firing threshold

physiology

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June 26, 2026

Quick Summary

The firing threshold is a critical point in physiology where a stimulus is strong enough to trigger an action potential in a neuron or muscle cell. Before reaching this threshold, a cell maintains a resting potential, typically around -75 millivolts, with a negative charge inside.

When stimulated, ions like sodium move into the cell, causing depolarization. If this depolarization reaches the threshold potential (around -60 mV), it triggers a rapid influx of sodium ions, creating an action potential. This all-or-none principle means the cell either fires a full response or none at all, regardless of stimulus strength beyond the threshold. This process is fundamental for transmitting nerve impulses and causing muscle contractions.123

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muscle
Acetylcholine-acetylcholine receptor interaction
At a critical point (the firing threshold for the muscle cell) a self-generating action potential is triggered, causing the membrane potential to reverse and become briefly positive. The action potential propagates over the muscle fibre membrane to activate the contractile process.
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At a critical point (the firing threshold for the muscle cell) a self-generating action potential is triggered, causing the membrane potential to reverse and become briefly positive. The action potential propagates over the muscle fibre membrane to activate the contractile process.
Read More