Modulation of Jaw Muscle Spindle Discharge during Mastication in the
Rabbit.
Masuda, Y., Morimoto, T., Hidaka, O., Kato, T., Matsuo, R., Inoue, T.
Kobayashi, M. and Taylor, A..
Department of Oral Physiology, Osaka University Faculty of Dentistry,
Osaka, Japan and *Department of Physiology, Charing Cross and Westminster
Medical School, London, UK.
APStracts 4:0001N, 1997.
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 of 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 in 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.
Received 1996; accepted in final form 1996.
APS Manuscript Number J.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 21 January 1997