Motor Control of masticatory muscles

Abstract

This chapter focuses on the brainstem and higher brain center mechanisms involved in the execution, initiation, reflex regulation, and sensorimotor coordination of the masticatory musculature. A brief overview is given of masticatory musculoskeletal biomechanics, but other chapters may be consulted for general aspects of biomechanics related to motor control and for the structural and functional features of this musculature and its motor units and muscle fibers and sensory innervation. Mastication is a complex motor function that involves the simultaneous bilateral coordinated activation and/or inactivation of the jaw, tongue and face muscles. Jaw opening occurs by downward traction of the mandible by the anterior belly of the digastric muscle and the mylohyoid muscle and anterior traction of the condyles by the lateral pterygoid muscle. Jaw closing occurs by activation of the masseter, temporalis, and medial pterygoid muscles. Jaw protrusion requires activation of the lateral pterygoid, the anterior fibers of the temporalis and the superficial masseter muscles, and jaw retrusion is brought about by activation of the posterior fibers of the temporalis muscles. During mastication, the tongue muscles (e.g., genioglossus-tongue protrusion; hyoglossus-tongue depression; styloglossus-tongue retrusion; palatoglossus-tongue elevation) assist in maneuvering the food bolus from side to side, and the lip muscles (e.g., orbicularis oris-perioral sphincter, zygomaticus major-elevation and retraction of the modiolus) and cheek muscles (buccinators-retraction of the modiolus), along with the tongue muscles, assist in maintaining the food bolus within the mouth on the occlusal table (Dubner et al. 1978; Lang 1995; Miles et al. 2004).