Wednesday, April 4, 2012
In addition to the afferent information from the spindle stretch receptors and Golgi tendon organs of the activated muscle, other input is fed into the local motor control systems. For example, painful stimulation of the skin activates the ipsilateral flexor motor neurons and inhibits the ipsilateral extensor motor neurons, moving the body part away from the stimulus. This is called the withdrawal reflex. The same stimulus causes just the opposite response on the contralateral side of the body—activation of the extensor motor neurons and inhibition of the flexor motor neurons (the crossed-extensor reflex). The strengthened extension of the contralateral leg means that this leg can support more of the body’s weight as the hurt foot is raised from the ground by flexion.