For Motor Neurons, A Long Path to Find a Mate

Dr. Andrea H. Brand CC BY-NC

While most brain cells stay closer to home, motor neurons must send axons out into the body to find one muscular mate. Studies of fruit fly larvae, which have simple enough bodies that researchers can easily track all their muscle groups, have found that a given motor neuron — such as the one above — always reaches the same muscle. From left to right, the cell’s axon pushes out into the fly’s body, feeling its way toward one particular target muscle as it grows.

How each neuron finds its partner is still a mystery, but researchers have found that chemical attractants and repellents solve part of the puzzle. These messenger molecules float along the route like traffic officers, bumping into the growing axon and directing it right or left. When the axon grows close, molecules wafting from the target muscle tell it that it’s found the right partner. Too many neuron-muscle pairs exist for each to have their own handshake molecules, however. Researchers suspect other guiding mechanisms remain to be discovered.

About the Author

Charlie Wood

Charlie Wood is a science writer with a bachelor’s degree in physics from Brown University and a master’s degree in science journalism from New York University. In previous lives he taught physics in Mozambique and English in Japan, but these days he freelances from his home in New York.