Hand atrophy/muscle paralysis in ALS

Is ALS a disease of the muscles or nerves?

ALS is a disease of the motor nerves, specific nerve cells in the brain and spinal cord that control voluntary movement. Motor nerves attach to muscles and when the motor nerves gradually degenerate and die, the muscles no longer receive nerve impulses. As a result of the nerve death, the muscles atrophy and waste away. When an ALS patient first notices neurological symptoms, more than half of the motor neurons may already be dead. The body has a remarkable ability to compensate for nerve loss and new nerves grow at the same time other nerves are dying. Eventually, nerve death becomes so pervasive that muscle paralysis is the result.