Figure 1.
Amplification of the EPSPs induced by sinusoidal stretches of the TS muscle. A, Control condition (no artificial PIC, A1) and effect of an artificial PIC (ḡPIC = 100 nS, A2–A4). Bottom traces, Variations of the muscle length when the frequency increases from 1 to 25 Hz. Top traces, Intracellular record of a TS motoneuron (average of 3 recordings). Dashed line, Resting potential in control condition. Hyperpolarization of the baseline at high frequencies was likely attributable to the deactivation of Ih. B, Amplification gain against stretch frequency. Filled circles, τPIC = 50 ms; open triangles, τPIC = 10 ms; filled triangles, τPIC = 1 ms. Gin = 1.1 μS. Axonal conduction velocity, 90 m/s. Inset, Response of a TS spindle primary ending. Bottom, Muscle length. Middle, Extracellular recording of an Ia afferent within the dorsal column. Top, Instantaneous frequency of the discharge. This afferent fiber was identified as an Ia fiber because: (1) its conduction velocity was 90 m/s; (2) although the receptor was silent at the initial length, a spontaneous stationary discharge at ∼10 Hz was observed when the length was increased by 160 μm (data not shown); (3) the frequency modulations increased with the stretch frequency because of the dynamic sensitivity of the primary ending.