ABOUT STROKES: A stroke is a type of cardiovascular disease that affects the arteries leading to and from the brain. When one of these becomes blocked, or bursts, blood and oxygen can't get to that part of the brain and it begins to die. Strokes can cause paralysis, affect language and vision, and lead to memory loss. Strokes kill nearly 163,000 people every year; it is the third leading cause of death, behind heart disease and cancer.
ABOUT MOTOR FUNCTION: Even a simple motor movement involves many different regions of the body, but the primary motor cortex of the brain is one of the most important. It sends out electrical impulses through nerve cells called neurons that control the execution of movement. Every part of the body is represented in the primary motor cortex; the left side of the brain controls the right side of the body, and vice versa. Certain diseases or brain damage can disrupt these basic functions. For instance, cerebral palsy is a disorder that affects body movement and muscle coordination because of brain damage, which interferes with messages from the brain the body, and vice versa.
HOW WE WALK: Walking is different from a running gait because only one foot at a time lifts off the ground. During forward motion, the leg that leaves the ground swings forward from the hip, like a pendulum. Then the leg strikes the ground with the heel and rolls through the toe in a motion similar to an inverted pendulum. The motion of the two legs is coordinated so that one foot or the other is always in contact with the ground -- a so-called 'double pendulum' strategy. The process of walking recovers about 60 percent of the energy expended thanks to the pendulum dynamics and the ground reaction force. The legs act as long levers that transfer ground reaction force to the spine.