Type Ia sensory fiber

For the body to keep moving properly and with finesse, the nervous system has to have a constant input of sensory data coming from areas such as the muscles and joints.

This change in length of the spindle is transduced (transformed into electric membrane potentials) by two types of sensory afferents, whose cell bodies are located in dorsal root ganglia located next to the spinal cord.

These connections are also called "annulospiral endings", deriving from the Latin word annulus which means "a ring-shaped area or structure".

Proprioceptive afferents send central axons through the dorsal root of spinal nerve bifurcating into ascending and descending branches, which in turn send branches to multiple spinal segments.

Ascending pathways to the brain have some similarities with the cutaneous afferents, but are different because the proprioceptive information also has to reach the cerebellum which controls the timings of muscle contractions for voluntary movements.