Question

Explain the transmission of nerve impulse through a nerve fibre with the help of suitable diagrams.

Accepted Answer

Neurons are electrically excitable cells of the nervous system that transmit messages from one part of the body to the other through generated action potential. The action potential is referred to as the altered membrane potential. The propagation of action potential (nerve impulse) is unidirectional, which occurs along the axon, away from the cell body towards the synapse. The origin and propagation of action potential occur in three phases: depolarisation, repolarisation, and reorientation.

Depolarisation: Neurons remain at a resting state when they are not conducting electrical impulses. In this state, the Na⁺ concentration is more on the outer side of the membrane than on the inner side, with the inner side having more negative charges. At this time, the membrane potential is about -70mV. When the membrane is stimulated, the sodium ion channels open up, allowing Na⁺ to rush into inside the axon, which is along its concentration gradient (no energy is utilised). Eventually, Na⁺ concentration on the inner side builds up, and the negative charges decrease, while the positive charge on the outer side decreases. This influx of Na⁺ continues till the membrane potential is increased to +30, and at this point, the electrical charges across the membrane at the site of stimulation is reversed transiently, resulting in the generation of an action potential.

Repolarisation: Following depolarisation, there is an efflux of K⁺ (outside the cell) through potassium ion channels down its gradient, which leads to building up in K⁺ concentration on the outer side of the neuron membrane. This phenomenon decreases the negative charges outside the membrane, and conversely, there is a decrease in the K⁺ concentration in the intracellular environment. This movement of charges takes place until the membrane potential again becomes -70 mV. This restoration of the membrane potential to a resting membrane potential state by the efflux of K⁺ is known as repolarisation.

Reorientation: After repolarisation, the membrane potential is restored at the resting membrane potential state, which is -70 mV. But the ionic distribution is reversed relative to that in the resting membrane, which means there are more Na⁺ inside the membrane and more K⁺ outside the membrane. At this stage, the normal charge distribution is achieved after a process called reorientation. The Na⁺ and K⁺ exchange their charges by the action of Na⁺ K⁺ ATPase, which requires the involvement of ATPs.

Explain the transmission of nerve impulse through a nerve fibre with the help of suitable diagrams.

Important Questions on Solved Zoology Paper-1

Learn and Prepare for any exam you want !