NCERT Solved Exercise Questions – Class 11 Biology Chapter 21 Neural Control and Coordination

21.1 Briefly describe the structure of the following:
(a) Brain
(b) Eye
(c) Ear

Ans – (a) Brain: The brain serves as the body’s primary coordination centre. It is a component of the nervous system, which regulates and keeps track of each body organ. The cerebral meninges, which are composed of an inner layer called pia mater, a thin middle layer called arachnoid, and an outside layer called dura mater, provide excellent protection for it.

There are three parts to it: the forebrain, midbrain, and hindbrain.

The forebrain is the portion of the brain responsible for thought. The cerebrum, thalamus, and hypothalamus make up this structure.
Cerebrum:

The brain’s main region, the cerebrum, makes up around one-fourth of its weight. A deep longitudinal cerebral fissure separates the brain’s two hemispheres. The corpus callosum, a bundle of nerve fibres, connects these hemispheres. A layer of cells called the cerebral cortex, also referred to as grey matter, covers the cerebral hemispheres. The cerebrum contains motor regions that direct the action of different muscles as well as sensory regions known as association areas that receive sensory impulses from diverse receptors. The white matter, which makes up the innermost layer of the brain, gives the layer an opaque white appearance.

Thalamus: The main centre for coordinating sensory and motor signalling is the thalamus. It is encased in the cerebrum.

Hypothalamus: This structure, which is located at the base of the thalamus, houses a variety of centres that control body temperature as well as the need to eat and drink. Along with the hypothalamus, several areas of the brain are involved in controlling sexual behaviour and the expression of emotions including excitement, pleasure, fear, etc.

Between the pons region of the hindbrain and the thalamus portion of the forebrain is the midbrain. Superior and inferior corpora bigemina as well as corpora quadrigemina, four circular lobes, make comprise the dorsal surface of the midbrain. The cerebral aqueduct, a canal, runs through the midbrain. The senses of hearing and sight are handled by the midbrain.

The pons, cerebellum, and medulla oblongata make up the hindbrain.

(a) The Pons is a band of nerve fibres that connects the midbrain to the medulla oblongata. It links the lateral cerebellar hemisphere regions together.

(b) The cerebellum is a sizable and fully formed portion of the hindbrain. It is situated above the medulla oblongata and under the posterior sides of the cerebral hemispheres. It is in charge of preserving the posture and equilibrium of the body.

(B) The eye: Eyes are three-layered, spherical structures.

(a) Sclera and cornea make up the outer layer.

(i) The sclera, also referred to as the eye’s white, is an opaque tissue. A thick connective tissue makes up its structure.

(ii) The anterior, transparent section of the eye known as the cornea lacks blood veins and is supplied with lymph from the surrounding region. It has a tiny forward bulge that aids the lens in focussing light rays.

(b) The choroid, ciliary body, and iris are located in the middle layer of the eye, which is vascular in nature.

(i) The choroid, which is located close to the sclera and is home to a large number of blood vessels, supplies the retina and other tissues with nutrients and oxygen.

(ii) The ciliary body is formed by the thickening of the anterior area of the choroid layer, which is thin over the posterior region. It has ciliary processes, ciliary muscles, and blood vessels.

(iii) Iris: The ciliary body advances to produce a thin, coloured partition known as the iris at the intersection of the sclera and cornea. It is the part of the eye’s colour that is visible.

Just behind the iris, the eye contains a translucent, biconvex, and elastic structure. It’s called a lens. Suspensory ligaments connected to the ciliary body stabilise the lens. The eyeball is split in half by the lens, creating an anterior aqueous and posterior vitreous chamber.

(C) Ear: The ear is a sensory organ used for both hearing and balance. The external ear, middle ear, and internal ear are its three component parts.

The outer ear

The pinna, external auditory meatus, and tympanic membrane make up this structure.

(a) The pinna is a delicate organ that gathers vibrations and directs them into the ear to make sound.

(b) An external ear tube supported by cartilage is known as the external auditory meatus.

Middle ear:

It is a tympanic chamber that is filled with air and connected to the pharynx by a eustachian tube. The Eustachian tube aids in balancing the air pressure on the tympanic membrane’s two sides. The ear ossicles, a flexible chain of three middle bones, are located inside the middle ear. The malleus, incus, and stapes are the three ear ossicles that are joined together.

