Friday, January 27, 2017

See Inside Your Own Eye and Hear Your Own Muscles


The human eye is not without its flaws.  Some of these include the blind spot, poor peripheral vision, and the fact that our retina is covered by blood vessels!  Normally, these arteries are invisible to us, but they can be made visible with only a cell phone flashlight.

In this video Anna Spitz explains how to use a flashlight to see your own retina.

The experimental set up – only a gently closed eyelid and flashlight are needed.

All human skin is partially transparent to light, especially red light, and we can use this to see through our own eyelids.  (This experiment works, no matter what skin color you have!). 

To perform the experiment, turn a flashlight on and hold it DIRECTLY UPON your gently closed eyelid.  Then wiggle the light as you look around with your eyes closed.  It seems to work best when the light is near the nose.

  A simulated image similar of what you will see on the surface of your retina.

When you succeed you will see several arteries emerging from a single location.  This is the optic nerve.  You might also notice a dark or grainy spot in the center of the retina that has very few arteries near it.  This spot is called the Fovea, the most sensitive part of your eye.

A view of the author’s retina from a recent visit to the eye doctor.  Notice there are very few arteries on the fovea, thereby not interfering with this most-sensitive part of the eye.

The optic nerve obstructs a small part of the retina from seeing.  This location is known as the blind spot.  Our brains hallucinate a patch over this blind spot so that we generally do not notice it.

The fovea is darker because it absorbs more light, being the most sensitive part of the eye.  It is also the part you use to read and see color.  Generally, light that is not landing on the fovea is quite blurry and the color vision is poor peripherally.  You can notice this by looking at the wall and trying to read what is on the computer screen.  YOU CAN’T DO IT!  Even though you know there are words, they aren’t legible.  Also, at night, your color vision is very poor so the fovea isn’t much help and your peripheral vision is just as good as your central vision. 

As a final note, everyone’s retinas are different as you will easily see by comparing these pictures, or any picture of a retina to your own.  Thus, you can use retinal scans as an alternative to finger print identification. 

If you are surprised that you have arteries in your eye and have been looking at them your whole life but haven’t noticed, then consider this test.  Are you wearing a shirt?  You didn’t notice until you were asked because you are used to it.  Similarly, we don’t notice we have arteries on our retina until a light hits them at an angle to which we are unaccustomed. 


Another experiment you can do with almost no equipment is to hear your muscles.  By simply putting your fingers in your ears.

Anna Spitz demonstrates that by putting your fingers in your ears, you can hear your own muscles.

That low frequency rumbling about 30 Hz is the twitching of the muscle fibers in your arms.  Muscle cells are fibrous bundles that grow and contract.  They are all over the body, but they only do one thing.  PULL.  Muscles pull on tendons.  They are even pulling when you think you are at rest.  They are pulling repeatedly just to hold you in place. 

A microscopic view of muscle cells.  All they ever do is pull.

Watch Anna Spitz explain how to hear your muscles in this video:

 Flexing will increase the loudness of the muscle twitching.

Many people mistakenly believe that this sound is the flowing of blood, but this is not the case.  The twitching sound is not timed with the heartbeat, and if you flex the muscle cells get louder. 
Flexing is when two or more muscle groups pull against each other.  For example, biceps and triceps can pull against each other and the arm will stay in place even through the muscle fibers are pulling and pulling.  The repeated pulling action of muscles we call twitching.  The frequency of this action must be between 20 and 40 Hz because that is the frequency we hear. 

Anna Spitz attempts to listen to other peoples’ muscles.

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