Brain Tour : Our Brain : Looking at the Cerebrum :

The basal ganglia (cerebral nuclei) are masses or grey matter within the white matter of each cerebral hemisphere. The basal ganglia control large subconscious movements of skeletal muscles, such as swinging the arms while walking, such gross movements are also controlled consciously by the cerebral cortex, and regulate muscle tone required for some body movements. Damage to the basal ganglia results in uncontrolled shaking (tremor) or involuntary muscle movements, such as Parkinson’s disease. Destruction of a substantial portion of basal ganglia results in total paralysis, or loss or impairment of motor and sensory functions, of the side of the body affected by the damage. The decision to move is usually prompted by sensory information that reaches the primary planning region, the association cortex. This sends signals to the basal ganglia and to the cerebellum where movement patterns , or motor commands , are evoked and sent to the motor cortex via the thalamus. The command is then executed as the impulse travels from the motor centers in the spinal cord via the brain stem. This shows how important the basal ganglia and its gang of brain areas play even in the simple throwing of a ball!