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NCERT Solutions for Class 11 Biology Chapter 21 - Neural Control and Coordination

iacst-2022

The process that assists in the interaction of two or more organs and through which complements each other's functions is called Coordination. It is the endocrine system and the neural system that jointly coordinate and integrate every activity of the organs inside the human body so that the organs keep working without any abnormalities. Thus, by now, students must have gotten the notion about the topics discussed in this chapter. Yes, it is the 'Neural Control and Coordination' that will be preached here.

Some of the topics discussed are the neural system of humans and neural coordination mechanisms, such as transfer of nerve impulse, physiology of reflex action, and impulse conduction beyond a synapse. Read the below explanations to understand better about the topics.

  • An overview of Neural System
  • Neural System in Human Organisms
  • Neuron - The Functional and Structural Unit of Neural System
  • Concept of Central Neural System
  • Meaning of Reflex Arc and Reflex Action
  • Meaning of Sensory Reception and Processing

This second-last chapter of class 11 biology is all about the neural system that humans have inside their bodies. Through the topic 'Neural Coordination and Control', the human neural system has been extensively explained. The subtopics highlighted in the introductory portion above are the mechanisms of neural coordination.

This chapter is also a part of the fifth unit of class 11 Biology syllabus. The central nervous system (CNS) components, such as the forebrain, hindbrain, peripheral nervous system, midbrain, autonomic nervous system, spinal cord, and sense organs, i.e. the ears & eyes are also a part that has been explained under this chapter. The students would also get to know about the process of impulse conduction, vision, and hearing in a captivating manner.

 

 

Q1. Briefly describe the structure of the following:

a. Brain

Answer:

The brain is the main coordinating center of the body. It is a part of the nervous system that controls and monitors every organ of the body. It is well protected by cranial meninges that are made up of an outer layer called dura mater, a thin middle layer called arachnoid, and an inner layer called pia mater.

It is divided into three regions —

  1. forebrain
  2. midbrain
  3. hindbrain

Forebrain:

It is the main thinking part of the brain. It consists of the cerebrum, thalamus, and hypothalamus.

  1. Cerebrum: The cerebrum is the largest part of the brain and constitutes about four-fifths of its weight. It is divided into two cerebral hemispheres by a deep longitudinal cerebral fissure. These hemispheres are joined by a tract of nerve fibre known as the corpus callosum.
  2. Thalamus: Thalamus is the main center of coordination for sensory and motor signaling. It is wrapped by the cerebrum.
  3. Hypothalamus: Hypothalamus lies at the base of the thalamus and contains several four-fifths centers that regulate body temperature and the urge for eating and drink. Some regions of the cerebrum, along with the hypothalamus, are involved in the regulation of sexual behavior and expression of emotional reactions such as excitement, pleasure, fear, etc.

Midbrain: It is located between the thalamus region of the forebrain and the pons region of the hindbrain. The dorsal surface of the midbrain consists of superior and inferior corpora bigemina and four round lobes called corpora quadrigemina.

Hindbrain: It consists of three regions - pons, cerebellum, and medulla oblongata.

- Pons is a band of nerve fibre that lies between the medulla oblongata and midbrain. It connects the lateral parts of the cerebellar hemisphere.

- The cerebellum is a large and well-developed part of the hindbrain. It is located below the posterior sides of the cerebral hemispheres and above the medulla oblongata. It is responsible for maintaining posture and equilibrium of the body.

-The medulla oblongata is the posterior and simplest part of the brain. It is located beneath the cerebellum. Its lower end extends in the form of the spinal cord and leaves the skull through the foramen magnum.

Q1. Briefly describe the structure of the following:

a. Eye

Answer:

Eye: We know that eyes are in spherical structures that consist of three layers.

1. The outer layer is composed of the sclera and cornea.

-The sclera is an opaque tissue that is usually known as white of the eye. It is composed of dense connective tissue.

- The cornea is a transparent anterior portion of the eye that lacks blood vessels and is nourished by lymph from the nearby area. It is slightly bulged forward and helps in focusing light rays with the help of the lens.

 2. The middle layer of the eye is vascular and contains the choroid, ciliary body, and iris.

- The choroid lies next to the sclera and contains numerous blood vessels that provide nutrients and oxygen to the retina and other tissues.

- Ciliary body: The choroid layer is thin over the posterior region and gets thickened in the anterior portion to form the ciliary body. It contains blood vessels, ciliary muscles, and ciliary processes.

