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Anatomy and function of the diaphragm.

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We've all had hiccups, and we've all tried the weird and wonderful ways to get rid of them, from holding your nose while drinking water to letting your friend scare you half to death. Did you know that hiccups are actually involuntary spasms of your diaphragm? Stick around to learn more about this muscle in our tutorial about the diaphragm.

The diaphragm is a domed sheet of skeletal muscle that resides in the trunk of the body and separates the thoracic cavity from the abdominal cavity. Looking from an inferior perspective we can see it has three peripheral attachments, which are the xiphoid process anteriorly, the costal cartilages of ribs seven to ten as well as ribs eleven and twelve laterally, and the lumbar vertebrae and arcuate ligaments posteriorly.

The muscle fibers of the diaphragm converge at the central attachment which is the central tendon. The parts of the diaphragm that arise from the vertebrae are tendinous in structure and are known as the left and right crura. The left crus arises from L1 and L2 and the intervertebral discs and the right crus arises from the lumbar vertebrae L1 to L3.

As you can see, the diaphragm has several openings, which allows structures to pass between the thoracic and abdominal cavities. It has three major openings and several minor openings. In this tutorial, we're going to talk about the major openings and the associated structures that pass through them.

The major openings are named after the larger structures that run through them and the first one we'll talk about is the aortic hiatus. The aortic hiatus sits at the level of T12 and transmits the aorta, the azygos vein, the hemiazygos vein, and the thoracic duct. Next, we have the esophageal hiatus which occurs at the level of T10. This opening transmits the esophagus, the vagus nerves, and the esophageal arteries. The last major opening is the caval hiatus, which lies at the level of T8. The caval hiatus transmits the inferior vena cava and the terminal branches of the right phrenic nerve.

Now close your eyes and take a deep breath in and out. Guess what? You just used your diaphragm. The diaphragm is the primary muscle of respiration. During inspiration, it contracts and flattens to increase the volume of the thoracic cavity causing the lungs to expand. During expiration, the diaphragm relaxes and returns to its dome-like shape, which reduces the volume of the thoracic cavity expelling air from the lungs.

Okay, time to move on to the neurovasculature of the diaphragm. The diaphragm receives most of its arterial supply from the left and right inferior phrenic arteries. The venous drainage mirrors this and is carried out by the inferior phrenic veins. The diaphragm receives motor innervation from the left and right phrenic nerves, which we can see here highlighted in green. Each phrenic nerve contains fibers from the spinal root C3 to C5, and luckily, I've got a nice rhyme to help you remember this. C3, 4, and 5 keep the diaphragm alive!

In today's clinical notes, we're going to talk a bit more about those dreaded hiccups. So, what causes hiccups? Often hiccups seem to start for absolutely no reason. However, there are some triggers including abdominal surgery, spicy food, and stress. Hiccups normally disappear after a few minutes, but in some unlucky individuals, they can last days, weeks, or even months. So how do we combat the hiccups?

The method that you'll all be aware of is holding your breath. This is meant to help reset the natural rhythm of your diaphragm and stop those hiccups. Others include sucking on a peppermint, biting a lemon, and breathing into a paper bag.

The pursuit of a cure for this mysterious ailment has even explored the effects of digital rectal massage in treating hiccups. However, if you’re hiccupping for more than 48 hours, it's time to see a doctor and get some medication.

And that brings us to the end of our short tutorial on the diaphragm.

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