Eye Dissection Analysis: How do we see things?

The un-dissected sheep eye. Baa.

Did you know that the image formed on our retina of everything we see is actually upside down? You may be thinking, "How do people see normally without constantly doing a handstand, then?" I shall explain this and the wonderful process that is vision now, through the aid of a dissected sheep's eye.

Our sheep had a beautiful blue iris.

The tapetum lucidum reflects the flash off my camera.

When light enters our eye, it passes first through the cornea. This is the tough exterior on the eye, which mainly serves as protection. Next, the image passes through the aqueous humor, which is a clear liquid in between the cornea and the lens. You can see the liquid on the mat of the dissection board, as it leaked out after the cornea was punctured. The image then passes through the pupil, which contrary to what you may think, is not a tangible black dot in the center of your eye. The pupil is actually a hole, an opening in the iris that allows light to pass through. The iris is the colored part of the eye, and it comes in many colors such as brown, blue, green, hazel, and purple if you're Elizabeth Taylor. The image passes through the pupil opening onto the lens, a very interesting structure that can actually change shape! The lens changes shape in order to focus light on the retina. This is what you see when someone's "pupils dilate." Their pupils seem to grow in size, which happens to allow more light in while in a darker environment. In sheep eyes, there is a secondary feature to allow even more light to be reflected into the retina at night called the tapetum lucidum. This is the reflective and iridescent part on the inside of the eye. After passing the lens, the light passes through another clear liquid called the vitreous humor, which is the jelly like substance sliding out of the eye in the attached pictures. The image then hits the retina, which contains the photoreceptors for vision, and is displayed upside down. Now, the brain does some pretty remarkable work to interpret the image. Where the retina and the optic nerve meet is a small divet called the "blind spot." The electrical signals are sent via the optic nerve to the occipital lobe, located in the back of the head. In the occipital lobe, vision is interpreted and flipped through complex tasks in order to match our perception with reality. Some studies say that at birth, babies still see the world upside down until the brain adjusts and corrects itself!

"The Woman Perpetually Falling..."

In the excerpt "The Woman Perpetually Falling..." from Norman Doidge's book The Brain that Changes Itself, a woman named Cheryl suffers from a severely debilitating vestibular disequilibrium symptoms, brought upon by a prolonged use of the drug gentamicin. This drug is known to be harmful, but is used anyway because it is cheap and effective. This highlights a dangerous conundrum: use cheap and easily attainable medicine, or ensure the safety of patients even if it sends them into a deep debt? Cheryl only has 2% function of her vestibular system, which is responsible for regulating the sense of balance. It is comprised of 3 semicircular canals that send signals of changing external situations, such as a tilting head, so the body can adjust accordingly. Without this system, Cheryl feels as though she is constantly falling, her body weighed down with the added gravity of her condition. In addition to this seemingly physical weight, her mind is constantly exhausted and overworked. Since she is always focused on not falling, her mental capacity has no room for seemingly mundane tasks such as memory, thinking, etc. However, a doctor presents a remarkable solution: "a construction hat with holes in the side and a device inside it called an accelerometer" (5). This deceivingly simple device changes Cheryl's life, allowing her to finally feel normal for the first time in 5 years. I was moved by her shift in demeanor after she experiences stability, when she "starts clowning and showing off" (9). It is as if she can finally be herself, free of the mental and physical symptoms holding her back. This truly shows the correlation between physical health and mental health. Additionally, I was saddened by her disappointment when the effects wore off, describing herself as "tired, exhausted... depressed" (9). This resonated with me as she reverted back to her pain-ridden self, having experienced normality to only recede into her former shell. Thankfully, Cheryl's use of the accelerometer caused the symptoms to disappear completely, giving her life back.

The Clay Brain Lab

In this lab, we created two models of different viewpoints of the brain: the right cerebral hemisphere view and the left hemisphere along the sagittal plane. We used different colors of Play-Doh to represent different parts of the brain, creating a colorful visual model of the locations of parts of the brain. For example, we used orange to represent the frontal lobe on the right cerebral hemisphere.

"The Woman With a Hole in Her Brain"

The newscientist.com article, "The Woman With a Hole in Her Brain" by Helen Thomson, describes a Chinese woman's remarkable survival without an entire cerebellum. Her condition led to only motor deficiency and speech problems, and she has surprisingly survived past the age of 24. The cerebellum is responsible for controlling voluntary movement and balance, as well as other motor functions like speech. Most patients with this condition pass away at an early age, which makes this woman's survival even more exceptional. Doctors say other parts of her brain, such as the cortex, are compensating for the absence of the cerebellum by taking over its functions.

What would happen if someone were born without, say, a pons? The pons relays signals from the forebrain to the cerebellum. It also contains nuclei that regulate sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture. Without a pons, the brain could not function even basically, as no information would be transmitted. So no, a person cannot survive without a pons. 

Unit 5 Reflection

The folds in the small intestine, which increase surface area

for better absorption.

This unit was focused on a few major organ systems in the body: the digestive system, the endocrine system, and the lymphatic system. Each system is interestingly interconnected. The digestive system consists of the mouth, pharynx, esophagus, stomach, appendix, small intestine (duodenum, jejunum, to ileum), the large intestine (ascending colon, transverse colon, to descending colon), rectum, and anus, traveling through those organs respectively. This pathway is the alimentary canal. The digestive system consists of digestion and absorption, digestion being the mechanical and physical breakdown of food through various processes. These can include peristalsis, which is the contraction movements of the esophagus, stomach walls contracting, chemical changes in the acidic stomach, and digestive juices/enzymes in the small intestine. Absorption is the absorbing of the broken down nutrients into the blood stream. This occurs due to the many folds in the small and large intestines, which are actually over 28 feet! We explored the surprising length of the intestines in our lab, which I debriefed here.

