Sähköimpulssi

Sähköimpulssi, also known as an electrical impulse or action potential, is a rapid and transient change in the electrical potential across the membrane of a cell, particularly nerve cells (neurons) and muscle cells. It is the fundamental mechanism by which these cells transmit signals over distances. The generation of an sähköimpulssi is a complex process involving the movement of ions across the cell membrane through specialized protein channels.

The resting state of a cell membrane is characterized by a negative electrical charge inside relative to the outside. This difference is maintained by ion pumps and channels. When a stimulus, such as a neurotransmitter binding to a receptor or mechanical stimulation, reaches a certain threshold, it causes voltage-gated sodium channels to open. This influx of positively charged sodium ions causes the inside of the membrane to become momentarily positive, a process called depolarization.

Following depolarization, voltage-gated sodium channels inactivate, and voltage-gated potassium channels open. The outward movement of positively charged potassium ions repolarizes the membrane, restoring the negative charge inside. In some cases, a brief period of hyperpolarization may occur, where the membrane potential becomes even more negative than the resting potential. This entire sequence of changes constitutes a single sähköimpulssi. These impulses propagate along the axon of a neuron, enabling rapid communication throughout the nervous system. In muscle cells, sähköimpulssit trigger muscle contraction.