 The brachial plexus connects the spinal cord to the nerves of the arm. Let's begin by drawing out where the brachial plexus begins. From the spinal nerves, C5, C6, C7, C8 and T1. Easiest way to remember that is like the fingers of your hand from pinky to thumb, five, six, seven, eight, T1's your thumb. Where the parts of the brachial plexus end up is the terminal nerves of the arm. We have the musculocutaneous, the axillary, the radial, the median and the ulna. The way I like to remember this is marmu, just like an alien would say. The sections of the brachial plexus we can remember with this mnemonic reach to drink cold beer. That's the roots, the trunks, the divisions, the cords and the branches. So we have these five start points and five end points. Let's begin by putting through the three main connections. The trunks and the cords are the simplest, there's only three of each. The trunks are superior, middle and inferior. The cords are lateral, posterior and medial. C6 contributes to the superior trunk, C8 contributes to the inferior trunk. Seeing as the middle trunk hasn't received anything, the superior and inferior trunks contribute to it. Making this arrow forward. And the middle trunk also throws off a division to the lateral cord. Making this X through the top of the arrow. The lateral cord branches to the musculocutaneous, as we can see. And also to the median. The medial cord contributes to the median nerve as well, making this big M for median. The posterior cord forms the radial nerve and the axillary nerve. So we've now got a succinct picture of the basics of the brachial plexus. But it's a bit too schematic for my liking. So we're going to turn it into a 3D model. We're going to have a look at it from this angle now to get a better understanding of the reasons behind the names of each section. So the trunks are in the same plane as the spinal vertebra. And just as C5 is superior to C7, the superior trunk is superior to the middle and inferior trunks. Next up is the divisions, the names of which I always found a little bit confusing. So we have three anterior divisions and three posterior divisions which together make up the posterior cord. Anterior and posterior to what though? The answer is the axillary artery which carves through the brachial plexus like this. The posterior cord ends up just behind it and the median nerves hits just in front. The key remaining question is how does the inferior trunk become the medial cord? They're two different planes, right? And the simplest way to understand it is to conceive of the path that these terminal nerves eventually make down the arm. The musculocutaneous ends up supplying the muscles of the anterior upper arm, the axillary, the posterior upper arm, the radial, the posterior forearm, the median, the lateral and anterior forearm. And just as the ulna is the medial bone of the forearm, the ulna nerve supplies medial muscles of the forearm. So the medial cord is in fact medial to the lateral cord because by this stage the plexus has begun to turn and fit the orientation of the upcoming limb. So when you're first set out to learn the brachial plexus, get a handle on some mnemonics so you can learn this 2D schematic and then make sure you apply that schematic to the real-life 3D anatomy. Thanks for watching, hit subscribe and we will see you next time.