Reflexes Lab

Some motions are automatic, things we do without thinking about, and can't stop even if we want to- like blinking if something is town at our face. These are called reflexes, and they work by sending a signal to the spine, which sends a signal directly back to the muscle, bypassing the brain entirely. In this lab, we tested some of our different reflexes.
First, we tested our photo pupillary reflex- the reflex that controls the contraction of our pupils in response to light. We covered one eye, then shined a light in it and watched, and we saw the pupil constrict. Humans have probably evolved this reflex to prevent us from being blinded by bright lights.

After that, we tested our patellar reflex, which is the one doctors test when you go in for a physical. It causes the lower leg to suddenly kick out in response to a sharp tap to a spot under the knee. It is sometimes hard to find, but my lab partner and I were able to find it, tapping the knee in the right place and causing the lower leg to suddenly kick out. I don't know exactly why this happens, but I think it could be some sort of defense mechanism.

We also tested our blink reflex by throwing a cotton ball at each other's faces while stretching a piece of plastic in front of our eyes to protect them. Obviously, we both blinked. This reflex evolved in order to protect our eyes from harm.

After that, we tested the reflex in our foot, drawing an object across the bottom of our feet and making our toes curl. This probably also evolved in order to protect our feet.

Finally, we tested our reaction time by having our partner drop a yardstick and catching it, then figuring out our response time. We did this both normally and while texting, and my average response time was slower by 0.03 seconds when texting, increasing from 0.27 to 0.3 seconds.

Brain Dissection

In this lab, we dissected a sheep's brain. We started by removing the meninges, a layer of tissue that surrounds the brain and forms the blood brain barrier. Then, we observed the outside of the brain, identifying and labeling (with pins) several different structures we could see. After that, we cut the brain in half by severing the corpus callosum and identified more structures inside. Finally, we took a cross section of the brain in order to see the white matter, which is an area containing more neurons, and gray matter, which contains fewer.
This dissection was very interesting. Even though I knew that the corpus callosum was the only thing connecting the two hemispheres, it was still surprising to look down in between the hemispheres and see only one small white thing at the bottom holding them together. I also liked looking at the white and gray matter, as it was interesting to see where the neurons were most concentrated.

Picture and drawing of outside of brain

*Black pin is posterior, white pin is anterior

Part of Brain	Pin Color	Function
Brainstem	Silver	Filtering/directing information, breathing, circulation, digestion
Cerebellum	Green	Motor control, coordination, muscle memory
Cerebrum	Yellow	Integrating/interpreting data

In a neuron, myelin surrounds the axon, helping the signal to go faster.

Picture and drawing of left hemisphere

Part of Brain	Pin Color	Function
Pons	Silver	Breathing/digestion
Medulla oblangata	White	Balance/coordination
Optic Nerve	Green	Sending information from eyes to brain
Midbrain	Blue	Filtering/directing information
Thalamus	Yellow	Sorting data
Hypothalamus	Black	Maintaining homeostasis
Corpus callosum	Red	Communication between hemispheres

Picture and drawing of brain cross-section

Sheep Eye Dissection

The eyeball

Cornea and sclera visible 

Retina (peeling off), choroid, and tapetum lucidum (top)

Lens and vitreous humor (bottom)

The lens

First, we looked at the outside of the eye, where we saw the sclera (the white of the eye), the cornea (which is where the light goes through), and lots of fatty tissue on the back. We then cut off most of the fatty tissue in  order to see the optic nerve, which sends electrical impulses to the brain, which then interprets them, letting you see. We then cut the eye in half, so we could see the retina, which converts the light hitting it into electrical impulses using cells called rods and cones, on the back, and in the middle of it was the blind spot, which is where the retina meets the optic nerve. We then peeled back the retina so we could see tapetum lucidum, which helps to give the sheep better night vision, and the choroid, which functions as a supplier of blood for the eye. We then looked at the front half of the eye and saw and the lens, which bends the light coming in from the pupil, and the vitreous humor, a clear jelly-like mass that helps the eye retain its shape. We then took out the lens and vitreous humor so we could see the ciliary body, which is a muscle that controls the shape of the lens, the suspensory ligament, which connects the lens and ciliary body, and the pupil. 

By dissecting the sheep's eye, we were better able to understand the path of light through the eye. We saw the cornea, where light first passes through, and the pupil, which is the hole between the cornea and lens, as well as the iris, which controls the size of the pupil. We also saw the lens, which bends the light, and the vitreous humor, which light also passes through. The size of the lens surprised me; I thought it would be much thinner, and a little smaller. Finally, we saw the retina, which is where the light hits and is transferred into electrical impulses, and the optic nerve, which caries those impulses to the brain.

Parts of the eye