ROM Resist & New Zealand

Spindles

Let's discuss spindles. Starting at 'C' (above) the short yellow bits represent spindles (named for their shape). Spindles are made of muscle & sensory tissue. When muscles elongate and have tension the pull includes the spindles which get elongated by the action. Think banana. The spindle outer peel is of longitudinal muscle. If these muscles are being stimulated then the spindle wants to get shorter and fatter. If not stimulated, then it stretches easier. Within that peel (the banana) is a lengthwise rod of three sections, of muscle<=sensor=>muscle. When the end muscles are stimulated, they tug on the central sensor which let's fly a scope of signals that vary with the stretch of this central rod. That output goes to the spinal cord with many connections to complex reflex arcs that are both local and widely distributed depending on the intensity. THIS IS WHERE SPASTICITY LIVES. If the gain (base tension) of the inner core muscle is set too high (as in spastic diplegia) then any tension added elicits a return response and that response may be in excess if the gain is set too high.