Touch

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Touch

Touch is one of the five senses (the others being smell, taste, vision, and hearing) through which animals and people interpret the world around them. While the other senses are localized primarily in a single area (such as vision in the eyes or taste in the tongue), the sensation of touch (or contact with the outside world) can be experienced anywhere on the body, from the top of the head to the tip of the toe. Touch is based on nerve receptors in the skin which send electrical messages through the central nervous system to the cerebral cortex in the brain, which interprets these electrical codes. For the most part, the touch receptors specialize in experiencing either hot, cold, pain, or pressure. Arguably, touch is the most important of all the senses; without it animals would not be able to recognize pain (such as scalding water), which would greatly decrease their chances for survival. Research has also shown that touch has tremendous psychological ramifications in areas like child development, persuasion, healing, and reducing anxiety and tension.

How we feel the outside world

Our sense of touch is based primarily in the outer layer of skin called the epidermis. Nerve endings that lie in or just below the epidermis cells respond to various outside stimuli, which are categorized into four basic stimuli: pressure, pain, hot, and cold. Animals experience one or a combination of these sensations through a complex neural network that sends electrical impulses through the spinal cord to the cerebral cortex in the brain. The cerebral cortex, in turn, contains brain cells (neurons) arranged in columns that specialize in interpreting specific types of stimuli on certain parts of the body.

The sensation of touch begins with various receptors in the skin. Although these receptors appear to specialize in reacting to certain sensations, there is some debate concerning this specificity since most touch stimuli are a combination of some or all of the four major categories.

Scientists have identified several types of touch receptors. Free nerve ending receptors, located throughout the body at the bases of hair, are associated primarily with light pressure (such as wind) and pain. Meissner corpuscles are nerve endings contained in tiny capsules and are found primarily in the fingertips and areas especially sensitive to touch (in the form of low-frequency vibrations), like the soles of the feet and the tongue. The Pacinian corpuscles look like the cross section of an onion and are found in deep tissues in the joints, the genitals, and the mammary glands. They are extremely sensitive to pressure and are also stimulated by rapid movement of the tissues and vibrating sensations. Ruffini endings, which are also located in the deeper layers of the skin, respond to continuous stimulation, like steady pressure or tension within the skin. Merkel disks, are found near the base of the epidermis and also respond to continuous stimulation or pressure. The skin also contains specific thermoreceptors for sensing hot and cold and nociceptors that identify high intensity stimulation in the form of pain.

Most, if not all of these receptors, are designed to adapt or become accustomed to the specific stimulation they interpret. In other words, the receptor does not continue to register a constant “feeling” with the same intensity as when it first begins and may even shut off the tactile experience. Imagine, for example, putting on a wool sweater over bare skin. The initial prickly sensation eventually abates, allowing the wearer to become accustomed to the feeling. Other examples include wearing jewelry such as rings, necklaces, and watches.

These receptors are also found in greater numbers on different parts of the body. For example, peoples’ backs are the least sensitive to touch, while their lips, tongue, and fingertips are most sensitive to tactile activity. Most receptors for cold are found on the surface of the face while thermoreceptors for warmth usually lie deeper in the skin and are fewer in number. A light breeze on the arm or head is felt because there tend to be more sense receptors at the base of the hairs than anywhere else.

Touch and health

Touch has a tremendous impact on most animals’ physical and psychological well being. Numerous studies of humans and other animals have shown that touch greatly impacts how we develop physically and respond to the world mentally. For example, premature babies that receive regular massages will gain weight more rapidly and develop faster mentally than those who do not receive the same attention. When baby rats are separated from their mothers for only 45 minutes, they undergo physiological or biochemical changes, specifically a reduction in a growth hormone. Touching of premature babies can also stimulate growth hormones (such as the hormone needed to absorb food) that occur naturally in healthy babies.

A baby does not have to be premature or sickly to benefit from touch. Even healthy babies show benefits from touch in terms of emotional stability. Difficult children often have a history of abuse and neglect. The reason is that touch serves as a type of reassurance to infants that they are loved and safe, which translates into emotional well being. In general, babies who are held and touched more tend to develop better alertness and cognitive abilities over the long run.

Touch continues to have a great psychological impact throughout peoples’ lives. Even adults who are hospitalized or sick at home seem to have less anxiety and tension headaches when they are regularly touched or caressed by caretakers or loved ones. Numerous studies have shown that touch also has a healing power. Researchers have found that touch reduces rapid heart beats and irregular heart beats

KEY TERMS

Biochemical —The biological or physiological chemicals of living organisms.

Central nervous system —The brain and spinal cord components of the nervous system, which controls activities of internal organs, movements, perceptions, thoughts, and emotions.

Cerebral cortex —The external gray matter surrounding the brain and made up of layers of nerve cells and fibers, thought to process sensory information and impulses.

Epidermis —The outer layer of the skin consisting of dead cells. It is the primary protective barrier against sunlight, chemicals, and other possible harmful agents. The epidermal cells are constantly being shed and replenished.

Free nerve endings —Touch receptors in the skin that detect light pressure.

Glucocorticoids —A steroid or hormone like compound that affects metabolism and can have an anti-inflammatory effect.

Meissner corpuscles —Touch receptors in the skin that are sensitive to touch. Named after German histologist Georg Meissner.

Neurons —Nervous system unit that includes the nerve cell, dendrites, and axons.

Pacinian corpuscles —Touch receptors in the skin that sense pressure and rapid or vibrating movement of the tissues, named after Italian anatomist Filippo Pacini.

(arrhythmias). Another study showed that baby rats who are touched often during infancy develop more receptors to control the production of biochemicals called glucocorticoids, which are known as stress chemicals because of their ability to cause muscle shrinkage, high blood pressure, elevated cholesterol, and more.

Touch’s psychological impact goes beyond physical and mental health. Researchers have shown that touch is a powerful persuasive force. For example, studies have shown that touch can have a big impact in marketing and sales. Salespeople often use touch to establish a camaraderie and friendship that can result in better sales. In general, people are more likely to respond positively to a request if it is accompanied by a slight touch on the arm or hand. In a study of waiters and waitresses, for example, those that lightly touched a patron often received better tips.

See also Perception.