Structure and Functions (Magill’s Medical Guide, Sixth Edition)
An essential attribute of the survival of a species is the ability to detect both the internal and the external environment. This is necessary so that appropriate and life-sustaining actions can be taken at all times. When changes or modifications of these environments take place, many responses can occur within an individual, ranging from rolling over during sleep to restore blood flow to an arm to avoiding contact with a prickly pear cactus. This kind of monitoring occurs within the general and special sense organs or structures found in humans and many other species.
One way in which the body monitors its internal and external environments is through the general senses. General sensations include temperature, pain, touch, pressure, vibration, tickle, and proprioception (internal sensations relating to how one’s body is situated in space). Sensations of touch usually originate at or very near the skin surface; some originate from receptors found in deeper, subcutaneous (below-the-skin) layers. Many of the general senses are collectively called the tactile senses, notably those of touch, pressure, vibration, and tickle. In addition, the term “somatic senses” refers to the sensory receptors associated with skin, muscles, joints, and visceral organs. Receptors in the muscles or joints are essential for the awareness of body movement. Visceral receptors play important roles in monitoring changes in body pain, as...
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Disorders and Diseases (Magill’s Medical Guide, Sixth Edition)
Loss of tactile senses is a symptom rather than a disease. In general, a lost ability to sense touch, pressure, vibration, or tickle is a result of physical damage to a group of nerves or of a disease of the nervous system. Sensory receptors are not themselves targets of disease, but they can be physically or chemically impaired, especially if the skin is severely damaged.
An example of severe damage to the skin that will cause a loss of tactile sensations is a third-degree burn of the body. Third-degree burns are marked by the total destruction of the full thickness of the skin. This destruction includes the epidermis, the dermis, and any associated skin structures, such as secretion glands, hair, and the general sensory receptors. No pain is sensed when regions of the body that have received a third-degree burn are touched, because the nerve fibers that innervate the touch receptors and the free nerve endings, as well as nerves located in the subcutaneous layers, have been destroyed by the burn. In such cases, total destruction of the nerve fibers and the skin has occurred. Third-degree burns can have a charred, dry appearance or a mahogany or ash-white color. Regeneration of the dermis and the subcutaneous structures is slow and painful as the healing occurs. Although skin grafting can facilitate the regeneration process, it is not uncommon for scarring to result from the rapid contraction of the wounded area as it...
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
Responsiveness to different kinds of touch at different locations on the body reveals a relationship between receptor structures and their subsequent function. Specifically, the hands of the human body are exquisitely sensitive to touch. The calculated innervation (number of nerve connections) for touch alone on the palms of the hands is 17,000 units.
On the palms, the most abundant type of touch receptors are Meissner’s corpuscles. Accounting for 43 percent of all the touch receptors of the palms, they are responsible for the sensations of texture, light touches, and low-frequency vibrations and clearly play an important role in the human experience. Meissner’s corpuscles are particularly abundant on the tips of all fingers and both thumbs. Although these receptors adapt at a moderately rapid pace, they are not so fast at adapting that the pleasure of stroking a cat or caressing a baby’s head is lost.
After Meissner’s corpuscles, Merkel’s disks are second most abundant on the palms. Constituting 25 percent of the touch innervation density, these cells are suited for fine touch and pressure. Mainly confined to the digits’ and thumbs’ full length, Merkel’s disks are important in tactile pursuits such as painting, drawing, sewing, writing, and dentistry. They are equally important in the expression of loving gestures to other people, animals, and plants via touch. Merkel’s disks are slow to...
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Møller, Aage R. Sensory Systems: Anatomy, Physiology, and Pathophysiology. Boston: Academic Press, 2003. An excellent text that describes how human sensory systems function, with comparisons of the five senses and detailed descriptions of the functions of each of them. Also covers how sensory information is processed in the brain to provide the basis for communication and for the perception of one’s surroundings.
Schmidt, Robert F., ed. Fundamentals of Sensory Physiology. Translated by Marguerite A. Biederman-Thorson. Rev. 3d ed. Berlin: Springer, 1986. Chapters 1 through 4—“General Sensory Physiology, Psychophysics,” “Somatovisceral Sensibility,” “Neurophysiology of Sensory Systems,” and “Nociception and Pain”—address the topics of touch sensations. Sketches and postreading quizzes assist the reader in comprehension.
Shier, David N., Jackie L. Butler, and Ricki Lewis. Hole’s Essentials of Human Anatomy and Physiology. 10th ed. Boston: McGraw-Hill, 2009. An academic textbook designed to give more detail about the human body than an introductory biology book. Chapter 12, “The Somatic and Special Senses,” has a section devoted exclusively to receptors and sensations. Related topics, such as the anatomy and organization of the brain and nervous system, are described in exquisite detail.
Tortora, Gerard J., and Bryan Derrickson. Principles of...
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Touch (Encyclopedia of Science)
Touch is one of the five senses through which animals interpret the world around them. (The other senses are smell, taste, sight, and hearing.) While the organs of the other senses are located primarily in a single area (such as sight in the eyes and taste in the tongue), the sensation of touch can be experienced anywhere on the body, from the top of the head to the tips of the toes.
Without the sense of touch, animals would not be able to recognize pain, which would greatly decrease their chances for survival. Research also has shown that touch is an important factor in child development, persuasion, healing, and reducing anxiety and tension.
How we feel the outside world
The sense of touch is based primarily in the outer layer of the skin called the epidermis. Nerve receptors in the epidermis respond to outside stimuli by sending impulses along nerves through the central nervous system to the brain. The brain, in turn, interprets these impulses as heat, cold, pain, or pressure.
Scientists have identified several types of touch receptors, or nerve endings. One type is associated mainly with light pressure (such as wind) and pain and occurs at the base of hairs throughout the body. Another is found in the fingertips and areas especially sensitive to touch, such as the tongue and the soles of the feet. A third type is...
(The entire section is 587 words.)