Electromyographic evidence for functional heterogeneity in the inferior head of the human lateral pterygoid muscle: a preliminary multi-unit study.
OBJECTIVE
Functional heterogeneity, i.e. regional or selective activation of subpopulations of fibres within a muscle, has been described in some jaw and limb muscles. Each head of the lateral pterygoid muscle may also be functionally heterogeneous. The aims of this investigation were to develop a technique to test this hypothesis, and to use this technique to determine whether there is any multi-unit electromyographic (EMG) evidence for functional heterogeneity within the inferior head of the lateral pterygoid (IHLP).


METHODS
In 3 human subjects without craniomandibular disorders, recordings were made of condylar movement and multi-unit EMG activity from two sites in the IHLP during repeated trials of a contralateral (n = 21) and a protrusive (n = 26) jaw movement. The recording sites within IHLP were approached extraorally (labelled IHLP-extra) and were verified by computer tomography (CT); the other (IHLP-intra) were from sites in IHLP approached intraorally.


RESULTS
In each subject, the time of occurrence of the peak filtered signal from IHLP-extra was significantly different (P<0.05) from IHLP-intra for all protrusion trials but not for contralateral trials.


CONCLUSIONS
The data suggest a task-dependent change in motor unit recruitment order within IHLP and that IHLP is functionally heterogeneous.
Murray
G M
GM
Faculty of Dentistry, Westmead Centre for Oral Health, NSW, Australia. gregm@mail.usyd.edu.au
Phanachet
I
I
Klineberg
I J
IJ
D000328:Adult; D004569:Electroencephalography; D004576:Electromyography; D006801:Humans; D008334:Mandible / Q000502:physiology*; D008335:Mandibular Condyle / Q000502:physiology; D011626:Pterygoid Muscles / Q000503:physiopathology*