Q.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.
(a) The action potential is determined by Na+ ions. The Na+ channels which are closed in the resting state, open and cause the inflow of Na+ ions by diffusion into the inside of axoplasm. The electrical potential of the membrane changes from 70 mV towards zero and then the membrane is said to be depolarised.
(b) The photopigments of the retina are photosensitive compounds in the eye that are composed of retinal and opsin. Light induces dissociation of retinal from opsin which changes the structure of the opsin. It generates action potential in the bipolar neurons. These impulses/action potential are transmitted by the optic nerves to the visual cortex of the brain where the neural impulses are analysed and the erect image is recognised.
(c) When sound falls over the ear drum, 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 lymphs. The waves induce a ripple in the basilar membrane that bend the hair cells, pressing them against the techtonial membrane. As a result nerve impulses are generated in the associated afferent neurons and transmitted to auditory cortex of brain via auditory nerves, where the impulses are analysed and the sound is recognised.