Neuromuscular Disorders affect the nerves that control the voluntary muscles. Voluntary muscles are those muscles that you can consciously control, such as flexing your elbow or raising your leg. Nerve cells, also known as neurons, send the messages that control these muscles. When the neurons become unhealthy or die, the messages or communication between the nervous system and muscles breaks down. As a result, muscles may weaken and waste away. The weakness can result in twitching, cramps, aches, and joint and movement problems. Some common types of neuromuscular disorders include amyotrophic lateral sclerosis (ALS), muscular dystrophy, and peripheral neuropathy. Many neuromuscular diseases are genetic, which means they run in families, or they can be caused by an immune system disorder or a gene mutation.