Närviaktsioonid

Närviaktsioonid, also known as nerve impulses or action potentials, are the fundamental units of communication in the nervous system. They are rapid, transient changes in the electrical potential across the membrane of a neuron or muscle cell. These electrical signals are generated and propagated along the length of the cell.

The generation of a närviaktsioon begins when a neuron receives a stimulus that causes the cell membrane to depolarize. If this depolarization reaches a certain threshold, it triggers a cascade of events. Voltage-gated ion channels in the membrane open, allowing sodium ions to rush into the cell. This influx of positive charge causes a rapid, brief reversal of the membrane potential, known as the rising phase.

Following the depolarization, potassium channels open, and potassium ions flow out of the cell. This outward movement of positive charge repolarizes the membrane, returning it to its resting potential. In some cases, the membrane may briefly hyperpolarize, becoming more negative than its resting potential, before eventually returning to normal.

Once generated, the närviaktsioon propagates along the axon of the neuron. This propagation occurs in an all-or-none fashion, meaning that a stimulus either triggers a full närviaktsioon or none at all. The speed of conduction can vary significantly depending on the diameter of the axon and the presence of myelin, a fatty insulating sheath that speeds up transmission. Närviaktsioonid are essential for transmitting sensory information, controlling motor functions, and enabling all aspects of thought and consciousness.