A high magnification photomicrograph of a single intrafusal muscle fiber that is part of a muscle spindle, a specialized sensory receptor found in nearly all muscles. The spindle fiber (red) responds to muscle lengthening and conveys information to the sensory fibers (green) that innervate it. In this case, the sensory fibers have been injured (one day prior) and the peripheral axons are in the process of degenerating. The lab is interested in muscle spindles because they are innervated by sensory axons that rely on the neurotrophic factor NT-3. A goal of the lab is to understand the role that NT-3 plays in the reinnervation of muscle spindles after injury.