Spontaneous discharges from muscle receptors of various functional types.

A study was done concerning the relationship between the presence or absence of spontaneous spike activity (SSA) and the discharge characteristics of 473 receptors located in deafferented muscles of anesthetized cats. The majority of the Golgi tendon organs, pressure receptors, and the elementary dynamic and static receptors of the muscle spindles did not produce spontaneous discharges. The SSA probability was especially high in spindle receptors of the phasic-tonic type. The absence or presence of SSA could be used for the identification of all known functional types of muscle receptors. Among universal receptors of dynamic and positional types, the probability of SSA increases in proportion to the degree of increase in the magnitude of the static response. There are fewer units in the soleus muscle which show spontaneous activity than in the gently isolated m. triceps surae. The presence or absence of SAA depends, evidently, upon the different ways in which sensory terminals are connected to intrafusal spindle fibers initially stretched in a relaxed muscle.