Explainthe following:
(a) Roleof Na+ in thegeneration 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.
Explainthe following:
(a) Roleof Na+ in thegeneration 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 ofaction potential. When a nerve fibre is stimulated, the membranepotential decreases. The membrane becomes more permeable to Na+ions than to K+ ions. As a result, Na+ diffusesfrom the outside to the inside of the membrane. This causes theinside of the membrane to become positively-charged, while the outermembrane gains a negatively charge. This reversal of polarity acrossthe membrane is known as depolarisation. The rapid inflow of Na+ions causes the membrane potential to increase, thereby generating anaction potential.
(b) Retina is the innermost layer of the eye. It containsthree layers of cells – inner ganglion cells, middle bipolarcells, and outermost photoreceptor cells. Photoreceptor cells arecomposed of a protein called opsin and an aldehyde of vitamin Acalled retinal. When light rays are focused on the retina through thecornea, retinal gets dissociated from opsin. As a result, thestructure of opsin gets changed. This in turn causes the permeabilityof the membrane to change, thereby generating a potential differencein the cells. Consequently, an action potential is generated in theganglion cells and is transmitted to the visual cortex of the brainvia the optic nerves. In the cortex region of the brain, the impulsesare analysed and the image is formed on the retina.
(c) The pinna of the external ear collects the sound wavesand directs them to the tympanic membrane (ear drum) via the externalauditory canal. The ear drum then vibrates the sound waves andconducts them to the internal ear through the ear ossicles. The earossicles increase the intensity of the sound waves. These vibratingsound waves are conducted through the oval window to the fluid in thecochlea. Consequently, a movement is created in the lymph. Thismovement produces vibrations in the basilar membrane, which in turnstimulate the auditory hair cells. These cells generate a nerveimpulse, conducting it to the auditory cortex of the brain viaafferent fibres. The auditory cortex region interprets the nerveimpulse and sound is recognised.
(a) Sodium ions play an important role in the generation ofaction potential. When a nerve fibre is stimulated, the membranepotential decreases. The membrane becomes more permeable to Na+ions than to K+ ions. As a result, Na+ diffusesfrom the outside to the inside of the membrane. This causes theinside of the membrane to become positively-charged, while the outermembrane gains a negatively charge. This reversal of polarity acrossthe membrane is known as depolarisation. The rapid inflow of Na+ions causes the membrane potential to increase, thereby generating anaction potential.
(b) Retina is the innermost layer of the eye. It containsthree layers of cells – inner ganglion cells, middle bipolarcells, and outermost photoreceptor cells. Photoreceptor cells arecomposed of a protein called opsin and an aldehyde of vitamin Acalled retinal. When light rays are focused on the retina through thecornea, retinal gets dissociated from opsin. As a result, thestructure of opsin gets changed. This in turn causes the permeabilityof the membrane to change, thereby generating a potential differencein the cells. Consequently, an action potential is generated in theganglion cells and is transmitted to the visual cortex of the brainvia the optic nerves. In the cortex region of the brain, the impulsesare analysed and the image is formed on the retina.
(c) The pinna of the external ear collects the sound wavesand directs them to the tympanic membrane (ear drum) via the externalauditory canal. The ear drum then vibrates the sound waves andconducts them to the internal ear through the ear ossicles. The earossicles increase the intensity of the sound waves. These vibratingsound waves are conducted through the oval window to the fluid in thecochlea. Consequently, a movement is created in the lymph. Thismovement produces vibrations in the basilar membrane, which in turnstimulate the auditory hair cells. These cells generate a nerveimpulse, conducting it to the auditory cortex of the brain viaafferent fibres. The auditory cortex region interprets the nerveimpulse and sound is recognised.
