Q.State the 'all-or-none' law of nerve impulse conduction and explain what is meant by the term 'threshold stimulus'.

[!TLDR] The all-or-none law states a neuron either fires a full-sized action potential or does not fire at all, once the stimulus reaches the threshold strength — there is no partial impulse. [!ANSWER] All-or-none law: a stimulus at or above threshold produces a full, maximal action pot …

The all-or-none law states that once a stimulus reaches the minimum strength needed to trigger a response — the threshold stimulus — the neuron fires a complete, full-amplitude action potential; a stronger stimulus does not produce a bigger or 'stronger' impulse. Conversely, a sub-threshold stimulus, however close to threshold, produces no propagated action potential at all. The threshold stimulus is therefore the minimum intensity of stimulation required to depolarize the membrane enough to open the necessary density of voltage-gated Na+ channels and trigger this self-regenerating action potential; stimulus intensity above threshold is instead encoded by the nervous system t …

Remember the law concerns a single neuron's single impulse; a stronger overall sensation is coded by MORE im …

A common error is to think a stronger stimulus makes a 'bigger' action potential — the amplitude of an individual ac …