AllornonePrinzip

AllornonePrinzip, also known as the all-or-none principle, is a basic concept in physiology describing how excitable cells respond to stimuli. In neurons and skeletal muscle fibers, a stimulus must exceed a threshold to elicit a complete response; if the threshold is not reached, no response occurs. Once threshold is reached, the resulting action potential or contraction has a characteristic, invariant magnitude and is conducted along the cell without decrement. The amplitude of a single action potential is essentially the same regardless of how much the stimulus exceeds the threshold. The strength of stimulation is instead conveyed by the frequency of action potentials or by the recruitment of additional cells, not by larger spikes.

In neurons, the action potential propagates along the axon with a nearly constant peak voltage, and refractory periods help maintain unidirectional propagation and amplitude stability. In skeletal muscle, a motor neuron's action potential triggers a fixed contractile response in the innervated muscle fiber, with overall muscle force determined by motor unit recruitment and firing rate.

Limitations: The principle applies to the all-or-nothing nature of individual action potentials, but many physiological signals are graded, such as synaptic potentials and calcium signaling. Subthreshold inputs can summate temporally or spatially to reach threshold. At the tissue level, force production is also influenced by recruitment dynamics and firing patterns, so it is not strictly all-or-none in aggregate.