Lou Gehrig's disease, otherwise known as, ALS damages motor neurons in the brain and spinal cord. Motor neurons are nerve cells that control muscle movement. Upper motor neurons send messages from the brain to the spinal cord, and lower motor neurons send messages from the spinal cord to the muscles. Motor neurons are an important part of the body's neuromuscular system.The neuromuscular system lets our bodies move and is made up of the brain, many nerves, and muscles. Things that we do every day -- like breathing, walking, running, lifting stuff, and even reaching for a glass of water -- are all controlled by the neuromuscular system.Over time, ALS causes the motor neurons in the brain and spinal cord to shrink and disappear, so that the muscles no longer receive signals to move. So, the muscles get smaller and weaker.

Gradually the body becomes paralyzed, which means that the muscles no longer work.However, someone with ALS, even at an advanced stage, can still see, hear, smell, and feel touch. The nerves that carry feelings of hot, cold, pain, pressure, or even being tickled, are not affected by Lou Gehrig's disease. In some people with ALS, the parts of the brain that allow us to think, remember, and learn also are affected by the disease.