Gujarat Board Textbook Solutions Class 11 Biology Chapter 21 Neural Control and Coordination

Gujarat Board GSEB Textbook Solutions Class 11 Biology Chapter 21 Neural Control and Coordination Textbook Questions and Answers.

Gujarat Board Textbook Solutions Class 11 Biology Chapter 21 Neural Control and Coordination

GSEB Class 11 Biology Neural Control and Coordination Text Book Questions and Answers

Question 1.
Briefly describe the structure of the following:

1. Brain
2. Eye
3. Ear

Answer:
1. Brain: The human brain is well protected by the skull. Inside the skull, the brain is covered by cranial meninges consisting of an outer layer called dura mater, a very thin middle layer called arachnoid, and an inner layer (which is in contact with the brain tissue) called the pia mater. The brain can be divided into three major parts:

• Forebrain
• Midbrain
• Hindbrain

The forebrain consists of the cerebrum, thalamus, and hypothalamus. The midbrain is located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain. The hindbrain comprises the pons, cerebellum, and medulla.

2. Eye: The adult human eyeball is nearly a spherical structure. The wall of the eyeball is composed of three layers. The external layer is composed of dense connective tissue and is called the sclera. The anterior portion is called the cornea. The middle layer, the choroid, contains many blood vessels and looks bluish in color. The choroid layer is thin over the posterior two-thirds of the eyeball, but it becomes thick in the anterior part to form the ciliary body.

The ciliary body itself continues forwards to form a pigmented and opaque structure called the iris which is the visible colored portion of the eye. The eyeball contains a transparent crystalline lens which is held in place by ligaments attached to the ciliary body. In front of the lens, the aperture surrounded by the iris is called the pupil. The diameter of the pupil is regulated by the muscle fibers of the iris.

The inner layer is the retina and it contains three layers of cells, i.e., from inside to outside, ganglion cells, bipolar cells, and photoreceptor cells. There are two types of photoreceptor cells, namely, rods and cones. These cells contain the light-sensitive proteins called photopigments. The daylight (photopic) vision and color vision are functions of cones and the twilight (scotopic) vision is the function of the rods. They contain a purplish- red protein called the rhodopsin or visual purple, which contains a derivative of vitamin A. In the human eye, there are three types of cones that possess their own characteristic photopigments that respond to red, green, and blue lights.

The optic nerves leave the eye and the retinal blood vessels enter it at a point medial to and slightly above the posterior pole of the eyeball. Photoreceptor cells are not present in that region and hence it is called the blind spot. At the posterior pole of the eye lateral to the blind spot, there is a yellowish pigmented spot called macula lutea with a central pit called the fovea.

The space between the cornea and the lens is called an aqueous chamber and contains a thin watery fluid called aqueous humor. The space between the lens and the retina is called the vitreous chamber and is filled with a transparent gel called the vitreous humor.

3. Ear: The ear can be divided into three major sections called the outer ear, the middle ear, and the inner ear. The outer ear consists of the pinna and external auditory meatus. The pinna collects the vibrations in the air which produce sound. The external auditory meatus leads inwards and extends up to the tympanic membrane (the eardrum).

The middle ear contains three ossicles called the malleus, incus, and stapes which are attached to one another in a chain-like fashion. The malleus is attached to the tympanic membrane and the stapes is attached to the oval window of the cochlea. A Eustachian tube connects the middle ear cavity with the pharynx. The Eustachian tube helps in equalizing the pressures on either side of the eardrum.

The fluid-filled inner ear called labyrinth consists of two parts, the bony and the membranous labyrinths. The bony labyrinth is a series of channels. Inside these channels lies the membranous labyrinth, which is surrounded by a fluid called perilymph. The coiled portion of the labyrinth is called the cochlea. The’ inner ear also contains a complex system called vestibular apparatus, located above the cochlea. The vestibular apparatus is composed of three semicircular canals and the otolith organ consisting of the saccule and utricle. Each semicircular canal lies in a different plane at right angles to each other. The saccule and utricle contain a projecting ridge called macula.

Question 2.
Compare the following.

1. Central neural system (CNS) and Peripheral neural system
2. Resting potential and action potential
3. Choroid and retina

Answer:
1. The human neural system is divided into two parts, namely,

• The central neural system (CNS)
• The peripheral neural system (PNS).

The CNS includes the brain and the spinal cord and is the site of information processing and control. The PNS comprises all the nerves of the body associated with the CNS (brain and spinal cord). The nerve fibers of the PNS are of two types, namely,

• afferent fibers
• efferent fibers.

