Proprioception 2.0: novel functions for muscle spindles.

PURPOSE OF REVIEW: Muscle spindles are encapsulated mechanosensory receptors within skeletal muscle tissue that inform the central nervous system about the contractile status of each muscle. This information is required for any coordinated movement and for stable posture. This review summarizes recent findings regarding novel functions for proprioceptive feedback information, muscle spindle disease and the molecular basis of mechanoreception.

RECENT FINDINGS: Muscle spindle function is not limited to regulating motor control but is also required for appropriate realignment of fractured bones, successful regeneration of spinal cord axons after injury and spinal alignment. Several proteins responsible for or modulating mechanotransduction in proprioceptive sensory neurons have been identified, including the Piezo2 channel as a candidate for the principal mechanotransduction channel. Many neuromuscular diseases are known to be accompanied by an impaired function of muscle spindles, resulting in a decline of motor performance and coordination in the patients.

SUMMARY: Our knowledge regarding the molecular basis of muscle spindle function is still incomplete. However, increasing our understanding of mechanotransduction in muscle spindles is a prerequisite for finding appropriate strategies to prevent injuries due to unstable gait and frequent falls.