Crayfish swimming: alternating motor output and giant fiber activity.

Many workers have suggested that the crayfish giant fibers trigger swimming movements or tail flips during escape responses. Recordings from intact animals show that this is often not the case; both swimming and single tail flips can occur in the absence of giant fiber activity. Swimming movements and tail flips are coordinated by neural mechanisms not involving the giant fibers. When giant fibers are active, they may trigger the first flexion in a swimming sequence, initiate a single tail flip, or synchronize the muscular activity in the several segments of the abdomen, but they are not a necessary part of the neural oscillator which drives swimming.