Reaksjonspotensial

Reaksjonspotensial, also known as action potential, is a fundamental concept in neuroscience and physiology. It refers to the rapid, transient, and large change in the electrical potential across the membrane of a neuron or muscle cell. This electrical signal is crucial for transmitting information along nerve fibers and for initiating muscle contraction.

The generation of a reaksjonspotensial is a complex process involving the coordinated opening and closing of voltage-gated ion channels embedded in the cell membrane. It begins when a stimulus, such as a neurotransmitter binding to a receptor, causes a slight depolarization of the membrane. If this depolarization reaches a critical threshold, it triggers a cascade of events.

First, voltage-gated sodium channels open, allowing a rapid influx of sodium ions into the cell. This influx causes a significant and rapid depolarization, making the inside of the cell positive relative to the outside. This phase is known as depolarization.

Following depolarization, voltage-gated sodium channels inactivate, and voltage-gated potassium channels open. This allows potassium ions to flow out of the cell, repolarizing the membrane and bringing the electrical potential back towards its resting state. This is the repolarization phase. In some cases, the membrane may hyperpolarize briefly, becoming even more negative than the resting potential, before returning to its normal state.

Once a reaksjonspotensial is generated at one point on the membrane, it propagates along the axon like a wave, ensuring that the signal is transmitted efficiently over long distances without diminishing. This all-or-none phenomenon means that a reaksjonspotensial either occurs fully or not at all, and its amplitude is independent of the strength of the initial stimulus, provided the threshold is reached.