Reflexes, Rhythms, and Posture

Abstract

One important function of sensory input to the CNS is to rapidly trigger relatively stereotyped movements designed to maintain posture or avoid injury. As we shall see, the proper spatial and temporal coordination of agonist and antagonist muscle contractions leading to reflex movements is encoded by synaptic circuits contained entirely within the spinal cord and brain stem. Although these lower circuits are activated by sensory input, they are also under the influence of descending axons from the brain. In fact, most reflexes depend for their full execution on contributions from brain stem structures. In such long-loop reflexes, the sensory data are conveyed to the brain stem and processed to generate the appropriate motor signals, which are then sent back down to the lower motor apparatuses to augment the excitation and inhibition of motoneurons.