-Iris: At the junction of the sclera and cornea, the ciliary body continues forward to form a thin-colored partition called the iris. It is the visible colored portion of the eye. The eye contains a transparent, biconvex, and elastic structure just behind the iris. It is known as a lens. The lens is held in position by suspensory ligaments attached to the ciliary body. The lens divides the eyeball into two chambers — an anterior aqueous and a posterior vitreous chamber.

3. The innermost nervous coat of the eye contains the retina. The retina is the innermost layer. It contains three layers of cells — inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells. The receptor cells present in the retina are of two types — rod cells and cone cells.

- Rod cells —The rods contain the rhodopsin pigment (visual purple) that is highly sensitive to dim light. It is responsible for twilight vision.

- Cone cells —The cones contain the iodopsin pigment (visual violet) and are highly sensitive to high-intensity light. They are responsible for daylight and color vision. The innermost ganglionic cells give rise to optic nerve fibre that forms the optic nerve in each eye and is connected with the brain.

Q1. Briefly describe the structure of the following:

d. Ear

Answer:

Ear: The ear is the sense organ for hearing and equilibrium. It consists of three portions external ear, middle ear, and internal ear.

External ear: It consists of the pinna, external auditory meatus, and a tympanic membrane. Pinna is a sensitive structure that collects and directs the vibrations into the ear to produce sound. The external auditory meatus is a tubular passage supported by cartilage in the external ear. The tympanic membrane is a thin membrane that lies close to the auditory canal. It separates the middle ear from the external ear.

Middle ear: It is an air-filled tympanic cavity that is connected with the pharynx through the eustachian tube. The eustachian tube helps to equalize the air pressure on both sides of the tympanic membrane. The middle ear contains a flexible chain of three middle bonescalled ear ossicles. The three ear ossicles are malleus, incus, and stapes that are attached.

Internal ear: It is also known as the labyrinth. The labyrinth is divided into the bony labyrinth and a membranous labyrinth. The bony labyrinth is filled with perilymph while a membranous labyrinth is filled with endolymph.

The membranous labyrinth is divided into 2 parts.

 

  • Vestibular apparatus: It is a central sac-like part that is divided into utriculus and sacculus. A special group of sensory cells called macula are present in the sacculus and utriculus. The vestibular apparatus also contains three semi-circular canals. The lower end of each semi-circular canal contains a projecting ridge called crista ampullaris. Each ampulla has a group of sensory cells called crista. Crista and macula are responsible for maintaining the balance of body and posture.
  • Cochlea: Cochlea is a long and coiled outgrowth of the sacculus. It is the main hearing organ. The cochlea consists of three membranes. The organ of Corti, a hearing organ, is located on the basilar membrane that has hair cells.

Q2. Compare the following:

a. Central neural system (CNS) and Peripheral neural system (PNS)

Answer:

 

Central Neural System (CNS)

 

Peripheral Neural System (PNS)

 

 

1. CNS is made of the brain and the spinal cord.

 

1. PNS consists of cranial nerves and spinal nerves.

 

2. Brain is protected by the skull and the spinal cord by the vertebral column.

 

2. There are no protective structures for PNS.

 

3. CNS does not have any subdivisions.

 

3. PNS is divided into the somatic nervous system autonomic nervous system.

 

4. CNS processes the information and controls the response to impulses.

 

4. Nerves of PNS carry impulses to the CNS responses from the CNS to different organs of the bo

 

5. Group of neurons in CNS is called nuclei.

 

5. Group of neurons in PNS is called ganglia.

Q2. Compare the following:

a. Resting potential and action potential

Answer:

 

Resting Potential

 

Action Potential

 

1. It is the potential difference (difference in electric charge) across the membrane when the neuron is at the resting phase.

 

1. It is the potential difference (difference in electric charge) across the membrane when a neuron is stimulated or excited.

 

2. The outer side of the neuron is positively charged and the interior of the neuron is negatively charged.

 

2. The outer side of the neuron is negative and the interior of the neuron is positively c

 

3. The plasma membrane of the neuron is more permeable to K + ions.

 

3. The plasma membrane of the neuron is permeable to Na + ions.

 

4. The sodium-potassium-ATPase pump is active and sends Na + ions outside the neuron to maintain the resting potential.

 

4. The sodium-potassium-ATPase pump forms a reverse manner and sends Na +ions into


Q2. Compare the following:

c. Choroid and retina

Answer:
 

 

Choroid

 

Retina

 

1. It is the middle coat of the eyeball.

 

1. It is the inner coat of the eyeball.

 

2. It does not have photoreceptor cells.

 

2. It has two kinds of photoreceptor cells-or cones.

 

3. It is the vascular layer of the eyeball.

 

3. It is the neurosensory layer of the eyeball
 

 

4. It nourishes the retina and prevents the reflection of light in the eye.

 

4. It imparts vision.

 

Q3. Explain the following processes:

a. Polarisation of the membrane of a nerve fiber

Answer:

Polarisation of the membrane of a nerve fiber:

- When the nerve fiber is at the resting phase, it is said to be in the polarised state.

