So that's a brief overview of the
autonomic nervous system for the specific
areas, the specific organs.
I just want to concentrate on the
referred pain now and before I do that,
I just want to review this diagram which we
looked at in the very first lecture of the surface anatomy.
And here we have the spinal
cord. The spinal cord
giving rise to two pairs of
spinal nerves. One here
and one here. These spinal nerves are
going to be running around the body wall
and they are going to be receiving cutaneous
innervation from the surface of the skin.
So this banding is what
we see on this diagram
this dermatomal distribution. So if
something was to irritate the skin here,
that cutaneous nerve say here,
will pick it up and it will take it
back to spinal cord at say, T9.
That may happen at T8 or T7 or
T6, or T5, L1, T12, whatever.
So the visceral afferent fibers,
these are not cutaneous afferent fibers.
These are visceral afferent fibers
These visceral afferent fibers
taking sensation from the visceral
travel retrograde from the
organ to the central nervous system,
just like sensation from the skin.
Except that is coming from the
skin, it's coming from the organ.
The point of this is to
promote visceral or somatic reflexes so we
can release more juice depending on the condition
and we are unaware of these happening.
This is just a feedback mechanism
to control our internal environment.
During various pathological states, however,
noxious stimuli, the accumulation
of the noxious stimuli
from an internal organ
can become so elevated
that it actually reaches our consciousness.
However, this is usually poorly localized.
It's poorly localized because we are not used to having it
and also because the body is served
by laterally, that it passes from both sides
into the central nervous system, so the
body is not clear where it's coming from.
So when you have a tummy ache, you tend to have
a dull ache right in the center.
It hasn't localized to
a specific region.
However, with time
this pain can radiate
to the dermatome level
that receives the visceral afferents.
So the dermatome level say here at T9,
we know that the 9th thoracic
spinal cord segment
gives rise to sympathetic fibers,
the greater splanchnic nerve
that go to serve the stomach.
Noxious stimuli from the stomach
are going to travel in this retrograde
direction back to T9.
Now, we are not really
used to feeling that.
What we are used to
feeling is pain coming from
the surface of the skin.
So our brain believes
that this pain is actually originating
from the surface of the skin
and that's why we
called it referred pain.
The pain is actually coming from
the stomach or whatever organ.
But it's been referred to the surface of the
skin. That's why we need to be confident
in knowing the spinal cord segment
that gives rise to those autonomic nerves.
So let's have a look at the appendicitis.
Appendicitis pain is initially felt in the
kind of periumbilical region.
Around about in this region here.
The appendix is part of the midgut
and the midgut is served from the
greater, lesser and least splanchnic
nerves. And these come
into the spinal cord following their
afferent fibers at around about the T10
level of lesser splanchnic nerve here.
If the inflammation of the appendix
irritates the parietal peritoneum.
Now remember that the parietal peritoneum
that could be irritated by the appendix
is down in your lower inguinal region.
Your appendix is in this right
inguinal region here.
Then the parietal peritoneum here
is going to become irritated.
So if the inflammation of the
irritates the parietal peritoneum
as this is supplied by the somatic
nervous system, the parietal peritoneum,
as this is supplied by the somatic
nervous system down in here
this pain can now be precisely
localized. So it's starting off here
and then its radiating
down here. It localizes
to the lower right quadrant, where
the appendix is located.