The sense of touch
– it’s all over the skin

We become aware of the versatility of our tactile sense when we think of such diverse experiences as caressing, fondling, itching, nibbling, tickling, scratching, and kissing. Or consider some special situations like jumping into a cold pool on a hot summer day, withdrawing your foot from a muddy patch, or the crunching of wet sand between your toes. People who are deaf and blind demonstrate that it is possible to orientate themselves by their sense of touch. If we had no tactile sense, it would have been like living in vague, dull surroundings where one could lose a leg or burn one’s skin, or get disorientated without even noticing it.

There are many metaphors in our language which refer to touching and feeling. Our emotions are called feelings, and when we are moved, we say that something has touched us. Problems can be “ticklish” or “tough”. Some people have to be handled “with kid gloves”. Music teachers chide their pupils for not having enough “feeling in their fingertips”, meaning that a difficult-to-describe “something” is lacking in their performance.

The physiological term for the transmission of information by means of receptors (Latin receptor = recorder) is sensibility (Latin sensibilis = observable). A receptor is the end of a nerve fibre, or a specialised cell, which can detect stimuli and convert them into neural impulses.

General sensibility:

Tremendous amounts of information are detected by receptors and are subsequently processed in the central nervous system. This complex process is known as sensibility.

The receptors are located in the skin, in structures like muscles and skeletal joints, or in internal organs, and are respectively known as superficial, deep, and visceral sensibility (Latin viscera = intestine). As distinct from the other four senses (hearing, seeing, smelling and tasting), these three types are known collectively as somato-visceral sensibility. Only a small fraction of all these signals are consciously perceived. Several kinds of receptors can be distinguished according to the stimuli which they detect, namely mechanical, thermal, chemical, osmotic, and polymodal receptors. The latter refer to more than one type of stimulus.

Sensibility of the skin:

We will here restrict ourselves to superficial sensibility, namely the perceptions mediated by the skin (cutis). This is a (nearly) watertight covering which protects all body tissues from physical damage. At the same time the skin is a highly sensitive sense organ which can simultaneously detect various stimuli that can be quite independent of one another. A large number of different sensations can be perceived via the skin: the softness of a cat’s fur, the roughness of a masonry wall, the smoothness of ice, the pleasant warm sensation of a sauna, but also the thorns of a rosebush, or the burning pain of a fresh wound. Strong emotions can be aroused through the skin, as by a passionate kiss or tender caresses. Many properties of objects cannot be appraised by hearing, seeing, or smelling, but only by touch, as for example, weight, temperature, hardness, roughness, dampness, stickiness, and elasticity. We recognise surface structures and shapes by touch.

There are very many sensitive points in the skin, but they are not evenly distributed. They are closer together on face and hands than, for example, on the back, which is therefore less sensitive. There are three independent skin senses, namely touch, temperature, and pain.

Not only do we have unique fingerprints, the patterns of our skin pores are also unique. The skin is a dual-layered membrane. The inner, spongy, leathery layer has a thickness of between one and two millimetres. It consists essentially of connective tissue which is rich in the protein collagen. It protects and cushions the body, and it contains hair follicles, nerve ends, and sweat glands, as well as blood capillaries and lymphatic vessels. In contrast, the thickness of the outer layer, the epidermis (Greek epi = upon, above; derma = skin), is only between 0.07 and 0.12 mm.

A section of human skin.

The layers of the epidemis, the dermis, and the inner skin are clearly visible.

Epidermis Dermis Subcutaneous layer Vein Artery Sweat gland Nerve Pacinian (Vater’s) corpuscle (pressure sensitive receptor)

Hair muscle (erector pili) Internal root Sheath Nerve sheath around hair root Sebaceous gland Meissner’s corpuscle (touch sensitive receptor)

Our skin separates our bodies from the outside world. It encloses us, gives us our individual shapes, protects us from intruders, cools or warms us, and conserves our body liquids. Surprisingly, it contributes about one sixth of our body weight, although the epidermis itself weighs only about 500 g. The total area of the skin amounts to approximately 1.6 square metres. It is watertight, washable, and elastic. The skin is thickest on the palms of our hands and on the soles of our feet, and thinnest in the armpits and on the eyelids.

