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Action potential

German: Aktionspotential

1 Definition

Action potentials are rapid changes of potentials across the cell's membrane. Their purpose is signal transduction along axons to other excitable cells (e.g. neurons).

2 Physiology

When a stimulus reaches the neuron, it triggers an action potential at the axon hillock. The cell generates action potentials by opening sodium channels. Due to the high concentration gradient of sodium ions, positive particles flow into the cell, changing the potential from ca. -75mV to ca. +30mV (depolarization). After this process the sodium channels close.

After a certain time interval, positively charged potassium ions leave the cell through potassium channels. This process is called repolarization because the resting potential of about -70 to -80mV is restored. In some cell types the restored resting potential is preceded by a minor hyperpolarization.

Action potentials are all-or-none signals, meaning that a uniform action potential is generated after a certain threshold voltage has been exceeded. The amplitudes of action potentials are independent of the voltages that generated them.

Action potentials are conducted along axons. Action potentials that arrive at other neurons are a result of temporal (several consecutive potentials) and spatial (multiple simultaneous potentials) summation of all postsynaptic potentials that reach the cell. The frequency of the resulting action potential depends on this sum of all potentials at the axon hillock

see also: receptor potential, compound action potential

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