The afferent nerve fibers transmit impulses from tissues/organs to the CNS and the efferent fibers transmit regulatory impulses from the CNS to the confirmed peripheral tissues/organs.

The PNS is divided into two divisions called the somatic neural system and the autonomic neural system. The somatic neural system transmits impulses from the CNS to the involuntary organs and smooth muscles of the body. The autonomic neural system is further classified into the sympathetic neural system and parasympathetic neural system.

2. The electrical potential difference across the resting plasma membrane is called the ‘resting potential’. The electrical potential difference across the plasma membrane at site A is called the ‘action potential’, which is in fact termed as a nerve impulse.

3. The middle layer, the choroid, contains many blood vessels and looks bluish in color. The choroid layer is thin over the posterior two-thirds of the eyeball, but it becomes thick in the anterior part to form the ciliary body. The ciliary body itself continues forwards from a pigmented and opaque structure called the iris which is the visible colored portion of the eye.

The inner layer is the retina and it contains three layers of cells, i.e., from inside to outside, ganglion cells, bipolar cells, and photoreceptor cells. There are two types of photoreceptor cells, namely rods and cones. These cells contain the light-sensitive proteins called photopigments. The daylight (photopic) vision and color vision are functions of cones and the twilight (scotopic) vision is the function of the rods.

Question 3.
Explain the following processes:

1. The polarisation of the membrane of a nerve fiber
2. Depolarisation of the membrane of a nerve fiber
3. Conduction of a nerve impulse along with a nerve fiber
4. Transmission of a nerve impulse across a chemical synapse.

Answer:
1. Neurons are excitable cells because their membranes are in a polarised state. Different types of ion channels are present on the neural membrane. These ion channels are selectively permeable to different ions. When a neuron is not conducting any impulse, i.e., resting, the axonal membrane is comparatively more permeable to potassium ions (K⁺) as well as chloride ions (Cl^–) and nearly impermeable to sodium ions (Na⁺). Similarly, the membrane is impermeable to negatively charged proteins present in the axoplasm. Consequently, the axoplasm inside the axon contains a high concentration of K⁺ and negatively charged proteins and a low concentration of Na⁺.

In contrast, the fluid outside the axon contains a low concentration of K⁺, a high concentration of Na^+, and chloride ions (Cl^–) and thus forms a concentration gradient. These ionic gradients across the resting membrane are maintained by the active transport of ions by the sodium-potassium pump which transports 3Na⁺ outwards for 2K⁺ into the cell. As a result, the outer surface of the axonal membrane possesses a positive charge while its inner surface becomes negatively charged and therefore is polarised. The electrical potential difference across the resting plasma membrane is called the ‘resting potential’.

2. When a stimulus is applied at a site on the polarised membrane, the membrane at site A becomes freely permeable to Na⁺. This leads to a rapid influx of Na⁺ followed by the reversal of the polarity at that site i.e., the outer surface of the membrane becomes negatively charged and the inner side becomes positively charged. The polarity of the membrane at site A is thus reversed and hence depolarised. The electrical potential difference across the plasma membrane at site A is called the ’action potential’, which is in fact termed as a nerve impulse.

At sites immediately ahead, the axon (e.g., site B) membrane has a positive charge on the outer surface and a negative charge on its inner surface. As a result, a current flows on the inner surface from site A to site B. On the outer surface, current flows from site B to site A to complete the circuit of current flow. Hence, the polarity at the site is reversed, and an action potential is generated at site B.

3. The mechanisms of generation of nerve impulse and its conduction along an axon. When a stimulus is applied at a site on the polarised membrane, the membrane at site A becomes freely permeable to Na⁺. This leads to a rapid, influx of Na⁺ followed by the reversal of the polarity at that site i.e., the outer surface of the membrane becomes negatively charged and the inner side becomes positively charged.

4. Transmission of an impulse across electrical synapses is very similar to impulse conduction along a single axon. Impulse transmission across an electrical synapse is always faster than that across a chemical synapse. Electrical synapses are rare in our system. A nerve impulse is transmitted from one neuron to another through junctions called synapses.

A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which may or may not be separated by a gap called the synaptic cleft. There are two types of synapses, namely, electrical synapses and chemical synapses. At electrical synapses, the membranes of pre and post-synaptic neurons are in very close proximity. Electrical current can flow directly from one neuron into the other across these synapses.

At a chemical synapse, the membranes of the pre and post-synaptic neurons are separated by a fluid-filled space called the synaptic cleft. Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses.

