ABSTRACT
The skin is the largest organ of the human body. It not only provides a protective layer, but also provides information that enables us to respond to potentially harmful stimuli. We need to know if the object we are touching is so hot that it is damaging our tissues, or if we are being touched by something that might be about to attack or damage us in some way. Stimulation of the skin gives rise to the cutaneous sensations of pressure (touch), temperature and pain. There are a variety of receptors embedded in the layers of the skin, and it has been proposed that different receptors are specialised for encoding different sensory properties. For example, basket cells, which are wrapped around the base of hairs embedded in the skin surface, detect movement of the hair so that when the hair is touched by, say, brushing against a twig, a message is sent to the brain indicating possible contact with an environmental stimulus. Not all the skin surface is equally hairy, and where hair is sparse or on hairless regions such as the palm of the hand, soles of the feet, lips and mouth, there are other structures specialised for sensation called encapsulated end organs. The majority of these are Pacinian corpuscles, which also provide information about pressure on the skin surface, and give rise to the sensation of being touched. All regions of skin contain free nerve endings, which are also sensitive to contact or pressure and produce the sensation of being touched. The skin also has receptors for temperature, although the absolute sensing of temperature is relative. We saw in Chapter 2 that water will feel hot or cold to your hand depending on whether your hand had previously been in cold or hot water.
