Neurophysiology of extraocular muscles.

E. lye movements may be divided grossly into "tonic" and "phasic" movements. Are both of these principal types produced by the same motor nerves and muscle fibers, or are separate systems present that are functionally suited to each of the types of movements? Morphological and physiological studies demonstrate that at least two and possibly three neuromuscular systems are present in eye muscles, and that these have characteristics which would suit them for different types of eye movements. Hess and Pilar have shown that cat extraocular muscles contain singly innervated twitch fibers with "en plaque" type motor endings, and smaller multiply innervated "slow" fibers with endings analogous to "en grappe" motor endings. In human eye muscles, cholinesterase staining techniques have been employed to demonstrate these two fiber types as well as fibers with multiple "en plaque" endings." Kupfer' estimated that two thirds to three quarters of all the extraocular muscle