Circus reexcitation as a cause of repetitive activity in crayfish lateral giant axons

Unpolarized electrotonic connections between the two lateral giant axons of crayfish nerve cord have been demonstrated. Presumably they are also the sites of the tightly coupled unpolarized ephaptic junctions by which activity from one axon may be transmitted to the other. Commissures between the segmental branches of the two axons are probably the sites of the junctions. If septal transmission is blocked in one axon, the inactive segment can be excited by the activity of the other axon. The segmentally arrayed ladder of ephaptic junctions forms a series of delay lines and circus activity can occur in the loops between the two axons. Two segments form a loop with a delay line of 4 msec. The frequency of repetition is about 250/second. Each additional segment introduces another delay of about 4 msec. For a three‐segment loop the repetition rate is about 125/second. The delays at ephaptic junctions between neurons in vertebrate nervous systems are probably too brief to cause repetitive activity.