Question

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.

Answer 1

(a) The steady of a resting nerve fibre, i.e., the normal difference in the ionic concentrations and electric potential b/w its outside and inside, is maintained by the active transport of sodium and potassium ions against the concentration and electrochemical gradients. Thus, sodium ions are pumped out of and potassium ions are forced into the nerve fibre. The process of expelling out sodium ions and drawing in potassium ions against concentration and electrochemical gradients is termed sodium pump or better sodium-potassium-exchange pump. the active transport of sodium and potassium ions across the membrane requires energy, which is provided by metabolic processes within the nerve fibre itself with the help of an enzyme, sodium and potassium-dependent adenosine triphosphate, present in plasma membrane. The differential distribution of ions on the two sides of the membrane produces a potential difference of minus 50 to 100 millivolts across the membrane. This difference is the resting membrane potential referred to above.

(b) Retina has photopigments , now these photopigments are photosensitive compounds for eyes. It is composed of retinal and opsin.Now when the light comes it dissociates the Retinal from Opsin , which leads to the changes in the structure of opsin.It generates action potential in the bipolar neurons. These impulses are transmitted to visual cortex of the brain via optic nerves. Now in the brain neural impulses are analysised and an erect image is formed.

(c) The external ear receives the sound wave and it is then collected by ear pinna.The sound then entres and strikes the membranous structure called as ear drum. Now as soon as the ear drum persives the sound starts to vibrate.Now these vibrations ate send to ear ossicles. It is Malleus which receives the sound. Malleus is attached to tympanic membrane.Then vibrations of Malleus is received by incus.Now the vibrations of incus is received by stapes. Stapes is the smallest bone of the body.It is attached to oval window of the cochlea. The ossicles increases the efficiency of transmission of sound waves to the inner ear. Now the passed waves reaches lymphs in cochlea and generated waves there.The waves in the lymphs induce a ripple in the basilar membrane. Now the basilar membrane bends the hair cell and presses them against the tectorial membrane. As a result impulse are generated in the afferent neurons. Now the nerves are transmitted to auditory cortex of the brain and finally the sound is recognized.

Answer 2

Answer:

Role of Na+ in the generation of action potential

When a nerve fiber is triggered, the sodium channels of the neurilemma is open and activated. From the outside, the sodium ions diffuse to the intracellular fluid due to the electrochemical gradient that is established. The membrane gets charged negatively from outside as the potassium ions move out and positively charged from inside. The immediate change that occurs in the membrane is known as action potential causing the membrane to get depolarized.

Mechanism of generation of light-induced impulse in the retina

Human eye consists of photo pigments known as retinal and opsin. These are dissociated when light induces bringing about a change in the structure of opsin, causing an action potential to generate in the bipolar neurons. These action potential or impulses are conveyed to the visual cortex of the brain by the optic nerves where these impulses are read to analyze, recognizing an erect image.

Mechanism through which a sound produces a nerve impulse in the inner ear

Vibrations are received through the membrane layering the fenestra ovalis by the perilymph of the internal ear. From here(the perilymph), vibrations are conveyed to the scala vestibule of the cochlea and furthermore to the scala media via the Reissner’s membrane, triggering the sensory hair of the organ of corti, which is the organ of hearing. These hair cells receive impulse to carry it to the brain through the auditory nerve, where the sense of hearing is felt.