In Vivo Microelectrode Studies of the Cat Retractor Bulbi Fibers.

In cats under pentobarbital sodium anesthesia, the characteristics of the muscle fibers of the retractor bulbi were studied, on stimulation of the VI nerve nucleus, by means of intracellular glass micropipettes. The muscles remained intact and attached to the globe; the blood and nerve supplies remained normal. The retractor bulbi is composed of a uniform population of twitch fibers with a mean resting potential of 71 mv., a mean action potential of 93 mv., and a mean latency of 2.6 msec. The retractor bulbi does not contract on the intravenous injection of succinylcholine, as do the four recti and two obliques. A functional organization of the VI nerve nucleus in relation to the several movements of the retractor bulbi and the nictitating membrane were noted.