Voluntary Motor Control

The motor hierarchy uses muscle twitches as building blocks for complex and consciously driven actions requiring neocortical involvement. Cortical regions operate in concert with the cerebellum and basal ganglia to generate well-timed and organized muscle contractions that produce movements, ranging from simple to complex. Once imbued with meaning, these movements are considered actions. Adjustments in motor commands are made to accommodate changes in muscle load, maintain an upright posture, and anticipate and avoid errors. Brainstem motor control centers employ circuits in lower parts of the motor hierarchy to produce fairly complex movements, such as ingestion or locomotion. Since the brain adds meaning to movements, two different actions can share the same component movements and serve different end goals. Brain lesions may independently impair movements made under different contexts. For example, patients may be unable to smile volitionally while retaining the ability to smile in response to a joke.