Psychology2016

116 CHAPTER 3

The sense of touch allows individuals
that are blind to “read” a Braille book with
their fingers. The fingertips are extremely
sensitive to fine differences in texture,
allowing readers to distinguish between
small dots representing the different letters
of the alphabet.

*intestinal: having to do with the tubes in the body that digest food and process waste material.

The Other Senses: What the Body Knows

So far, this chapter has covered vision, hearing, taste, and smell. That leaves touch. What

is thought of as the sense of touch is really several sensations, originating in several dif-

ferent places in—and on—the body. It’s really more accurate to refer to these as the body

senses, or somesthetic senses. The first part of that word, soma, means “body,” as men-

tioned in Chapter Two. The second part, esthetic, means “feeling,” hence the name. We

will discuss four somesthetic sense systems.

Somesthetic Senses

3.12 Describe how we experience the sensations of touch, pressure, tempera-

ture, and pain.

Here’s a good trivia question: What organ of the body is about 20 square feet in size?

The answer is the skin. Skin is an organ. Its purposes include more than simply keeping

bodily fluids in and germs out; skin also receives and transmits information from the

outside world to the central nervous system (specifically, to the somatosensory cortex).

to Learning Objective 2.12. Information about light touch, deeper pressure, hot,

cold, and even pain is collected by special receptors in the skin’s layers.

TYPES OF SENSORY RECEPTORS IN THE SKIN There are about half a dozen different

receptors in the layers of the skin. (See Figure 3.16.) Some of them will respond to only

one kind of sensation. For example, the Pacinian corpuscles are just beneath the skin and

respond to changes in pressure. There are nerve endings that wrap around the ends of

the hair follicles, a fact people may be well aware of when they tweeze their eyebrows

or when someone pulls their hair. These nerve endings are sensitive to both pain and

touch. There are free nerve endings just beneath the uppermost layer of the skin that

respond to changes in temperature and to pressure—and to

pain.

How exactly does pain work? Why is it that

sometimes I feel pain deep inside? Are there

pain receptors there, too?

Yes, there are pain nerve fibers in the internal organs as

well as receptors for pressure. How else would people have

a stomachache or intestinal* pain—or get that full feeling of

pressure when they’ve eaten too much or their bladder is

full?

There are actually different types of pain. There are

receptors that detect pain (and pressure) in the organs, a type

of pain called visceral pain. Pain sensations in the skin, mus-

cles, tendons, and joints are carried on large nerve fibers and

are called somatic pain. Somatic pain is the body’s warning

system that something is being or is about to be damaged

and tends to be sharp and fast. Another type of somatic pain

is carried on small nerve fibers and is slower and more of a

general ache. This somatic pain acts as a kind of reminder

system, keeping people from further injury by reminding

them that the body has already been damaged. For example,

if you hit your thumb with a hammer, the immediate pain

somesthetic senses
the Dody senses consisting of the sMin
senses, the kinesthetic and proprio-
ceRtive senses and the vestiDular
sense.

Pressure-sensitive nerves

Sweat gland

Hair

Skin surface

Subcutaneous
fat

Pain-sensitive and touch-sensitive

free nerve endings

Blood

vessels

Skin layers

Meissner’s corpuscle

Pacorpusclecinian Ruffini ending

Figure 3.16 Cross-Section of the Skin and Its Receptors
The skin is composed of several types of cells that process pain, pressure, and
temperature. Some of these cells are wrapped around the ends of the hairs on the
skin and are sensitive to touch on the hair itself, whereas others are located near
the surface and still others just under the top layer of tissue.