Rod+Cells+-+EH

THE MAGIC OF THE EYE = = toc =Introduction = If you are given an apple, the first thing you sense is that it’s big, red, and shiny. Then you notice it feels smooth, it smells sweet, and finally, it tastes juicy. But the first thing you notice about something is almost always the shape, size, and color. This is your first and most important sense; sight. The question now is how do you see? Rods and cones are the cells that collect the light that goes into your eye and send it to the brain so can see. You will also need to know, what makes up rods and cones? And finally, what is it like to not have functioning cone cells, to not be able to distinguish color?

=The Magic of the Eye =  How does the eye work it´s magic? There are two different types of eye cells: rods and cones. According to BrainPOP, there are about 6-7 million cones and more than 12 million rods in your eye! Rods and cones are both photoreceptive cells that take in light and send it to the brain. However, there are many differences, big and small. For example, the shape of each eye cell is self-explanatory; rods are long and narrow, but cones are, well, cone-shaped. Also, multiple rods are attached to a neuron (Bipolar and sensory), but only one cone. The most important difference is that rods only collect shades of black and white, but cones collect color (red, blue, and green).

=Your First Sense = There are two types of eye cells: rods and cones. Each of these cells help to make you see. Both rod and cone cells are photoreceptive, meaning “they are sensitive to light”(brainpop). However, cones are photoreceptive to color, and rods are only photoreceptive to shades of black and white. These cells are called specialized cells because they have different parts and features so they can do their job, just like doctors are specialized to keep you healthy and police are specialized to keep you safe. Eye cells are specialized to receive light and transform it into electric impulses that make an image in the brain. What does that mean?? Let’s break it down. When light bounces off an object and into your eye, it passes through the pupil (the black dot in the center of your eye) and hits the retina in the back of your eye. The retina is a tissue lining the back of your eye. This is where rods and cones are located. Next, the light breaks down chemicals in rods and cones, signaling the cells. Then, the rod and cones transform the light into messages that they send through cords called neurons that connect the eye to the brain. Finally, the brain deciphers the messages into an image. This process is complicated and requires a cell with specialized parts and features to help it do it's job. =Smaller Than You Can See = Your eye is like a camera. It has many parts like the iris and cornea. However, the rods and cones have special features for the eye to function. At the top of the rod cell, there are flat disks called membranes. These discs are stacked on top of each other like dinner plates. These membranes are renewed quickly by going through a cycle. First, the mitochondria (see below) creates new disks at the bottom of the stack. According to the book Principles of Anatomy, the mitochondria “produce one to three disks per hour.” Then, the stack is pushed upward. Finally, the old disks at the top are pinched off. Below the membranes are the mitochondria. Mitochondria are organelles that convert energy into food or energy the cell can use. In a rod cell there are four to five times as many membranes as in a typical cell. This is because these cells need a lot of energy. Membranes are ovalish in appearance and are not flat like the membranes. Located around a membrane is a chemical called rhodopsin. Rhodopsin is the chemical that is broken down when light reaches the cell. This is the chemical that sends signals through the synaptic terminal to the brain. The synaptic terminal attaches the rod to long cells called neurons. This terminal is where signals travel through to get to the neurons and the brain, where they are transferred into the images you see every day. = = =The World Without Color = Imagine waking up and not being able to tell the difference between colors such as red and green, blue and purple, brown and green, and red and orange. How would you get dressed? How would you be able to tell between the colors on traffic lights? How would you draw pictures? This seems crazy, but believe it or not, there are people in this word who experience this every day! You have probably guessed the name of this: color blindness. 8% of men and .5% of women experience color blindness. Lots of people think this means you can not see any color at all, only black and white. This is not true. Color blindness is just when you have trouble telling colors apart. There are three types of color blindness: mild color blindness, color blindness, and severe color blindness. Mild color blindness is the effect of when al three types of cones, red, blue, and green, are present, but one cell functions abnormally. Mild color blindness causes people to have difficulty distinguishing colors in dim light. Regular color blindness happens when one or more of the cone cells are absent or malfunctioning. This causes people to not be able to distinguish color in any light. Severe color blindness is when all three cones are absent or malfunctioning and can cause some people to only see shades of grey! <span style="color: #615f5f; font-family: Tahoma,Geneva,sans-serif; font-size: 105%;">According to the website, Teen Health and Wellness, “Change in color vision can signify a more serious condition.” This means that most people have color blindness from birth. If your color vision is altered later in life, this is a may lead to more serious problem and an ophthalmologist, or eye doctor,should be consulted.

=<span style="color: #509fe8; font-family: Tahoma,Geneva,sans-serif;">Conclusion =

<span style="color: #615f5f; font-family: Tahoma,Geneva,sans-serif; font-size: 105%; vertical-align: baseline;">The eye is a magical thing, but once you know about rods and cones, how they work, what they're made of, and what happens when you have problems with your eye cells, you know it´s not magic, it's science.

=<span style="color: #509fe8; font-family: Tahoma,Geneva,sans-serif;">References = <span style="color: #615f5f; font-family: Tahoma,Geneva,sans-serif; font-size: 105%;">“Cone-Rod Dystrophy.” Genetics Home Reference, 4 Jan. 2017, ghr.nlm.nih.gov/condition/cone-rod-dystrophy. Accessed Feb. 2016.

<span style="color: #615f5f; font-family: Tahoma,Geneva,sans-serif; font-size: 105%;">“Eyes.” BrainPOP, 1999, www.brainpop.com/health/bodysystems/eyes/. Accessed 30 Jan. 2017.

<span style="color: #615f5f; font-family: Tahoma,Geneva,sans-serif; font-size: 105%;">“Eyes.” Power Knowlage Life Science, The Rosen Publishing Group, Inc. 2017, www.pklifescience.com/app;jsessionid=F15F14F423C8192D402439A0A54874F4?service=externalpagemethod&page=main/ViewDocument&method=view&sp=426&sp=Sbody&sp=8&.

<span style="color: #615f5f; font-family: Tahoma,Geneva,sans-serif; font-size: 105%;">Miller, Kenneth R., and Joseph S. Levine. Biology. 4th ed., Englewood Cliffs, Prentice Hall, 1998. <span style="color: #615f5f; font-family: Tahoma,Geneva,sans-serif; font-size: 105%;">---. Biology. 4th ed., Englewood Cliffs, Prentice Hall, 1998.

<span style="color: #615f5f; font-family: Tahoma,Geneva,sans-serif; font-size: 105%;">Teen Health and Wellness. American Academy of Ophthalmology 2016, www.aao.org/eye-health/diseases/what-is-color-blindness.

<span style="color: #615f5f; font-family: Tahoma,Geneva,sans-serif; font-size: 105%;">Tortora, Gerard J., and Nicholas Peter Anagnostakos. Principles of Anatomy and Physiology. 6th ed., New York, Harper & Row, 1990. <span style="color: #615f5f; font-family: Tahoma,Geneva,sans-serif; font-size: 105%;">---. Principles of Anatomy and Physiology. 6th ed., New York, Harper & Row, 1990.

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