The inner ear

Labyrinth is another name for it. There are two types of labyrinths: a bony labyrinth and a membranous labyrinth. Perilymph fills a bony labyrinth, whereas endolymph fills a membrane labyrinth. The membraneous labyrinth is split into two sections.

(a) Vestibular apparatus

The core, sac-like vestibular apparatus is separated into the utriculus and sacculus. The sacculus and utriculus contain a particular class of sensory cells known as macula.

Three semi-circular canals are also part of the vestibular apparatus. A protruding ridge known as the crista ampularis can be found at the lower end of each semicircular canal. The crista, a collection of sensory cells, are found in each ampulla. The body’s balance and posture are kept in check by the crista and macula.

(b) Cochlea:

The cochlea is a long, coil-like extension of the sacculus. It is the primary organ of hearing. The cochlea has three membranes. On the basilar membrane, which has hair cells, is where the organ of corti, a hearing organ, is situated.

21.2. Compare the following:
(a) Central neural system (CNS) and Peripheral neural system (PNS)
(b) Resting potential and action potential
(c) Choroid and retina

Ans – (a)

(b)

(c)

21.3. 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

Ans – (a) When a neuron is at rest, or not conducting any impulses, it has a high concentration of K+ and negatively charged proteins inside the axon and a low quantity of Na+. In contrast, there is a concentration gradient in the fluid outside the axon due to the low K+ and high Na+ concentrations. The sodium-potassium pump, which moves 3 Na+ outward in exchange for 2K+ entering the cell, actively transports ions to maintain these ionic gradients across the resting membrane. As a result, the axonal membrane’s inner surface acquires a negative charge and becomes polarised, while the membrane’s exterior has a positive charge.

(b) The polarised membrane at site A becomes freely permeable to Na+ when a stimulus is administered to that site (for example, site A). As a result, there is an immediate influx of Na+ and polarity is reversed at that location, causing the membrane’s outside surface to become negatively charged and its inner side to become positively charged. Thus, the membrane’s polarity at site A is reversed, leading to depolarization.

(c) Nerve impulse travel along a nerve fibre:

1. The membrane at site A of the polarised membrane becomes freely permeable to Na+ when a stimulus is administered to that location.

2. As a result, a sudden input of Na+ reverses polarity.

3. The membrane becomes depolarized once the polarity is reversed.

4. The plasma membrane’s electrical potential difference at the location 5. A is referred to as the action potential, often known as a nerve impulse.

6. The axon membrane (site B) is negatively charged on the inside and positively charged on the outside. As a result, a current moves from site A to site B along the inner surface.

(d) A nerve impulse crossing a chemical synapse

A synapse is a tiny space that exists between the final segment of one neuron’s axon and the dendrite of the following neuron. Vesicles made of a chemical substance or neurotransmitter, such as acetylcholine, fuse with the plasma membrane when an impulse reaches the end plate of an axon. This substance travels over the cleft and binds to chemo-receptors found on the membrane of the subsequent neuron’s dendrite. When a chemical binds to chemo-receptors, the membrane depolarizes and a nerve impulse is produced across the nerve fibre.

The enzyme acetylcholinestrase inactivates the substance, acetylcholine. The post synaptic membrane of the dendrite contains the enzyme.

This hydrolysis of acetylcholine enables the membrane to repolarise.

21.4. Draw labelled diagrams of the following:
(a) Neuron
(b) Brain
(c) Eye
(d) Ear

Ans –

(a) Neuron

(b) Brain

(c) Eye

(d) Ear

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

Ans – (a) Coordinated neural activity

The body’s organs can quickly coordinate thanks to the neurological system. Electric impulses are used to coordinate in this fast and fleeting manner. The body’s physiological functions are all interconnected and interdependent. For instance, our body needs more food and oxygen when we are exercising. As a result, the heartbeat quickens and breathing rate rises naturally. As a result, the muscles receive oxygenated blood more quickly. Furthermore, constant regulation is needed for cellular processes. The hormones are responsible for performing these tasks. Therefore, the neural system and endocrine system work together to regulate and coordinate physiological processes.

