[Types of spontaneous muscle receptor discharges].

462 receptors of passive muscle spindles from m. triceps in cat were divided into two classes--205 units with spontaneous impulse activity (SIA) and 257 units without it. Three types of SIA have been established. 87% of units exhibited a stable long-lasting discharge, the interspike interval distribution being monomodal and symmetrical. The spikes trains in 8% of units were unstable, interval distribution being bimodal. The remaining 5% of units discharged by sporadic irregular single pulses. The first two types of SIA bear no relation to random processes. The static threshold discharge (STD) of previously silent receptors was also divided into the same three types. With the exception of 26 units which did not respond to the maintained discharge at 10 mm static stretch of the muscle, STD of 70% of units of the remaining 231 ones were related to type 1, while 17% and 13% of units--to types 2 and 3, respectively. The comparison of the SIA and STD characteristics may lead to an assumption that impulse generation in the two classes of receptors has the same mechanism. STD is a trivial response to the experimental external static load, whereas SIA may also be considered as a static response. The latter appears in some spindle receptors due to intrinsic static stretching load which is caused by the extra-intrafusal interaction.