- In a polarised state, the membrane of the nerve fiber experiences resting potential.

- The following steps take place during the process of polarization of the membrane of a nerve fiber:

- When a depolarised region of a nerve fiber starts becoming polarised initially, there are more K +ions outside the nerve fiber and the axon membrane contains a large amount of Na + ions.

- As the region of the membrane starts attaining the polarised state, the membrane becomes more permeable to K + ions and impermeable to Na + ions and negatively charged proteins.

- 3 Na + ions are sent outside the axon and 2 K + ions are sent into the axon by a sodium-potassium pump by active transport.

- The inner side of the membrane becomes electronegative (negatively charged) and the outer side becomes electropositive (positively charged) because of the movement of sodium and potassium ions. This makes the nerve fibre polarised.


Q3. Explain the following processes:

b. Depolarisation of the membrane of a nerve fibre

Answer:

  • When the nerve fibre is stimulated, it is said to be in a depolarised state.
  • In a depolarised state, the membrane of the nerve fibre experiences an action potential.
  • The following steps take place during the process of depolarization of the membrane of a nerve fibre:
  • In a polarised state, the axon has more concentration of K + ions and outside the axon, the concentration of Na + ions is more.
  • When the nerve fibre gets excited by the stimulus, the permeability of the membrane for Na +ions and K + ions is reversed.
  • The membrane becomes highly permeable for Na + ions.
  • There is a rapid influx of Na + ions into the axon.
  • This makes the inner side of the membrane positively charged and the outside of the membrane becomes negatively charged.
  • This results in depolarization of the membrane of the nerve fibre and its experiences an action potential.

Q3. Explain the following processes:

c. Conduction of a nerve impulse along with a nerve fiber

Answer:

- A nerve impulse is conducted across the length of a nerve fibre in an organized manner.

- On the nerve fibre during the conduction of an impulse, a region is always depolarised and a region next to it will be polarised. To send the impulse forward, the depolarised region repolarizes and the polarised region depolarises. This is repeated across the length of the nerve fibre which helps in the conduction of impulse.

- It occurs in the following steps:

- At a depolarised region, consider site A, there will be a positive charge on the inner surface of the membrane and a negative charge on the outer surface of the membrane.

- The region next to it which is polarised, consider site B, there will be a B positive charge on the outer surface of the membrane and a negative charge on the inner surface of the membrane.

- Hence, at site A, the current will flow on the inner surface of the membrane from A to B, and at site B, the current will flow on the outer surface from B to A. This will complete the circuit of the current flow.

- This will help site B to depolarise so that the impulse is conducted to site B.

- As soon as the impulse is conducted to site B, site A will get depolarised.

- When site B will be in the depolarised state, the region next to it, consider site C, will be polarised.

Q3. Explain the following processes:

d.Transmission of a nerve impulse across a chemical synapse

Answer:

 

  • A synapse is formed by the membranes of the pre-synaptic neuron and the postsynaptic neuron.
  • A synapse may or may not be separated by a gap which is called the synaptic cleft.
  • At a chemical synapse, the pre-synaptic and post-synaptic neurons are separated by the synaptic cleft.
  • When an impulse arrives at the axon terminal, the calcium ions present in the synaptic cleft enter the synaptic knobs present at the axon terminals of the pre-synaptic neuron.
  • The synaptic vesicles in the synaptic knobs of the pre-synaptic neuron move towards the plasma membrane and fuse with it.
  • The vesicles release the neurotransmitter acetylcholine in the synaptic cleft. (Empty synaptic vesicles return to the cytoplasm of the pre-synaptic neuron where they are refilled.)
  • The molecules of acetylcholine bind to the protein receptors present on the plasma membrane of the post-synaptic neurons.
  • This binding opens the channels and sodium ions enter the post-synaptic neuron, while potassium ions leave the post-synaptic membrane.
  • This generates an action potential in the membrane of the post-synaptic neuron, and hence, the impulse is transmitted to the post-synaptic neuron.

