Morphology of motor units in cat extraocular nodule

Muscle fibers from single motor units in cat inferior oblique were marked iontophoretically with procion red injected through an intracellular pipette. The fibers were isolated by dissection and characterized by electron microscopy. A fiber in a slow motor unit with non-conducted electrical responses showed slow fiber morphology of the amphibia-type. Fast, twitch motor units contained fibers with twitch fiber morphology. Thus, a good correlation between muscle fiber structure and function was obtained in these eye motor units, examined with both physiological and morphological techniques.