Our skin – by numbers: One square centimetre of skin contains:

6,000,000 cells 100 sweat glands 15 sebaceous glands 5,000 sensory corpuscles 200 pain points (receptor areas) 25 pressure points 12 cold-sensitive points 2 heat-sensitive points

The most important property of the skin is that it contains our sense of touch, which is located in the dermal layer. The outer layer is insensitive, rubs off easily, and causes the ring left in the bath after bathing.

The sense of touch is difficult to investigate. All the other senses have a definite key organ which can be studied, but the skin is spread over the entire body and cannot easily be delimited or “switched off”. In the case of vision, scientists can observe blind persons to learn more about seeing, and they can study deaf people to learn more about hearing. But this is impossible for the sense of touch.

Touching is ten times as strong as verbal or emotional contact. If touching were not pleasant, living things would not procreate. If we did not enjoy touching and caressing, there would be no sex.

A foetus feels the moist warmth inside the womb; it perceives the heartbeats and the internal rhythms of its mother. The sense of touch is the first sense to develop. It functions automatically, before the newborn baby’s eyes even open to observe the world.

It has been discovered that there are many more kinds of receptors than the four basic ones through which we experience warmth, coldness, pain, and pressure. All the different tactile sensations are more complex than these four, and they cause us to respond variously.

Tactile experiences (Latin tactilis = touchable): Mechanical stimuli cause several different sensations: stroking, touching, vibration, pressure, and tension. The fingertips and the tip of the tongue are especially sensitive. The fingertips can feel a sharp point if the impression is only 10 μm, and in the case of a vibrating stimulus pressed into the skin, can feel it even if this is less than 1 μm.

Other functions of the skin: In addition to its important function as a tactile sense organ, there are several others, of which only a few are mentioned below:

1 The skin protects passively, as well as actively, against injurious external influences. It can destroy invading infective agents.

2 The skin plays an important role in controlling the temperature of the body, which should not deviate from 37° C because most organs function optimally at this temperature. Heat loss can be increased or reduced by increasing or reducing the flow of blood through the skin’s network of small blood vessels. About three quarters of the heat loss is effected by radiation and conduction. The other quarter is effected by the evaporation of water, partly unnoticed through the skin and the lungs, and partly by perspiration. The invisible evaporation through the skin comprises one third of the total dermal loss of water.

3 In addition to sweat, the skin also secretes sebum, an oily substance which lubricates the hairs and the epidermis. Sweat-glands are exceptionally numerous on the hands and the soles of the feet. There are about 200 million sweatglands which secrete approximately one litre of water per day through orifices in the skin.

4 The skin also performs a respiratory function, handling between one and two percent of the total gas exchange of the body. It absorbs oxygen, and carbon dioxide can pass through it in both directions.

5 Pain acts as a guardian of our health. It is usually invoked indirectly by pain mediating chemicals accumulating in body tissues, which then stimulate free nerve endings.

The Bible and the sense of touch:

God has all the senses which we have. Since we are made in His image, He blessed us with our various senses. King Belshazzar was told that he had set himself up against the Lord of heaven, because he “praised the gods of silver and gold, of bronze, iron, wood and stone, which cannot see or hear or understand” (in the German translation “understand” is rendered as “feel”, Daniel 5:23). Man-made idols are characterised as having no sense organs. In contrast, the living God can see, hear, and feel. The risen Christ wasn’t an imaginary figure, but He was so real that He could be seen, heard, and touched. When Jesus appeared suddenly amongst his disciples, they were frightened, because they thought that they were seeing a ghost. To convince them that He was genuine and real, He allowed them to touch Him: “Look at my hands and my feet. It is I myself! Touch me and see; a ghost does not have flesh and bones, as you see I have” (Luke 24:39). John begins his first epistle by testifying that he has observed the Son of God by means of his own senses. He is an eye-witness as well as an aural and a tactile witness of Jesus: “That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked at and our hands have touched – this we proclaim concerning the Word of life... We proclaim to you what we have seen and heard ...” (1 John 1:1,3).