Any movement arises as a result of a series of steps. At first the information is acquired from the environment, this stage is known as “stimulus identification.” A second step called “response selection” processes the information and selects the most appropriate response. Finally, an abstract idea of the response becomes a movement.
All movements (voluntary or involuntary) are produced by muscle contractions directed by the brain and the spinal cord. There are four systems responsible for controlling the movement, although they are different, they work interactively. The first system consists of inferior motor neurons, whose cell bodies are located in the spinal cord or brain stem from which they send their axons to the skeletal muscles of the body and head, respectively. In addition there are local circuit neurons that receive information from both sensory ends and superior centers; therefore, they are able to coordinate between different groups of muscles. The second system consists of the superior motor neurons whose cell bodies are located in the brainstem or motor cortex. From there their axons go down to synapse with neurons in the local circuit. The third (cerebellum) and fourth (basal ganglia) systems are complex circuits that control movement through the superior motor neurons.