Modulation of Jaw Muscle Spindle Discharge During Mastication in the Rabbit

Abstract

Discharges of jaw muscle spindles were recorded during chewing carrot from mesencephalic trigeminal nucleus (Mes V) in the awake rabbit to evaluate contribution of the muscle spindles to the development of complete sequences of masticatory movements. The Mes V spindle units were divided into two types according to the maximum firing rates during mastication, with a dividing line at 200 Hz; high-frequency units and low-frequency units. Although both types of units fired maximally during the jaw-opening phase of chewing cycles, their firing rates and pattern varied according to three sequential stages of mastication (stages I, IIa, and IIb). The high-frequency units often increased firing before the start of mastication and built up firing in the first few chewing cycles. Their maximal firing rate was sometimes lower during stage IIa (chewing stage) than during stage I (ingestion stage) and stage IIb (preswallowing stage), although the jaw movements were greater in stage IIa than in other stages. The phase relationship of the firing to a jaw movement cycle in stage IIa was consistent in individual units. The low-frequency units did not build up activity before the onset of movements. They fired mostly during the jaw-opening phase, but the peak of firing did not necessarily coincide with the time of maximal opening. It was concluded that the difference in the firing pattern among masticatory stages may be ascribed to a stage-dependent modulation of both fusimotor activity and jaw movement pattern.

Relationships between Geriatric Oral Health Assessment Index scores and general physical status in community‐dwelling older adults

“…A biological mechanism may explain the relationship between masticatory ability and body muscle strength. Masticatory movements stimulate various orofacial sensory inputs via the trigeminal nerve: epithelial and periodontal mechanoreceptors, temporomandibular joint receptors, jaw-closing muscle spindles and Golgi tendon organs [23][24][25][26][27][28][29][30] . Although peripheral sensory inputs may not be the only reason for the association between mastication and body muscle strength, it is possible that peripheral orofacial sensory inputs may influence motor-neural control of muscle activity in other parts of body 30,31 .…”

Involvement of histaminergic inputs in the jaw-closing reflex arc

“…Moreover, the amplification of MesV afferent inputs through gap junctions may be reduced because of a decrease in the input resistance of MesV neurons, as mentioned above. During mastication, muscle spindles in the jaw-closing muscle discharge during the jawopening phase as well as during the jaw-closing phase (Cody et al 1975;Goodwin and Luschei 1975;Masuda et al 1997), which means that the jaw-closing motoneurons are invaded by excitatory inputs through the jaw-jerk reflex arc during the jaw-opening phase. To facilitate the jaw-opening movement during the jaw-opening phase, such excitatory inputs during the jaw-opening phase have been thought to be canceled by simultaneous inhibitory inputs to jaw-closing motoneurons from the central pattern generator for mastication (Chandler and Goldberg 1982;Nakamura and Katakura 1995).…”

Analysis of moment structures for assessing relationships among perceived chewing ability, dentition status, muscle strength, and balance in community‐dwelling older adults

“…Muscle strength and balance may be influenced by orofacial sensory inputs from the trigeminal nerve, namely from epithelial mechanoreceptors, temporomandibular joint receptors, jaw-closing muscle spindles and Golgi tendon organs. [20][21][22][23][24][25][26] Therefore, these peripheral orofacial sensory inputs possibly influence motoneural control of the exertion of muscle strength in other parts of the body.…”