Proprioception revisited: where do we stand?

Originally referred to as 'muscle sense', the notion that skeletal muscle held a peripheral sensory function was first described early in the 19 century. Foundational experiments by Sherrington in the early 20 century definitively demonstrated that proprioceptors contained within skeletal muscle, tendons, and joints are innervated by sensory neurons and play an important role in the control of movement. In this review, we will highlight several recent advances in the ongoing effort to further define the molecular diversity underlying the proprioceptive sensorimotor system. Together, the work summarized here represents our current understanding of sensorimotor circuit formation during development and the mechanisms that regulate the integration of proprioceptive feedback into the spinal circuits that control locomotion in both normal and diseased states.