In this video I want to discuss the nerves that we can see on the plexus plaque that
has the white background.
And we can see the spinal cord traveling within the vertebral column.
Again we can see the ventral median fissure of the spinal cord, On this plaque it is a
little hard to see the conus medullaris.
And then the cauda equina.
But this plaque show some things that the other plaque didn't.
First I want to focus in on the cervical region of this nervous system.
So we can see some of the features of the cervical plexus.
This one is a little bit tough to make out, we can we can see a loop here.
This loop of nerve tissue is the ansa cervicalis.
And we can see some of the branches from that ansa.
But on this model it is very hard to tell what any of those branches would be.
The other nerve from the cervical plexus we see here is coming from C3,4, and 5 and forms
this nerve which they have cut off right here on this model.
That would be the phrenic nerve.
From vertebral column levels C3, C4, and C5.
Phrenic nerve, innervation to the diaphragm.
That's about all we can see of the cervical region as far as cervical plexus.
Now we can also see the brachial plexus on this model.
Remember the brachial plexus comes from C5, C6, C7, C8, and T 1.
So the brachial plexus is nerves for the upper extremity.
And the majority of those nerves, C5,6,7, and 8 are coming from the cervical region
of the spinal cord.
Now the brachial plexus is divided into roots, then trunks, then divisions, and cords.
Here we can see the roots of the brachial plexus.
Then we come out, and these are trunks of the brachial plexus.
And then we go into the divisions, and the divisions will divide into anterior and posterior
divisions.
And the anterior divisions are going to send branches into the anterior part of the upper
extremity.
Whereas the posterior divisions will go mostly posterior upper extremity.
If we look at the anterior divisions, we have to use our imagination a little bit on this
model, because the things intermingle so much, but I see a nerve here, and here, and here,
and it forms somewhat of an M shape.
Ignore this nerve right here that is intersecting our M, we will talk about that later.
This M is for anterior upper extremity.
The lateral part of the M is the musculocutaneous nerve, and musculocutaneous nerve innervates
all of the muscles in the anterior arm and it innervates the skin on the lateral aspect
of the forearm.
The middle part of our M is the median nerve.
The median nerve actually does not innervate anything in the arm but rather passes through
the arm into the forearm.
And once in the forearm it will innervate all but one and a half muscles in that anterior
forearm, and it will innervate four and one half muscles in the hand.
The most medial part of our M shape is the ulnar nerve.
Notice here the ulnar nerve is passing through the arm to reach the forearm.
It innervates nothing in the arm.
It will pass posterior to the medial epicondyle of the humerus.
And many times we bump this nerve and it causes some tingling and burning sensations in our
forearm and hand.
When we bump that nerve we say we have bumped our funny bone.
The funny bone is not actually a bone.
The funny bone is the ulnar nerve passing behind the medial epicondyle of the humerus.
So ulnar nerve passing through the arm, behind the medial epicondyle of the humerus, then
into the anterior forearm running along the ulna, where it will innervate 1 1/2 muscles
in this anterior forearm.
And then it passes into the hand where it innervates all but 4 1/2 muscles in the hand.
Now we can see the same thing on the other side of this model, its left upper extremity.
Only on this left side they have pronated the forearm.
So this gets to be a little bit more confusing in the forearm.
But if we start in the cervical region we can follow the nerves out.
Again we come down with our M shape a little harder to see right here, the musculocutaneous
nerve, taking care of the muscles in the anterior arm.
The median nerve comes down, now we lose it on this model because it is going to go to
the anterior aspect of the forearm, but we have pronated this forearm, so we are looking
at posterior forearm.
And then the ulnar nerve comes down here and it gets lost in the pronation, but we know
this is ulnar nerve right here because it is going behind the medial epicondyle of the
humerus.
And it comes across here to follow the ulna in the forearm.
Now I didn't cover the posterior structures on either side.
So let's hop back to the other side and go over the posterior cords of this brachial
plexus.
And then we will return to this side.
We get posterior divisions of brachial plexus which give rise to the posterior cord and
the nerves thereof.
The first nerve I can see leaving that posterior cord goes right behind the surgical neck of
the humerus.
You can see the beginning of the nerve here, and the end of the nerve here.
That is the axillary nerve.
The axillary nerve is going to innervate the deltoideus muscle and the teres minor muscle.
The other portion of the posterior cord is traveling right here, and it is passing behind
this ulnar nerve, continuing on behind the humerus in what we call the radial or spiral
groove, and then coming on down along the radius as the radial nerve.
The radial nerve.
The radial nerve innervates all of the muscles in the posterior arm and the posterior forearm
and the overlying skin of the posterior arm and posterior forearm.
Now if we look at the same thing on the other side of the model, this left upper extremity
where we have pronated the forearm, we can see again here we know that this must be the
axillary nerve passing behind the surgical neck of the humerus, going to the deltoideus
and the teres minor muscle.
And then we can follow along right here, and going through the spiral groove, so coming
along right here going through the spiral groove, or the radial groove, of the humerus
and then along the radius in the forearm, we will see the radial nerve.
Now keep in mind the radial nerve should be should be the lateral and posterior aspect
of the forearm.
But we have pronated this forearm, so we have brought the radius over.
So here it appears as though this radial nerve is to the medial aspect of the forearm.
It is not.
It is just that we have pronated the forearm.
