As you read this article, the retina in your eye is catching the light emitted by the text on your phone’s screen to create a reverse image of them. The brain then decrypts each letter, putting them together in reverse order to help you understand what I’m writing.
That’s a simple explanation for how vision works. But let’s go a little deeper:
Light is made up of photons, discrete tiny packets of energy that travel through space as waves. The photons interact with a highly specialized type of nerve cell in your retina – called the photoreceptor.
And somehow the light energy was converted to ‘language‘Neural power that your brain can understand. How did that complicated process happen after all? What is actually going on in your retina?
The senses operate according to the laws of physics
Basically, all of our 5 senses function exactly according to the laws of physics. They take in some form of energy from the external environment and convert it into a set of neural signals that the brain can interpret and understand.
This is how your brain draws information from the outside world to assess risks and make decisions, directing your motor system to react to the environment in order to survive and thrive. For example, touch is actually the mechanical pressure on your skin, or the sense of temperature in case you touch a fire. Your hand will immediately retract to keep you safe.
When you’re on the road and hear a rushing car horn behind you, the sound waves are vibrations of air molecules that vibrate the eardrums in your ears, transmitting nerve signals back to your brain and brain. Your foot steer jumps aside.
Taste and smell are involved in the transmission of odorous chemicals. Molecules in food interact with receptors on your tongue to help your brain understand their taste. Whereas the molecules that get into the nose are understood as odors. Strange and unpleasant flavors are what help you know food is spoiled and cannot be eaten.
Your vision works with a retina at the back of your eyeball – but it’s actually nerve cells extending from the brain.
Yes, the retina is a thin sheet of paper that contains highly specialized, functional nerve endings and cells. They connect to the rest of the brain via optic nerves, each with a single strand that acts as a high-bandwidth optical cable.
When photons of light enter the eye through the pupil, they are focused on the lens and then transmitted the image back inward like a convex lens. This image will usually focus on the retina. If it is outside the retina you may be nearsighted or long-sighted.
What you need now is a pair of glasses to add extra layers of optics that correct the bending of light, helping the focus return the image to the correct retina. Only then can you see clearly.
Optical transmission: From photons of light to nerve signals
Now, when the photons reach the retina, the cells absorb them and convert the light energy into an electrochemical signal through phototransduction.
But the energy of each photon is characterized by its wavelength. The shorter the wavelength, the greater the amount of energy – or punch they are hitting, the retina. Specifically, the photoreceptor neurons are the receptors of these photons’ punch.
Within those cells, there is a specialized molecule called a photopigment. These are molecules capable of interacting with photons. The photopigment itself is divided into several categories, each reacting only most strongly to photons of a particular wavelength and absorbing less photons of other wavelengths.
Wavelength is related to the color of light, so it is understandable that some photopigments are molecules that help you perceive colors. The more different wavelengths deviate from the absorbance of the photopigment, the less they absorb, creating a bell-shaped curve called the color absorption spectrum.
When a photon of light is absorbed by a photopigment molecule in a photosensitive cell, the energy in the photon is like a punch that breaks the chemical bond in the photopigment. It changes the natural flow of ions that are flowing out into the photoreceptors, causing the cell to become hyperpolarized.
The superpolar state of the photosensitive cell inhibits a neurotransmitter called glutamate. Its decreased concentration leads to a series of reactions that run from the retina to the area of the brain that processes the images and tells it to signal light stimulation.
Here, all of the information in the 137 million photosensitive cells will be aggregated. Your mind will re-create them into images of the outside world. At this point, you can really “see“get them.
Interestingly, everything that you see right now, an instant before or after, always begins with a photon punch into the photopigment in the photoreceptor. That means a photopigment is like a cotton bag suffering billions and billions of punches all the time.
As soon as a photon activates it, a protein molecule called arrestin shields the photopigment, waits until another punch from the photon arrives and resumes the same chemical cycles.
It could be understood that arrestin was like a shutter working at a rate of billions and billions of times a second. In fact, no real digital camera can do this without damage. Arrestins do that because of their number, which has millions of molecules in a photosensitive cell, readily shielding the photopigment.
It is like a pond filled with mulberry flowers. Each time you throw a stone down it, the duckweed will expand and close immediately to shield the water surface.
The video explains the optical transmission that takes place in a photosensitive cell, namely a rod-shaped cell, containing photopigments of the rhodopsin type.
The shutter speed in the eye is so high, but unfortunately the nerve signals transmitted from the photoreceptors to the brain are always delayed. You can find out about that in this article: “Thoughts run in your head at 180km / h, but not fast enough for people to get rid of the lag.”
Also due to the delay in visual information, the human eye can only see the outside world at a refresh rate of 75 FPS – or 75 frames per second. You can read more about how the scientists found that number in the article: “What is the FPS of the reality we live in?”
These are more in-depth explanations on how your retina, or camera sensor in your eye, works. Interestingly, right?
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