Muscle Spindle: Afferent & Efferent
1. 2 afferent innervations
Ia fiber-annulospinal endings (primary muscle spindle endings)--nuclear bag░˙ nuclear chain fiber
group-II fibers (9 umm diameter, thinner than annulospinal endings)--secondary muscle-spindle endings, nuclear chain fiber

2. efferent innervation
gamma fiber (2-8 um)
synapse at the end of the Intrafusal fiber
gamma-endplate (nuclear bag fiber)
gamma-trail endings (nuclear chain fiber)