Figure 4. Initial surge and saturation in activation of a dendritic PIC corresponds to similar events in motoneurone firing.

The left panel shows the effective synaptic current generated in a cat ankle extensor motoneurone (medial gastrocnemius) during voltage clamp by a slow stretch of the Achilles tendon. The middle panel shows the firing response of the same cell to the same stretch during unclamped conditions. The right panel shows the firing pattern of a human motor unit during a linearly rising volitional command that produced a linearly rising force (biceps muscle; data courtesy of Carol Mottram, at the Rehabilitation Institute of Chicago). Note in all three examples, there is an initial steep increase (surge) followed by a saturation that, during firing, produced rate limitation.