Aktiopotentiaali

Aktiopotentiaali, also known as a nerve impulse or action potential, is a rapid and transient change in the electrical potential across the membrane of a neuron or muscle cell. This electrical signal is the fundamental unit of communication in the nervous system. It is generated when a stimulus causes the cell membrane to depolarize beyond a certain threshold. This depolarization is primarily due to the rapid influx of sodium ions into the cell through voltage-gated sodium channels.

Following the initial depolarization, a repolarization phase occurs, where the cell membrane's potential returns to its resting state. This is achieved by the efflux of potassium ions out of the cell through voltage-gated potassium channels. During a brief period called the refractory period, the cell is less likely or unable to generate another action potential, ensuring unidirectional propagation of the signal along the axon.

Action potentials are "all-or-none" events, meaning they either occur with full amplitude or not at all. The frequency of action potentials, rather than their amplitude, encodes information about the strength of the stimulus. This electrochemical signal is crucial for transmitting information from one neuron to another at synapses, enabling everything from sensory perception to motor control.