Anatomic Organization of the Cat Facial Nerve

Abstract

The location of efferent neurons supplying muscles innervated by the facial nerve was studied in the brain stem of the cat; horseradish peroxidase (HRP) was used as a tracer of retrograde protein transport. One to 15 μl of HRP was injected into various muscles. Orbicularis oculi and orbicularis oris muscles were represented in the lateral division of the facial nucleus. The Platysma, posterior belly of digastric, auricularis superior, and frontalis muscles were represented in the medial division of the facial nucleus. No labeled neuron was found in the trigeminal nerve nucleus or any other brain stem nuclei. The grouping of the motor neurons into relatively discrete areas of the nucleus and the fact that the facial nerve innervates various muscles through separate branches suggest that these motor neurons travel together in discrete groups within the facial nerve trunk. However, orientation of the facial nerve fibers was demonstrated by use of the Marchi method and an osmium stain after complete and partial transection of the nerve at the internal auditory meatus; this showed that the motor axons to the peripheral branches are diffusely located throughout the temporal course of the facial nerve.