 Hey everybody, Dr. O here. So I want to talk about spinal nerves a little bit here, but I really want to talk about peripheral nerves. So spinal nerves are the ones that come directly from the spinal cord. The dorsal root being sensory, ventral root being motor form those mixed spinal nerves that then leave your spinal column and travel out toward your body. And as they take this long convoluted path, many of them fuse together to form the peripheral nerves, the actual nerves that innervate different structures. So for example, like you see sciatic nerve down there. The sciatic nerve is a massive nerve. It comes from L4 to S3. So from the spinal nerves from L4 to S3 fuse together to form the sciatic nerve. So the typical, again we talked about the typical spinal nerve becoming these peripheral nerves. I'm not asking you to memorize the whole list of them, I just want you to get the gist of it. Let me give you a few examples. The phrenic nerve controls the diaphragm. So if you damage the spinal cord above the level of the spinal roots that make the phrenic nerve, you wouldn't be able to breathe. The radial nerve controls the triceps and then all the posterior forearm wrist extensor muscles. The median nerve will come back and talk about that one and then the sciatic nerve controls basically the entire back of the leg. If you're looking at monitoring the health and function of peripheral nerves, let's say you're worried about a herniated disc or something, there are three main simple clinical tools you can use. First being the dermatomes, which you see here. So a dermatome is an area of skin monitored by a specific spinal nerve. So if someone has a nerve being impinged, then you would typically see a loss of sensation to a given area. So maybe their fingers are going numb, there's some numbness on the front of the leg, wherever that might be. That's one of the three first signs that I would look for. So if someone says that they're feeling pins and needles or numbness or tingling or a loss of sensation in a patch of their skin, then I would look at the dermatomes and try to see if that spinal nerve is the problem. So the dermatome will be one way to do that. The other two pieces to that clinical evaluation will be your reflexes and then just muscle testing. So reflexes, you all have heard of the knee jerk reflex where you strike the patellar tendon with a reflex hammer and you get that reflexive jerk. Well, if that reflex is working properly and you're always testing side to side, you compare the dermatomes to the other side, compare the reflexes to the other side. If that reflex is working properly, then we know that the L3 and L4 nerve roots, mainly L4, are working if you have that knee jerk reflex there. But you can do that in other parts of the body as well. You can do the same reflex with the biceps tendon, the brachioradialis tendon, and the triceps tendon. Those would monitor C5, C6, and C7. You can do the same thing with the achilles tendon, pretty much any tendon, but that's going to be how you can use reflexes to make sure that certain spinal segments are working as well. So you've tested their dermatomes, you've tested these key reflex areas. Then you can just do muscle testing. If a nerve that controls a muscle is working well, then we know that it's getting the nerve innervation that it needs. So for example, if you have someone flex their elbow using the biceps, that would be testing C6, elbow extension would be testing C7, flexing the fingers would be testing C8, knee extensions, just having somebody stand up would test spinal segments L3 and L4. And then dorsiflexion of the ankle. So having someone walk on their heels would test L4 and L5. I'm not asking you to know these. This is not a clinical course, but I'm just showing you that you can learn a lot about the nervous system with something as simple as a handful of muscle tests, some reflex testing, and then monitoring these dermatomes using just a pinwheel or something like that. All right. So I want to do one more specific example of why it's so important to know where a nerve comes from and where there could potentially be problems. And that is the median nerve, which you see here, which is associated with the carpal tunnel syndrome. So carpal tunnel syndrome, the carpal tunnel is your wrist bones there with that flexor retinaculum on top of it. And if there's problems at that tunnel, inflammation or some sort of obstruction, it can impinge the median nerve and lead to pain or numbness and weakness in the area. But, and I'll show you the kind of pattern here, but a lot of people think they have carpal tunnel, think they have problems there. But remember, anywhere that median nerve is traveling or where those spinal nerve roots are coming from could be the problem. So someone could have a herniated disc that looks a little bit like carpal tunnel syndrome. I've seen many patients where they have just really tight forearm muscles, and the median nerve runs under a muscle called the pronator teres in most people, but in about 10% of people that runs through the pronator teres. So it could be a tight forearm that's irritating the same median nerve and causing those symptoms. So it's very important to do a complete and thorough evaluation with a patient like that just to make sure that before you do carpal tunnel surgery that the actual carpal tunnel is the problem. Reason I wanted to show you this image is because just generic numbness in the hand is not an issue with the median nerve. The median nerve would only be these blue areas. So like the fingers, the tops of the fingers there is called the exclusive area because it's the only place where the median nerve is only innovating it. So if you have numbness and tingling in those areas, then you probably have a problem with the median nerve. But notice if you're having numbness down the side of your hand, that's a completely different nerve that controls that. All right, so again, this is not a clinical course. I just wanted to give you some examples of why peripheral nerves are so important and knowing how to monitor their function. OK, I hope this helps. Have a wonderful day. Be blessed.