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First published online on January 10, 2003.
 Copyright © 2003 by The Physiological Society
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2003.030221v1
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Received August 6, 2002
Accepted after revision December 4, 2002

Pulsatile control of the human masticatory muscles

Shapour Jaberzadeh1, Pål Brodin2, Stanley C. Flavel1, Nicholas J. O'Dwyer3, Michael A. Nordstrom1, and T. S. Miles4*

1 Department of Physiology, The University of Adelaide, Adelaide SA 5005, Australia
2 Department of Oral Biology, University of Oslo, Oslo, Norway
3 School of Physiotherapy, The University of Sydney, New South Wales 1825, Australia
4 Department of Physiology, The University of Adelaide, Adelaide, SA 5005, Australia

* To whom correspondence should be addressed. E-mail: timothy.miles{at}adelaide.edu.au.

Spectral analysis of jaw acceleration confirmed that the human mandible 'trembles' at a peak frequency around 6 Hz when held in its rest position and at other stationary jaw openings. The 6 Hz tremor increased during very slow movements of the mandible, but other lower-frequency peaks became prominent during more rapid jaw movements. These lower-frequency peaks are likely to be the result of asymmetries in the underlying, voluntarily produced, 'saw-tooth' movements. In comparison, finger tremor at rest and during slow voluntary movements had a mean peak frequency of about 8 Hz: this frequency did not change during rhythmical finger flexion and extension movements, but the power of the tremor increased non-linearly with the speed of the movement. The resting jaw tremor was weakly coherent with the activity of the masseter and digastric muscles at the tremor frequency in about half the subjects, but was more strongly coherent during voluntary movements in all subjects. The masseter activity was at least 150 deg out of phase with the digastric activity at the tremor frequency (and at all frequencies from 2.5-15 Hz). The alternating pattern of activity in antagonistic muscles at rest and during slow voluntary movements supports the idea that the masticatory system is subject to pulsatile control in a manner analogous to that seen in the finger.




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