I have always been intrigued with the five senses, and as I grow older have suggested that "dignity" be added, if only because this quality appears to be on the decline.

My earlier articles have described smell, sound and vision, leaving only taste and touch. This time I chose the latter because of something I read in the New Yorker earlier this year.

Touch, according to the author, has become a new science, and neuroscientists continue to learn more about how skin is busily sensing our relationships to others. The study is rapidly gaining new advocates who often refer to it by the term "haptics," which is Greek for touch.

Touch is highly complex and closely related to the other senses as well as to the emotions. It is the unsung sense, the one we depend on most and talk about least. All of the senses can be, and have been thought of, as having tactile dimensions.

Touch lies at the heart of our experience of ourselves and the world, yet it often remains unspoken. The omission of tactile experience is noticeable not only in the field of history, but across the humanities and social sciences. We have so often been warned "not to touch" that we are reluctant to probe the tactile world even with our minds.  

The historical study of touch has also been slighted because of the difficulty in coming to terms with the sense. A study is made difficult because it is at the same time the most complex and the most undifferentiated of the senses. Sight, hearing, smell and taste all have specific, limited sensory organs, all of which have specific limited functions. By contrast, skin is not only an organ of sense, but it serves as the canvas upon which we "see" touch and its cultural associations.

Skin, our largest and most visible organ, is the flexible, continuous covering of the body that safeguards our internal organs from the external environment. This covering protects us from the attack by physical, chemical and microbes and shields us from the most harmful rays of the sun while working hard to regulate our body temperature. The skin is constantly at work as a watchful sentinel, letting some things in and others out, and home to hundreds of millions of microorganisms that feed on its scales and secretions.

Skin is the interface through which we touch one another and sense much of our environment. Our skin reflects our age, our ancestry, our state of mind, our cultural identity and much of what we want the world to know about us.

Skin color is one of the ways evolution has fine-tuned our bodies to the environment, acting as a gradient to the intensity of the ultraviolet radiation that falls on different latitudes of the earth's surface. No other organ in the body can boast of so many diverse and important roles.

The sense of touch is controlled by a huge network of nerve endings and touch receptors in the skin known as the somatosensory system. It is responsible for all of the sensations, including cold, hot, smooth, rough, pressure, tickle, itch, pain and vibrations. Within the system there are four types of receptors: mechanoreceptors, thermoreceptors, pain receptors and proprioreceptors.

Mechanoreceptors perceive sensations such as pressure, vibrations and texture. The most sensitive ones are found in the top layers of the dermis and epidermis and are generally found in nonhairy skin such as the palms, lips, tongue, soles of the feet, fingertips, eyelids and the face.

Thermoreceptors perceive sensations related to the temperature of objects the skin feels. They are found in the dermis layer of the skin and include two categories – hot and cold. Thermo-receptors are found all over the body, but cold receptors are found in greater density than heat receptors. The highest concentration of thermoreceptors can be found in the face and ears (which explains why the nose and ears get colder faster than the rest of the body on a chilly winter day).

Pain receptors detect pain or stimuli that cause damage to the skin and other body tissues. There are more than 3 million throughout the body, found in skin, muscles, bones, blood vessels and some organs. They can detect pain caused by mechanical stimuli, burns or chemicals (i.e., poisons from an insect bite). Pain receptors help keep the body safe from serious injuries or damage by sending early signals to the brain.

Propioreceptors sense the position of the different parts of the body in relation to each other and the environment. They are found in tendons, muscles and joint capsules. This location in the body allows these special cells to detect changes in muscle length and tension. Without propioreceptors, we could not feed or even clothe ourselves.

Touch has widespread distribution. While the sensory receptors for sight, smell, taste and hearing are clustered together in the head close to the brain, touch receptors are scattered throughout the skin and muscle tissue and convey their signals via the spinal cord.

Max Sherman is a medical writer and pharmacist retired from the medical device industry. He has taught college courses on regulatory and compliance issues at Ivy Tech, Grace College and Butler University. Sherman has an unquenchable thirst for knowledge on all levels. Eclectic Science, the title of his column, will touch on famed doctors and scientists, human senses, aging, various diseases, and little-known facts about many species, including their contributions to scientific research. He can be reached by email at maxsherman339@gmail.com.