This is a tutorial on the brachial plexus.
The brachial plexus is the somatic plexus formed by the anterior rami of C5-C8 and most
of the anterior ramus of T1.
So the brachial plexus as you can see, it originates in the neck.
And then it passes over the 1st rib.
You can see that here.
And then it goes underneath the clavicle to enter the axilla.
So we're going to take a look at some of the structures in relation to the brachial plexus.
We're also going to take a look at the basic layout of the brachial plexus.
So immediately exiting the intervertebral foramen, you've got the parts of the brachial
plexus which are referred to as the roots.
We're going to switch over to a diagram, which you'll see over and over again.
This is used to explain and demonstrate the basic layout of the brachial plexus.
This is a diagram you need to familiarize yourself.
It gives you the basic concept of brachial plexus.
So proximally here, we're looking at the roots of the brachial plexus.
You can see the numbers on the right.
These number the spinal nerves which gives rise to these roots.
Like I mentioned, the brachial plexus is formed from the ventral rami of the spinal nerve
C5-C8 and most of the anterior ramus of T1.
These are called roots.
And then these roots form trunks.
So C5 and C6 converge to form the superior trunk.
C7 continues to form the middle trunk.
And the C8 and T1 form the inferior trunk.
So then next, each trunk gives rise to an anterior and a posterior division.
So the superior trunk has an anterior and a posterior division.
The middle trunk has an anterior and posterior division.
And so does the inferior trunk, a posterior and an anterior division.
And then these divisions give rise to cords.
So you've got the lateral cord, the posterior cord and the medial cord.
So you've got roots, trunks, divisions and cords.
You'll notice that there are several different branches coming off the various parts of the
brachial plexus.
You've got nerves coming off the roots, you've got nerves coming off the trunk and you'll
notice that there's no nerves coming off the divisions, but then you've got nerves coming
off the cords and then you've got terminal nerves.
So I remember the roots and trunks by just thinking of a tree.
A tree starts from the root, then you've got the trunk.
So the roots are the first thing of the brachial plexus and then you've got the trunk.
And then a tree divides, so you've got the divisions.
So you've got the anterior and posterior divisions after the trunks.
And then you've just got to remember that cords are at the ends.
I don't have any special way of remembering that.
So you've got the lateral, posterior and medial cords at the end.
So just coming back to the 3D model, I've dissected away all the additional nerves that
come off the brachial plexus and you can see the basic structure with the roots, the trunks,
the divisions lie under the clavicle which I've removed (so the clavicle would run between
this sternum and the acromion process of the scapula) and then you've got the cords further
down -- so around here.
The roots and the trunks lie in the posterior triangle of the neck.
They pass between the anterior scalene and the middle scalene muscle and they run posterior
and superior to the subclavian artery.
So you can see this posterior triangle here.
The posterior border is the anterior part of the trapezius, the anterior border is the
posterior border of the sternocleidomastoid and the base is the middle third of the clavicle.
So the brachial plexus, the roots and the trunks emerge from this posterior triangle.
If I just rotate the model around, I can just show you the anterior and middle scalene muscles.
These muscles attach to the 1st ribs.
We've got the anterior scalene here and the middle scalene here.
The roots and the trunks run between the anterior and the middle scalene muscle.
So then the brachial plexus then passes underneath the clavicle and over the 1st rib.
So behind the clavicle, you get the divisions of the brachial plexus.
So you get the anterior and posterior divisions of the trunks.
And then you've got the cords, which lie in the axilla -- this region here.
We've got the lateral, the posterior and medial cord lying in the axillary region.
They've got an important relationship with the axillary artery.
So the cords lie around the second part of the axillary artery.
This diagram here shows it quite nicely.
You've got the axillary artery here.
You've got the lateral cord running lateral to the axillary artery.
The medial cord, you can just see here.
It runs medial to the axillary artery.
And the posterior cord runs behind the axillary artery.
So just to illustrate the point about the axillary artery, let's just take a look at
this diagram.
So you've got the C5, C6, C7, C8, T1 roots.
C5 and C6 unite to form the superior trunk.
C7 continues to form the middle trunk.
And C8 and T1 unite to form the inferior trunk.
So then you've got these divisions.
So each trunk has an anterior and posterior division.
So the superior trunk has an anterior division, which continues like this.
The posterior division goes posteriorly to form the posterior cord.
The middle trunk has an anterior division which contributes to the lateral cord.
So this passes anteriorly.
The posterior division contributes to the posterior cord.
And then the inferior trunk has a posterior branch which contributes to the posterior
cord.
It's got an anterior branch which continues to form the medial cord.
But all of the posterior branches from the three trunks go towards forming the posterior
cord.
So let's just draw on the axillary artery.
So the axillary artery likes this.
I'm just roughly drawing it on.
And then it goes up to form the subclavian.
So the posterior cord is shown in brown because it lies behind the lateral and the medial
cord posteriorly.
So let's just kind of fill it in.
You can see that the middle cord lies medial to the axillary artery and the lateral cord
lies lateral to the axillary artery, whereas the posterior cord with its formed from the
posterior divisions of the three trunks runs behind the axillary artery.
So that should have given you a basic understanding of the structure of the brachial plexus and
its location in relation to the other areas of the body.
You know that the roots and the trunks pass through the posterior triangle of the neck.
And then you've got the divisions which lie under the clavicle.
And you've got the relationship with the posterior cord to the axillary artery and the lateral
and medial cords sitting on either side, lateral and medial to the axillary artery.
So next, we'll take a look at the various branches of the brachial plexus, the terminal
nerves and the branches which comes off the roots and the trunks and the cords.