Neck Muscle Afferents: The Sensory Innervation of the Sternomastoid Muscle of the Rat

Abstract

The proprioceptive information from the neck obviously plays an important role for the coordination of body, head and eye movements. The contribution of muscle afferents to the sensory input from the neck gained increasing attention in recent years. The question whether neck muscles, in the light of their potentially particular afferent role, differ in their sensory innervation from the majority of other muscles, is being discussed lively. A clear answer will remain pending until sufficient data from all neck muscles will be available and can be compared with those from other muscles. Certainly, it has been shown that there is an exceptionally high density of muscle spindles in different neck muscles (Voss, 1958; Richmond and Abrahams, 1975; Bakker and Richmond, 1982; Pfister and Zenker, 1984). However, the fact cannot be neglected that, e.g., in the rat, there are considerable differencees between different neck muscles: we calculated 200 spindles per gram muscle weight for rectus capitis minor, but only 53/g for rectus capitis major and 86/g for sternomastoid muscles (Bank-oul, unpublished results). Moreover, the content of other types of sensory receptors has to be taken into consideration.