Q4. Draw labeled diagrams of the following:

a.Neuron

Answer: Neuron-




Q4. Draw labeled diagrams of the following:

b. Brain

Answer: Brain-

brain




Q4. Draw labeled diagrams of the following:

(c) Eye

Answer: Eye-


eye
Q13. Draw labeled in diagrams of the following:

(d) Ear

Answer: Ear-

 

ear


Q5. Write short notes on the following:

a. Neural coordination

Answer:

  • Coordination is a characteristic feature of living organisms. It is the process through which two or more organs interact and complement the functions of one another.
  • Coordination is achieved by two ways in humans and other higher-order animals—neural coordination and chemical coordination.
  • Neural coordination is carried out by highly specialized cells called neurons.
  • The neural system is a network of point-to-point connections between the neurons and the organs and it operates through nerve impulses.
  • Neural coordination is always between the stimulus and the response—receptors, and effectors.
  • All body functions are carried out and controlled by neural coordination.
  • The stimulus is received from organs such as the skin and a response is generated which is sent to the muscles or glands.
  • The previous stimulus is always stored in memory by the neural system.
  • Neural coordination helps in controlling and harmonizing voluntary actions such as running, walking, writing, and talking.
  • It helps us to remember, analyze, think and reason because the brain, a part of the neural system, is the site of intelligence.
  • All vital functions such as breathing, working of the heart, and digestion are controlled by neural coordination.
  • It helps maintain homeostasis by coordinating various metabolic activities of the body.

Q5. Write short notes on the following:

b. Forebrain

Answer:

The forebrain consists of these three: Cerebrum, Thalamus, and Hypothalamus 

Cerebrum:

  • It forms the major part of the brain.
  • The cerebrum is divided into halves longitudinally by a deep cleft. Each half is called a cerebral hemisphere.
  • Both hemispheres are connected by the corpus callosum -a tract of nerve fibres.
  • The cerebral hemispheres are hollow internally.
  • The walls of the cerebrum have an outer cortex and an inner medulla.
  • The cerebral cortex contains cell bodies of neurons and hence appears greyish. It is called grey matter.
  • The grey matter is thrown into many grooves and folds called sulci and gyri, respectively.
  • A higher number of convolutions leads to greater intelligence.
  • The cerebral cortex contains motor areas, sensory areas, and association areas. Association areas are neither sensory nor motor.
  • These areas are responsible for complex functions such as memory, communication, and intersensory associations.
  • The cerebral medulla consists of axons of nerve fibers and appears whitish. It is called white matter.
  • The inner part of the cerebral hemispheres and a group of associated deep structures such as the hippocampus and amygdala form a complex structure called the limbic lobe or limbic system.

    Functions:
  • The cerebrum is the center of intelligence, memory, consciousness, willpower, and voluntary actions.

Thalamus:

  • It is made of grey matter.
  • It is situated superior to the midbrain.

    Functions:
  • The thalamus relays motor and sensory impulses to the cerebrum.
  • It also regulates the manifestation of emotions and recognizes heat, cold, and pain.

Hypothalamus:

  • It lies at the base of the thalamus.
  • It consists of the optic chiasma, a point where the fibers of optic nerves cross to opposite sides.
  • Behind the optic chiasma is the infundibulum. It is a greyish protuberance of the hypothalamus.
  • The infundibulum holds the pituitary gland.

    Functions:
  • The hypothalamus contains the centers which control body temperature, blood pressure, and homeostasis.
  • It contains the centers to control hunger, thirst, sleep, fatigue, emotions, anger, pleasure, and penance.
  • The neurosecretory cells of the hypothalamus secrete certain hormones or releasing factors that control the activity of the pituitary hormones.
  • The hypothalamus along with the limbic system is involved in the regulation of sexual behavior.

Q5. Write short notes on the following:

c. Midbrain

Answer: The midbrain consists of cerebral peduncles and corpora quadrigemina.

Cerebral Peduncles:

  • Cerebral peduncles are fibrous thick tracts.
  • They connect the cerebrum and the cerebellum.

    Functions:
  • They relay the sensory and motor impulse between the forebrain and hindbrain.

Corpora quadrigemina:

  • On the dorsal portion of the brain, there are two pairs of solid lobes present. These lobes are called corpora quadrigemina.
  • One pair is called superior colliculi and the other pair is called inferior colliculi.

    Functions:
  • The corpora quadrigemina controls the visual reflexes. They control the movement of the head and the eye.
  • They also control auditory reflexes. They control the movement of the head to locate and detect the source of the sound.

