The other senses are exquisite sensitizations to touch: compressions of air on the ear drum; vibrant chemicals on the nasal membranes and taste buds; energetic photons hitting the retina.
Reflecting skin’s protective role, pain receptors outnumber all others. Pressure sensors come in second; different ones detect light or heavy, pressure transitory or constant. Then cold receptors, and finally, the sense of warmth.
Heat and cold have specific nerve receptors. Other nerve endings may pick up on several or a wide variety of stimuli. 8 different tactile nerve endings are known, but that’s an undercount. Nerve receptors are packed so closely to make unraveling exceedingly difficult.
One sensor found everywhere on the skin are free nerve endings. Free nerve endings can sense light touch, pressure, and pain, as well as reacting to specific chemicals spilled from damaged cells.
Touch sensors (mechanoreceptors) are most concentrated on the lips (hence the pleasure of kissing, especially lightly); and most sparsely on the back (hence the pleasure of back rubs).
The acutely sensitive tactile corpuscle, located just below the epidermis, is most abundant on the lips and fingertips. This ending is particularly sensitive to a moving light touch, but quickly adapts (ceases to register) to constant contact.
Expanded tip tactile receptors are like tactile corpuscles except that they continue to respond to long-continuing contact, affording the ability to pinpoint an object in stationary touch.
The human skin is covered with hairs that act as a proximate sense of touch, and as a defense: one readily notices a small insect crawling on the skin because of hairs being disturbed, not the skin per se being touched.
Every hair on the body has a follicle wrapping: a hair end organ, which registers the slightest movement of each hair. There are distinct hair types, each with specific sets of sensory receptors.
The network of receptors distributed throughout the skin lets us construct a model of the proximate world. These receptors also connect to emotion processing, and so help suss and convey social intentions. A gentle touch speaks volumes.
Bulbous corpuscles – pressure sensors located deep in the skin – are touched by massage. They do not rapidly adapt, and therefore sense continued pressure on deep tissues. Bulbous corpuscles are particularly abundant at joints, thus informing about the location and movement of limbs.
Pacinian corpuscles are in the skin and deeper tissues, but unlike bulbous corpuscles, Pacinian corpuscles adapt within a tiny fraction of a second, and so detect tics, fleeting pressures and distortions, and vibrations.
Although the density distributions vary from one body area to another, no substantial patch of skin lacks nerve endings. Interpenetration is so thorough that single tactile stimulation almost never occurs. The sense of touch is an interdependent dynamic, informing about forms and textures without and within.
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Touch is central in building the foundations of social interaction, attachment, and cognition. ~ German psychologist Antje Gentsch et al
Tactile pleasure and pain are gradients that commonly mix in the mind. The nature of touch, its intensity and repetition, as well as control over the source, shape the interpretation of touch.
Affectionately touching the skin of someone else gives an illusory impression of soft skin. The mind has the skin of a loved one feel silkier than it really is.
Physical contact is essential to health: a form of psychological nutrition. Sensory malnutrition at any age can be debilitating, but especially, like other deficiencies, is more alarmingly harming to the young.
Biochemists point to elevated oxytocin levels to quantify the effect of nutritional touch, but that is like pointing to elevated glucose levels to quantify dietary nutrition: the measure is an inadequate statement of holistic effect.
Trust and touch are often intertwined, as touch can be both a physical and emotive experience. While everyone enjoy socially-affirming touch, women are more susceptible to tactile manipulation than men.
Caressing can also be a vicarious pleasure. As a physical facet of empathy, the mind naturally reacts strongly to the sight of pleasurable contact between others – hence the popularity of romantic movies and pornography.
Babies are learning a great deal about touch in the uterus. They suck on their thumbs, grab the umbilical cord, and are constantly bumping against the walls of the mother’s abdomen. ~ American touch researcher Tiffany Field
A human embryo develops a sense of touch in its 6th week, when it is less than 2 cm long. Beginning in the womb, touch guides development of brain regions related to social behaviors.
Touch is central to the way that babies interact. ~ American neurobiologist Carissa Cascio
Tactile stimulation is essential to infant survival. Studies from the early 20th century reported infant mortality reaching 99% within a year of admission into orphanages where caretakers gave no care. Those that survived were forever marred by stunted growth and mental retardations.
The same happens to young abandoned animals put into shelters or zoos where the time is not taken to act humanly to the inmates. Animals who receive early affectionate contact develop superior functionalities and immunological resistances.
The effects are strengthened if fondled throughout maturation. Licking is a common form of affectionate contact for many animals, the equivalent to human kissing.
Mental disorders of all sorts are worsened by lack of positive physical contact with others. Violence, rage, and other emotional disturbances are related to tactile deprivation.