Biology Class 11 NCERT Solutions: Chapter 21 Neural Control and Coordination Part 6

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Q: 8. Explain the following:

(A) Role of 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.

Answer:

(A) Sodium ions play an important role in the generation of action potential. When a nerve fibre is stimulated, the membrane potential decreases. The membrane becomes more permeable to ions than to ions. As a result, diffuses from the outside to the inside of the membrane. This causes the inside of the membrane to become positively-charged, while the outer membrane gains a negatively charge. This reversal of polarity across the membrane is known as depolarisation. The rapid inflow of ions causes the membrane potential to increase, thereby generating an action potential.

Q 8 Image of Resting and Depolarised Never Fibre

Q 8 Image of Resting and Depolarised Never Fibre

(B) Retina is the innermost layer of the eye. It contains three layers of cells – inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells. Photoreceptor cells are composed of a protein called opsin and an aldehyde of vitamin A called retinal. When light rays are focused on the retina through the cornea, retinal gets dissociated from opsin. As a result, the structure of opsin gets changed. This in turn causes the permeability of the membrane to change, thereby generating a potential difference in the cells. Consequently, an action potential is generated in the ganglion cells and is transmitted to the visual cortex of the brain via the optic nerves. In the cortex region of the brain, the impulses are analysed and the image is formed on the retina.

(C) The pinna of the external ear collects the sound waves and directs them to the tympanic membrane (ear drum) via the external auditory canal. The ear drum then vibrates the sound waves and conducts them to the internal ear through the ear ossicles. The ear ossicles increase the intensity of the sound waves. These vibrating sound waves are conducted through the oval window to the fluid in the cochlea. Consequently, a movement is created in the lymph. This movement produces vibrations in the basilar membrane, which in turn stimulate the auditory hair cells. These cells generate a nerve impulse, conducting it to the auditory cortex of the brain via afferent fibres. The auditory cortex region interprets the nerve impulse and sound is recognised.

Q: 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

Answer:

(A) Myelinated and non-myelinated axons

Table of Myelinated and Non-Myelinated Axons
Table of Myelinated and Non-Myelinated Axons

Myelinated Axons

Non-Myelinated Axons

1

Transmission of nerve impulse is faster

1

Transmission of nerve impulse is slower

2

Myelinated axon has a myelin sheath.

2

Myelin sheath is absent

3

Node of Ranvier is present between adjacent myelin sheaths.

3

Node of Ranvier is absent

4

Found in the brain, the spinal cord, the cranial and spinal nerves

4

Found in autonomous and somatic neural systems

5

Schwann cells are observed inside the myelin sheath

5

Schwann cells are not observed inside the myelin sheath

6

Image of the Myelinated Axons

Image of the Myelinated Axons

6

Image of the Non-Myelinated Axons

Image of the Non-Myelinated Axons

(B) Dendrites and Axons

Dendrites and Axons in image

Dendrites and Axons in Image

Q_9_B_Table of Dendrites and Axons
Q_9_B_Table of Dendrites and Axons

Dendrites

Axons

1

Dendrite is a small projection arising from the neuron. It conducts the nerve impulse toward the cell body.

1

Axon is a single, long projection that conducts the nerve impulse away from cell body to the next neuron.

2

Nissl’s granules are present in dendrites.

2

Nissl’s granules are absent from axons.

3

Dendrites are always non-myelinated.

3

Axons can be myelinated or non-myelinated.

(C) Rods and Cones

Rods and Cones in figure

Rods and Cones in Figure

Q_9_C_Table of Rods and Cones
Q_9_C_Table of Rods and Cones

Rods

Cones

1

Rods help in twilight vision.

1

Cones help in colour vision.

2

They have visual purple pigment called rhodopsin.

2

They have visual violet pigment called iodeosin.

3

Rods are the photoreceptor cells of the retina that are sensitive to dim light.

3

Cones are the photoreceptor cells of the retina that are sensitive to bright light.

(D) Thalamus and Hypothalamus

Thalamus and Hypothalamus in figure

Thalamus and Hypothalamus in Figure

Q_9_D_Table of Thalamus and Hypothalamus
Q_9_D_Table of Thalamus and Hypothalamus

Thalamus

Hypothalamus

1

Thalamus is the part of the forebrain that receives nerve impulses of pain, temperature, touch, etc., and conducts them to the cerebral hemisphere.

1

Hypothalamus is the part of the forebrain that controls involuntary functions such as hunger, thirst, sweating, sleep, fatigue, sexual desire, temperature regulation, etc.

(E) Cerebrum and Cerebellum

Cerebrum and Cerebellum in figure

Cerebrum and Cerebellum in Figure

Q_9_E_Table of Cerabrum and Cerebellum
Q_9_E_Table of Cerabrum and Cerebellum

Cerebrum

Cerebellum

1

It is the part of the forebrain that controls voluntary functions. It is the place where intelligence, will power, memory, etc., reside.

1

It is the part of the hindbrain that controls voluntary functions and controls the equilibrium.

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