Abstract
Frequencies of firing of single motor units were investigated primarily in four muscles; genioglossus, geniohyoid, mylohyoid, and anterior belly of the digastric during isometric and isotonic contractions. Isometric contraction was studied as subjects maintained units at regular firing rates by use of feedback provided by auditory and visual displays of the units (motor unit training). Representative results from relatively small samples obtained so far are as follows. Modal firing rates of individual units ranged from about 10 to 40 impulses per second in different units, with most rates between 20 and 30 ips. The latter values can be compared with values of 10–14 ips from brachial biceps. The frequency range within which regular firing can occur appears to be larger in these units than, for example, in biceps. Differences in typical firing rates from muscle to muscle will be considered. Isotonic contraction in speech gestures was accompanied in some units by firing rates of up to eight times their modal isometric value. [This work was supported by grants from the National Science Foundation.]
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