A muscle spindle, with γ motor and Ia<unk>  fibers A<unk> , or a primary afferent fiber is a<unk>  of afferent nerve fiber. It is the<unk>  fiber of a stretch receptor called the muscle spindle found in muscles, which constantly monitors the rate at which a muscle stretch changes. The information carried by<unk>  Ia fibers contributes to the sense of proprioception.
Type Ia sensory fiber
Special somatic afferent fiber
Preganglionic nerve fibers
Postganglionic nerve fibers
Secondary sensory endings
Gamma motor neuron
Efferent nerve fiber
Special visceral afferent fiber