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Functional Activity of Superior Head of Human Lateral Pterygoid Muscle during Isometric Force

¹ Faculty of Dentistry, Khonkaen University, Mittraphab Rd., Muang, Khonkaen, 40002 Thailand, and Faculty of Dentistry, University of Sydney; and
² 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;

View larger version (59K): [in a new window]   Figure 1. Task apparatus, CT verification, and recording site location. (A) (Upper) Force transducer. The force bar and rod could be swiveled horizontally. (Lower) The custom-made upper acrylic bite block. Five isometric force directions were used: P, protrusive; CL, contralateral; IL, ipsilateral; CL-P, contralateral protrusive; and IL-P, ipsilateral protrusive. Ipsilateral refers to the side of the SHLP recording electrode. The average opening with the bite-blocks compared with postural jaw position was 5.7 mm (range, 3–8 mm). (B) Example of CT-verified electrode placement within the SHLP. (Upper) Horizontal slice (1 mm thick) and (lower) reformated oblique sagittal image through the long axis of the SHLP, showing electrode tip within the SHLP. (C) Two-dimensional mapping of electrode location in the SHLP in all subjects. Lower Fig. was taken along the long axis of the lateral pterygoid. Horizontal axis represents the long axis of the SHLP; the vertical axis represents the supero-inferior dimension of the SHLP. Task relations: O+, SMUs were active during CL, CL-P, P, and IL-P, with or without IL; +, SMUs were active during CL, CL-P, and P; P, SMUs were active during P only; and –, no activity. (D) Same data as in C, but plotted in the horizontal plane.

View larger version (28K): [in a new window]   Figure 2. Example of SHLP EMG data during one trial of isometric protrusion. (A) Five steps of force-tracking [400 gwt (3.92 N) to 800 gwt (7.84 N)] and filtered EMG. Regions between the vertical lines indicate the defined stable periods (see METHODS) for each force step. (B) Four SMUs were discriminated during the most stable two-second holding period from this trial. Each trace represents the spike train of a SMU. Each short vertical line of the spike train is an action potential of a SMU. The period delineated by the vertical lines in A and B is expanded in (C) and illustrates the waveforms of 4 SMUs and their spike trains.

View larger version (33K): [in a new window]   Figure 3. Force tracings, filtered EMG, and spike trains from 6 SMUs (waveforms on right) from 1 representative trial of each direction in one subject. SMUs no. 1, 2, 3, and 4 were active during CL. SMUs no. 1 and 3 were active during CL-P and P. SMUs no. 5 and 6 were active during IL-P. None of these SMUs was active during IL.