is called the resting membrane potential. (b) Depolarisation of the membrane of a nerve fibre:The impulse spreads through the length of the nerve fibre in the form of a wave of depolarisation. Depolarisation is a state of reverse polariy. Depolarisation occurs as a result of the opening of Na+ channels whereas K+ channels remain closed. As a result there is an entry Na+ ions into the neuroplasm which leads to reversed potential difference as inside of the membrane starts turning positive i.e. from – 70 mV towards zero. At zero mV, the membrane is said to be depolarized (c) Conduction of a nerve impulse alone a nerve fibre:Electrical events in the nerve conduction. The electrical events involve the following changes in the electrical potential of nerve fibre. Resting potential state. The nerve cells remain bathed in a fluid called interstitial fluid. In this fluid remain dissolved sodium (Na+) and potassium (K+). During the resting phase, the neurilemma is comparatively 30 times more permeable to potassium ions (K+) than to sodium ions (Na+). As a result Na+ ions are present in high concentration outside the membrane and in low concentration on the inner side. Thus other surface whose (+ve) electric charge and inner surface (-ve) charge due to organic anions. The membrane at this state is said to be in polarised state and the resting potential remains at a value of 70 mm. Depolarization and action potential. When a stimulus of any kind is applied to the nerve, it disturbs the set up. There is marked change in the potential and it is called action potential. The polarity of membrane gets reversed after excitation because the Na+ ions move inward and K+ ions move outward. Thus the membrane is said to be depolarised. It is termed active phase, during which the inner surface is positively charged and outer surface is negatively charged. Conduction of impulse. The electrochemical changes are conducted up to synapses as the electric wave of change of potential progresses forward along the fibre. Repolarization. In the recovery phase, the axon again restores the original +ve concentration by the outside of movement of Na+ ions from the inner side of membrane. The process of change requires something during which nerve cannot be stimulated again. It is of the duration 1/ 1000 second and called refractory period. (d) Transmission of nerve impulses across a chemical synapseSynapse. Synapse is the close proximity of terminal branch of the axon of one neuron with dendrites of the next neuron in a chain without actual contact. There are two types of synapses i.e. electrical and chemical depending upon the nature of transfer of information across the synapse. In transmission of nerve impulse across a synapse the impulse reaches the end knob, a neurotransmitter called acetylcholine is released from the synaptic vesicles present in the end knob of axon. It results in depolarization of dendrite membrane initiating a new impulse (action potential- passes along the next neuron). The neurotransmitter is released by synaptic membrane and received by post – synaptic membrane and received by post-synaptic membrane of dendrite of next neuron. To check continued stimulation of dendrite membrane an enzyme acetylcholinestrase inactivates the acetylcholine. Some sympathetic fibres norepinephrine as neurotransmitter. It is inactivated by enzyme monoamino oxidase to prevent continued stimulation of muscle. It involves two processes neurosecretion by axon endings and chemoreception by dendrites and get into state of excitation.
Question 4.
Give a brief account of (a) Mechanism of synaptic transmission(b) Mechanism of vision(c) Mechanism of Hearing
Answer: (a) Mechanism of synaptic transmission is a device of synaptic transmission. Synapse is the close proximity of terminal branch of the axon of one neuron with dendrites of the next neuron in a chain. As the impulse reaches the end knob, a neurotransmitter e.g. acetylcholine is released from synaptic vesicles present in the end knob. This results in depolarisation of dendrite membrane initiating a new impulse in it. The neurotransmitter is released by syanptic membrane and received by postsynaptic membrane of dendrite of next neuron. To check continues stimulation of dendrite membrane; an enzyme acetyl cholinesterase in activates acetylcholine. (b) Mechanism of VisionFormation of Inverted Image on Retina. The rays of light coming from an object pass through cornea, aqueous humor, pupil, lens, vitreous humor and then fall on retina and a small inverted image of the object is formed. Accomodation. The ability to the eye to focus objects at various distances is know as accommodation. Changing the convexity of the lens and size of pupil does this. Photoreception. Light splits rhodopsin pigment into retinene (an aldehyde derivative of Vitamin A) and a protein opsin. This depolarises the rod cells to release a neutotransmitter, transmitting the nerve impulse to different cells and then to optic nerve fibres. Eye to Brain. Nerve impulses are then transmitted from the optic nerve to the brain. The centre for sight is in the occipital lobe of the cerebral hemisphere where an erect image is formed and perceived. (c) Mechanism of hearing: The phonoreceptors of organ of Corti of cochlea are sensitive to sound waves of frequency ranging from 20 to 20000 cycles / second or Hertz (Hz) (Maximum sensitive to 1000 cycles per second). In hearing, different parts of ear perform different functions: Internal ear (i) Vibrations of fenestra ovalis cause pressure changes in perilymph of scala vestibuli, vibration in Reissner’s membrane, pressure changes in endolymph of scala media, vibrations in basilar membrane and pressure changes in perilymph of scala tympani. (ii) Due to vibration of basilr membrane auditory hair phonoreceptors are distorted in the tectonial membrane and are stimulated. The phonoreceptoors initiated nerve impulses, which are conducted to the auditory area of cerebral cortex of occipital part of cerebral hemisphere. Auditory area interprets the nerve impulses. (iii) Fenestra rotunda membrane acts as a pressure relief valve in hearing. Its movements are always in opposite direction to that of fenestra ovalis membrane. (iv) Human ear can differentiate quality as well as quantity of sound waves. Sound waves depends the area in maximum displacement e.g. sound waves of high frequencies (high notes) cause maximum displacement at the base of basilar membrane. Quantity of sound waves depends upon the number of phonoreceptors stimulated in a particular area.
