Neurons - Nerve Impulses

Table of Contents

• Introduction
• Neurons
• Impulse Generation and Conduction

A living organism is made up of different types of cells, which help them to control and coordinate with its surroundings. In an animal body, coordination is the effective outcome of two systems i.e. nervous system and endocrine system. Have you ever noticed how fast we respond to a stimulus like withdrawing the hand from hot objects? Thanks to neurons! Let’s see how neurons generate and conduct impulses (signals).

Neurons are the structural and functional units of the nervous system of humans and animals. The ability of neurons to generate and conduct impulses makes them special. The different types of ion channels present on the neural membranes help in the generation of impulses.

When neurons are not conducting any impulses, they are in a resting state. The membrane, in this event, is not permeable to sodium ions and negatively charged proteins found in the axoplasm and are more permeable to potassium ions. There is a high concentration of proteins and potassium ions in the plasma in the axon, while the concentration of sodium ions is low. The fluid in the periphery of the axon has a low concentration of potassium ions and a high concentration of sodium ions. As a result, a concentration gradient is established.

Active transportation of ions takes place through the membrane via the sodium-potassium pump, wherein 2 potassium ions enter the cell, and 3 ions of sodium are transported outwards. Consequently, the inner surface is negatively charged, and the membrane’s outer surface is positively charged. The cell is now in a polarised state. Resting potential is the electrical potential difference established through the resting plasma membrane.

The membrane, at a particular region on the polarised membrane, turns freely permeable to ions of sodium when a stimulus is applied. As a result, sodium ions pass into the cell. The inner side of the membrane turns positively charged, while the outer side becomes negatively charged. Now, the membrane is in a depolarised state. An electrical potential difference is hence established. This difference at the site through the plasma membrane is referred to as a nerve impulse or action potential. The area turns into a stimulus for the adjacent region of the membrane that turns depolarised. The previous membrane is repolarised as a result of the exit of the sodium ions from the cell.  Hence, the conduction of impulses.

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