Simple, everyday movements require the coordination of dozens of muscles, guided by the activity of hundreds of motor neurons. Now, researchers have revealed an important step in the process that guides the early development of neurons themselves, as they establish the precise connections between the spinal cord and muscles. This knowledge will help scientists search for drugs to treat diseases that destroy motor neurons, such as amyotrophic lateral sclerosis, or Lou Gehrig's disease.

As a vertebrate organism develops, the long, outstretched processes of motor neurons wend their way from the spinal column to wire up every muscle in the body. In mammals, many hundreds of different types of motor neurons are needed to control the variety of muscle types used to coordinate movement. The highly specialized motor neurons that innervate muscles in the arms, legs, hands, and feet are the most recent of these to evolve. As an animal develops, these neurons become increasingly specialized – first establishing themselves as motor neurons, then taking on the characteristics needed to control a limb, then preparing to target a specific muscle. Proper function depends on each of these neurons finding its way from the spinal cord to the group of muscle cells that it is equipped to control.
Read full Howard Hughes Medical Institute article.