Many animals rely on tactile (pertaining to touch) stimuli to obtain information about their environment. Mechanical sensory receptors in vertebrate skin detect stimuli that the brain interprets as light touch, touch-pressure, and vibration.
Light touch is perceived when the skin is touched, but not strongly deformed. Receptors of light touch include bare sensory nerve endings and tactile (Meissners) corpuscles (figure 2.26). Bare sensory nerve endings are the most widely distributed receptors in the vertebrate body, and are involved with pain and thermal stimuli, as well as light touch. The bulbs of Krause are mechanoreceptors, found in the dermis in certain parts of the body, that respond to some physical stimuli, such as position changes. Other receptors for touch-pressure are Pacinian corpuscles and the organs of Ruffini. Fig. 2.26
Figure 2.26 Different Sensory Receptors to Mechanical stimuli.
Many mammals have specially adapted sensory hairs called vibrissae (sing., vibrissa) on their wrists, snouts, and eyebrows (e.g., cat whiskers). Around the base of each vibrissa is a blood sinus. Nerves that border the sinus carry impulses from several kinds of mechanoreceptors to the brain for interpretation.
What is a sonar or biosonar?
Bats, shrews, several cave-dwelling birds (oilbird, cave swiftlet), whales, and dolphins can determine distance and depth by a form of echolocation called sonar (biosonar). These animals emit high-frequency sounds and then determine how long it takes for the sound to return after bouncing off objects in the environment. For example, some bats emit clicks that last from 2 to 3 milliseconds and are repeated several hundred times per second, The returning echo created when a moth or other insects flies past the bat can provide enough information for the bat to locate and catch its prey. Overall, the three-dimensional imaging achieved with this auditory sonar system is quite sophisticated.