Numbers and contraction-values of individual motor-units examined in some muscles of the limb

Abstract

“The muscle with its nerve may be thought of as an additive assemblage of motor-units, meaning by motor-unit an individual motor nerve-fibre with the bunch” [or “squad” (E. L. Porter, 1929 (1))]“ of muscle-fibres it activates.” (2) The components of such a unit can claim sufficiently close and sufficiently analysed interrelation to warrant acceptance for many purposes as a single functional entity. In application to reflexes, the unit thus resulting favours brevity and directness of quantitative statement. Its correspondence with a so-to-say quantum reaction, which forms the basis, by combinations temporal and numerical, of all grading of the muscle as effector-organ, fits it for measuring that grading. It is, moreover, applicable centrally as well as peripherally, since the motor-units active number the motoneurones discharging. Such mensuration, the total of the pool of motoneurones being known, evaluates per se the given reaction in terms of the total potential reaction. 1. Contraction-Tension of the Individual Motor-Unit. In the following experiments it was therefore sought to find the physiological size of the motor-unit, i. e., to measure its contraction-tension. The muscles examined (cat) have been gastrocnemius (median head) soleus, semitendinosus, extensor longus digitorum, and, less fully, tibialis anticus and crureus.