(a) Role of Na+ in the generation of action potential.
(b) Mechanism of generation of light-induced impulse in the retina.
(c) The mechanism through which a sound produces a nerve impulse in the inner ear.
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Solution
Sodium ions play an important role in the generation of action potential. When a nerve fiber is stimulated, the membrane potential decreases. The membrane becomes more permeable to Na+ ions than to K+ ions. As a result, Na+ 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 negative charge. This reversal of polarity across the membrane is known as depolarization. The rapid inflow of Na+ ions causes the membrane potential to increase, thereby generating an action potential.
b) In the eye, retina have photopigments like retinal and opsin. Light dissociates the retinal from opsin which changes the structure of opsin and generates an action potential.
c) When sound falls over the eardrum, it is then transmitted to the inner ear by ear ossicles. The vibrations are passed through the oval window onto the fluid of the cochlea, where they generate waves in the lymph. These waves induce the hair cell. As a result nerve impulses are generated in the associated afferent neurons and transmitted to the auditory cortex of the brain via auditory nerves.