Question 4.
Draw labeled diagrams of the following

1. Neuron
2. Brain
3. Eye
4. Ear

Answer:
(1)

(2)

(3)

(4)

Question 5.
Write short notes on the following:

1. Neural coordination
2. Forebrain
3. Midbrain
4. Hindbrain
5. Retina
6. Ear ossicles
7. Cochlea
8. Organ of Corti
9. Synapse

Answer:
1. Neural coordination: Coordination is the process through which two or more organs interact and complement the functions of one another. For example, when we do physical exercises, energy demand is increased for maintaining an increased muscular activity. The supply of oxygen is also increased. The increased supply of oxygen necessitates an increase in the rate of respiration, heartbeat, and increased blood flow via blood vessels. When physical exercise is stopped, the activities of nerves, lungs, heart, and kidney gradually return to their normal conditions.

Thus, the function of muscles, lungs, heart, blood vessels, kidney,s, and other organs are coordinated while performing physical exercises. In our body, the neural system and the endocrine system jointly coordinate and integrate all the activities of the organs so that they function in a synchronized fashion. The neural system provides an organized network of point to point connections for quick coordination. The endocrine system provides chemical integration through hormones.

2. Forebrain: The forebrain consists of the cerebrum, thalamus, and hypothalamus. The cerebrum forms the major part of the human brain. A deep cleft divides the cerebrum longitudinally into two halves, which are termed as the left and right cerebral hemispheres. The hemispheres are connected by a tract of nerve fibers called the corpus callosum. The layer of cells which covers the cerebral hemisphere is called the cerebral cortex and is thrown into prominent folds. The cerebral cortex contains motor areas, sensory areas, and large regions that are neither clearly sensory nor motor in function.

These regions called the association areas are responsible for complex functions like intersensory associations, memory, and communication. Fibers of the tracts are covered with the myelin sheath, which constitutes the inner part of the cerebral hemisphere. It is called the white matter. The cerebrum wraps around a structure called the thalamus, which is a major coordinating center for sensory and motor signaling. The hypothalamus contains a number of centers that control body temperature, eating, and drinking. It also contains several groups of neurosecretory cells, which secrete hormones called hypothalamic hormones.

3. Midbrain: The midbrain is located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain. A canal called the cerebral aqueduct passes through the midbrain. The dorsal portion of the midbrain consists mainly of four round swellings (lobes) called corpora. Midbrain and hindbrain from the brain stem.

4. Hindbrain: The hindbrain comprises pons, cerebellum, and medulla. Pons consists of fiber tracts that interconnect different regions of the brain. Cerebellum has a very convoluted surface, in order to provide additional space for many more neurons. The medulla of the brain is connected to the spinal cord. The medulla contains centers that control respiration, cardiovascular reflexes, and gastric secretions.

5. Retina: The inner layer is the retina and it contains three layers of cells, i.e., from inside to outside, ganglion cells, bipolar cells, and photoreceptor cells. There are two types of photoreceptor cells, namely, rods and cones. These cells contain the light-sensitive portions called the photopigments. The daylight (photopic) vision and color vision are functions of cones and the twilight (scotopic) vision is the function of the rods.

The rods contain a purplish red protein called the rhodopsin or visual purple, which contains a derivative, of vitamin A. In the human eye, there are three types of cones that possess their own characteristic photopigments that respond to red, green, and blue lights. The sensations of different colors are produced by various combinations of these cones and their photopigments. When these cones are stimulated equally, a sensation of white light is produced.

6. Ear ossicles: The ear ossicles increase the efficiency of transmission of sound waves to the inner ear. A Eustachian tube connects the middle ear cavity with the pharynx. The Eustachian tube helps in equalizing the pressures on either side of the eardrum.

7. Cochlear: The bony labyrinth is a series of channels. Inside these channels lies the membranous labyrinth, which is surrounded by a fluid called perilymph. The membranous labyrinth is filled with a fluid called endolymph. The coiled portion of the labyrinth into an upper scale vestibule and a lower scala tympani. The space within cochlea called scala media is filled with endolymph. At the base of the cochlea, the scala vestibule ends at the oval window, while the scala tympani terminates at the round window which opens to the middle ear.

8. Organ of Corti: The organ of Corti is a structure located on the basilar membrane which contains hair cells that act as auditory receptors. The hair cells are present in rows on the internal side of the organ of Corti. The basal end of the hair cells is in close contact with the afferent nerve fibers. A large number of processes called stereocilia are projected from the apical part of each hair cell. Above the rows of the hair cells is a thin elastic membrane called the tectorial membrane.

