A receptor that responds to such mechanical stimuli as touch, sound, and pressure. The skin is rich in mechanoreceptors, including Meissner’s corpuscles, Pacinian corpuscles, Merkel’s discs, and Ruffini’s capsules. These provide information to the brain about the pressure, texture, and shape of objects in contact with the body. Their density varies according to site; in humans they are most abundant in the skin of the fingertips, palms, soles of the feet, and genitalia. Stretch receptors in muscles, tendons, and ligaments are mechanoreceptors that respond to stretching of muscles and changes in the position of limbs. Their input to the central nervous system is essential for control of posture and coordination of movements (see golgi tendon organ; muscle spindle). Hair cells are found in various sensory organs, including the mammalian ear and the lateral line system of fishes and amphibians. They respond to movements of the fluid medium surrounding the body, and hence can detect sound waves in air and motion in surrounding water. See also baroreceptor.