Q5. Write short notes on the following:

d. Hindbrain

Answer: The hindbrain consists of the cerebellum, pons Varolii, and medulla oblongata:

Cerebellum:

  • It is located at the base of the cerebellum.
  • The outer cerebellar cortex is made of grey matter and the inner cerebellar medulla is made of white matter.
  • The white matter has fibre tracts that connect the cerebellum with the medulla oblongata and the cerebrum.

    Functions:
  • It coordinates muscular activity and the balance of the body.
  • The impulse of performing muscular activity originates in the cerebrum.
  • It modulates the voluntary movements initiated in the cerebrum.

Pons Varolii:

  • It is made of a thick bundle of white nerve fibers.
  • It lies above the medulla oblongata.

    Functions:
  • It coordinates the two lobes of the cerebellum.
  • The pneumatic center which controls breathing is located in the pons Varolii.

Medulla oblongata:

  • It is located at the base of the skull.
  • It is conical in shape.
  • It continues behind the brain as the spinal cord.
  • Injury to the medulla oblongata results in death.

    Functions:
  • It acts as a pathway and conducts impulses from the spinal cord to the brain.
  • It controls the activities of the internal organs, heartbeat, and breathing.

Q5. Write short notes on the following:

e.Retina

Answer:

The retina is the innermost, neurosensory, thin layer of the eyeball. The external surface of the retina is in contact with the choroid and its inner surface is in contact with the vitreous humor. The retina is the site of image formation.

  • The external surface consists of four layers: Pigmented layer:
  • This layer is made of a single layer of cells. The cells contain dark-brown pigment.
  • A layer of photoreceptor cells:
  • It contains two types of photoreceptor cells - rods and cones.

Rods:

  • Rod cells are elongated and rod-shaped.
  • They contain a purplish-red protein pigment called rhodopsin or visual purple . Rhodopsin contains a derivative of vitamin A.
  • Rods are sensitive to dim light and provide vision in dark called twilight vision or scotopic vision.
  • Rods do not respond to colors.

Cones:

  • Cone cells are sensitive to bright light and colors. Hence, they are responsible for photopic vision or daylight vision.
  • The pigment present in the cone cells is iodopsin.
  • Three kinds of cone cells respond to red, green, and blue light.
  • The other colors are detected by the simultaneous stimulation of more than one kind of cone cell.
  • When all three types of cells are stimulated simultaneously, a sensation of white light is produced.
  • Cone cells are insensitive to dim light, and hence, color cannot be recognized in the dark.

    Blindspot:
  • The optic nerve leaves the brain and the retinal blood vessels enter the brain at a point where the photoreceptor cells are absent. It is called the blind spot.

Macula lutea:

  • Lateral to the blind spot is a yellowish pigmented spot called macula lutea or yellow spot.
  • It lies exactly opposite the center of the cornea.
  • Macula lutea has a central pit called the fovea.
  • Fovea lack blood vessels and rods.
  • The fovea has only cone cells, and it is the region of the most distinct vision. e cells and it is the region of most distinct vision.

Q5. Write short notes on the following:

f. Ear ossicles

Answer:

  • Three small bones called ear ossicles are present in the tympanic cavity of the middle ear.
  • They are malleus, incus and stapes.
  • The handle of the malleus is attached to the central part of the tympanic membrane which is called the umbo.
  • The other end of the malleus is attached to the incus by ligaments.
  • The incus on its other end is attached to the stapes by ligaments.
  • The other end of the stapes covers an opening called fenestra ovalis or the oval window of the cochlea.
  • Ear ossicles transfer the vibration from the external ear to the inner ear.

Q5. Write short notes on the following:

(g) cochlea:

Answer:

  • The cochlea is a bony coiled structure. It is the part of the inner ear. It arises from the saccule.
  • The cochlear cavity is divided into three chambers by the two membranes-Reisnner's membrane and basilar membrane.
  • The upper chamber is called the fiber scalehumorfall vestibule, the middle chamber is scala media and the lower chamber is scala tympani.
  • Scala tympani and scala vestibule are filled with the perilymph, while scala media is filled with the endolymph.
  • The basilar membrane bears the organ of Corti.
  • The organ of Corti is connected with the nerve fibers of the auditory nerve which connects to the brain.
  • The organ of Corti is the organ of hearing.

Q5. Write short notes on the following:

h. Organ of Corti

Answer:

- It is the organ of hearing. It is located on the basilar membrane of the inner ear.

