CONTRACTILE PROPERTIES OF A HIGH-FREQUENCY MUSCLE FROM A CRUSTACEAN .1. ACTIVATION PATTERNS IN-VIVO

1.The flagella of crustaceans are small appendages, borne on the maxil lipeds, which beat repetitively when active. Flagellar movement is bro ught about by contraction of a single muscle, the flagellum abductor ( FA). 2. The stroke frequency of the flagella of the green crab, Carcin us maenas, was about 11 Hz at 15 degrees C and was relatively independ ent of animal size [frequency is proportional to (animal mass)(-0.07)] , even though scaling considerations suggest that, for constant muscle stress, frequency should be proportional to mass(-0.33). The coeffici ent of variation for intervals between successive strokes of a flagell um was about 4%. 3. The FA is innervated by two excitatory motoneurone s. Each of the neurones fired 0-5 times during a stroke. The interspik e interval when a neurone fired more than once during a stroke was 3-4 ms.