So an important play between the
somatic and the autonomic nervous system.
A similar arrangement happens here, when we
are looking at the rectum and the anal canal.
And in this diagram, unlike the
previous, we can actually see
the hypogastric plexus that
I have been talking about.
So just spend some time
just reviewing this now.
We can see we have the coeliac
plexus and the coeliac ganglion
around the coeliac trunk here. And you
generally have a flow of autonomic nerves
down the aorta, enabling parasympathetic
fibers to pass down from the vagus.
Allowing the sympathetic fibers from
coeliac trunk to actually pass down
and you can have the flow of autonomic
fibers from superior mesenteric plexus
down to the inferior mesentery plexus.
And then it carries on
down to the bifurcation
of the aorta.
And at the bifurcation of the
aorta, you can find we have
the superior hypogastric plexus.
The superior hypogastric plexus.
This is going to be a mixed plexus. It's contains
both parasympathetic and sympathetic.
We can then see if we look at our
S2, 3, 4 parts of our sacral plexus.
This is going to give rise to
our pelvic splanchnic nerves.
These pelvic splanchnic nerves then
run towards the internal iliac
and they meet autonomic fibers coming down
from the superior hypogastric fibers.
From the superior hypogastric plexus.
And these fibers are running
down as hypogastric nerves.
They merge with the pelvic
splanchnic nerves to form
the inferior hypogastric plexus.
So we had one superior hypogastric plexus
gives rise to two hypogastric nerves.
These hypogastric nerves merge
with pelvic splanchnic nerves
to form the inferior hypogastric plexus.
We're concerned with the rectum. So
this inferior hypogastric plexus
gives autonomic fibers that
go towards the rectum
and they form this rectal plexus.
We can then follow the formation
of the rectal plexus.
Sympathetic, we have these
lumbar splanchnic nerves that pass in
to the inferior mesenteric plexus.
They then run down to the
superior hypogastric plexus
and then they communicate with
the inferior hypogastric plexus
via hypogastric nerves and here
they get to the rectal plexus.
Parasympathetic is going to be via pelvic
splanchnic nerves which we can see here
and these pass into the left and right
inferior hypogastric plexus
which gives rise to the rectal plexus.
This is the autonomic control of the rectum.
However, this controls our ability to defecate
and again we have the sensation
that we need to defecate.
Yeah, we also have the ability
to limit ourselves from defecating.
We can control it.
And that is because inferior
to the pectinate line
we have the external anal sphincter.
The external anal sphincter is
innervated via the inferior
rectal nerve. And this is
a somatic branch from S2,
S3, S4, we can see it here.
Now confusing I appreciate, the S2, 3, 4
gives rise to parasympathetic fibers.
It also gives rise to the
somatic pudendal nerve
and this controls the
external anal sphincter.
So when you have the urge to defecate,
you can contract this sphincter.
You don't walk around with it contracted.
When you have the urge to defecate
you can contract this sphincter.
You can make your way to a toilet. Then
you control, you relax it and you defecate.
So that's the autonomic innervation
to the rectum and anal canal.