Definition

Amyotrophic lateral sclerosis (ALS; pronounced ay-MY-eh-TRO-fik LA-ter-el skler-OH-sis) is a neurodegenerative disease. A neurodegenerative disease is one in which nerve cells are damaged or killed. In the case of ALS, the nerve cells that are damaged are motor neurons. Motor neurons are nerve cells that control movement. ALS is also known as motor neuron disease and Lou Gehrig's disease. Lou Gehrig (1903–41) was a famous baseball player who died of the disease.

Description

Under normal circumstances, muscles move because of messages sent from the brain through the spinal cord to the muscles. These messages are carried by motor neurons. In ALS, those motor neurons die off and messages from the brain to the muscles do not flow normally. Muscles do not respond when they are supposed to or as well as they should.

The death of motor neurons affects voluntary muscles. These muscles are...