Proprioception is the mechanism by which we sense the strength that our muscles develop. Sensors of Golgi tendon organs are located near muscle–tendon junctions. Muscle spindles function to regulate muscle length. They lie parallel to the skeletal muscle fibers and contain their own intrafusal muscle fibers. There are two types of intrafusal muscle fibers i.e. nuclear chain fibers (P sensors) and nuclear bag fibers (D sensors).
The endings of type Ia afferent neurons coil around both types, whereas type II neurons wind around the nuclear chain fibers only. The efferent gamma (γ) motorneurons innervate both intrafusal fiber types, allowing variation of their length and stretch sensitivity.