 nerve plexuses are basically braids or intermingling of spinal nerves with each other to form peripheral named nerves, like the sciatic nerve. If this is at all like what the heck is she talking about? Let's orient ourselves to the brachial plexus. This is the actual anatomy of the brachial plexus. Don't panic yet. You can see something here that's familiar, right? What do you think these are? These are spinal nerves. They're actually, each one of these cords right here, is actually the anterior ramus for this spinal nerve. So this is the anterior ramus of C5. This is the anterior ramus of C6 and so on. The brachial plexus is made of several named nerves that we'll look at and they come from C5 through T1. Those are all the spinal nerves that are contributing pathways to make up the brachial plexus. If we're good with that, then the concept of a plexus is like a net or a knot or a tangle. And I just want you to take a deep breath because I just want you to get this conceptually. Parts of the anterior ramus of C5 split off. Now check out the split and combine with C6. Combine again, like different parts, combine with C6. This part is actually combining with a piece of C7. Here we've got C6 combining with pieces of C7 and C8. Do you see how we could do a map of the brachial plexus and have to know all like the, like which piece connected with which part, you're not going to have to do that. In fact, I'm going to take a red pen and I'm going to show you what you're going to have to know. I want you to know who's contributing fibers to the brachial plexus named nerves that we're responsible for. I want you to know the musculocutaneous nerve, the axillary nerve, the median nerve, the ulnar nerve and the radial nerve. Are there more nerves that are a part of the brachial plexus? Yeah, these are the ones that we're going to know. Hopefully you look at this and go, whoa, can we even see that in our cadavers? And the answer is yes. We will have a brachial plexus pro-section ready for you to look at. You will also need to know generally what muscles are innervated by these different nerves. And that's something that if you know one muscle that's innervated by each nerve, you're good to go and you can totally look that information up and make it happen. There's not just a brachial plexus. We have a cervical plexus, the cervical plexus, we have one named nerve that you're going to be responsible for. And that, hold on just a second, before we do that, I want to show you this picture of the brachial plexus. This was my map. This is what it actually looks like. Do you agree that you can totally see, oh, those are spinal nerves coming out of the spinal cord. And then we've got actual structures that we can name and here are my peripheral named nerves of the brachial plexus. We do have the cervical plexus. I'm going to write it right here, even though cervical plexus is up here. Cervical plexus. Cervical plexus is C, let's see, C1 through C4. In part, technically, they don't include C5 in this mix. However, there are some C5 fibers that contribute to cervical plexus nerves. And in fact, there's one, the only cervical plexus nerve that we have to know is the phrenic nerve. And the phrenic nerve fibers that contribute or spinal nerves that are contributing fibers to the phrenic nerve are C3, C4, and C5. And what do you think the phrenic nerve innervates? The diaphragm. The diaphragm, if you have an injury to spinal nerve C3, C4, or C5, chances are excellent that you are going to stop breathing. In fact, in clinical settings, we have a mnemonic 3, 4, 5, stay alive to help you remember that if we have damage that high in your cervical region, that you run the risk of not being able to breathe anymore because of damage to the phrenic nerve. We have two other plexuses that we have nerves to know from. We have the lumbar plexus. We have the sacral plexus. And the lumbar plexus includes L1 through L4. And the sacral plexus includes L4 through S4. That's easy to remember. And we've got some named nerves from these guys. The lumbar plexus gives rise to the femoral nerve. We probably will not see the actual plexus. We will just be able to see the named nerve itself. It also gives rise to the obturator, obturator nerve. The sacral plexus, sacral, contributes fibers to the sciatic nerve. And the sciatic nerve, you're probably already aware of this, actually splits into two nerves. And it's the tibial nerve and the common fibular nerve. Let's see if there's anything else that you should know. I think you're good to go. Does the concept of a plexus make sense? Contemplate? Why? Why would we do this? What's the advantage to doing this? While you're contemplating, I'm going to go get ready to talk to you about cranial nerves. We've been doing spinal nerves. Now we've got our named peripheral nerves. And now we're going to do our last set of 12 cranial nerves. These guys all come out of the brainstem. Let's do it.