00:01
So now let's have a look at a couple
of these muscles quite specifically
starting with external oblique.
00:06
So external oblique muscle
is a very thin muscle.
00:10
It's the most superficial of
those three paired muscles
I spoke about a moment or two ago,
that originate laterally.
00:17
And here we can see them coming
from the outer surface of the ribs.
00:20
Ribs 5 to 12.
There can be some variation.
00:23
And forgive me, if some textbooks
maybe say things
slightly differently.
00:27
But typically, from the
outer surface of ribs 5 to 12,
you'll find the origin of
the external oblique muscle.
00:35
And you can see these fibers
are radiating downwards,
as if you're just sliding your hands
into your pockets on your jacket.
00:42
The direction of your fingers
really is the direction
of those external oblique
muscle fibers.
00:49
They went all the way down
to attach to the anterior half
of the iliac crest,
which can be located on the
iliac aspect of the pelvic bone.
00:58
And they also run down
as an aponeurosis
to help form the inguinal ligament.
We'll come back to that in a moment.
01:05
And you can see how the fibers run
indicated by these green lines,
they run towards the midline.
But the muscle themselves,
the muscle fibers themselves
don't reach the midline,
they give rise to
a flat tenderness structure.
01:18
So you may recall
that muscle say like biceps
gives rise to a nice
cord like tendon,
the tendon of biceps brachii.
01:28
It doesn't happen like this here.
01:30
Here, we can see the muscle fibers
give rise to this
flat connective tissue sheath
which is known as an aponeurosis.
01:36
And that aponeurosis runs towards
what we've seen before
the linea alba,
and then most inferiorly,
the pubic tubercle.
01:44
So this is a thin muscle layer
that runs towards the midline
linea alba pubic tubercle.
01:49
But it does by giving rise
to a thin connective tissue sheet
called an aponeurosis.
01:56
There you can see it's attached
to the inguinal ligament.
01:59
The function of this muscle
is relatively straightforward.
02:02
And as those muscles contract,
so the distance between the
inferior aspect the subcostal region
and the midline
and the pubic tubercle,
the inguinal ligament
is going to shorten
and obviously that's going to lead
to bending to the right.
02:15
So if the right one contract
so you bend to the right.
02:18
And then conversely,
if the left one contracts,
you bend across to the right.
02:22
So very important functions
in relation to movement
of these muscles.
02:26
But what they also do is they help
to compress the abdominal contents.
02:30
So they're always carrying
a basic level of tones.
02:34
They're always contracted
to a certain extent
if all of our muscles were
permanently flaccid and relaxed.
02:39
We wouldn't be able to withstand
the forces of gravity
and will just fall over.
02:42
So all of our muscles even though
we may think they're relaxed,
do have a basal tone
of contraction there.
02:48
And that helps to maintain
abdominal pressure.
02:51
Contraction of both
of these muscles,
the left and right side
and simultaneously
help to flex the trunk. So helping
to move the head forwards.
02:59
So now let's look at the origins and
insertions of Rectus Abdominis.
03:04
We can see the rectus Abdominus originates
from the pubic symphysis and the pubic crest
inferiorly, and it passes all the way up to
the xiphoid process superiorly. We also have
lateral attachments on the costal cartilages
of ribs 5 to 7, and then we actually have
within the body of rectus Abdominus a series
of what are known as tenderness insertions.
03:25
These are not attachment sites per se, but
very much their thickenings of that muscle
fiber to help increase the ability for the
muscle to contract, running down the midline,
separating the two vectors abdominal muscles.
We have the linea Alba, a tough connective
tissue bead that runs all the way down the
midline of the abdomen. Here we can identify
the lateral border of the rectus abdominus
muscle and we can see here on the surface of
the skin where we have that lateral boundary
of rectus abdominus demarcated as the
semilunar line.
03:58
The function of rectus abdominis
is very similar
to when both external
oblique muscles contract.
04:03
And in addition to that
of flexion of the abdomen,
it also helps to compress
the abdominal contents as well.
04:10
Helps to tense up the abdominal
wall, which is important.
04:13
If you were to be attacked,
it can have a protective function,
not that helpful from a sharp
blade or sharp instrument
but actually as a muscle
band around the abdomen,
it can serve some protection
to the abdominal contents.
04:26
And as I've alluded to before,
contraction of this muscle
will help to flex the trunk.
04:33
A muscle I haven't
mentioned before,
it wasn't in that general overview
because we couldn't see it,
but a very small
muscle that is situated
really the inferior aspects
of rectus abdominis.
04:43
And a muscle I've only seen
a handful of times
within the Anatomy Lab
is a very small muscle
known as pyramidalis.
04:49
And pyramidalis muscle,
you can see there is running up from
the pubic symphysis and iliac crest,
and it runs up into the linea alba.
04:57
It's a very small muscle that is
rarely seen within the anatomy lab.
05:01
But it can also serve with you can
see that the attachments there.
05:05
It can help to support
the rectus abdominis muscle.