Sheep Eye Dissection

Today in class, my lab partner and I dissected a sheep eye in order to fully understand the anatomy and physiology of the eye, although some features on the sheep eye are different from those of a human eye. First, we looked at the external surface of the eye, identifying fatty and muscle tissue that we had to remove.

Excess tissue is the white around the eye; we stopped cutting once we reached tough tissue (sclera).

After cutting away the excess tissue, we identified the cornea and sclera. We did not take a picture of this step, so here is a picture from online:

1. cornea

2. sclera

The cornea is the layer that forms the front of the eye and allows light to come in; the cornea is slightly cloudy because the eye is not in a living state.

We also identified the optic nerve, which is directly behind the eye:

1. optic nerve

The optic nerve transmits the signals to the brain so the brain can interpret the light coming in.

Then, we made an incision between the sclera and the optic nerve and cut the eyeball in half all the way around. When we separated the two hemispheres of the eye, we discovered the retina on the posterior hemisphere and the vitreous humor on the anterior hemisphere. The vitreous humor and the aqueous humor (fluid) maintains the shape of the eye. Underneath the retina was the thin, black choroid layer, which also contained a shiny, bluish structure called the tapetum lucidum. 

Lifting up the choroid layer from the sclera.

The choroid layer contains a network of blood vessels that bring nourishment and oxygen to itself and the other two layers.

Shiny, bluish material is the tapetum lucidum.

In order to fully expose the tapetum lucidum like in the picture above, we removed most of the retina, but kept the retina attached at its one point of attachment, which is the blind spot. The retina uses photoreceptors to send signals from the light to the brain through the optic nerve. The tapetum lucidum reflects light onto the retina, which helps animals with night vision; humans do not have this feature. 

Next, we removed the vitreous humor from the anterior hemisphere of the eye, revealing the lens, ciliary body, and suspensory ligaments. 

The small opening through all the black (iris) is the pupil, through which light enters the eye. The circular structure to the very right is the lens. Around the pupil, there is also the ciliary body, which is muscle fibers that contract and relax to increase or reduce the bending of the light rays. 

We then removed the lens and noted that it was slightly cloudy. When we removed the lens, the suspensory ligaments were still somewhat attached to the lens:

The suspensory ligaments are the black bits around the lens. These ligaments hold the lens in place and join with the smooth muscle containing the ciliary body.

We observed that the shape of the pupil was not completely circular like it is in humans, which is another difference between the sheep and human eye. After observing the iris and cornea, we removed the cornea from the front of the eye and noticed that it was tough, but definitely not as thick as the sclera. 

This lab was simple but offered many insights into the anatomy and physiology of the human eye!

Update #3: Moving Along...

In these past two weeks, I have almost finished my story and I have also begun on the first few pages of my book. While trying to finish up my story, I have discovered that many of the main character's experiences, excluding the LGBT experiences, are similar to problems I had earlier in my life, although mine were definitely not so severe. For example, the main character in my story has difficulty keeping up with her honor and AP courses, as she feels she needs to maintain very high grades in order to succeed. Last year, I had a similar situation, except I did not fall into depression, but instead tried to manage my stress through other outlets.
My setbacks have not really changed over the past few weeks. As I am trying to finish up my story, I am trying to leave out as many details as possible and simply keep the main events, because my story is already a decent length. However, I feel that if I leave out details, then the reader will miss out on all of the factors that truly cause depression; I am in quite the dilemma.
Although I said this in my previous blog post, I plan to make more progress with my physical book and make a final copy of my story to base my book off of for the next two weeks. I also plan to first draw everything in pencil before outlining and coloring my drawings, so I will finish a decent number of pages by the next two week check-in, hopefully.

The Clay Brain

For this lab, my lab partners and I constructed two 2D models of the brain from two different points of view, the left hemisphere along the sagittal plane and the right cerebral hemisphere. After constructing the models, we labeled each important structure on the brain. We also used different colors so as to make it easier for the viewer to distinguish among the different structures in the brain. First, we made the model of the left hemisphere along the sagittal plane and labeled structures with pins and tape:

Because we thought that it might be difficult to read the labels, we chose to write the structure names directly on the cardboard for the next model (right cerebral hemisphere): 

The Woman with a Hole in her Brain

In this article (https://www.newscientist.com/article/mg22329861.900-woman-of-24-found-to-have-no-cerebellum-in-her-brain#.VSq-1ouKrVv), the author talked about a woman who had lived basically all of her life without her cerebellum. She never really realized what was wrong until she suffered more significant symptoms, like dizziness and nausea. For the majority of her life, she had problems with balance and coordination, and also had trouble talking; the space that is normally occupied by the cerebellum was instead occupied by cerebrospinal fluid. I can relate to this quite well because I actually went to the hospital myself and received numerous brain scans due to an infection of my inner ear, which in turn affected my cerebellum; I had severe vertigo for a period in my life. Because the cerebellum controls motor control and balance, I was dizzy every time I stood up.

For example, if the hypothalamus was missing or severely damaged, I do not think that a person would be able to survive. Because the hypothalamus controls homeostasis, which includes regulation of temperature, heart rate, and blood pressure, the body would react very badly if one's environment changed. For example, the body shivers to generate heat when the environment is cold. If the hypothalamus were to be damaged, there would be no message telling our body to shiver, and as a result we could die due to exposure. Furthermore, the hypothalamus also controls the secretion of certain hormones from the pituitary gland, so damage to the hypothalamus would affect the function of the pituitary gland as well. Because the function of the hypothalamus is rather unique, I do not think it would be possible for another structure of the brain to "take over" for the hypothalamus.