TIL: [This may sound like medical babble, but I'll have a go at translating it in a sec.] The ciliary muscle of the eye is innervated by parasympathetic fibers of the oculomotor nerve (cranial nerve III). It is well known that the contraction of this muscle results in the accommodation of the eye through the counteraction of zonular fibers, whereby the lens becomes more spherical and decreases the focal length.
Put more simply: When you are relaxed, you brain contracts a muscle that changes the shape of the lens of the eye, causing your eyes to focus closer to your face.
The mechanism for this is not 100% understood, but the best guess is that it works like this: imagine you have a rubber dodgeball held in the center of a pillowcase. Normally, you have 4 super strong people pull on each of the corners of the pillowcase, flattening the pieces of cloth against each other and squishing the ball inside so that it's no longer round. All this tension makes you uneasy, so you send in a strong but relaxing guy (think The Dude from The Big Lebowski) and have him pull on one of the flat surfaces of the pillow case. This counteracts some of the tension from the folks pulling from the corners and allows the ball to get a little rounder again.That's it! The ball is the lens of the eye, the pillowcase is zonular fibers, and The Dude is the ciliary muscle.
*This block is 3 months of the 4 years of medical school, or 1/4th of 1/4th of medical school. However, since we don't have class for the summer between 1st and 2nd year, we lose a block and are left with 15 3-month segments, of which we have completed one - thus 1/15th.
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