Generation and Conduction of Nerve Impulse

First, let’s discuss why the membrane of the nerve is polarized. ​Neural membrane contains different types of ion channels, that are selectively permeable to different ions.

At the resting phase (when the neuron is not conducting any impulse), the axonal membrane is permeable to potassium ions and impermeable to sodium ions, and also ​to negatively charged proteins present in the axoplasm. Therefore, inside the axon, there is a high concentration of potassium ions and negatively charged proteins and a low concentration of sodium ions. Outside the axon, there is a low concentration of potassium ions and a high concentration of sodium ions. Thereby, creating a concentration gradient.

This ionic gradient is maintained by the sodium-potassium pump, which transports 3 ​Na^​+ outwards ​for 2 K​⁺ into the cell. Hence, the axonal membrane’s outer surface ​possesses a positive charge, and the inner surface negative charge, therefore is polarized. The electrical potential difference across the resting plasma membrane is called the resting potential. Now let’s discuss the mechanism of conduction of impulse.

Mechanism of Generation and Conduction of Impulse

When the polarized membrane is stimulated, the membrane at site A becomes permeable to sodium ions, leading to a rapid influx of sodium ions, that results in the reversal of polarity at site A. Now, the outer surface of the membrane is negatively charged and the inner surface is positively charged. This reversal of polarity is known as depolarization. This difference in electrical potential across the membrane at site A is called a nerve impulse.

At site B, the outer surface of the membrane is positively charged, and the inner surface is negatively charged, therefore the current flows on the inner surface from site A to site B and on the outer surface from site B to site A, thus completing the circuit of current flow. The action potential is generated at site B, and the impulse generated at site A arrives at site B. The cycle is repeated along the length of the axon and an impulse is conducted.

NCERT Notes for Class 11 Biology Chapter 18 – Neural Control and Coordination: The neural system controls and coordinates various ​functions, and homeostatic and metabolic activities of all the organs in the body. Neurons​​ are ​the ​functional unit of the neural system. The human nervous system is divided into two parts: The central nervous system (CNS) and the Peripheral nervous system (PNS). You will find neural control and coordination class 11 notes self-study here. Also, see the solutions of NCERT Class 11 Biology Chapter 18: Neural Control and Coordination.