Explain the following. (a) Role of Na+ in the generation of an 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.
Hint: a) Na+ plays important role in generating the action potential by the rapid flow of ions in and out across the membranes of the axon b) The retina produces the light-induced impulses mainly because of the presence of photopigments. c) The nerve impulse in the inner ear is produced by the sound waves are transferred from the eardrum to the cochlea and impulses are generated.
Complete answer: A) Whenever the nerve fiber is stimulated, the membrane potential is generated and this membrane potential decreases because it is more permeable to sodium ions than potassium ions. So that all the sodium ions diffuse from outside to inside the membrane and the inside of the axon, it is more positively charged. So the outside of the membrane is negatively charged and the inside is positively charged. As the polarity becomes reverse, ( during the resting phase, it is opposite in nature) this process is called depolarization. Due to this rapid inflow of the Na+ ions accord the membrane generates the action potential. B) Normally the retina contains photopigments called retinal and opsin. This retinal and opsin are associated with each other, whenever the light enters the retina, it degenerates the structure of opsin, so that both pigments are disassociating with each other and during this process, the impulse produced and the action potential is generated. C) Whenever the sound waves travel to the ear, it falls on the eardrum and then it transmits to the inner ear by the ear ossicles. The sound travels through the inner small window to the fluid of cochlea and where it generates the waves and these waves induce the hair cells and finally generates the impulse and the action potential is generated.
Note: In the inner ear after the nerve impulse forms and the action potential generates, which is associated with the afferent neurons and transmitted to the brain to the auditory cortex of the brain.