Somatosensation

Abstract

The somatosensory system enables organisms to feel, to ache, to chill, and, perhaps most importantly, to know which parts of the body are involved in these sensations. This comprises proprioceptive and cutaneous sensitivity. Somatosensory receptors are distributed throughout the body rather than being concentrated at specialized locations and are able to sense different modalities of stimuli such as pressure against the skin, limb position, distention of the bladder, and body temperature. If a stimulus becomes so strong that it may be harmful, the somatosensory system is also responsible for feeling pain (nociception).

The skin is the largest sensory organ, and a variety of stimuli from the external environment are constantly contacting its surface. These stimuli are sensed by specialized endings of sensory neurons associated with special cells (keratinocytes, Merkel cells, Schwann-like cells) called receptors, which then transmit signals throughout complex pathways to the brain for interpretation and response. A single stimulus usually activates many receptors, and each receptor is capable of encoding stimulus features such as intensity, duration, and direction. It is the central nervous system (CNS) that interprets the activity of the different receptors involved in the sensation and uses these interpretations to generate coherent perceptions.

In this chapter, the skin as a sensory organ will be discussed and its role in the sense of touch, nonpainful changes of temperature, itch, and pleasant touch.