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The development of the
nociceptor concept.
As many scientists in
the previous centuries,
the famous philosopher
Rene Descartes
believed that pain can be
caused by the stimulation
of any nerve in our body.
The often recorded
drawing from his book
on the functioning of the
human body may illustrate this.
According to his assumption, pain
is induced by noxious stimuli which
over-excite all kinds of nerves.
Any nerve will transmit an
alarm signal into the brain,
which leads to pain.
This assumption has been
called intensity hypothesis.
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In the late 19th century, the
German physiologist, Max von Frey,
challenged this assumption.
Nowadays, he's best known for the
development of the Von Frey hairs,
which allow application of
graded mechanical stimulation
to the body surfaces.
The figure in blue shows an original
depiction of this device in a paper
of Von Frey published in 1897.
The pointed stiff hair, nowadays,
usually a nylon filament
of defined diameter is
used, attached to a handle,
is pressed against the skin
so that it slightly bends.
The exerted pressure defines
the strengths of this stimulus.
With this simple
device, Von Frey made
the discovery which made him
famous, the pain points in the skin.
He writes in one of his papers: "It
is possible to stimulate the skin
in such a way as to
produce a painful sensation
with no proceeding or
accompanying pressure sensation.
That this can be done
leads to the conclusion
that pain is the result of
exciting special organs.
The pain points are a
sign of the irregular
distribution of specifically pain
sensitive organs over this skin."
The characteristic features
of the pain points are:
they can be distinguished
from touch, warmth and cold points.
The stimulation induces a sustained,
often increasing pain sensation.
And they require stronger
deformation than touch points.