(b) Frontal lobe

It is the brain’s primary thinking region. The cerebrum, thalamus, and hypothalamus make up this structure.

(i) Cerebrum :

The brain’s main region, the cerebrum, makes up around one-fourth of its weight. A deep longitudinal cerebral fissure separates the brain’s two hemispheres. The corpus callosum, a bundle of nerve fibres, connects these hemispheres. A layer of cells called the cerebral cortex, also referred to as grey matter, covers the cerebral hemispheres. The cerebrum contains motor regions that direct the action of different muscles as well as sensory regions known as association areas that receive sensory impulses from diverse receptors. The layer’s appearance is made by the deepest region of the cerebrum, which is referred to as the white matter.

Midbrain (c)

It is situated halfway between the pons of the hindbrain and the thalamus hypothalamus of the forebrain.
The corpora quadrigemina, or dorsal section of the midbrain, is made up of four tiny lobes.
The cerebral aqueduct, which runs through the midbrain. neural coordination and control.

(d) The hindbrain

Pons, cerebellum, and medulla oblongata make up this structure.
The surface of the cerebellum is highly convoluted, creating extra room for many more neurons.
The portion that continues as a spinal cord is the medulla.
The medulla is home to the centres that regulate breathing, heartbeat, and stomach secretions.

(e) Retina

The innermost layer is the retina. Inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells make up its three layers of cells. Rod cells and cone cells are the two different types of receptor cells found in the retina.

(i) Rod cells – Rhodopsin pigment, which is visible as purple and is extremely sensitive to low light, is found in the rods. Twilight vision is a result of it.

(ii) Cone cells. Cones are highly sensitive to intense light and contain the pigment iodopsin (visual violet). They are in charge of our colour and day vision.

(f) Ear ossicles

The ear ossicles, a flexible chain of three middle bones, are located inside the middle ear. These are the three ossicles in the three ears.

(i) Malleus

(ii) Incus

(iii) Stapes

On one side, the malleus is joined to the tympanic membrane, and on the other, to the incus. The stapes and incus are linked. Stapes are connected to the internal ear’s fenestra ovalis, an oval membrane. In order to convey sound waves from the external ear to the internal ear, the ear ossicles function like a lever.

(g) Cochlea :

The bony and membranous labyrinths are the two components of the fluid-filled inner ear known as the labyrinth. Cochlea is the name for the labyrinth’s coils.
The lower scala tympani and upper scala vestibuli of the surrounding perilymph-filled bone labyrinth are separated by the reissner’s and basilar membranes, which make up the cochlea.
Endolymph is present in the scala media, a region of the cochlea. The scala tympani stops at the round window that opens to the middle ear at the base of the cochlea, while the scala vestibuli ends at the oval window.

(h) Organ of corti

The hearing organ is part of the cortex. It can be found on the basilar membrane, which is home to hair cells. Hearing receptors are hair cells. They can be found on the cortical organ’s internal side.

(i) Synapse

A synapse is a point where the dendrite of one neuron meets the axon terminal of another neuron. It is divided by a tiny opening called a synaptic cleft.

Synapses come in two different flavours.

(a) Electrical synapse

(b) Chemical synapse

The pre and post synaptic neurons are located close to one another in electrical synapses. As a result, the impulse can pass directly through the synapse between two neurons.

21.6. Give a brief account of:
(a) Mechanism of synaptic transmission
(b) Mechanism of vision
(c) Mechanism of hearing

Ans – (a) Synaptic transmission mechanism

A synapse is the intersection of two neurons. It exists where a fissure separates the dendrite of one neuron from the axon terminal of the following neuron.

Synaptic transmission can occur in one of two ways.

(1) Transmission of chemicals

(2) Transmission of electricity

Chemical transmission – An electrical impulse releases the neurotransmitter acetylcholine across the synaptic cleft when it reaches the end plate of the axon. This substance is produced in the neuron’s cell body and then transferred to the axon terminal. Acetylcholine diffuses through the cleft and attaches to receptors on the membrane of the following neuron. The membrane becomes depolarized as a result, starting an action potential.

