Decremental propagation of reflex spikes along giant axons of the earthworm Amynthas hawayanus.

The constant-velocity conduction of an action potential evoked by stimulating the isolated nerve cord of the earthworm Amynthas hawayanus differs from the propagation of a reflex spike evoked by stimulating the epithelium of an epithelio-muscular-nerve-cord (EMNC) preparation and recorded between pairs of microelectrodes spaced every 10 segments along either giant axon. The reflex spike is decremental and lasts for no more than 20 segments before it eventually disappears. Secondary and tertiary spikes sometimes arise even before the disappearance of the primary spike, and disappear after propagating for a short distance. This decremental propagation is tentatively attributed to the summation of excitatory postsynaptic potentials from the synaptic impingings of afferent interneurons in a polysynaptic reflex arc.