Chapter 12 Motor System 2: Cerebellum
The cerebellum does not initiate motor movements, nor does it alter sensation. It functions as a servomechanism, constantly monitoring all body motor activities and comparing intended movements (planned by the motor and premotor cortex) against the updated sensory information it receives. By calculating discrepancies between sensory and motor states, it regulates the quality of motor movements generated elsewhere in the motor cortex, brainstem, or spinal cord. With its ability to make alterations for greater precision and smoothness during ongoing movement, the cerebellum contributes to muscle synergy, tone, and equilibrium. Signs of cerebellar dysfunction include paresis, hypotonia, ataxia, asymmetry, intention tremor, dysdiadochokinesia, dysarthria, and disequilibrium. Patients with cerebellar pathology lack the ability to control and regulate motor functions. Small lesions of the cerebellar cortex may cause minimal impairments that can be compensated for. However, massive cerebellar damage involving the deep nuclei or superior cerebellar peduncle can cause permanent and lasting deficits unless it occurs at a very young age. Cerebellar impairments do not affect reasoning, thinking, memory, or the comprehension of language.