all right hello anatomy friends we have come to one of the most terror producing parts of
anatomy but really I think that once we kind of break down some of this and go through why
we know certain things are parts of the brachial plexus I think you'll feel a lot more comfortable
regarding this I do know that in one of dr. Gelb's sessions he kind of goes through a kind of stick
figure way to draw out the brachial plexus and I think that is an amazing way to go about it when
you were learning the basics and we can apply that knowledge to the actual structures of the
brachial plexus to be able to identify in terms of in a practical setting so when you're looking
at something like this it can seem a little intimidating in terms of how am I ever gonna
be able to tell which things are which in the in the parts of the brachial plexus so we'll spend
time kind of figuring out how you know you're looking at roots and Trunks in this area then
we're getting into divisions here cords and then of course some of the terminal branches the MARMU
in terms of the five terminal branches and then some other branches that you can see coming off
of the brachial plexus a bit more approximately so we'll like I said well review once again in terms
of how you're going to be able to identify these certain structures but if you see that on the list
of structures for the practical the majority of the focus is going to be on these terminal
branches but I do want to at least introduce some of these more proximal portions of the brachial
plexus so we can kind of build our knowledge from there and then you can focus your identification
in terms of some of the terminal branches or the nerve branches coming off all right so let us
start very proximally with the proximal most portion of the brachial plexus and these are
of course the roots of the brachial plexus as we recall these are going to be those ventral marry
Rami of c5 through t1 and don't forget we're talking eventual primary Rami these are not
dorsal primary Rami so if you're looking here just to kind of get our bearings as to what we
can see hopefully you recall the common carotid and your subclavian right here arteries and you
can see the roots in this region here you can see the middle scalene the anterior scalene has been
removed in order to better view these and you can see here c5 I'm just going to write the numbers 6
7 8 and then t1 and of course all these up here are C's or cervical so c5 c6 c7 c8 and t1 now if
you recall that some of these roots are going to combine their fibers to form trunks which if we're
moving down in terms of our mnemonic this is going to be the Randy Travis randy is roots Travis is
going to be the trunks and so you can see here that c5 and c6 are coming together to form the
superior trunk also referred to as the upper trunk same thing so c5 and c6 come together to form this
trunk and you can see that pretty well in this particular image c7 will continue on as the middle
trunk so we don't have the combination of the two roots for the middle trunk and then c8 and t1 will
form the inferior trunk or the lower trunk you can see those nicely kind of coming together here to
form the inferior trunk and what you can see also is if you're looking at the subclavian artery you
see this fairly prominent branch and this is that dorsal scapular artery that's heading towards the
posterior scapula it will run between the superior trunk in the middle trunk and that's a fairly
distinct anatomical relationship right there so that's always running in that region now we're
going back to or we're going to this image that's a little bit bigger picture or bigger scale I do
want to note on this if you're trying to get your bearings in terms of the roots you can see c5 c6
7 8 and you cannot see t1 in this particular image right here so be aware that you cannot see the t1
route but of course it's there and of course it's helping to form that it's just deep to the muscles
right here then the muscle was kept in this particular donor in this particular dissection
so you can see how they're combining c5 and c6 to the superior trunk c7 is that continuation
you would see t1 and c8 coming together to form this inferior trunk here and then once we get past
the trunks each trunk is going to be divided into these anterior and posterior divisions you do not
need to ID the divisions because honestly there's some variation here and it's it's difficult this
there is this is where a lot of that combination of fibers is occurring but in some areas I do
find it useful to locate these particularly in terms of the posterior divisions you can see
all three of these coming together to help form this posterior cord so I do like to try to locate
that one anterior divisions are a little bit more difficult to identify but just keep in mind that
we're going from those roots to the trunks to the divisions of the anterior and posterior divisions
and then we get to the cords so let's talk about each one of those as mentioned in the active
learning session and in other areas the the names of these courts are based on the relative position
to the axillary artery specifically the second part when when an individual is in an anatomical
position but usually in order to see all parts of the brachial plexus particularly in a dissection
or in other areas the upper limb rule will need to be a little bit a B ducted or ABducted so not
quite an anatomical position so often the lateral cord is going to look more superior and the medial
cord will look more inferior than say medial or lateral but that is why they are named that way
okay so let's get our bearings in terms of these chords I always look at the posterior just like
I said because I find that one the easiest to be able to identify because I can see all those
posterior divisions coming together so this is the posterior cord the the medial cord is going to be
the anterior division of that inferior trunk and so here's that inferior trunk up here so this is
going to be the medial cord and then the lateral cord it's going to be the anterior divisions which
you can see those two coming together there of the superior and middle trunks so this is going
to be lateral cord all right you can see in terms of that medial and the lateral cord that there's
going to be contributions of those cords heading to the median nerve so that looks they'll be kind
of an extension of those cords as they reach to the median nerve but for the most part they're
going to be right around this region in this axillary region okay so let's talk about some
of the named branches and then we'll spend some time on the terminal branches there's going to be
two named branches that are not those terminal branches of the brachial plexus that we want
you to know one is going to be the super scapular which we'll talk about right now the second will
be the Thoracodorsal which we'll talk about in a moment so super scapular nerve is going to
