Rheobase

Rheobase is the minimum threshold level of neuron excitation at which a change in membrane potential occurs. The number of mediator molecules at the site of application of the stimulus must reach a value corresponding to the rheobase and exceeding it. If the level of excitation is weak, then the neuron ignores it and continues to be at rest. If the level of excitation is strong enough, then it affects the postsynaptic membrane. The relationship between stimulus and rheobase is called force-time and provides information about the firing rate and number of neurons involved at a given activation level.

For a number of molecules (for example, Ca2+ ions, acetylcholine molecules), the activation threshold depends on the concentration in the synaptic cleft. The activation level of a cell can be characterized by the strength of activation (current amplitude or action potential) as well as the time required to reach the rheobase level.

When the strength of stimulation increases to a value that exceeds the rheobase, but does not reach saturation, the transfer of excitation can occur, despite the fact that the active conductivity of the membrane remains high for a long time compared to the initial one. The mechanism of such stable excitation is called long-term ionization. Due to rheobasis, the amplitude of the wave increases in proportion to the strength of stimulation. Under constant current conditions, the magnitude of the constant component (“current through the membrane”) is equal to the product of the rheobase and the stimulation frequency. Under these conditions, if the membrane resistance does not depend on the current strength, its shape remains constant despite changes in the amplitude of the waves. The property of information infinity can be explained by the combined action of the triggering and reverberation mechanisms.