Mechanosensation

Mechanosensation is the sense of mechanical stimuli produced by touch, pressure, vibration, stretch and movement; includes somatosensory modalities, proprioception, hearing, balance, and certain cardiovascular reflexes such as baroreception. Mechanotransduction is the conversion of mechanical energy into neural signals by specialized receptor cells and ion channels.

In vertebrates, mechanosensitive ion channels such as Piezo1 and Piezo2 play central roles, opening in response to membrane tension or force on tethering structures and generating receptor potentials. In auditory hair cells, deflection of stereocilia relative to the hair bundle tension opens mechanotransduction channels, a process linked to tip links formed by cadherin-23 and protocadherin-15; in mammals, transduction involves TMC1/TMC2 channels. Other mechanosensors include potassium channels and cytoskeleton-associated complexes in various tissues.

The major somatosensory receptors are specialized end organs in the skin: Merkel cells (fine touch), Meissner's corpuscles (light touch), Pacinian corpuscles (vibration), Ruffini endings (stretch) and hair follicle receptors. Proprioception depends on muscle spindles and Golgi tendon organs, providing position and force information; vestibular system detects head motion and orientation.

Afferent signals travel through peripheral nerves to the spinal cord and brain, with processing in somatosensory cortex and integrative areas, underlying perception of touch, proprioception, and balance. Baroreceptors and other mechanosensory systems contribute to autonomic reflexes.

Clinically, defects in mechanotransduction can cause loss of touch or proprioception, as seen with PIEZO2 mutations; defects in auditory mechanotransduction underlie certain forms of hereditary deafness. Research spans across species and includes plant mechanosensing.