by Jennifer Wineke

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Your skin is divided into 30 sections called dermatomes, and each dermatome is supplied by nerves branching from a single spinal root housed in the vertebrae of your spine. These nerves transmit sensations like pain, touch, and temperature. Since the feelings map is more or less the same for everybody, you can use the map to figure out the root of someone’s feelings.

For example, if someone feels tingling down the back of their arm and numbness in their middle finger, you might be suspicious about a pinched nerve arising from the seventh cervical vertebra (C7), because that’s the vertebra that corresponds to those places on the body map. There is so much hidden logic to this carbon-bag of flesh and blood!

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A developing fetus doesn’t use its lungs to breathe—it relies on oxygen-rich blood from the mother delivered via the placenta. Because its heart doesn’t want to pump blood to non-functional lungs, oxygenated blood bypasses the lungs by sneaking through a hole between the pulmonary artery and the aorta. When a baby is born and takes its first breath, the hole begins to close, and for most babies it closes by the time they’re a couple of days old.

So you had already weathered some heartbreak by the time you were born! Good to get some practice in early.

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Your cornea is the transparent surface of your eye that covers your anterior chamber (a space in your eyeball filled with watery fluid), your iris (the colored part), and your pupil (the black dot in the center). It has to be transparent so that light can enter your eye and allow you to see, so it can’t get its oxygen from clunky blood vessels like most parts of your body. Instead, oxygen from the air dissolves in your tears and diffuses throughout your cornea—and the waste product of your eye, carbon dioxide, diffuses out.

Unfortunately the amount of oxygen diffused through your tears is only enough to keep the cornea healthy, so you can’t hold your breath, cry a lot, and expect your eyeballs to breathe for you. But the cornea is the fastest healing tissue in the body—scratch your cornea, and it will usually heal in 1-3 days, thanks in part to the oxygen from your tears. Sounds to me like crying is pretty good for you.

Jen Wineke is an MD/MBE student at the Perelman School of Medicine at the University of Pennsylvania. She likes reading and writing and doodling.