Motoneuronal commands during swimming behaviour in the shore crab.

Neurograms of proximal leg motor nerves were obtained during swimming in the shore crab. Whereas excitor motoneurones fire in bursts, the common inhibitor motoneurone discharges tonically with simultaneous spikes in all the motor nerves. The average firing frequency of the common inhibitor increases as the period of the swimming cycle decreases. Moreover, greater fluctuations of the firing frequency of the common inhibitor occurs within long rather than short swim cycle periods.