TOUCH
T
THE SENSE OF TOUCH
The skin contains many thousands of specialized cells that
respond to a variety of external stimuli, such as touch, heat,
cold, and pressure. These cells (receptors) are divided into
two different types. One type of receptor consists only of a
thin nerve fibre, which may wrap around an individual hair
and respond to its movement. The other type of receptor has
a specialized structure, which is known as an end organ,
that surrounds the nerve ending. Some skin receptors consist
of several layers of cells that are attached to one nerve fibre.
Others contain several nerve fibres that are arranged in a loop
or coil. It is probable that several varieties of receptors play a
part in each of the different types of touch modality.
Free nerve
endings
Epiderm is
Organ of
Ruffini
Pacinian
corpuscle
Skin receptors
These receptors vary from free nerve endings to corpuscular or bulb-
like structures. Individual receptors do not seem to be associated
exclusivelywith anyone skin sensation (e.g. cold or pain).
TOUCH PERCEPTION
General sensations that emanate from various parts ofthe body are perceived
at specific points within the brain’s cerebral cortex. Some ofthe more highly
sensitive body parts, such as the lips and hands, are represented in the brain
by correspondingly large regions within the cortex.
Delicate touch
The ability to
detect light
contact between
an object and the
skin. Areas with
more receptors are
more sensitive.
Pain
Pain warnsthe brain
about possible injury
from an external
stimulus and can
trigger a reflex
withdrawal.
Heat
Some free nerve
endings respond to
heat. The inner wrist
is good for testing
temperature. Extreme
heat stimulates pain
receptors.
Cold
Cold on the skin
is detected by
specialized end
organs. Extreme
cold also
stimulates pain
receptors.
Pressure
A change in
pressure on the
skin is detected
byspecialized
end organs
called pacinian
corpuscles.
Pacinian corpuscle
These receptors are 1 mm
to 4 mm
long and occur
in hairless areas of skin, especiallythe fingers.
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