Eye muscle proprioception and the semilunar ganglion

Abstract

A cellular pool was found in the medial dorsolateral part of the semilunar ganglion of lambs which contains the soma of afferent proprioceptive fibers from extraocular muscles. The unitary discharge of these cells was recorded by means of tungsten microelectrodes. The responses of the units to stretching the extraocular muscles were characterized by a sustained increase in the discharge rate which ceased as soon as the stretch was released. The latencies were very short: 1–3 msec. The firing of the units during stretching was inhibited by electrical stimulation of the extraocular muscles. The units could thus be identified as muscle spindle afferents. The units responsive to stretching the extraocular muscles were unaffected by stimulation of other trigeminal fields or by jaw movements. Nembutal anesthesia did not eliminate the responses. The responses were abolished completely by severing the ipsilateral ophthalmic branch of the trigeminal nerve. The conclusion was reached that the semilunar ganglion contains the cells bodies of afferent fibers from the extraocular muscles coursing through the ophthalmic branch of the trigeminal nerve.