nerveimpuls

A nerve impulse, sometimes referred to as a nerveimpuls in some languages, is an electrical signal that travels along a neuron to convey information. It arises from rapid, controlled changes in the membrane potential of the neuron's membrane.

Propagation along an axon begins with a resting membrane potential of about -70 millivolts. When a stimulus depolarizes the membrane to a threshold of roughly -55 mV, voltage-gated sodium channels open and Na+ enters the cell. This causes rapid depolarization, generating an action potential that rises to about +30 mV. Subsequently, voltage-gated potassium channels open, K+ exits the cell, and the membrane repolarizes. A brief hyperpolarization may occur before the resting potential is restored. The action potential travels along the axon as a self-propagating wave of depolarization.

Conduction velocity depends on axon diameter and myelination. Unmyelinated fibers conduct slowly, while myelinated fibers use saltatory conduction, with impulses jumping between nodes of Ranvier. This speeds signaling dramatically and allows rapid communication over long distances.

At synapses, the impulse is converted to chemical signaling. Arrival of the action potential at the presynaptic terminal opens calcium channels, triggering the release of neurotransmitters into the synaptic cleft. Neurotransmitters bind to receptors on the postsynaptic membrane, producing excitatory or inhibitory postsynaptic potentials that may trigger or modulate a new action potential.

Termination and regulation involve neurotransmitter reuptake, enzymatic degradation, or diffusion away from the synapse. Refractory periods ensure the impulse propagates in one direction and regulate firing rate. Nerve impulses are fundamental to rapid, precise communication within the nervous system.