9. Synapse: A nerve impulse is transmitted from one neuron to another through junctions called synapses. A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which may or may not be separated by a gap called the synaptic cleft. There are two types of synapses, namely, electrical synapses and chemical synapses.

Question 6.
Give a brief account of:

1. Mechanism of synaptic transmission
2. Mechanism of vision
3. Mechanism of hearing

Answer:
1. Mechanism of synaptic transmission: Coordination is the process through which two or more organs interact and complement the functions of one another. For example, when we do physical exercises, energy demand is increased for maintaining an increased muscular activity. The supply of oxygen is also increased. The increased supply of oxygen necessitates an increase in the rate of respiration, heartbeat, and increased blood flow via blood vessels.

When physical exercise is stopped, the activities of nerves, lungs, heart, and kidney gradually return to their normal conditions. Thus, the function of muscles, lungs, heart, blood vessels, kidneys, and other organs are coordinated while performing physical exercises. In our body, the neural system and the endocrine system jointly coordinate and integrate all the activities of the organs so that they function in a synchronized fashion.

The neural system provides an organized network of point to point connections for quick coordination. The endocrine system provides chemical integration through hormones.

The transmission of an impulse across electrical synapses is very’ similar to impulse conduction along a single axon. Impulse transmission across an electrical synapse is always faster than that across a chemical synapse. Electrical synapses are rare in our system.

A nerve impulse is transmitted from one neuron to another through junctions called synapses. A synapse is fonned by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which may or may not be separated by a gap called the synaptic cleft. There are two types of synapses, namely? electrical synapses and chemical synapses. At electrical synapses, the membranes of pre and post-synaptic neurons are in very close proximity. Electrical current can flow directly from one neuron into the other across these synapses.

At a chemical synapse, the membranes of the pre and post-synaptic neurons are separated by a fluid-filled space called the synaptic cleft. Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses.

2. Mechanism of vision: The light rays in visible wavelength focus on the retina through the cornea and the lens generate potentials (impulses) in rods and cones. The photosensitive compounds (photopigments) in the human eyes are composed of opsin (a protein) and retinal (an aldehyde of vitamin A). Light induces dissociation of the retinal from opsin resulting in changes in the structure of the opsin.

This causes membrane permeability changes. As a result, potential differences are generated in the photoreceptor cells. This produces a signal that generates action potentials in the ganglion cells through the bipolar cells. These action potentials (impulses) are transmitted by optic nerves to the visual cortex area of the brain, where the neural impulses are analyzed and the image formed on the retina is recognized based on earlier memory and experience.

3. Mechanism of hearing: The external ear receives sound waves and directs them to the eardrum. The eardrum vibrates in response to the sound waves and these vibrations are transmitted through the ear ossicles (malleus, incus, and stapes) to the oval window. The vibrations are passed through the oval window on to the fluid of the cochlea, where they generate waves in the lymph.

The waves in the lymph induce a ripple in the basilar membrane. These movements of the basilar membrane bend the hair cells, pressing them against the tectorial membrane. As a result, nerve impulses are generated in the associated afferent neurons. These impulses are transmitted by the afferent fibers via auditory nerves to the auditory cortex of the brain, where the impulses are analyzed and the sound is recognized.

Question 7.
Answer briefly:

1. How do you perceive the color of an object?
2. Which part of our body helps us in maintaining the body balance?
3. How does the eye regulate the amount of light that falls on the retina?

Answer:
1. In the human eye, there are three types of cones that possess their own characteristic photopigments that respond to red, green, and blue lights. The sensations of different colors are produced by various combinations of these cones and their photopigments. When these cones are stimulated equally, a sensation of white light is produced.

2. The crista and macula are the specific receptors of the vestibular apparatus responsible for the maintenance of the balance of the body and posture.

3. The diameter of the pupil is regulated by the muscle fibers of the iris. Photoreceptors, rods, and cones regulate the amount of light that falls on the retina.

Question 8.
Explain the following:

1. Role of Na⁺ in the generation of the action potential.
2. Mechanism of generation of light-induced impulse in the retina.
3. The mechanism through which a sound produces a nerve impulse in the inner ear.

Answer:
1.This leads to a rapid influx of Na followed by the reversal of the polarity at this site i.e. the outer surface of the membrane becomes negatively charged and the inner side becomes positively charged.

2. Light induces dissociation of the retinal from opsin resulting in changes in the structure of the opsin. This causes membrane permeability changes. As a result, potential differences are generated in the photoreceptor cells. This produces 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 sorted area of the brain, where the neural impulses are analyzed and the image formed on the retina is recognized based on earlier memory and experience.