-It contains hair cells which are auditory receptor cells.

-These cells are present in rows on the internal side of the organ.

-The apical ends of the hair cells have processes called stereocilia.

-The basal parts of the hair cells have synaptic contacts with the afferent nerve fibers.

-Above the rows of hair cells is a smooth gelatinous layer called the tectorial membrane.


Q5. Write short notes on the following:

i. Synapse

Answer:

Synapse:

-A synapse is formed by the membranes of the pre-synaptic neuron and the postsynaptic neuron.

-A synapse may or may not be separated by a gap which is called the synaptic cleft.

-There are two kinds of synapses-electrical synapse and chemical synapse.

Q6. Give a brief account of:

a. Mechanism of synaptic transmission

Answer:

-The mechanism of synaptic transmission at the electrical synapse:

- In this case, the pre-synaptic and post-synaptic membranes are in proximity.

- Impulse in the form of electric current directly flows from the pre-synaptic neuron to the post-synaptic neuron.

- Transmission is faster than the chemical synapse. four-fifths labeled in fibers the mechanism of synaptic transmission at the chemical synapse:

- The pre-synaptic and post-synaptic neurons are separated by the synaptic cleft.

- When an impulse arrives at the axon terminal, the calcium ions present in the synaptic cleft enter the synaptic knobs present at the axon terminals of the pre-synaptic neuron.

- The synaptic vesicles present in the synaptic knobs present in the pre-synaptic neuron move towards the plasma membrane and fuse with it.

- The vesicles release the neurotransmitter acetylcholine in the synaptic cleft. (Empty synaptic vesicles return to the cytoplasm of the pre-synaptic neuron where they are refilled.)

- The molecules of acetylcholine bind to the protein receptors present on the plasma membrane of the post-synaptic neurons.

- This binding opens the channels, and sodium ions enter the post-synaptic neuron, while potassium ions leave the post-synaptic membrane.

-This generates an action potential in the membrane of the post-synaptic neuron, and hence, the impulse is transmitted to the post-synaptic neuron.

Q6. Give a brief account of:

a. Mechanism of vision

Answer:

  • The light rays pass through the pupil, lens, aqueous humor, vitreous humorfallrecognized on the retina.
  • The light induces the dissociation of the photo-pigment rhodopsin into opsin and retinal.
  • The dissociation of opsin from the retinal brings changes in the structure of opsin.
  • This generates an action potential in the rods and cones of the retina.
  • The action potential is further transmitted to the ganglion cells through bipolar neurons.
  • It is finally transmitted to the visual cortex of the brain via the optic nerve.
  • The impulses are analyzed at the visual cortex and the responses are sent back to form the image on the retina.

Q6. Give a brief account of:

b. Mechanism of hearing

Answer:

Mechanism of hearing is given below:

  • Sound waves are collected by the pinna of the external ear.
  • The waves pass through the external auditory meatus to the eardrum.
  • The eardrum begins to vibrate.
  • The vibrations through the air drum are passed on to the malleus, incus, and stapes of the middle ear. Here, the frequency of vibrations increases.
  • Through the oval window, vibrations are further passed to the cochlea of the inner ear.
  • The vibrations set in the endolymph of the cochlea induce vibrations in the basilar membrane.
  • Vibrations of the basilar membrane cause sensory hair of the organ of Corti to vibrate.
  • The receptor hair cells press themselves against the tectorial membrane which converts the sound energy into the action potential or nerve impulse.
  • The nerve impulse is transmitted to the auditory cortex of the brain.
  • The impulses are analyze cortex and the sound is recognised.

Q7. Answer briefly:

a. How do you perceive the color of an object?

Answer:

Cone cells present in the retina of the eye are responsible for color vision. Three kinds of cone cells respond to red, green, and blue light. Different cone cells get stimulated at different wavelengths of light. The other colors are detected by the simultaneous stimulation of more than one kind of cone cells. When all three types of cells are stimulated simultaneously, a sensation of white light is produced.

Q7. Answer briefly:

b. Which part of our body helps us in maintaining body balance?

Answer:

Crista ampullary present in the three semicircular canals, the macula utriculi present in the utricle, and the macula sacculi present in the saccule of the inner ear help us in maintaining body balance.

Q7. Answer briefly:

c. How does the eye regulate the amount of light that falls on the retina?

Answer:

Light enters the eye through the pupil, an aperture present in the center of the iris. The iris has two types of muscles-circular smooth muscles and radial smooth muscles-which regulate the amount of light that falls on the retina.