Question 5.
Answer briefly –(a) How do you perceive the colour of an object?(b) Which part of our body helps us in maintaining equilibrium?(c) How does the eye regulate the amount of light that falls on the retina?
Answer: (a) The colour of an object is under the control of the pigment visual violet that is Rodopsin that works in daylight and is sensitive to bright light and colours. There are three different types of pigments under the catogory of Rodopsin: (i) Erythrolable. It is most sensitive to red light. (ii) Chlordolable. It is most sensitive to green light. (iii) Cyanolable. It is sensitive to blue light. The combination of these three pigments produces all the colours that we can see. (b) Equilibrium. It is the controlled by statoreceptors present in the cristae ampullaes or semicircular ducts and the maculae of vestibule. Cristae control the dynamic equilibrium (when in motion) and equilibrium during angular head). As three semicircular ducts are in three different directions so these can detect the disturbances in position in different directions. Maculae control the static equilibrium (tilting of head or body at rest) and linear acceleration (rapid forward movements). (c) The amount of light entering the retina is under the control of two types of muscles present in the iris (sphincters) and radial muscles (dilators). The iris controls the amount of light falling over the retina by the radial muscles contracting in dim light and the circular muscles contracting in bright light.
Question 6.
Explain the following:(a) Role of Na+ in the generation of action potential.(b) Role of Ca++ in the release of neurotransmitters at a synapse.(c) Mechanism of generation of light induced impulse in the retina.(d) Mechanism through which a sound produces a nerve impulse in the inner ear.
Answer: (a) Role of Na+ in the generation of action potential. The action potential is determined by Na+ ions. The Na+ channels which are closed in the resting state, open and cause the inflow of Na+ ions by diffusion into the inside of axoplasm. The electrical potential of the membrane changes from 70 mV towards zero and then the membrane is siad to be depolarised. (b) Role of Ca++ ions in the release of neurotransmitters at a synapse. When an impulse arrived at presynaptic cell, Ca++ ions from the synaptic cleft enter the presynaptic cell. The Ca2+ ions cause the movement of the synaptic + vesicles to the surface of the cell and then get fused with the membrane. Rupturing of the vesicles and release of neurotransmitters of exocytosis follow this into the synaptic cleft. (c) Mechanism of generation of light induced impulse in the retina. The photopigments of the retina are photosensitive compounds in the eye that are composed of retinal (an aldehyde of vitamin A) and opsin (a protein). Light induces dissociation of retinal from opsin that leads to a change in membrane permeability. Consequently membrane potential differences are generated producing a signal that generates action potentials in the ganglion cells through the bipolar cells. These action potentials (impulses) are transmitted by the optic nerves to the visual cortex areas of the brain where neural impulses are analysed and image is recognised based on earlier memory and experience. (d) Mechanism through which a sound produces a nerve impulse in the inner ear. When sound falls over the ear drum, it is then transmitted to the inner ear by ear ossicles. The vibrations are passed through the oval window onto the fluid of the cochlea, where they generate waves in the lymphs. The waves induce a ripple in the basilar membrane that bend the hair cells, pressing them against the techtonial membrane. As a result nerve impulses are generated in the associated afferent neurons and transmitted to auditory cortex of brain via auditory nerves, where the impulses are analysed and the sound is recognised.
Question 7.
Differentiate between(a) Myelinated and Non Myelinated axons(b) Dendrites and axons(c) Rods and cones(d) Thalamus and hypothalamus(e) Cerebrum and cerebellum.
Answer: (a) Differences between myelinated axon non myelinated axon.
(b) Differences between dendrites and axons. (c) Differences between rods and cones (d) Differences between thalamus and hypothalamus. (e) Differences between cerebrum and cerebellum.
Question 8.
Answer the following(a) Which part of the ear determines the pitch of a sound?(b) Which part of the human brain is the most developed?(c) Which part of our central neural system acts as a master clock?
Answer: (a) Cochlea, -receptor cells in the organ of corti(b) cerebrum, (c) Brain.
Question 9.
The region of the vertebrate eye where the optic nerve passes out the retina, is called the –(a) fovea(b) iris(c) blind spot(d) optic chiasma.
Answer: (c) blind spot.
Question 10.
Distinguish between – (a) Afferent neurons and efferent neurons (b) Impulse conduction in a myelinated nerve fibre and unmyelinated nerve fibre (c) Aqueous humor and vitreous humor (d) Blind spot and yellow spot. Cranial nerves and spinal nerves.
Answer: (a) Differences between Afferent neuron and Efferent neuron.
(b) Conduction of nerve impulse in myelinated and non- myelinated nerve fibre. (c) Differences between vitreous humor and aqueous humor. (d) Difference between yellow spot and blind spot Difference between cranial nerves and spinal nerves.