FACILITATION BY PREVIOUS ACTIVITY IN A PACINIAN CORPUSCLE

A period of supernormal excitability is left by a propagated impulse in a Pacinian corpuscle. The increase in excitability is found 6 to 10 msec. after an impulse occurs in the corpuscle. Supernormality is produced by either mechanically elicited dromic impulses, or by electrically excited antidromic impulses. Generator potentials do not cause supernormality. Local potentials discharged spontaneously by the corpuscle, and which fall on the supernormal trail left by an antidromic impulse, become enhanced in amplitude, an eventually are turned into propagated dromic potentials. The supernormal period is interpreted as caused by a negative after-potential left at the first intracorpuscular node of Ranvier which outlasts both the recovery time of the firing level and that of the generator potential during the corpuscle's relative refractory period.