Action potential

An action potential is a brief, regenerative change in membrane voltage that travels along an excitable cell’s membrane. It enables rapid signaling in neurons, muscle cells, and some other cells.

Resting membrane potential: The voltage difference across a cell membrane when the cell is not producing an action potential. Its departure from this baseline begins the voltage change.
Membrane potential: The electrical potential difference between the inside and outside of a cell membrane. An action potential is a rapid, propagating change in this voltage.
Neuronal coding: The representation of information by patterns of activity across neurons, including the timing and rate of spikes. Neurons encode many signals through action-potential timing and frequency.
Graded potential: A local change in membrane voltage whose size varies with stimulus strength and fades with distance. Unlike an action potential, it is not an all-or-none regenerative signal.
Voltage-gated sodium channel: A membrane protein that opens in response to voltage changes and selectively conducts sodium ions. Sodium influx drives the rising phase of many neuronal action potentials.
Ion channel: A membrane protein that forms a pathway allowing particular ions to cross a cell membrane. Selective ion movement through channels creates the currents behind voltage changes.
Neuromuscular junction: The synapse where a motor neuron communicates with a skeletal muscle fiber. A motor-neuron spike triggers transmission that can produce a muscle-fiber action potential.
Cable theory: A mathematical framework for describing how electrical signals spread through passive neuronal processes. It explains decaying passive spread, while action potentials require active regeneration.
Voltage-gated potassium channel: A membrane protein that opens in response to voltage changes and selectively conducts potassium ions. Delayed potassium efflux repolarizes the membrane after its voltage rises.
Electrochemical gradient: The combined effect of an ion’s concentration difference and electrical forces across a membrane. It determines the direction and strength of ion flow during a spike.

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