Unit 6 Reflection

This unit covered the sense and the brain, beginning with the overall anatomy of the brain then going more into depth on the function of each part of the brain. We then covered the two hemispheres and lobes of the brain. The right hemisphere focuses on overall context, while the left brain focuses more on specific facts and details. The brain is also very flexible and adaptable and can heal from trauma or in response to new stimulation. We then moved onto our 5 senses and how the brain receives and reacts to sense stimuli, through sight, hearing, touch, taste, and smell. For example, the brain contains proprioceptors to sense pain and thermoreceptors for heat. Neurons send signals from the external stimuli to the brain, through integration in either the Peripheral Nervous System or the Central Nervous System. Each different system represents a section of the overall neural system and plays an important role in integrating messages and responding to the motor neurons to perform a reaction.

This is the analysis of the sheep brain dissection lab we did this unit, and here is the sheep eye dissection lab. Both were engaging and helped me really understand the location of each part of the brain or eye.

We read many interesting articles this unit. The first was "How to become a Superager" by Lisa Barret.This article was about how older people called "superagers" are able to function and have the same brain capacity of that of young people. While they might look old physically, mentally they are still functioning at their peaks. To keep the brain at this level of function, you must engage it through solving challenges, exercising, and doing difficult problem solving beyond simple sudoku. The second was "Fit Body, Fit Brain, and Other Fitness Trends" by Gretchen Reynolds. She explains how exercise also helps to keep our brain fit, most notably through an increase in neurons. She mentions studies that show how weight training can lead to fewer lesions in the brain's white matter. She also discusses how in a set of twins, the twin with more muscle mass has a stronger brain in the future.  We already knew exercise is super important to staying healthy, and this just reaffirms that. The last article we read was "How We Get Addicted" by Michael D. Lemonick, a former addict and alcoholic who overcame his addiction. Humans innately want to feel pleasure, which explains why they've turned toward drugs since the beginning of time. Drugs create a salience overdrive, causing an uncontrollable desire that turns into a severe craving. In addicts, the reasoning part of our brain that tells us, "Hey, drugs are bad!" doesn't function correctly, allowing them to continue in a negative cycle of addiction. This unit has been hard, but this time of the year is never easy for me. It's hard because I'm not trying to be the typical senior who flakes on responsibility second semester, but I just feel overwhelmed and emotional all the time. It's not like I want to feel like this or that I'm actively trying to be a bad student, but it's difficult to balance and prioritize things when I feel like I can't focus on anything but the negatives. 

Reflex Lab

In the reflex lab, we tested different reflexes on our lab partners. These reflexes included the photo pupillary reflex, the knee-jerk (patellar) reflex, the blink reflex, the plantar reflex, and our general response time in reaction to a stimulus. In essence, a reflex occurs on an arc, the most simplistic one being monosynaptic. That means the reflex has only two neurons: a sensory neuron and a motor neuron. Most reflexes, however, tend to be polysynaptic, containing multiple relay neurons in between. Most sensory neurons synapse in the spinal cord rather than the brain, allowing for a quick reaction time without the need for transferring information to the brain.
Claims Evidence Reasonings:
The photo pupillary reflex is when the pupil dilates in response to a changing environment. The evidence of this reflex is visible in the video we took of Michelle's eye after shining a flashlight into her eye that had been deprived of light for two minutes prior. Her pupil clearly increases size. This is a response that controls the amount of light entering the eye and adjusts rapidly to quickly adapt to a changing external environment, allowing for humans to see faster to react to any threats.
The patellar reflex is a contraction of the thigh muscle in response to a light tap below the kneecap. We know that a mechanoreceptor sensory receptor felt the pressure of the tap and in turn, through a monosynaptic reflex to the spinal cord, the thigh muscle contracted to kick the foot forward. We saw this happen after Hayley and I took turns tapping each other below the knee, and each time our feet involuntarily lifted. We found out that this occurs as a way to allow humans to catch their balance: the contraction of the quads puts the torso back upright during a falling motion.
The blink reflex is the closing of the eyelids in response to a rapidly approaching object, whether it touches the eye or not. When I threw the cotton at Hayley, she not only blinked, but she flinched too. Same with when I pretended to punch her. ;) The reasoning for this reflex is so that no foreign objects get in the eye.
The plantar reflex is the clenching of your toes when something drags along the bottom of your foot. When Hayley dragged her pen across the sole of my foot, I not only giggled and squirmed as I am severely ticklish, but my toes also clenched inward. I think the reasoning for this is that when your foot feels the ground while you're running, your toes clench downward to allow for more grip on the ground to propel you forward in your run.
Our response time was the time it took to react to a stimulus, in this case, a falling ruler. Hayley had the faster average response time, at 0.20 seconds. However, after we introduced texting into the experiment, both of our reaction times slowed significantly, with hers slowing to 0.30 seconds. This is because it's extremely difficult to multitask and devote attention to both texting and catching the ruler.

Sheep Brain Dissection Analysis

My rendition of the surface of the brain.

The sheep brain before any incisions.

In this lab, we dissected a sheep's brain to observe the different sections of the brain and how they work in relation to each other. As we learned before, the brain is divided into different sections. By simply observing the surface of the brain, we can distinguish a few structures, including the cerebrum, which is the front parts of the brain, the cerebellum or bell-shaped lump near the back of the brain, and the brainstem, which protrudes out of the back and bottom of the cerebellum. The cerebrum controls higher brain function, such as thought and action. The cerebellum receives sensory information and regulates voluntary movement, like posture for example. The brain stem controls the flow of messages between the brain and the rest of the body, while also controlling basic bodily functions like breathing.

After making a longitudinal incision to sever the brain into two halves, the right and left hemispheres, even more structures became apparent. What looked like a mere chicken cutlet at first glance now became a complex and organized network of thoughts, each specialized part of the brain controlling its own important part of the sheep's life. Now we could see myelin layers, which appeared as a paler color than the surrounding brain tissue. You can clearly see a
tree-shaped branching bunch of myelin fibers in the cerebellum. Myelin acts as an insulator on the neurons to speed up the process of interpretation, which is why it concentrates in areas of the brain that require ultra-fast processing, like the cerebellum, which I thought looked a lot like cauliflower. We observed the corpus callosum, which was the only thing connecting the two hemispheres, allowing for communication between the two. This is what was severed in split brain patients. We also saw the midbrain, the collective of multiple structures involved with the central nervous system, vision, hearing, etc. Towards the front of the brain was the optic nerve, which transfers visual information from the retina to the brain. The first lump, going from the posterior to the anterior of the brain, was the pons, which controls breathing, communication, taste, hearing, balance and more. The next bump was the medula oblongata, the regulator of breathing, heart and blood vessel function, digestion, sneezing, and swallowing. In front of that was the thalamus, which correlates consciousness, sleep, and sensory interpretation, and then the hypothalamus, which connects the nervous system to the endocrine system through the pituitary gland and the hormones released from it. After making a cross sectional cut, we could see even more clearly the aforementioned myelin, whose presence created white matter. The darker brain matter is called grey matter.

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!