HOW TO SEE YOUR RETINA
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.
HOW TO HEAR YOUR MUSCLES
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: https://www.youtube.com/watch?v=B5xlLaO8e-A
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.
Check out more videos like these at PhysicsVideos.com
