 This is going to be our last video in our series about dermatomes. We're going to end with a topic that's adjacent to dermatomes and spinal nerves, which is referred pain. Referred pain is pain that's perceived at a location other than the site where the pain originates. It's the result of multiple sensory nerves with the same origin that supply many different tissues. When there's an injury at one site, it's possible that when the signal is interpreted by the brain, it can be felt in other areas supplied by the same sensory nerves. If this sounds confusing, that's okay. It can be hard to wrap your head around this concept. Stay tuned and the examples we cover are going to help you understand referred pain. Sometimes you'll get questions about pain that's felt in an area that's distant from the actual diseased organ. It can be really confusing to figure out these questions if you're not familiar with the concept of referred pain. For example, the classic case of cholecystitis, where inflammation of the gallbladder that causes pain in the shoulder. So let's run through some high yield examples of referred pain, starting with the heart. Pain originating from problems in the heart is classically felt in the left chest. It can radiate to the left arm and sometimes the left side of the neck and jaw. So things like myocardial infarctions and pericarditis can classically be felt in these areas. Also keep in mind that pain from the heart can be felt in the back as well. Referred pain from the appendix is something you'll get a lot of bored questions on. Even though the appendix is located in the right lower quadrant, pain from the appendix classically begins in the carium vocal region and migrates to the right lower quadrant specifically to a site called McBernie's point. McBernie's point is the point that's one third of the distance between the anterior superior iliac spine and the umbolechus, which is right about here. The reason for this is that early appendicitis causes inflammation and pain in the peritoneum, which is felt more in the peri-embilical area and then migrates to McBernie's point as the appendicitis worsens. Next up is pain from the liver or gallbladder. This pain is classically felt in the right upper quadrant, which is anatomically where the hepatobiliary system is located. This pain can also be felt in the right shoulder and right scapular area. It's important to know that this is due to diaphragmatic irritation. The liver and gallbladder are located right under the diaphragm, so in cases of hepatitis or cholecystitis, the diaphragm can become inflamed. You might remember that the sensory innervation to the diaphragm is carried by the phrenic nerve, which traces back to the C3 through C5 nerve roots. The supraclavicular nerves also originate from the C3 through C5 spinal nerves. Therefore, intense pain signals traveling along the phrenic nerve can also be felt in the C3 through C5 dermatomes. And if you remember our video on the dermatome map, you'll remember that the C3 through C5 dermatomes correspond with the neck and the shoulder. Irritation to the left side of the diaphragm caused by problems with the spleen, such as splinic rupture or splinic abscess, can also be felt in the left shoulder. This is known as Kerr's sign. Finally, referred pain from the lung can also be felt in the neck and shoulders. In particular, something like an apical pneumothorax can be felt in these regions. These are just some of the high-yield examples of referred pain that you need to know not just for step one, but for many of the board exams you'll take in the future. We hope you found this video useful. Be sure to keep an eye on our channel for more future review videos, and leave us some suggestions for topics you'd like to see.