2. Electrical transmission – A neuronal electric current is created in this sort of transmission. An action potential is produced by this electric current, which causes a nerve impulse to travel across the nerve fibre. Compared to the chemical mechanism of transmission, this is a quicker method of nerve conduction.

(b) The visual system

The retina is the eye’s innermost layer. Inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells make up its three layers of cells. Opsin, a protein, and retinal, a vitamin A aldehyde, make up the photoreceptor cell. Retinal from opsin protein separates when light rays are focused on the retina through the cornea. As a result, opsin’s structure is altered. As opsin’s structure alters, the permeability of membrane changes, generating a potential difference in the cells.

(c) Hearing mechanisms

The external region’s pinna gathers sound waves and guides them into the external auditory canal or eardrum. The tympanic membrane vibrates when these waves hit it. The three ear ossicles known as malleus, incus, and stapes then send these vibrations to the oval window, fenestra ovalis. These ear ossicles serve as a lever to send sound waves to the inner ear. The cochlear fluid receives these fenestra ovalis vibrations. The lymph produces sound waves as a result. The basilar membrane trembles as a result of wave production. The sensory hair cells of the cortical organ are bent by this motion against the tectorial membrane. This causes sound waves to transform into nerve impulses.

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

Ans – (a) Rods and cones are photoreceptor cells that contain photopigments, which are light-sensitive proteins. Cones are responsible for our ability to see in the daytime and in colour. Cones come in three different varieties, and they all react to red, green, and blue lights. These cones’ photopigments and diverse combinations of them result in the perception of distinct colours. White light is felt when both of these cones are equally activated.

(b) The vestibular apparatus’s specialised receptors, the crista and macula, are in charge of preserving the body’s equilibrium.

(c) The eye’s pupil serves as an aperture. This controls how much light falls on the retina by expanding in low-light conditions and contracting in high-light conditions.

21.8. Explain the following:
(a) Role of Na+ in the generation of action potential.
(b) Mechanism of generation of light-induced impulse in the retina.
(c) Mechanism through which a sound produces a nerve impulse in the inner ear.

Ans – (a) The polarised membrane at site A becomes freely permeable to Na+ when a stimulus is provided there (for example, at site A). As a result, there is a sudden inflow of Na+ and polarity is reversed at that location, causing the membrane’s outside surface to become negatively charged and its inner side to become positively charged. Thus, the membrane’s polarity at site A is reversed, leading to depolarization. Thus, across the plasma membrane, an action potential is produced.

(b) The visible wavelength light rays focused on the retina by the cornea and lens create potentials (impulses) in the rods and cones. Opsin and retinal make up the photosensitive substances (photopigments) in human eyes. The opsin’s structure is altered when light causes the retina and opsin to separate. Changes in membrane permeability result from this.

(c) Hearing mechanism: Sound waves are picked up by the external ear and sent to the eardrum. In reaction to sound waves, the eardrum vibrates, and these vibrations are carried to the oval window by the ear ossicles. The cochlea’s fluid receives the vibrations through the oval window, where they create waves that travel to the lymphs.

The basilar membrane trembles as a result of the lymphatic waves. The hair cells are bent by these basilar membrane movements and are pressed up against the tectorial membrane. As a result, the connected afferent neurons produce nerve impulses. The afferent fibres send these impulses to the auditory cortex of the brain, where they are analysed and translated into speech.

21.9. Differentiate between:
(a) Myelinated and non-myelinated axons
(b) Dendrites and axons
(c) Rods and cones
(d) Thalamus and Hypothalamus
(e) Cerebrum and Cerebellum

Ans –

Differnces of the following

21.10. 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?

Ans -(a) The apparent fundamental frequency of a sound is represented by pitch . A listener’s subjective perception of pitch involves placing heard tones in relation to one another on a musical scale, mostly based on the frequency of vibration. It might be claimed that the cerebral cortex perceives the pitch of the sound because it is the temporal lobe of the brain that ultimately perceives spund.

(b) Cerebral cortex

(c) Hindbrain

21.11. The region of the vertebrate eye, where the optic nerve passes out of the retina, is called the
(a) fovea
(b) iris
(c) blind spot
(d) optic chaisma

Ans – (c) blind spot

21.12. 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
(f) cranial nerves and spinal nerves.

Ans-