Distribution of the chain of stretch receptors on masticatory muscles of the rat.

The existence of stretch receptors on the fasciae of masticatory muscles of the rat was demonstrated by means of methylene blue vital staining. A single cord of connective tissue on each side extends over the surfaces of the superficial masseter, temporal, and medial pterygoid muscles. The complex arborizations of unmyelinated nerve terminals originated from branches of the buccal nerve gathered closely within the cord forming the chain of stretch receptors. The chain was lengthened during the jaw closing phase, when the firing rates of stretch receptors probably increased. Results suggested that the chain of stretch receptors signaled position or movement of the mandible. The same stretch receptors were also detected on the masticatory muscles of some other rodents.