Summary
Motor unit (MU) firing frequency is an important determinant of reflex inhibition in the human jaw muscles. Masseter MUs may be driven steadily by various intraoral tasks, but their lowest sustainable firing frequency varies according to task. In this study we examined the effect of task on masseter MU reflex behaviour under controlled conditions, in which the prestimulus MU firing frequency and stimulation were constrained. All MUs tested were inhibited by a non-noxious electrical stimulus applied to the oral mucosa, but there were significant differences in the magnitude of single MU inhibition depending on the task employed to drive the MUs. It appears that single masseter MU reflex behaviour can alter according to task, even when the prestimulus excitation of the masseter motoneuron pool is apparently constant. This suggests that masseter MU reflex behaviour may be modulated by task-related peripheral afferent input.
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References
Bonte B, van Steenberghe D (1989) Single motor unit and surface electromyogram analysis of human jaw-closing reflexes after tapping an upper tooth. Arch Oral Biol 34:903–910
Dubner R, Sessle BJ, Storey AT (1978) The neural basis of oral and facial function. Plenum Press, New York
Eriksson P-O, Stalberg E, Antoni L (1984) Flexibility in motor-unit firing pattern in the temporal and masseter muscles related to types of activation and location. Arch Oral Biol 29:707–712
Granit R, Kernell D, Shortess GK (1963) Quantitative aspects of repetitive firing of mammalian motoneurons caused by injected currents. J Physiol 168:911–931
Hannam AG (1982) The innervation of the periodontal ligament. Berkovitz BKB (ed) The periodontal ligament in health and disease. Pergamon Press, Oxford UK, pp 173–196
McMillan AS, Hannam AG (1990) Task dependence of limit frequencies in human masseter motor units. J Dent Res 69:272
McMillan AS, Hannam AG (1989) Reflex inhibition in single motor units of the human lateral pterygoid muscle. Exp Brain Res 96:97–102
Miles TS, Turker KS, Le TH (1989) Ia reflexes and EPSPs in human soleus motor neurones. Exp Brain Res 77:628–636
Miles TS, Turker KS, Nordstrom MA (1987) Reflex responses of motor units in human masseter muscle to electrical stimulation of the lip. Exp Brain Res 65:331–336
Miles TS, Turker KS (1986) Does reflex inhibition of motor units follow the size principle? Exp Brain Res 62:443–445
Sessle BJ (1981) Mastication, swallowing, and related activities. Roth GI, Calmes R (eds) Oral biology. CV Mosby, St Louis, pp 51–89
Thomas CK, Ross BH, Stein RB (1987) Human motor-unit recruitment during isometric contractions and repeated dynamic movements. J Neurophysiol 57:311–324
Thomas CK, Ross BH, Stein RB (1986) Motor-unit recruitment in human first dorsal interosseous muscle for static contractions in three directions. J Neurophysiol 55:1017–1029
Turker KS, Miles TS (1989) Surface electromyography, force and single motor-unit data for inhibitory reflex responses in human masseter at two levels of excitatory drive. Arch Oral Biol 34:731–737
Turker KS, Seguin JJ, Miles TS (1989) Modulation of an inhibitory reflex in single motor units in human masseter at different joint angles. Neurosci Lett 100:157–163
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McMillan, A.S., Hannam, A.G. Task dependence of human masseter motor unit reflex behaviour. Exp Brain Res 88, 443–446 (1992). https://doi.org/10.1007/BF02259119
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DOI: https://doi.org/10.1007/BF02259119