The motor system is the part of the central nervous system that is responsible for movement.
Much of the brain and nervous system are dedicated to processing sensory information, to build detailed representations of the external environment.
Through vision, hearing, touch, and the other senses, we perceive the world and interact with it. However, all this processing would have very little value if we did not have an effective way to act on it..
In some cases, the relationship between sensory input and motor output is simple and straightforward; for example, touching a hot stove causes an immediate withdrawal of the hand. But, in general, our actions are conscious and require not only sensory information but also a large number of different cognitive processes that allow us to choose the most appropriate motor production at each moment. In any case, the final movement is a set of orders for certain muscles in the body to move in a certain way..
Motor behavior is one of the most important ways of expressing people. All behavior, whether conscious or unconscious, is based on a set of muscle contractions orchestrated by the brain and spinal cord..
The motor system is characterized by receiving constant sensory information and presenting a double organization: hierarchical and in parallel..
Our motor system can do three types of movement:
The functioning of the motor system is closely related to the functioning of the sensory systems.
Vision, hearing and receptors located on the body surface inform about the situation of objects in space and of our body with respect to these objects. The proprioceptors of the muscles and joints, and the vestibular system report the length and tension of the muscles and the position of the body in space. The motor system uses this information to select the appropriate response (plan the movement) and to make necessary adjustments while performing the movement (refine the movement)..
The motor system needs to receive sensory information to plan and refine the movements that are carried out.
When we want to grasp an object with our hand, the motor system uses the information provided by the sensory systems to correct, if necessary, the marked trajectory (feedback or feedback processes). Sometimes it is more effective to use forefeeding mechanisms. For example, when we want to catch a ball that has been thrown at us, we have to predict the trajectory it will follow in order to position our hands correctly. In this case, the forefeeding system must interpret the visual signals correctly to be able to tighten the muscles in anticipation of the impact of the ball..
Hierarchical organization: the motor system is made up of different components related by pathways that follow a downward path. All movements are produced by motor neurons in the spinal cord and brainstem that innervate the muscles. These motor neurons are controlled and coordinated by the brain, by neurons in the cerebral cortex and the brain stem..
We found three main levels of motor control: spinal cord, brainstem, and cerebral cortex..
After the spinal cord is disconnected from the higher centers, appropriate stimulation can produce reflex motor responses..
Descending motor pathways originating in the cortex and brain stem are essential for the control of voluntary movements and provide the link between thoughts and actions..
Parallel organization: from higher levels of the motor hierarchy, orders reach lower levels directly through the brain stem. This fact shows that the motor systems are not only organized in series, but also in parallel. Serial and parallel processing of the descending motor pathways provides greater processing and adaptive capacity in motor control.
As we have commented, there are three levels related to motor control: the motor neurons of the spinal cord and the brainstem, the brainstem and the cerebral cortex. It should be noted the existence of two other subsystems related to motor control:
These systems do not have direct access to alpha motor neurons, but rather regulate the activity of the motor neurons that give rise to the descending pathways..
One of the main functions is to correct errors in movement by comparing the motor commands produced in the cortex and brainstem with sensory feedback on the movements that are actually taking place..
The importance of the basal ganglia in movement is evidenced by observing the motor alterations that accompany dysfunctions of the basal ganglia, Parkinson's disease and Huntington's disease..