So that should take care of the nerves on this model that we can see for the upper extremities.
Next I want to focus in on the thoracic region.
Because this model shows some of the thoracic nerves and the associated sympathetic nervous
system.
So we see the thoracic cord.
Keep in mind in the thoracic region we do not have any plexuses to the muscles, but
yet at every vertebral level we simply have what is called an intercostal nerve.
And then when we get underneath the 12th rib it is no longer the intercostal nerve, it
is a subcostal nerve.
But also on this particular plaque we can see, running just beside the vertebral column,
the paravertebral ganglia.
Also known as the sympathetic chain ganglia.
Each one of these little globular structures is a paravertebral ganglion.
And you can see that they are all connected to each other like beads on a string.
These are the paravertebral ganglia, or the sympathetic chain ganglia.
And on this model we can see a rami communicans traveling between the ganglia and the intercostal
nerve.
But we do not really have enough information on this model to decide whether that is a
white ramus or a gray ramus communications.
Judging from its position it is probably a white ramus communications.
After the thoracic region we will pass into the lumbar region where we will see the lumbar
plexus.
The lumbar plexus is normally embedded within the psoas major muscle.
This model does not show that.
But it does show the nerves fairly well of this lumbar plexus.
The first nerve of the lumbar plexus will actually divided into two nerves.
From the L1 vertebral level we will come out and have the iliohypogastric and the ilioinguinal
nerves.
So the top one is iliohypogastric nerve.
The next one is the ilioinguinal nerve.
Then if we drop down a little further we can see from L2, L3, and L4, we can see the lateral
femoral cutaneous nerve.
It always travels over the superior surface of the iliacus muscle, and then passes to
the skin on the lateral side of the thigh.
The lateral femoral cutaneous nerve.
Also well depicted on this model is the femoral nerve.
The femoral nerve will pass anterior to the rim of the pelvis and into the anterior thigh,
where it supplies the majority of the muscles in the anterior thigh.
It does have a cutaneous branch known as the saphenous nerve which will travel along the
medial side of the knee and into the medial side of the leg.
So this is all femoral nerve.
And then we can also see in the background, a little bit of our sciatic nerve.
But that will be better seen on the other side of this model.
So lateral femoral cutaneous, femoral, sciatic nerves.
If we look at the left side of this model they have taken his left lower extremity and
laterally rotated it.
So we are actually looking at the medial side of the thigh and the medial side of the leg.
Here we can see another nerve, it was not real obvious on this side, it started on the
other side is the obturator nerve, they cut it off so we could not see where it was going,
so I didn't discuss it on that side.
On this side we will see the obturator nerve coming down and passing through the obturator
foramen, which we don't see on this model, and into the medial side of the thigh.
Now remember this lower extremity has been laterally rotated so we are looking at medial
thigh here.
So this is the obturator nerve, they run it through here and then they cut it off.
The obturator nerve supplies the majority of the muscles in the medial compartment of
the thigh, or the adductor compartment of the thigh.
Again we can see the lateral femoral cutaneous nerve here.
But what we could really see better on this side is the largest nerve in the body, known
as the sciatic nerve.
The sciatic nerve will pass from, actually not the lumbar plexus, but the sacral plexus,
and pass through the greater sciatic notch and into the posterior thigh region as the
sciatic nerve.
Now the sciatic nerve is really the tibial nerve and the common peroneal nerve wrapped
in one common nerve sheath.
As we get near the knee on this model we can see that it divides into a nerve here and
a nerve here.
And some other muscular branches.
This is the common peroneal nerve.
This is the tibial nerve.
The tibial nerve will continue down into the posterior compartment of the leg, where it
innervates all of the muscles in the posterior leg.
It will then go behind the medial malleolus of the ankle onto the plantar surface of the
foot.
And when it does that it divides into the medial and lateral plantar nerves.
In this case we know we are looking at the medial side of the foot so it has come down
and formed the medial plantar nerve.
If we go back up above the knee where we have the common peroneal nerve, that common peroneal
heads out toward the head of the fibula.
Well on this lower extremity you can't see the fibula, it is in the background because
it has been laterally rotated.
So it is hidden behind this tibia.
But if we look at the other lower extremity we can follow this, and we can see, right
here the common peroneal nerve coming around by the head of the fibula where it is just
sub cutaneous.
So a blow to the lateral head of the fibula can damage that common peroneal nerve.
At this point it will divide into a superficial peroneal nerve and a deep peroneal nerve.
The superficial peroneal nerve travels along the fibula to innervate muscles in the lateral
compartment of the leg.
The deep peroneal nerve will travel over anterior to the interosseous membrane between the tibia
and the fibula, and it will travel down the anterior compartment of the leg and out onto
the dorsum of the foot.
It will innervate all of the muscles in the anterior leg and on the dorsum of the foot.
If we look at this left lower extremity again, remember it has been laterally rotated, we
can see that anterior compartment of the leg.
Here we can see the deep peroneal nerve traveling in the anterior compartment of the leg and
then out onto the dorsum of the foot.
The deep peroneal nerve.
It is important to note that the common peroneal nerve is also known as the common fibular
nerve, which gives you a big hint that it needs to go out by the fibula.
The deep peroneal nerve and the superficial peroneal nerve can also be called the deep
fibular nerve and the superficial fibular nerve.
So those are all of the nerves that we expect you should be able to find on this particular
plexus plaque.