RESPONSES OF MUSCLES OF THE SQUID TO REPETITIVE STIMULATION OF THE GIANT NERVE FIBERS

Abstract

With increasing frequency of stimulation of a giant nerve fiber in the squid, Loligo pealii, the only increase in the tension developed by the circular muscle fibers of the mantle is a small amount (5 to 10 per cent) over the range of incomplete relaxation. The absence of any increased response at higher frequencies shows that in the fresh muscle a single nerve impulse is capable of activating every muscle fiber which it reaches. However, the isolated muscle very readily becomes fatigued when stimulated at high frequency and thereafter greater tension is produced at the higher rates. In the normal animal there would be no use for peripheral facilitation and each contraction of the mantle is produced as an all-or-nothing response.