New News Biology #36
The Eye - Part（1）
Of the five senses that have accompanied humans from the stone age to the present, the eyes are by far the most important. Our ancestors could talk for ages about ‘the lion near the river’, and go on and on about its gruesomeness, its jaws dripping with the blood of its last prey, its roar that could be heard miles away, and its smell, a smell that is like death himself. However, you can’t know for certain until you see it for yourself, only to discover that this ‘lion’ was merely a cute little cat quenching its thirst on the riverbank. The eye is very important, whether its distinguishing friend from foe, or just taking in the beautiful sights of this world.
Despite its greatness, the eye is a rather fragile object, that needs to be put to good care, or else it may have a fit, and blur your door to seeing wonders.
To ensure that you can use it when needed, the eye is made up of 6 crucial parts, which together help you see. These are:
1)The Cornea, this is a transparent layer which has no blood vessels. Because of its unique structure, oxygen has to diffuse through it in order to suffice the cells’ needs.
2)The Iris, the colored part of a person’s eye is what’s known as the iris.
3)The Pupil, although it sounds like yet another structure of the eye, the pupil is actually just a circular gap in the iris that lets light pass through into the eyeball
4)The Lens, that light that just passed through the pupil reaches the lens, which if you’ve ever handled a camera, would be quite familiar. This lens can change shape and refract the light to focus on a particular spot within the eyeball.
5)The Retina, the entire purpose of the lens is to focus light. But where to? Well, at the very back of your eyeball, there is an area that are full of light-sensitive cells, and this part is known as the retina.
6)The Optic Nerve, the last part of the eyeball is this nerve, which sends all the impulses generated by the light-sensitive cells in the retina to the brain to be interpreted into an image.
The Retina’s Receptor Cells (those light-sensitive cells that we talked about earlier) come in two kinds. First are the cone cells. These are responsible for detecting the colour of light, which is what makes our vision multi-colored and not monochrome. However, they do not work well (or don’t work at all) in the dark, which is why we don’t see color in the dark. Second are the rod cells. The reason that we can still partially see in dark places is because of these rod cells. They’re more sensitive than the cone cells, but come in black and white.
The Iris Reflex. When talking about the eye, we can’t go without talking about the iris reflex, which is a ‘preinstalled’ protective capability of the eye. If the eye receives too much light in as short period of time (in other words, too much bright light), then our retina may become damaged, which isn’t good. So our iris has evolved to protect the retina. When there is low light, the retina becomes bigger to let more light in. However, when there is a bright light source, it makes the opening (the pupil) smaller to let in less light. This feat is accomplished with two types of muscles in the iris, the circular and the radial. When the radial contracts and the circular relaxes, the pupil become bigger, and vice versa for the pupil to become smaller.