Let's talk about the innervation going on here and we're going to start with a complicated area called the brachial plexus.
We're going to try to keep it simple
and just describe what's happening
and then we're really going to talk about the nerves
that come out of the brachial plexus a little bit later
so don't feel overwhelmed by all of this confusing network
of connections you're about to see.
The key thing to focus in on is that the nerves
of the upper limb being fed by this brachial plexus
are coming from these nerve roots
that are mostly cervical with one thoracic.
So they're coming from the spinal nerves,
C5, C6, C7, C8, and T1.
Now, they're going to do a lot of mixing and matching here
because as you're going to see,
they're going to merge, at least the first two
and the last two, into trunks
and C7's going to remain itself so all of a sudden there's going to go from one, two, three, four, five spinal nerves to three trunks
and then they're going to divide into anterior and posterior divisions and then they're going to recombine as three chords.
The important thing though is really the beginning and the end
that the spinal nerves you need to worry about in the upper limb
are those between C5 and T1,
and don't worry too much about this mixing and matching
because we're going to eventually talk about the named nerves
such as median nerve or ulnar nerve
that actually do the innervation
after they've done this crisscrossing
but just to let you know there's a lot of complicated stuff happening here
between the neck and the upper limb.
So let's talk about those nerves of the arm
that come out of the brachial plexus.
So the anterior muscles we saw are going to be innervated
by something called musculocutaneous nerve.
Now, musculo referring to the fact
that it's going to innervate our biceps brachii, and whatnot
but cutaneous refers to the skin so it's also going to provide
some cutaneous sensation and a lot of nerve do both.
Both, what we would say, motor innervation to cause a muscle
to move but also sensory innervation to the skin.
We also have a median nerve that we'll see a little bit later
in the forearm and hand along with the ulnar nerve
and then the radial nerve is going to go posteriorly
and take care of that triceps muscle for us.
What about the arteries?
So we need to have a pretty good blood supply out to the upper limb
and so we have some major vessels that head out towards it.
The story's going to begin much more medially at the subclavian artery
and then after it crosses under the first rib,
it's going to change names to become the axillary artery.
Axilla is sort of our anatomic term for armpit area.
It just doesn't sound great to say the armpit artery
so we call it the axillary artery
and there are different parts to this artery.
There's a first, a second, and a third part,
and they have one branch, two branch, and three branches,
respectively so at least that part lines up.
It makes it a little bit easier to remember.
After it reaches the teres major,
it's going to change names again
and become the brachial artery and that's okay
because we just said arm and brachia
mean the same thing
so by the time it reaches the arm,
we know that it's going to change names into brachial.
Let's go back and look at those parts, first, second,
and third of the axillary artery.
The first part has one branch, the superior thoracic artery
and it tells you generally where it's located.
The second part is the part hidden by the pectoralis minor
and the second part has two arteries.
It has the thoracoacromial trunk
and the lateral thoracic artery.
Both giving you an idea of their location, then after it passes
the pectoralis minor, the third part has three arteries.
It has a subscapular artery telling you where it's going
and anterior and posterior humeral circumflex artery
and those names are also descriptive.
One tells you the direction, humeral referring to the humerus,
and circumflex meaning they're going around the bone
and forming a junction or anastomosis with each other.