Biology Class 11 NCERT Solutions: Chapter 21 Neural Control and Coordination Part 6 (For CBSE, ICSE, IAS, NET, NRA 2022)

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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.


(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_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


(A) Myelinated and non-myelinated axons

Table of Myelinated and Non-Myelinated Axons
Myelinated AxonsNon-Myelinated Axons
1Transmission of nerve impulse is faster1Transmission of nerve impulse is slower
2Myelinated axon has a myelin sheath.2Myelin sheath is absent
3Node of Ranvier is present between adjacent myelin sheaths.3Node of Ranvier is absent
4Found in the brain, the spinal cord, the cranial and spinal nerves4Found in autonomous and somatic neural systems
5Schwann cells are observed inside the myelin sheath5Schwann cells are not observed inside the myelin sheath
The Myelinated Axons
The Non-Myelinated Axons

(B) Dendrites and Axons

Dendrites and Axons in Image
Q_9_B_Table of Dendrites and Axons
1Dendrite is a small projection arising from the neuron. It conducts the nerve impulse toward the cell body.1Axon is a single, long projection that conducts the nerve impulse away from cell body to the next neuron.
2Nissl՚s granules are present in dendrites.2Nissl՚s granules are absent from axons.
3Dendrites are always non-myelinated.3Axons can be myelinated or non-myelinated.

(C) Rods and Cones

Rods and Cones in Figure
Q_9_C_Table of Rods and Cones
1Rods help in twilight vision.1Cones help in colour vision.
2They have visual purple pigment called rhodopsin.2They have visual violet pigment called iodeosin.
3Rods are the photoreceptor cells of the retina that are sensitive to dim light.3Cones are the photoreceptor cells of the retina that are sensitive to bright light.

(D) Thalamus and Hypothalamus

Thalamus and Hypothalamus in Figure
Q_9_D_Table of Thalamus and Hypothalamus
1Thalamus is the part of the forebrain that receives nerve impulses of pain, temperature, touch, etc. , and conducts them to the cerebral hemisphere.1Hypothalamus 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
Q_9_E_Table of Cerabrum and Cerebellum
1It is the part of the forebrain that controls voluntary functions. It is the place where intelligence, will power, memory, etc. , reside.1It is the part of the hindbrain that controls voluntary functions and controls the equilibrium.

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