Reflex fractionation of a muscle

Abstract

Studying spinal reflexes Camis (1) (1910) from observations on M. semitendinosus (cat) reached the conclusions that “ the cells of a spinal motor centre ca be regarded from a functional point of view as divided into several independent groups,” but that “such independence is however not absolute.” The present experiments pursue a like inquiry. That in a reflex evoked by weak excitation of the afferent nerve the resulting contraction of the muscle may involve a portion only of the muscle has common acceptance. Camis’s observations, however, employed maximal stimuli and yet the muscle evidenced fractional responses ; whereas later (3) Dreyer and one of us found, contrary to previous (4) experience, that reflex tetani in some instances activated the sum-total of the muscle. Both of these observations are confirmed by the present experiments. Method . The sample muscles taken have been a hip-flexor, tensor fasciœ femoris , a knee flexor, semitendinosus , and an ankle flexor, tibialis anticus . The preparation (cat) has been spinal, with cord transection, performed under deep anæsthesia, in the anterior lumbar region, prior to intereollicular decerebration, the anæsthesia being later relaxed. All other muscles of the limb except that one attached to the myograph have been paralysed by resection or nervesection. The limb has been securely fixed by steel drills clamped to the table. For exciting reflex contraction various afferent nerves, as cited below, of the ipsilateral limb have been stimulated by faradisation. The inductorium has been coreless and its primary circuit fed by a current of less than 0·2 amp. An optically recording myograph with isometric registration and of the pattern described in a previous paper (2) has been used.