Responses of Golgi tendon organs to active contractions of the soleus muscle of the cat.

Abstract

The responses of tendon organs in the soleus muscle of the cat to active contractions were investigated by stimulating small filaments of ventral root. By stimulating single motor units in this way, it was shown that a tendon organ will respond whenever actively contracting fibers lie directly in series with the receptor. Contractions of fibers not in series with the receptor may cause a tendon organ which is discharging to a passive force to pause during the contraction. Four-15 different motor units drive each receptor. Since 3-25 muscle fibers are connected in series with the receptor, it may respond to the contraction of only 1 or 2 muscle fibers. Thus, the absolute threshold is less than 0.1 g. The responses of a single tendon organ to contraction of more than 1 motor unit may sum, but not linearly. Tendon organs continuously transmit to the spinal cord a filtered sample of the active forces being produced in the muscle.