Threshold potential

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In connection with the transmission of signals in nerves and muscle fibers, the threshold potential is the potential difference at which an action potential is triggered. Values ​​of the membrane potentials below the threshold potential are called "subliminal", those above the threshold "supra-threshold".

While the resting membrane potential (around −70 mV) is a membrane potential that is essentially determined by potassium and is therefore close to the value for the potassium equilibrium potential (around −90 mV), the fast voltage-activated sodium channels responsible for an action potential have an activation threshold of about −50 mV.

In order to open these ion channels for sodium , the cell membrane must be depolarized to at least this threshold value . Depending on the cell type and conditions, this happens either through the action of neurotransmitters that cause post- synaptic local depolarization ( EPSP ), or through a generator potential ( receptor potential in sensory cells), or electrotonically on the axon hill or through a transmitted action potential on the axon .

The threshold potential has a value that is characteristic of the excitable cell and is determined by the type of ion channel or by the specific molecular properties of the channel proteins .