Importance of equatorial region
Action potential are generated from this equatorial region by stretching. Muscle spindle receptors lie parallel to the extra fusal fibers.
Functionally these receptors are connected to the origin and insertion of the tendon i.e. lengthening of the whole muscle will stretch the equatorial region.
Contraction of polar ends also generate action potential, which passes in the sensory nerve, in proportion to lengthening of the equatorial region.
Sensory fibres are capable of detecting the changes in length during the dynamic phase of muscle lengthening and during resting stage.
When CNS receives the sensory inception, it causes excitatory mono-synaptic connection with alpha-motor neurons (that supplies extra fusal fibres of the same muscle)
This leads to contraction of the whole muscle which results in shortening of the muscle spindle (especially the equatorial region)
This shuts-off the action potential from spindle receptor and muscle contraction is stopped.
