Sensory control of masticatory jaw movements according to food consistencies in the rabbit

Publisher Summary This chapter examines the roles of periodontal and muscle spindle afferents on regulating mastication, andfocuses on an experimental study carried out to study the same. This experiment makes use of awake and anesthetized rabbits. After the bilateral combination of the maxillary and inferior alveolar nerves in the awake rabbits, the jaw movements become smaller both vertically and horizontally, their trajectories become irregular, and electromyograms (EMGs) activities of their jaw-closing muscles are greatly reduced during mastication. During their rhythmic jaw movements induced by repetitive electrical stimulation of cerebral cortex in the anesthetized rabbits, one of polyurethane foam strips of varying hardness are inserted between the upper molars and the force transducers. The peak and buildup speed of the masticatory force and the EMG of the masseteric muscles increase in proportion to the hardness of the test strip-by-strip application. After the sectioning of the maxillary and inferior alveolar nerves, the buildup speed of the masticatory force is significantly slowed down and the peak force tends to decrease during the strip application. Lesioning trigeminal mesencephalic nucleus (MesV), where the cell bodies of the muscle spindle afferents are located, also reduces the enhancement of the masseteric EMG during the strip application. When the MesV is lesioned in combination with sectioning the maxillary and inferior alveolar nerves, the facilitatory responses of masseter nucleus is almost abolished. It is therefore concluded that both periodontal and muscle spindle afferents are mainly responsible for the regulation of masticatory muscle activities and jaw movements.