When you walk around, you don’t need to consciously think about which muscles you’ll move or which foot will step next. The process is automatic. Your brain sends signals to cells in your spinal cord, which then relay the message to the motor neurons that control muscle movements. 

Scientists have found a new way to see motor neurons in action, as a group of researchers from the Salk Institute report in the journal Neuron. They added a fluorescent protein to mice motor neurons, allowing them to see which cells were activated by movement using a microscope. In the video below, you can see motor neurons lighting up as the scientists stimulate the nerves associated with walking. The fluorescent activity alternates between the lateral and median divisions of the lateral motor column (LMCl and LMCm)—motor neurons that control the muscles in the animal’s back and underside, respectively. 

This research gives scientists a better idea of how cells in the spinal cord relay information from the brain to the motor neurons, and is important for developing new treatments for spinal cord injuries and neurodegenerative diseases like ALS

All images by Christopher Hinckley / Pfaff Lab, Salk Institute