Action potential

Definition

A rapid, transient, self-propagating depolarization of the cell membrane in an excitable cell, triggered when the membrane potential reaches a threshold and mediated by voltage-gated ion channels. In arthropods, action potentials transmit signals along axons of sensory neurons, motor neurons, and interneurons, as well as in muscle fibers and some glandular cells. The all-or-none character ensures faithful signal transmission over long distances, such as from a spider's trichobothrium to its central nervous system or from a cockroach's giant interneuron to its leg muscles during the escape response.

Etymology

Example

In the femoral chordotonal organ of a locust, stretching of the receptor apodeme triggers a train of action potentials in the sensory neuron, with spike frequency encoding the degree of joint flexion for proprioceptive feedback during walking.

Synonyms

• nerve impulse
• spike

Related Terms

• Resting potential
• depolarization
• repolarization
• voltage-gated channel
• Axon
• Synapse
• electrophysiology
• giant fiber
• neuromuscular junction

Usage Notes

In arthropod literature, 'spike' is often used interchangeably in electrophysiological recordings, though 'action potential' is preferred for formal description. The term distinguishes propagated signals from graded local potentials (receptor potentials, synaptic potentials) that decay with distance. In insect muscle, action potentials typically arise from excitatory junction potentials rather than direct muscle excitation as in vertebrates. Some arthropod neurons exhibit calcium-dependent action potentials or plateau potentials distinct from the classic sodium-based spike.