Relation between spinal level and peripheral location of afferents in calf muscles of the cat

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Abstract
The relationship between the location of sensory endings in the medial gastrocnemius or soleus muscles of the cat and the level of entrance into the cord of their afferents has been studied. The hind legs were denervated except for the medial gastrocnemius or soleus muscle and the lumbosacral cord bathed in an oil pool. Afferent rootlets in the dorsal roots of L7 and S1 were examined in cranio-caudal sequence in search of filaments coming from the muscle under study. Indirect stimulation of the muscle permitted identification of the afferent as a muscle spindle or tendon organ, and distinction between annulospiral and flower-spray afferents was made on the basis of conduction rates. The position of the afferent ending in the muscle was found by probing the surface lightly with a blunt instrument. Results indicate that: a) since only one sensitive focus in the muscle is detectable for an isolated dorsal root filament, only one spindle or Golgi organ is innervated by an afferent fiber; b) the regions of inflow of annulospiral, flower-spray and Golgi afferents coincide; c) the relation between position of the afferent within the muscle and exact level of entrance in the cord is largely a random one.