We also learned about fuel metabolism, which changes depending on what state your body is in. If you have just eaten, you are in the fed state, and the sugars you absorbed in the digestive system travel to the liver, where they are converted into glycogen. The pancreas releases insulin to stop the release of glucagon. The amino acids, fatty acids, and glucose are sent to body cells to be stored as adipose tissue. If a person consumes and does not expend the energy stored in the form of fat, said fat will accumulate, causing obesity. Obesity can lead to many health complications, one of which is diabetes. Diabetes is a disruption in fuel metabolism. Diabetes can be one of two forms: Type I diabetes or Type II. Type I occurs when insulin is not correctly produced by the body, and those who are diagnosed are dependent on insulin shots. Insulin is a hormone that allows glucose to be absorbed into cells, triggering the migration of Glut4 receptors to the outside of the cell membrane, which allow glucose to enter the cell. This only affects 5-10% of all people with diabetes. The more common form of diabetes is Type II, which occurs when the body is insulin-resistant, meaning that insulin's intended effects do not work in the body. If not correctly managed, diabetes can be deadly. My grandfather had Type II diabetes, and my brother was pre diabetic until he changed his lifestyle.

Insulin's effect on Glut4 receptors in cells. Exercise also
triggers the movement of the Glut4 receptors.

The main struggle I had this unit was missing the Fuel Metabolism lecture. The printed handout had run out by the time I went to get one, so I had to write the whole thing by hand, which muddled the information, and also meant I don't have some diagrams in my notebook. I also realized that it was incredibly complex, and I am still slightly confused on exactly what some terms mean. In regards to my New Year goals, I am doing mas o menos. I completely forgot that we had a temp check, and at that point I still had not done my Fuel Metabolism notes, so that went poorly. I wish I had taken initiative and done them earlier. However, I am eating much healthier, and I've eliminated my snacking habit. Now I stick to my 3 wholesome meals a day, with one small snack before I go to work. Having a job and being a second semester senior is a catch 22; now that it is competition season, I have increasing obligations and commitments to my students, (including rhinestoning over 45 costumes...) and I have to continue to do well in school while juggling changing social aspects.

Digestive System Lab

1) In the Digestive System Lab, we made a model to represent the length of our digestive system from mouth to anus. To do so, we used different colored yarn to represent each different organ/part of the system, and measured certain parts of our bodies and heights to calculate the size of each organ. For example, our stomach was the length of our thumb to pinkie finger while making the "hang loose" sign. Our bodies are very specialized, and remarkable in almost unimaginable ways. Many people describe me as "tiny," so it's crazy to think that so much stuff is in my body. We calculated the length of our digestive system, which is staggeringly longer than expected. The "takeaway" from the lab is that organs so long and large can fit into such a small space.

2) I am 5 foot 2 inches tall, fairly short for my age and gender. This is 62 inches. The length of my digestive system is 8.604 meters, or 338.74016 inches. That is actually insane to think about. I think the only way this length of organs is able to fit in my abdomen is through tons and tons of folding and coiling. It is compressed into many micro-folds, increasing surface area while maintaining the small volume.
3) I think it takes 3 1/2 hours for food to move through the digestive system. I shall now look up the answer. It actually takes about 6 to 8 hours. I find this surprising because sometimes when I eat dairy foods, (I am intolerant) it seems to only take 20 minutes to pass through. (TMI) I know that this is the body's mechanism of getting the dairy out of my body as quickly as possible, but it seems surprisingly fast compared to the normal 6 to 8 hours. This may be a factor that influences the time it takes, in addition to things like fiber intake.
4) Digestion is the breaking down of food into smaller particles and molecules, done mostly by the mouth, the stomach, and the small intestine. Absorption is the actual intake of those broken down molecules into the bloodstream for use throughout the body, taking place mainly in the small intestine and large intestine.
5) I want to learn more about dietary intolerances, mostly because of my lactose intolerance, and also because I have friends who have Celiac disease.

New Year Goals

1. As a newly minted Second Semester Senior™, I am bound to suffer from the plaguing disease currently crippling the class of 2017: Senioritis. I will not let my diagnosis detract from my academic successes; I will finish the year with no grades lower than a B-. I will do so by maintaining the amount I study for tests, and continuing to attend classes. By allowing myself some Bs, I can regain lost sleep time from 3 1/2 stressful years and relax more before I leave for college. 

2. I will fit into my NCL Presents dress by March 4, with no visible fat rolls or reliance on Spanx. 

I will do this by consistently going to the gym, at least 3 days a week in addition to being more active while I teach dance classes. This will knock 2 birds out with 1 stone, allowing my students to have a more engaged and fun instructor while I get in shape myself. I will practice my dance solos more, so I can win first overall at competitions and get more confidence about myself. I will eat healthier, and stop taking late night Yogurtland runs. I will enlist others to help me keep my goals and have a selection of gym-buddies to accompany me on my workouts, making it a little more fun. Although weight shouldn't be the driving factor, I want to lose at least 7 pounds, hopefully more.