Single motor units from the medial pterygoid muscle can be active during isometric horizontal and vertical forces.

OBJECTIVES: To determine (a) whether the medial pterygoid muscle is active in an isometric vertical force task and in isometric horizontal force tasks in the contralateral, protrusion and ipsilateral directions; (b) whether the same single motor units (SMUs) could be active across different directions of isometric force generation; and (c) whether different regions of the medial pterygoid muscle exhibit different patterns of SMU activation during the generation of any one direction of isometric force. METHODS: Intramuscular electromyographic (EMG) recordings were made from the right medial pterygoid muscle in 15 healthy participants during isometric force tasks: vertical and horizontal contralateral, protrusion and ipsilateral. A computed tomography scan divided the EMG recording site into a medial or lateral part in each participant. Single motor units were discriminated in each task. RESULTS: Medial pterygoid SMU activity was recorded in 100% of participants for the vertical biting tasks, 86% of participants for the horizontal contralateral and horizontal protrusion tasks and 57% of the horizontal ipsilateral tasks. Of the 72 SMUs that were discriminated, 36% were active in all tasks; 18% were active only in the vertical tasks and 17% were active in the vertical, horizontal contralateral and horizontal protrusion tasks. The proportion of SMUs that was active in at least 1 horizontal task in the lateral part (33/39) was significantly higher than the proportion (21/33) in the medial part (Chi-Square, P < 0.05). CONCLUSION: The data are consistent with a stabilisation role for the medial pterygoid muscle in isometric jaw forces in the vertical and horizontal planes.

An electromyographic study of parkinsonian swallowing and its response to levodopa.

BACKGROUND: Few studies have investigated the effect of levodopa on parkinsonian swallowing with findings thus far being equivocal. METHODS: We used surface electromyography and accelerometry to investigate submental and laryngeal muscle activation during swallowing in 14 parkinsonian subjects before and after levodopa and in 22 age-matched controls. Our aims were (1) to demonstrate the clinical utility of noninvasive electromyography, (2) to identify electromyographic features of parkinsonian swallowing, and (3) to investigate the effect of levodopa on parkinsonian swallowing. RESULTS: The parkinsonian group showed increased burst amplitudes and durations and increased swallow duration, clearing activity and latency between submental and laryngeal bursts (P < .05) and used more swallows than did controls to consume water boluses (P < .001). Levodopa decreased the latency between submental and laryngeal bursts (P < .05) but did not produce effects on individual muscle bursts. CONCLUSIONS: The clinical utility of electrophysiological and biomechanical methods of swallowing assessment was demonstrated. Levodopa tended to normalize the timing of the combined swallow response but not the activity of individual muscles.