The motor neurons in the crab ventilatory system have previously been considered to be passive output elements in that the generation of bursts of action potentials in these neurons during ventilation was thought to be due to cyclic inhibition and excitation from the interneurons in the ventilatory central pattern generator. This study demonstrates that the large-amplitude depolarization that underlies bursts of action potentials in ventilatory motor neurons is produced by a plateau potential. These motor neurons satisfy a number of the experimental tests that have been proposed for plateau potentials, such as triggering of the burst by a brief depolarization, termination of the burst by a hyperpolarizing input, and an all-or-none suppression of the depolarizing potential by the injection of hyperpolarizing current.

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