3. The vibrations are passed through the oval window on to the fluid of the cochlea, where they generate waves in the lymph. The waves movements of the basilar membrane bend the hair cells, pressing them against the tectorial membrane. As a result, nerve impulses are generated in the associated afferent neurons. These impulses are transmitted by the afferent fibers via auditory nerves to the auditory cortex of the brain, where the impulses are analyzed and the sound is recognized.

Question 9.
Differentiate between:

1. Myelinated and non-myelinated axons
2. Dendrites and axons
3. Roads and cones
4. Thalamus and Hypothalamus
5. Cerebrum and Cerebellum

Answer:
1. The myelinated nerve fibers are enveloped with Schwann cells, which form a myelin sheath around the axon. Myelinated nerve fibers are found in spinal and cranial nerves. Nonmyelinated nerve fiber is enclosed by a Schwann cell that does not form a myelin sheath around the axon and is commonly found in autonomous and somatic neural systems.

2. Short fibers that branch repeatedly and project out of the cell body also contain Nissl’s granules and are called dendrites. These fibers transmit impulses towards the cell body. The axon is a long fiber, the distal end of which is branched. Each branch terminates as a bulb-like structure called a synaptic knob which possesses synaptic vesicles containing chemicals called neurotransmitters. The axons transmit nerve impulses away from the cell body to a synapse or to a neuromuscular junction.

3. The daylight vision and color vision are functions of cones. The twilight vision is the function of the rods. The rods contain a purplish- red protein called the rhodopsin or visual purple, which contains a derivative of Vitamin A.

4. The cerebrum wraps around a structure called the thalamus, which is a major coordinating center for sensory and motor signaling. Another very important part of the brain called the hypothalamus lies at the base of the thalamus. The hypothalamus contains a number of centers that control body temperature, eating, and drinking. It also contains several groups of neurosecretory cells, which secrete called hypothalamic hormones.

5. Cerebrum forms the major part of the human brain. A deep cleft divides the cerebrum longitudinally into two halves, which are termed as the left and right cerebral hemispheres. Cerebellum has a very convoluted surface in order to provide additional space for many more neurons.

Question 10.
Answer the following:

1. Which part of the ear determines the pitch of a sound?
2. Which part of the human brain is the most developed?
3. Which part of our central neural system acts as a master clock?

Answer:

1. Inner ear
2. Forebrain (cerebrum)
3. Somatic neural system.

Question 11.
The region of the vertebrate eye, where the optic nerve passes out of the retina is called the

1. Fovea
2. iris
3. blind spot
4. Optic charisma

Answer:
4. Optic charisma

Question 12.
Distinguish between :

1. Afferent neurons and Efferent neurons
2. Impulse conduction in a myelinated nerve fiber and Unmyeli-nated nerve fiber.
3. aqueous humor and vitreous humor
4. blind spot and yellow spot
5. cranial nerves and spinal nerves

Answer:
(1) Differences between the afferent neurons and efferent neurons:
Afferent neurons:

1. The afferent nerve fibers transmit impulses from tissues/ organs to the CNS.

Efferent neurons:

1. The efferent fibers transmit regulatory impulses from the CNS to the concerned peripheral tissues/organs.

(2) Differences between the impulse conduction in a myelinated nerve fiber and unmyelinated nerve fiber:
Myelinated nerve fiber:

1. The myelinated nerve fibers are enveloped with Schwann cells, which form a myelin sheath around the axon

Unmyelinated nerve fiber:

1. Unmyelinated nerve fiber is enclosed by a Schwann cell that does not form a myelin sheath around the axon.

(3) Differences between the aqueous humor and vitreous humor

Aqueous humor:

1. The space between the cornea and the lens is called an aqueous chamber and contains a thin watery fluid called aqueous humor.

Vitreous humor:

1. The space between the lens and the retina is called the vitreous chamber and is filled with a transparent gel called the vitreous humor.

(4) Differences between the blind spot and yellow spot
Blindspot:

1. Photoreceptor cells are not present in that region and hence it is called the blind spot.

Yellow spot:

1. At the posterior pole of the eye lateral to the blind spot, there is a yellowish pigmented spot called macula lutea with a central pit called the fovea.

(5) differences between cranial nerves and spinal nerves:
Cranial nerves:

1. There are 12 pairs of cranial nerves in man which either arise from or end into different parts of the brain.

Spinal nerves:

1. There are 31 pairs of spinal nerves in man. A pair of spinal nerves arise from each segment of the spinal cord.