How is muscle atrophy caused?

2 Types: There are 2 forms of muscle atrophy: disuse atrophy, i.e. This come actual lack of activity or 'using' the muscle. Astronauts on space developed disuse atrophy, and exercise programs were instituted. 2nd type is neurogenic atrophy. This result from injury or damage to the spinal cord or spinal nerves, also from nerve disease such as als, polio, guillain-barre syndrome, muscular dystrophy, etc.