Histochemical characteristics of mandibular muscles of monkeys

Abstract

Histochemical profiles were obtained for several jaw closing muscles and for one jaw opening muscle. The jaw closing muscles were found to vary widely in their percentages of fast glycolytic (FG) fibers, fast oxidative glycolytic (FOG) fibers, and slow oxidative (SO) fibers. The masseter and the posterior portion of the temporalis muscles had high percentages of fast-contracting fibers (FG and FOG), whereas the medial pterygoid, zygomaticomandibularis (ZMM), and anterior portion of the temporalis muscles were composed largely or entirely of SO fibers. We conclude that the mandibular muscular system, like the limb muscular systems, contains both muscles which are well suited for strong phasic contractions and muscles which are well suited for the production of tonic, low force, vernier contractions. The high degree of compartmentalization of the temporalis muscle may provide a model for studying the distribution of proprioceptors within such a muscle and for studying the role which these receptors play in the control of vernier contractions.