A high magnification photomicrograph of a cross section through a muscle spindle, a specialized sensory receptor found in muscles. The section has been stained with hematoxylin and eosin in order to see the components within the spindle. A tough capsule surrounds 4-5 intrafusal muscle fibers. The intrafusal fibers respond to change in muscle length and signal to central nervous system. The lab is interested in what role the neurotrophic factor NT-3 plays in the development and function of muscle spindles.