Research on the muscle spindle has been concerned with a wide range of
aspects, including morphology and receptor mechanisms, the functional
properties and central actions of spindle afferent neurones, and the central
control and peripheral actions of fusimotor neurones. This article focuses
on the properties of spindle afferents and efferents and on their role during
natural movement. Morphology is considered mainly in its historic
context and where it aids the understanding of function; the receptor
mechanisms and the central actions of spindle afferents are dealt with but
in passing.