Structural Biochemistry/Motor Systems
Sensory systems provide the initial inputs to cognitive processes, and motor systems deliver the physical behavioral output that carries out movements. All body movements are generated by the stimulation of skeletal muscle fibers by the lower motor neurons- neurons whose cell bodies are located in the brain stem and spinal cord. The activation of lower motor neurons is coordinated by local circuits consisting of inter neurons, also located in the spinal cord and brainstem. Complex reflecxes and rhythmic locomotor movements can be generated and sustained by the coordinated activation of such local circuits in the absence of inputs from higher motor centers. At higher levels of the motor system, upper motor neurons in the cerebral cortex and brainstem provide descending control of local circuitry in the spinal cord and brain stem. The other two parts, the cerebellum and basal ganglia, modulate the activity of upper motor neurons in order to make online corrections in response to perturbations in ongoing movements and to help initiate goal directed movements.
Levinthal, Charles, "Drugs, Behavior, and Modern Society", Pearson Education, Inc., 2008 Purves, Dale, "Principles of Cognitive Neuroscience", Sinauer Associates, Inc., 2008