18.6 : Hierarchy of Motor Control

The hierarchy of motor control refers to the different levels of organization and processing involved in controlling movement in the body. These levels range from higher cortical areas involved in planning and decision-making to lower spinal cord reflexes that respond automatically to external stimuli.

1. Segmental Level: This is the lowest level of motor control and consists of spinal cord segments. It is responsible for generating simple reflexes and rhythmic movements such as walking. Neural circuits in the spinal cord, known as central pattern generators or CPGs, play an important role in generating and coordinating these rhythmic movements.
2. Projection Level: This level is responsible for the execution of voluntary movements and comprises the primary motor cortex and the brainstem. These structures receive input from the segmental level and send output down to the spinal cord to initiate movement. It directly controls the movements through the segmental level and sends a copy of the information as internal feedback to the higher motor centers for planning and decision-making.
3. Precommand Level: This is the highest level of motor control and is involved in the planning and initiation of complex movements. The precommand level includes the basal nuclei and the cerebrum, which integrates sensory information and past experiences to plan and execute movements.

Overall, the three levels of motor control — segmental, projection, and precommand — illustrate the different levels of organization and processing involved in controlling movement, from basic reflexes to complex, voluntary movements.