hello anatomy friends this is dr alsup and it is time to identify parts of the brachial plexus
everyone's favorite you've been hearing about it and now it's time to identify it
and we will start proximally and make our way to the major terminal branches
the most proximal portion of the brachial plexus are the roots now it is important to note
that these are ventral primary rami of spinal nerves c5 through t1 so these ventral primary
rami have both motor and sensory fibers and you have to go all the way back to the neck
to locate these remember our old friends the common carotid artery which you can see right here
you can see the vagus nerve right here so you have to go all the way back towards the neck in order
to do this fortunately these go in order from superior to inferior so this will be c5 this is c6
c7 so we're just going straight inferior c8 remember the cervical spinal nerves have one extra
nerve then vertebrae and then of course don't forget t1 so you go from the the smallest number
back down to t1 from superior to inferior moving distally we get to the trunks fibers from c5
and c6 combine in order to form the superior trunk the c7 root will continue
and it will form the middle trunk and then the roots of c8 and t1 will combine to form
the inferior trunk so these are very well named the superior trunk is the more superior one the
middle is in between the superior and inferior and the inferior is the most inferior of the trunks
so let us get our bearings here in terms of a much wider view of the brachial plexus
you can see the superior middle
and inferior trunks here
and um these only run a short distance before each trunk divides into anterior and posterior
divisions i'm going to change my pen color here so we can differentiate between some of these
so the anterior divisions are going to innervate anterior compartments of the upper limb
whereas the posterior divisions will innervate posterior compartments now it's when we get to
the divisions in the brachial plexus where i start to panic a little because there's considerable
amount of dividing splitting combining so i always always always find it easiest to
locate the posterior divisions from each trunk as they will unite to form the posterior cord
so let's kind of go through these here so you have a posterior division of the superior trunk
you have a posterior division of the middle trunk and a posterior division of that inferior trunk
and they come together to form the posterior cord right here so
that's where those posterior divisions kind of come together in order to form that posterior cord
now let's change pen color again just to kind of help us work through some of these
green okay the anterior divisions of the superior trunk
as well as the middle trunk will come together in order to form the lateral cord
so you have the once again you have the anterior divisions of the superior trunk
as well as the middle trunk forming the lateral cord okay one more change in terms of pink color
and then for the um when we get to the anterior division of the inferior cord it's really just
it looks like a continuation of the inferior cord and that will form the medial cord because recall
that posterior division of the inferior cord went this way and then the anterior division
just looks like the continuation so you have a lateral cord a posterior cord and a medial cord
in these regions now the cords are actually named based on their relative position to
the axillary artery which has been removed to better see the brachial plexus in this image
but if you imagine the axillary arteries kind of running right through the middle region right here
it would be superficial to the posterior cord so it'd be almost completely blocking
the posterior cord's view and then if you put the arm back into anatomical position
the lateral cord would be lateral to the axillary artery which would be right about
here and the medial cord would be medial when the arm is abducted which is what happens in
most dissections in order to really get to the brachial plexus it often looks like the
lateral cord is going to be more superior whereas the medial cord looks more inferior
okay last but not least we are with the um we are with the same image here so again let's refine
all of our fun stuff so this right here is the lateral cord this is the posterior cord
and this is going to be the medial cord and from here we're going to discuss the terminal branches
there are branches throughout the brachial plexus but really there are five what we refer
to as terminal branches that we want to be able to identify now the major branch of the medial cord
is going to be this right here that i'm kind of tracing and this is the ulnar nerve
all right the ulnar nerve is the major branch of the medial cord again there are other smaller
cutaneous branches that you can see right here coming off the medial cord but this larger one is
the ulnar nerve and in terms of motor innervation it will supply the muscles in the supply a muscle
and a half in the anterior forearm but it's really in the hand that the ulnar nerve shines
it provides motor innervation to most muscles of the hand also importantly the medial cord
provides a contribution which i'm going to trace right here to the median nerve okay
so that it's going to have a portion of the medial cord that is providing
innervation or providing some fibers to what is the median nerve which you can see right here so
let's discuss the other contribution to the median nerve and that is going to come from the lateral
cord so here's that lateral cord up here and it's also going to provide a contribution to the median
nerve and you can see it looks like kind of like a v right here and then from there you have the
median nerve so the median nerve in terms of motor innervation supplies the majority of muscles in
the anterior compartment of the forearm and a few muscles in the hand finishing the lateral
cord this also gives off the musculocutaneous so this right here is the musculocutaneous
and this you can only see for a short bit right here because it's going to dive deep into the
anterior compartment of the arm where it is the dominant motor nerve all right so we have
three of the five terminal branches you have the ulnar nerve from the medial cord you have the
contributions from both the medial cord and the lateral cord for the median nerve and then the
lateral cord will give off the musculocutaneous so that only leaves the large posterior cord
in terms of the terminal branches so again here is that posterior cord
right here and you can see right about here where it splits and it will split into two terminal
branches of the posterior cord this smaller one right here is the axillary nerve which you can see
is going directed towards the shoulder region and it's on its way to innervate the deltoid muscle
this portion here that looks like a continuation of the posterior cord
which i'm going to kind of trace until we can't see it anymore
this is going to be the radial nerve the radial nerve is the largest nerve in the upper limb
and it efferently innervates posterior compartments both of the arm and the
forearm as always my favorite saying radial nerve equals posterior so again in terms of the terminal
branches from the medial cord you have the ulnar nerve and a contribution to the median nerve
from the lateral cord you have a contribution to the median nerve as well as the musculocutaneous
and then from the posterior cord you have the smaller axillary nerve and the larger radial nerve
and that is the brachial plexus i highly recommend you take this image here that has been color coded
and try to name the parts here so try to label particularly the trunks so superior middle
inferior try to label the chords and then also try to label those terminal branches and as always
there are labeled versions of these images on the blue link website as well to check your work but
kind of take your time make sure you understand the different components of the brachial plexus
and which forms will kind of combine in order to get to these terminal branches okay excellent
thank you for your time and attention here and i hope you have an excellent rest of your day