Our sense organs 45

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-
39