Evoked potentials in cat extraocular muscle.

Cat extraocular muscle consisted of a peripheral portion ivith red histochemical properties and a central part with white muscle findings. Recordings were obtained from the two regions by extracellular electrodes. Third nerve stimulation produced action potentials which were prolonged monophasic units (slow units) along the edge, and short-duration, biphasic spikes (fast units) in the center of the muscle. Third nucleus stimulation induced an immediate fast eye movement and an electro7nyographic pattern similar to III nerve stimulation. Vestibidar complex stimidation brought about a sloio movement that did not begin until several seconds after excitation. The motor unit activity consisted of slow units throughout the muscle which began at the start of stimulation. Intravenous succinylcholine produced fast and intermediate spike activity from all layers but very few slow units. Evoked fast eye movement appeared to be accompanied by fast and slow action potentials while slow vestibular movement was associated with only slow units. The motor unit pattern appeared to correlate with the histochemical organization and the type of movement.