be a direct branch of the superior trunk so before I do it I want you to look at this image and try
to identify your yourself on your own where the superior trunk is okay so here are some clues if
this is c5 and this is c6 we know that those two roots come together to form the superior trunk so
you're looking at this and you're seeing that there's not really a branch on this particular
dissection coming off of the superior trunk and that's true you can see it a little bit right
here you see that so that but I'm gonna make this go away and come back so it's clean right here so
you can see at that superior trunk right there a small branch coming directly off the superior
trunk you can see it's heading directly towards the scapula region because we recall that the
suprascapular is going to innervate your Supra and your infraspinati muscles on the
posterior scapula so you can see it heading in that direction so if you see a branch coming
directly off the superior trunk you are looking at your suprascapular nerve now talking about the
ulnar nerve and I do have these images up here that are color-coded I do think it will help in
terms of the discussion you are more than free to kind of look at it without this as well there are
going to be blue link images that have it without this as well but for the purposes of this session
we are going to kind of work through this here so the ulnar nerve is going to be the terminal
branch of your medial cord so here's your medial cord and you can see it looks like almost just a
continuation of that medial cord the dominant roots nerve fibers are coming from c8 and t1
and a lot of resources you will only see C8 and t1 for the ulnar nerve more recent literature is really
kind of honing in on the fact that there is often some contributions from the lateral cord in terms
of from c7 and that's what you can see and why we have this highlighted here but really we're
gonna focus mainly on the the traditional and so you'll see this I think in dr. Gelb's sessions as
well c8 and t1 we won't test on any of these discrepancies that there are between the two
sources so but you can really see how it looks like a continuation of the medial cord here and
then occasionally there's some contributions from c7 and the lateral cord so really we want to focus
on the fact that it's it's mainly coming from the medial cord as you can see here okay next we have
musculocutaneous and musculocutaneous nerve the lateral cord and you can see over here is that
lateral cord right here and then you can see this continuation of a nerve branch that looks
like it's heading towards that coracobrachialis in the anterior compartment of the arm and that
that is going to be a very characteristic way to identify musculocutaneous in the anterior
arm as it pierces through krakow brachialis else cutaneous is dominantly derived from c5 and c6
it can have contributions from c7 but we will focus more on the c5 and c6 contributions and
you can see that it looks pretty clear like it's coming directly as a continuation from the lateral
cord okay median nerve one of my favorite ones and the reason it's one of my favorite ones is because
it's a little bit easier to identify you can kind of pick up all the terminal branches and it almost
looks like a nice M and really this this portion the middle portion of the M is going to be the
median nerve it is going to receive contributions from two different cords all the rest report we
from one with perhaps smaller contributions but these are fairly large contributions from both the
medial and the lateral courts and then once they kind of combine together these contributions then
you call the nerve at that point the median nerve and like I said this is where you're getting that
middle portion of the M you can see kind of that M right here and so that's a continuation there
as it heads to innervate predominantly that anterior forearm region okay now let's talk
about some branches of the posterior cord when you're talking about terminal branches from the
posterior cord the main ones that come up are the axillary and of course the radial nerve but you
can see that there is going to be a additional branch which is your thoracodorsal so let's
return I want you to take a moment to see if you can identify the posterior cord here before I
kind of point out some of the hints to get to it so try to find the posterior cord okay so if you
are feeling a little lost perhaps I can help out so you can see these posterior divisions from the
trunks coming together to form this posterior cord here so right here where I'm kind of highlighting
this is going to be the posterior cord and you are gonna have a small branch that will come off
of the posterior cord that's not axillary and that's not radial and this is the thorah code
or so which you can see right here the thoracodorsal is going to innervate your latissimus
dorsi and you can see that it's heading towards the region where the latissimus dorsi would be
located so it's heading in kind of inferiorly to head to that fairly large muscle belly that's
associated with the latissimus dorsi okay the other two or the last two terminal branches and
these are both coming from the posterior cord the first that we're going to discuss is your axilla
which you can see here shaded in pink and it is going to be the smaller the terminal branches of
the posterior cord radial nerve is by far larger you can see it's also heading towards the humerus
specifically that surgical neck of the humerus which it will wrap around the posterior portion
on its way to innervate the deltoid muscle and the infraspinatus lastly is the radial nerve and
the radial nerve I feel isn't one of the easier ones to identify as well just due to its size
it's going to be slightly larger than even the median nerve typically it is very posterior lis
placed and as I mentioned it's quite large it's typically the largest in terms of diameter of
the terminal branches of the brachial plexus which makes sense because you have all these
posterior divisions coming together to form the posterior cord and so you have these posterior
divisions then here is the cord here and then what just looks like a continuation kind of once
it gives off the axillary right here it kind of divides into axillary and then the name changes
to radial from this region and of course heading towards the posterior compartments of both the arm
in the forearm so those are the things that we are going to have you identify in terms of the
brachial plexus wow you don't have to memorize specifically some of the how to identify some
of the roots and the trunks it is helpful in terms of being able to identify some of the more distal
branches or the terminal branches of the brachial plexus alright I hope you have a wonderful rest
of your day as always please feel free to reach out to myself or any of the anatomy faculty as
you would imagine brachial plexus system is one of our favorite areas thanks and have a good day