[Static sensitivity of the primary endings of muscle spindles].
Static discharges have been studied in 75 primary endings of the muscle spindle at the stepwise stretch of m. triceps surae in anesthetized cats. The sampled afferents possessed the conduction velocity between 72  and 115 M/s, high dynamic sensitivity and the static thresholds below 8 mm. The main firing rates (MFR) of the discharges were computed during 30 s after each step of the muscle stretch at 0.8 mm from complete slack up to 10 mm. The measurements of the MFR of the discharge were started 40 s after completing a dynamic phase of stretch. The following criteria of the "good" position sensitivity of the receptors were used: high probability of an increase in the MFR per step of stretch, a linear "muscle length-MFR" relationship, a wide range of position detection and high value of static and differential static responses. Only 30% of the analyzed primary endings are characterized by linear (up to 4.5 pps/mm) or by a monotonous increase of the MFR (up to 40 pps) with a probability of more than 0.7 per step of muscle stretch. The remaining primary endings detected the change in the stationary muscle length "poorly" because of the presence of nonsensitive areas which are conditioned either by high static thresholds or by lack of an increase in the MFR. The primary endings did not possess obvious length sensitivity.
D000200:Action Potentials; D000818:Animals; D002415:Cats; D009470:Muscle Spindles / Q000502:physiology*; D009132:Muscles / Q000502:physiology; D009431:Neural Conduction; D010812:Physical Stimulation
Staticheskaia chuvstvitel 'nost' pervichnykh okonschaniĭ myshechnykh vereten.