Zoology - Neural Control and Coordination Question with Solution | TestHub

The axon is immersed in the extracellular fluid (ECF). In the axoplasm negatively charged protein molecules are present, which are neutralized due to the presence of large amount of $K^{+}$ ions. In the ECF (outside the axon) the negatively charged $C{I}^{-}$ ions are neutralized by the presence of +vely charged Na+$N{a}^{+}$ ions. To maintain resting potential, sodium potassium metabolic pump operates. This pump which is located on the axon membrane pump $N{a}^{+}$ from axoplasm to ECF and $K^{+}$ from ECF to axoplasm. It pumps more positive charges (3 $N{a}^{+}$) from axoplasm to ECF than in the reverse direction (2$K^{+}$), and is run by an enzyme called as sodium potassium-ATPase. When a stimulus is applied to the membrane of the nerve fibre, its permeability changes and sodium potassium pump stop operating. Sodium ions rush inside and potassium ions rush outside. This results in the positive charge inside and negative charge outside. The nerve fibre is said to be in action potential or depolarized.