The smooth circular muscles contract in bright light which makes the pupil smaller in size; hence, the lesser amount of light falls on the retina. In the dim light, the pupil is widened by the contraction of radial smooth muscles so that a sufficient amount of light falls on the retina.

Q8. Explain the following:

(a) Role of Na+ in the generation of the action potential.

Answer: Sodium ions diffuse from the outside to the intracellular fluid because of the electrochemical gradient. The potassium ions move out, and the membrane becomes negatively charged from outside and positively charged from inside. This sudden change in the membrane potential is called the action potential, and the membrane is said to be depolarised.

Q8. Explain the following:

( b) Mechanism of generation of light-induced impulse in the retina.

Answer: The photosensitive compounds (photopigments) in the human eye are composed of opsin and retinal. Light induces dissociation of retinal and opsin which changes the structure of opsin. It generates an action potential in the bipolar neurons. These impulses/action potentials are transmitted by the optic nerves to the visual cortex of the brain where the neural impulses are analyzed and the erect image is recognized.

Q8. Explain the following:

(c) Mechanism through which a sound produces a nerve impulse in the inner ear.

Answer: From the perilymph, the vibrations are transferred to the scala vestibuli of the cochlea and then to the scala media through Reissner's membrane and stimulate the sensory hair of the organ of Corti. The impulses thus received by the hair cells are carried to the brain through the auditory nerve where the sensation of hearing is felt.

Q9. Differentiate between: (a) Myelinated and non-myelinated axons

Answer:

 

Myelinated Axons

 

Non-myelinated Axons

 

1. Myelin sheath is present.

 

1. Myelin sheath is absent.

 

2. Nodes of Ranvier are present.

 

2. Nodes of Ranvier are absent.

 

It is found in the grey matter of the brain, spinal cord, and autonomous nervous system.

 

3. It is found in the white matter of the brain, spinal cord, and autonomous nervous system.

 

4. The conduction of nerve impulses is node to node.

 

4. The conduction of nerve impulses is smooth.

 

5. The speed of conduction of impulse is 50 times faster than in non-myelinated axons.

 

5. The speed of conduction of impulse is slow.



Q9. Differentiate between: (b) Dendrites and axons

Answer:

 

Dendrites

 

Axons

 

1. They are short processes.

 

1. Axons are long processes.
 

 

2. Dendrites carry impulses towards the cell body of the neuron.

 

2. Axons carry impulses away from the cell body of the neuron.

 

3. Dendrites are always branched.

 

3. Axons may or may not be branched.

 

4. Nissl's granules are present in the neuroplasm.

 

4. Nissl's granules are absent in the neuroplasm.


Q9. Differentiate between:

c. Rods and cone

Answer:

 

Rods

 

Cones

 

1. They are sensitive to dim light.

 

1. They are sensitive to bright light.

 

2. Rods contain the pigment rhodopsin.

 

2. Cones contain the pigment iodopsin.

 

3. They have no role to play in color vision.

 

3. They are responsible for color vision.

 

4. Only one kind of rod exist.

 

4. There are three kinds of cones-red, blue and green.

Q9. Differentiate between:

d. Thalamus and Hypothalamus

Answer:

 

Thalamus

 

Hypothalamus

 

1. It is made of only grey matter.

 

1. It is made of white and grey matter.

 

2. The thalamus does not secrete any hormone.

 

2. The hypothalamus secretes certain hormones which control the activity of the pituitary gland.

 

3. It is situated superior to the midbrain.

 

3. It is situated at the base of the thalamus.

 

4. It contains the centers of sensations such as heat, cold, and pain.

 

4. It contains the centers which control body temperature, blood pressure, and homeostasis.


Q9. Differentiate between:

e. Cerebrum and Cerebellum

Answer:

 

Cerebrum

 

Cerebellum
 

 

1. It is the largest part of the brain.

 

1. It is the second-largest part of the brain.

 

2. It is part of the forebrain.

 

2. It is part of the hindbrain.

 

3. The cerebrum is divided into two cerebral hemispheres.

 

3. The cerebellum is divided into three lobes- the central vermis and the two lateral cerebellar hemispheres.

 

4. It is the site of memory and intelligence.

 

4. It is the site of body equilibrium and posture.



Q10. Answer the following:

a. Which part of the ear determines the pitch of a sound?

Answer: The cochlea determines the pitch of a sound.

Q10. Answer the following:

b. Which part of the human brain is the most developed?

Answer: The cerebrum is the most developed.

