Rotterman, et al. The Journal of Neuroscience, 2014.
To twiddle your fingers or wiggle your toes, your brain must send signals that travel along a complex web of neurons. Motor neurons — specialized brain cells (pictured above in blue) that extend from the spinal cord to muscle fibers — are a major junction in this journey. Motor neurons receive signals from muscle stretch receptors and communicate with muscle fibers, controlling how they stretch and contract. This image shows synapses from muscle stretch receptors connecting with the dendrites of the motor neuron. After nerve injury, many of these synapses permanently disappear, leaving stretch reflexes and motor function compromised.