närviaktsioonide

Närviaktsioonid, also known as nerve impulses or action potentials, are rapid, transient changes in the electrical potential across the membrane of a neuron or muscle cell. They represent the fundamental way in which these cells communicate and transmit information. The process begins with a stimulus that causes the cell membrane to depolarize, meaning the inside of the cell becomes less negative relative to the outside.

If this depolarization reaches a certain threshold level, a cascade of events is triggered. Voltage-gated sodium channels in the membrane open, allowing a rapid influx of sodium ions into the cell. This influx causes further depolarization and the rising phase of the action potential. Shortly after, the sodium channels inactivate, and voltage-gated potassium channels open, allowing potassium ions to flow out of the cell. This efflux of positive charge repolarizes the membrane, bringing it back towards its resting potential, and even causes a brief hyperpolarization where the inside of the cell becomes more negative than the resting potential.

Following repolarization, the sodium-potassium pump actively works to restore the original ion concentrations across the membrane, returning the cell to its resting state and preparing it for another action potential. Närviaktsioonid are an all-or-none phenomenon, meaning they either occur fully or not at all, and their speed is influenced by factors such as the diameter of the axon and the presence of myelin. They are crucial for processes ranging from sensory perception and muscle contraction to complex cognitive functions.