04.26.2016 Sheep Eye Dissection

Today we dissected a sheep's eye to help us learn about the anatomy and physiology of an eye.

a sheep's eye

First, we studied the external structures of the eye. These included the eyelid, the cornea (clear part of the eye to let light in), the sclera (white of the eye), extrinsic eye muscles that move the eye around, fatty tissue that cushions the eye, and the optic nerve that sends visual information to the brain.

optic nerve

extrinsic eye muscle

Then we cut the eye open to study the internal structures. As we cut through the sclera, we found that it was very thick and tough and hard to cut through. Also, a liquid oozed out of the eye as we cut. This liquid, called the vitreous humor, has a jelly-like consistency and is also clear to let light through. On the inside of the posterior hemisphere of the eye, we found the retina, which is a very thin layer of sensory cells that receives light and converts it to nerve impulses that they send to the brain through the optic nerve. Underneath the retina is a dark-colored layer called the choroid layer, which brings nutrients and blood to the retina. It has a dark color so that it does not reflect light around the eye. In some nocturnal animals (i.e. not humans), the part of the choroid layer is bluish and reflective. This is called the tapetum lucidum, which reflects light around the eye and allows the animals to see better in the dark.

the choroid layer and the tapetum lucidum

the thickness of the sclera

In the front of the eye, we found the lens attached to the ciliary body by suspensory ligaments. The lens and the ciliary body, which is made of smooth muscle, work together to allow the eye to focus on an object. The ciliary body can contract to flatten the lens and reduce the bending of light rays entering the eye, or it can relax to allow the lens to thicken and increase the bending of light rays entering the eye.

We also removed the cornea from the front of the eye to expose the iris and the pupil. The iris is the colored part of the eye, and the pupil is the hole in the middle. The pupil is what regulates the amount of light entering the eye by constricting or dilating.

back of the lens showing where the suspensory ligaments once attached (black parts)

the cornea, iris, and pupil

You Otter Help: 20 Time Project, Week 8

These past two weeks, I have been building my website and creating pages for the information I have gathered. I am using Weebly to build my website because I have used it before to build other websites. However, I have found that Weebly has changed their site themes and structure a little, so I am still getting the hang of the giant (and in my opinion, unnecessary) headers that seems to be the default for every webpage.

I have also started drafts of what the designs of the organisms are going to be. I guess for puns I'll settle for "bee aware" and "you otter help," unless anyone has any other suggestions.

A Clay Brain

In class, we learned about the different structures of the brain and their functions. To help us learn the structures and where they are located in the brain, we made a diagram of the brain out of clay. The diagram on the left is an inside view of the brain showing the internal structures, while the diagram on the right is an outside view of the brain.

a diagram of the brain

The Woman with the Hole in Her Brain

Today I read this article about a woman who is missing her cerebellum. The twenty-four year old woman went to a Chinese hospital because of dizziness and nausea and found that there was a hole in her brain where the cerebellum should be. The cerebellum is a small structure located under and to the back of the brain and controls voluntary movement, balance, and learning. Although problems with the cerebellum normally lead to severe mental impairment, movement disorders, or death, this woman only had slight problems, showing the resilience and plasticity of the brain.

After reading the article, I had to speculate what would happen if some other part of the brain was missing or severely damaged. For example, what would a person be like if they had no basal ganglia, a group of neurons in the middle of the brain connected to the thalamus? Normally, the basal ganglia controls voluntary movement, learning, eye movement, cognition, emotion, and decision making. If the basal ganglia were missing or damaged, then these functions would not work properly; for example, Parkinson's disease and Huntington's disease, which are caused by the degeneration of the basal ganglia, cause loss of motor control. Eventually, these diseases also lead to the death of the victim.