THE REFRACTORY STATE OF THE GENERATOR AND PROPAGATED POTENTIALS IN A PACINIAN CORPUSCLE

A propagated potential produced in the Pacinian corpuscle in response to mechanical stimuli leaves a refractory state of 7 to 10 msec. duration. The refractory state is presumably produced at the first intracorpuscular node of Ranvier. The recovery of receptor excitability for producing an all-or-none response to mechanical stimulation follows the same time course as that of the electrically excited axon. Upon progressive reduction of stimulus interval (mechanical), the propagated potential falls progressively to 75 per cent of its resting magnitude and becomes finally blocked within the corpuscle. A non-propagated all-or-none potential, presumably corresponding to activity of the first node, is then detected. The critical firing level for all-or-none potentials increases progressively during the relative refractory period of the all-or-none potential, as the stimulus interval is shortened. Thus generator potentials up to 85 per cent of a propagated potential can be produced in absence of all-or-none activity. Generator potentials show: gradual over-all increase in amplitude and rate of rise as a function of stimulus strength; constant latency; and spontaneous fluctuations in amplitude. A generator potential leaves a refractory state (presumably at the non-myelinated ending) so that the amplitude of a second generator response which falls on its refractory trail is directly related to the time elapsed after the first generator response and inversely to its amplitude. The generator potential develops independently of any refractory state left by a preceding all-or-none potential.