Fig. 2. Opener muscle in the crayfish claw showing regional variation in excitatory postsynaptic potential (EPSP) amplitudes. The excitatory motor neuron was stimulated at 50 Hz (20 stimuli per train). The largest potentials were measured in proximal fibres, with smaller potentials in distal fibres; the smallest potentials occurred in central fibres. The double-headed arrows indicate where the medial EPSP traces originated on the muscle. The numbered arrows indicate where the lateral EPSP traces were sampled and correspond to the numbered traces on the right. The regional differences are similar for both lateral and medial halves of the muscle.