Q10. Answer the following:

c.Which part of our central neural system acts as a master clock?

Answer: The hypothalamus of the central neural system acts as a master clock.


Q11. The region of the vertebrate eye, where the optic nerve passes out of the retina, is called

     a) fovea    b) iris   c) blind spot     d) optic chaisma

Answer:

c) Blind spot 

The region of the vertebrate eye, where the optic nerve passes out of the retina, is called the blind spot. Photoreceptors are absent in this region.

 

Q12. Distinguish between:

a. afferent neurons and efferent neurons

Answer:

 

Afferent Neurons

 

Efferent Neurons

 

1. They conduct sensory impulses from the receptors to the central nervous system.

 

 1. They conduct motor impulses from the central  nervous system to the effector organs such as muscles.

 

2. They are present in the sense organs.



 

2. They are present in the brain and the spinal cord.

 

3. They are sensory neurons.

 

3. They are motor neurons.


Q12. Distinguish between:

b. impulse conduction in a myelinated nerve fibre and unmyelinated nerve fibre

Answer:

 

Impulse Conduction in a Myelinated Nerve Fibre

 

Impulse Conduction in Non-myelinated Nerve Fibre

 

1. Impulse travels from node to node.

 

1. Impulse travels along the length of the entire nerve fibre.

 

2. The speed of conduction is 50 times faster than the non-myelinated nerve fibre.

 

2. The speed of conduction is slower.

 

3. Energy expenditure during impulse transmission is less.

 

3. Energy expenditure during impulse transmission is more.



Q12. Distinguish between:

c. aqueous humor and vitreous humor

Answer:

 

Aqueous Humour

 

Vitreous Humour

 

1. It is present in the aqueous chamber between the lens and the cornea.

 

1. It is present in the vitreous chamber between the lens and the retina.

 

2. It is secreted by the ciliary processes.

 

2. It is secreted by the retina of the eye.

 

3. It is a jelly-like fluid.

 

3. It is watery fluid.

 

4. It supports the lens.

 

4. It supports the lens and retina.

Q12. Distinguish between:

d. blind spot and yellow spot

Answer:

 

Blind Spot

 

Yellow Spot

 

 

1. It is the point on the retina at which the optic nerve leaves the eye and retinal blood vessels enter the eye.

 

1. It is the point on the retina which lies exactly opposite the center of the cornea.

 

2. It is void of photoreceptor cells.

 

2. It contains two kinds of photoreceptor cells-rods and cones.

 

3. It is insensitive to light.

 

3. It is very sensitive to light.

 

4. It has no function concerning vision.

 

4. It is the area of the most distinct vision.

 

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Also See    
NCERT Solutions for Class 11 Biology Chapter 1 - The Living World NCERT Solutions for Class 11 Biology Chapter 2 - Biological Classification NCERT Solutions for Class 11 Biology Chapter 3 - Plant Kingdom
NCERT Solutions for Class 11 Biology Chapter 4 - Animal Kingdom NCERT Solutions for Class 11 Biology Chapter 5 - Morphology of Flowering Plants NCERT Solutions for Class 11 Biology Chapter 6 - Anatomy of Flowering Plants
NCERT Solutions for Class 11 Biology Chapter 7 - Structural Organization in Animals NCERT Solutions for Class 11 Biology Chapter 8 - Cells: The Unit of Life NCERT Solutions for Class 11 Biology Chapter 9 - Biomolecules
NCERT Solutions for Class 11 Biology Chapter 10 - Cell Cycle and Division NCERT Solutions for Class 11 Biology Chapter 11 - Transport in Plants NCERT Solutions for Class 11 Biology Chapter 12 - Mineral Nutrition
NCERT Solutions for Class 11 Biology Chapter 13 - Photosynthesis in Higher Plants NCERT Solutions for Class 11 Biology Chapter 14 - Respiration in Plants NCERT Solutions for Class 11 Biology Chapter 15 - Plant Growth and Development
NCERT Solutions for Class 11 Biology Chapter 16 - Digestion and Absorption NCERT Solutions for Class 11 Biology Chapter 17 - Breathing and Exchange of Gases NCERT Solutions for Class 11 Biology Chapter 18 - Body Fluids and Circulation
NCERT Solutions for Class 11 Biology Chapter 19 - Excretory Products and their Elimination NCERT Solutions for Class 11 Biology Chapter 20 - Locomotion and Movement NCERT Solutions for Class 11 Biology Chapter 22 - Chemical Coordination and Integration

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