Motor Output

Motor output to the eyes
The motor impulses that go to the eyes coordinate their movement to produce clear vision during active head movements (as while running or watching a tennis match) or passive head movements (as while sitting in a moving car).

Eye movement during head motion is controlled automatically by the vestibular system. When the head is not moving, the number of impulses from the right side is equal to the number of impulses coming from the left side. When the head turns toward the right, the number of impulses from the right semicircular canals increases and the number from the left decreases. This difference controls eye movements and allows for clear vision as the head is turning.

Motor output to the muscles and joints
The motor impulses that are sent from the brain to the other muscles of the body control their movement so that balance is maintained whether a person is sitting, standing, or turning cartwheels.

For example, when a person is turning cartwheels, some of the impulses that leave the brain stem go back to the cerebral cortex, carrying information to the thinking centers that acknowledge that it's okay to see trees whirling in circles. With practice at this and similar new activities, the brain learns to "read" different kinds of sensory input as normal.

This is exactly what happens as a baby learns to balance through practice and repetition. The impulses from the sensory receptors to the brain stem and then out to the muscles form a pathway. With repetition, it becomes easier for the impulses to travel over the same network or pathway, until maintaining balance during any activity becomes automatic. Physiologists say that these nerve pathways become "facilitated." This is the reason why dancers and athletes practice their activities over and over again.

Even very complex movements become almost automatic over a period of time. Anyone who has learned to ride a bicycle, swim, or ski can relate to this idea. This is also the basis for physical therapy in treating people with a damaged vestibular system—the exercises mimic the movements that make them feel dizzy and lose their balance. After a time, the brain "learns" that the input from this activity is "normal" for the damaged system, and the side effects of dizziness and balance decrease.