Reconstruction of sodium and potassium ion concentration
The sodium ions that have diffused into the cells during the action potential and the potassium ions that have just diffused out must be returned to their original state.
The propagation of an action potential across the length of a nerve slightly reduces the difference in sodium and potassium concentrations inside and outside the membrane because sodium ions diffuse inward during depolarization and potassium diffuses. diffuse outwards during repolarization.
Figure. Heat production in a nerve fibre at rest and at an increasing rate of arousal.
For a single action potential, this effect is so short that it cannot be measured. Indeed, between 100,000 and 50 million impulses can be transmitted through large nerve fibres before the concentration difference reaches the termination of the action potential. However, with time it becomes necessary. to re-establish the difference in sodium and potassium concentrations at the membrane, this is achieved by the action of the Na + -K + pump in the same way as described earlier for establishing the resting potential. That is, the sodium ions that have diffused into the cells during the action potential and the potassium ions that have just diffused out must be returned to their original state by the Na + -K + pump. Since this pump requires energy to function, the "recharging" of nerve fibres is an active metabolic process, uses energy derived from the cell's adenosine triphosphate energy system. The figure shows that nerve fibre that produces heat increase during reloading, which is a measure of energy expenditure as nerve impulses increase in frequency.
A distinctive feature of the Na + -K + Adenosine triphosphate pump is the degree of activity that is strongly stimulated when excess sodium ions accumulate inside the cell membrane. In fact, the pumping activity increases approximately in proportion to the third power of sodium concentration in this cell. When the intracellular sodium concentration increases by 10-20 mEq/L, pump activities are not merely doubled but increased approximately eightfold. So, it's actually very easy to understand how the 'loading' process of nerve fibres can be quickly set into motion whenever the differential concentration of sodium and potassium ions across the membrane begins. "reduced".