This week, I introduced the Nervous System which consists of the brain, spinal cord, sensory organs (skin, eyes, ears, nose, and tongue), and all of the nerves that connect these organs with the rest of the body. Together, these organs are responsible for the control of the body and communication among its parts.
The brain and spinal cord form the control center known as the central nervous system (CNS), where information is evaluated and decisions made. The sensory nerves and sense organs of the peripheral nervous system (PNS) monitor conditions inside and outside of the body and send this information to the CNS. Efferent nerves in the PNS carry signals from the control center to the muscles, glands, and organs to regulate their functions.
As the nervous system includes all our sensory organs, our focus activity was dissection of a cow eye. A cow eye is very similar to the eye of a human. By dissecting and examining the anatomy of a preserved cow eye, we can learn how our own eye forms images of the world around us and sends these images to our brain.
Cow Eye Dissection
Distributed around the table were dissection tools and one cow eye per pair of students. I then walked them through the steps of the dissection process elaborating upon the function of each structure as we went along.
We first observed the external parts that were visible: the cornea, slera, optic nerve, as well as the fat and muscle tissue surrounding the eye.
In the cow eye, we observed four muscles that allow for the eye to move up and down and side to side. As we learned, humans have these same muscles. Humans also have ocular muscles, which allow for involuntary and voluntary eye movements that contribute to our overall vision.
We then began to look at the internal structures of the eye: vitreous humor, lens, iris, iris, ciliary body or suspensory ligaments, and tapetum.
One of the structures the kids found the most interesting was the lens. As the lens ages, it becomes more rigid and the ability to accommodate reduces. This is why as people get older; they wear bifocals or reading glasses. This condition is called presbyopia and results in difficulty seeing objects that are near.
We also observed the retina which composes the inner layer of the wall of the eye. The retina contains the photoreceptors: rods for black- and-white vision and cones for color vision. The neuron fibers coalesce at the optic disc, where they form the optic nerve exiting the posterior side (or back side) of the eye and carries impulses to the brain. The optic disc is known as the blind spot since it has no receptors.
Bring it Home
At the conclusion of our lab, I gave each of the students a handout that expanded upon our discussion and included questions for review. It included a diagram of an eye to label, a couple of activities to discover one’s blind spot, and a list of vocabulary words. Subscribers to my newsletter will receive these in the November newsletter that will be sent next week.
I also provided a “menu” of activity choices for homework. Students are required to choose one but may do as many as they feel inclined.
Menu Choices (choose at least one):
- There are many perception activities listed on The Exploratorium website [ http://www.exploratorium.edu/snacks/iconperception.html ]
- Design an experiment to test the fact that different parts of the tongue are able to sense only one of four basic tastes: sweet, salty, sour, or bitter.
- Tasting food involves more than just the taste receptors on your tongue. Smell, texture, temperature ,and look of food all contribute to how you perceive its taste. The olfactory nerve in either side of your nose sends smell information as impulses to your brain. Design an experiment to test how ones sense of smell affects their ability to taste.
Join us next week as we explore the Skeletal System.