Sensory components facilitating jaw-closing muscle activities in the rabbit

Abstract

The role of oral and facial sensory receptors in the control of masticatory muscle activities was assessed from the effect of acute deafferentiation on cortically induced rhythmic jaw movements (CRJMs) in anesthetized rabbits. When a thin polyurethane-foam strip (1.5, 2.5 or 3.5 mm thick) was placed between opposing molars during CRJMs, masseteric activities were facilitated in association with an increase in the medial excursion of the mandible during the power phase. The effects varied with the pattern of CRJMs, and the rate of facilitation was greater for small circular movements than for the crescent-shaped movements. Furthermore, the response of the masseter muscle was greater in the anterior half of the muscle, where muscle spindles are most dense, than in its posterior half. It was also demonstrated that the response increased with an increase in the thickness of the test strip. In contrast, the activities of the jaw-opening muscle were not affected significantly. The duration of masseteric bursts increased during application of the test strip and the chewing rhythm tended to slow down. However, the latter effect was not significant. After locally anesthetizing the maxillary and inferior alveolar nerves, the facilitative responses of the masseter muscle to the test strip was greatly reduced but not completely abolished. Lesioning of the mesencephalic trigeminal nucleus (Mes V) where the primary ganglion cells of muscle spindle afferents from jaw-closing muscles and some periodontal afferents are located, also reduced the facilitative effects. Similar results were obtained in the animals with the kainic acid injections into the Mes V 1 week before electrical lesioning of this nucleus. In these animals the effects of electrical lesioning of the Mes V could be attributed to the loss of muscle receptor afferents since the neurons in the vicinity of the Mes V were destroyed and replaced by glial cells, whereas the Mes V neurons are resistant to kainic acid. When electrical lesioning of the Mes V and sectioning of the maxillary and inferior alveolar nerves were combined in animals with a kainic acid injection into the Mes V, the response of the masseter muscle to application of the strip was almost completely abolished. From these findings, we conclude that both periodontal receptors and muscle spindles are primarily responsible for the facilitation of jaw-closing muscle activities.(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation of mandibular loading and bite force in mammals during mastication

“…Several studies have shown that increases in food 'hardness' are associated with increases in EMG burst duration (Hidaka et al, 1997;Lavigne et al, 1987;Liu et al, 1993;Lund et al, 1998;Morimoto et al, 1989). On the basis of these EMG data, it might seem reasonable to hypothesize that variation in bite force magnitudes in mammals is significantly correlated with variation in the duration of force generation.…”

“…Rate modulation rather than time modulation may allow rhythmic mastication to proceed at a relatively constant frequency, simplifying motor control computation. Masticatory bone strain and bite force modulation 1989;Nakajima et al, 2001). These studies reveal that descending control and afferent information from muscle spindles, Golgi tendon organs, and stretch receptors in the periodontal and 'periarticular' ligaments modulate the motor program and temporal and spatial patterns of jaw movement (Sessle, 2006).…”

Participation of Sodium Currents in Burst Generation and Control of Membrane Excitability in Mesencephalic Trigeminal Neurons

“…Additionally, there is evidence that Mes V neurons form coupled networks among themselves via electrical and excitatory recurrent connections (Baker and Llinas, 1971;Luo and Dessem, 1996). Although they are not directly responsible for setting the oral-motor rhythm during mastication or sucking, they are important for production of appropriate jaw movements (Miles, 1979;Morimoto et al, 1989) and could participate as interneurons because of their central brainstem location and synaptic connectivity (Kolta et al, 1995). As such, they are active during fictive mastication and local stimulation of nearby interneurons produces synaptic potentials, subthreshold oscillations, and spike activity in some Mes V neurons (Verdier et al, 2004).…”

Alternatives to Radiation Investigations in Orthodontics

“…Cross-talk can be minimized by standardizing the experimental conditions. Moreover, double deferential techniques can also assist in eliminating cross-talk [37][38][39][40][41][42][43] . This is the prime cause of criticism in telemetry sEMG recording where cross-talk and noise can compromise the results 44 .…”