Minimal tonic firing rates of human lateral pterygoid single motor units.
OBJECTIVE
The minimal tonic firing rates (the lowest firing rates at which motor units fire regularly; MTFR) of single motor units (SMUs) within the lateral pterygoid muscle have not been widely investigated. The aims of this study were (a) to identify MTFR of SMUs within the inferior head (IHLP) and superior head (SHLP) of the lateral pterygoid muscle during horizontal jaw movements, and (b) to determine whether these MTFR vary with movement direction.


METHODS
Twenty subjects moved the jaw to maintain SMU firing at the lowest continuous firing rate. SMU activity was recorded from computer-tomography-verified sites within the IHLP or SHLP.


RESULTS
In the IHLP, the mean (+/-SD) MTFR for contralateral movement (15.6+/-2.3 imp/s; n=22 SMUs) were not significantly different from those during protrusion (16.3+/-3.4 imp/s; n=19). In the SHLP, the mean (+/-SD) MTFR for contralateral, ipsilateral movement, and protrusion were 14.7+/-2.5 imp/s (n=10), 13.2+/-2.1 imp/s (n=8), and 16.2+/-3.7 imp/s (n=2), respectively.


CONCLUSIONS
Lateral pterygoid SMUs have greater MTFR than previously reported in the masseter and IHLP, namely 5-8 and 8-10 imp/s, respectively. The MTFR did not vary with the task within each muscle head.


CONCLUSIONS
Some physiological properties of lateral pterygoid SMUs may be different from those in other jaw muscles.
Phanachet
I
I
Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, University of Sydney, Level 3, Professorial Unit, Centre for Oral Health, Westmead Hospital, Westmead, NSW 2145, Australia.
Whittle
T
T
Wanigaratne
K
K
Murray
G M
GM
D000328:Adult; D004566:Electrodes; D004594:Electrophysiology; D005260:Female; D006801:Humans; D007180:Incisor / Q000294:innervation / Q000502:physiology; D007568:Jaw / Q000294:innervation / Q000502:physiology; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009068:Movement / Q000502:physiology; D032342:Muscle Cells / Q000502:physiology*; D011626:Pterygoid Muscles / Q000166:cytology / Q000294:innervation / Q000502:physiology*