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!

"The Woman Perpetually Falling..."

In the excerpt "The Woman Perpetually Falling..." from Norman Doidge's book The Brain that Changes Itself, a woman named Cheryl suffers from a severely debilitating vestibular disequilibrium symptoms, brought upon by a prolonged use of the drug gentamicin. This drug is known to be harmful, but is used anyway because it is cheap and effective. This highlights a dangerous conundrum: use cheap and easily attainable medicine, or ensure the safety of patients even if it sends them into a deep debt? Cheryl only has 2% function of her vestibular system, which is responsible for regulating the sense of balance. It is comprised of 3 semicircular canals that send signals of changing external situations, such as a tilting head, so the body can adjust accordingly. Without this system, Cheryl feels as though she is constantly falling, her body weighed down with the added gravity of her condition. In addition to this seemingly physical weight, her mind is constantly exhausted and overworked. Since she is always focused on not falling, her mental capacity has no room for seemingly mundane tasks such as memory, thinking, etc. However, a doctor presents a remarkable solution: "a construction hat with holes in the side and a device inside it called an accelerometer" (5). This deceivingly simple device changes Cheryl's life, allowing her to finally feel normal for the first time in 5 years. I was moved by her shift in demeanor after she experiences stability, when she "starts clowning and showing off" (9). It is as if she can finally be herself, free of the mental and physical symptoms holding her back. This truly shows the correlation between physical health and mental health. Additionally, I was saddened by her disappointment when the effects wore off, describing herself as "tired, exhausted... depressed" (9). This resonated with me as she reverted back to her pain-ridden self, having experienced normality to only recede into her former shell. Thankfully, Cheryl's use of the accelerometer caused the symptoms to disappear completely, giving her life back.

The Clay Brain Lab

In this lab, we created two models of different viewpoints of the brain: the right cerebral hemisphere view and the left hemisphere along the sagittal plane. We used different colors of Play-Doh to represent different parts of the brain, creating a colorful visual model of the locations of parts of the brain. For example, we used orange to represent the frontal lobe on the right cerebral hemisphere.

"The Woman With a Hole in Her Brain"

The newscientist.com article, "The Woman With a Hole in Her Brain" by Helen Thomson, describes a Chinese woman's remarkable survival without an entire cerebellum. Her condition led to only motor deficiency and speech problems, and she has surprisingly survived past the age of 24. The cerebellum is responsible for controlling voluntary movement and balance, as well as other motor functions like speech. Most patients with this condition pass away at an early age, which makes this woman's survival even more exceptional. Doctors say other parts of her brain, such as the cortex, are compensating for the absence of the cerebellum by taking over its functions.

What would happen if someone were born without, say, a pons? The pons relays signals from the forebrain to the cerebellum. It also contains nuclei that regulate sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture. Without a pons, the brain could not function even basically, as no information would be transmitted. So no, a person cannot survive without a pons. 

Unit 5 Reflection

The folds in the small intestine, which increase surface area

for better absorption.

This unit was focused on a few major organ systems in the body: the digestive system, the endocrine system, and the lymphatic system. Each system is interestingly interconnected. The digestive system consists of the mouth, pharynx, esophagus, stomach, appendix, small intestine (duodenum, jejunum, to ileum), the large intestine (ascending colon, transverse colon, to descending colon), rectum, and anus, traveling through those organs respectively. This pathway is the alimentary canal. The digestive system consists of digestion and absorption, digestion being the mechanical and physical breakdown of food through various processes. These can include peristalsis, which is the contraction movements of the esophagus, stomach walls contracting, chemical changes in the acidic stomach, and digestive juices/enzymes in the small intestine. Absorption is the absorbing of the broken down nutrients into the blood stream. This occurs due to the many folds in the small and large intestines, which are actually over 28 feet! We explored the surprising length of the intestines in our lab, which I debriefed here.

We also learned about fuel metabolism, which changes depending on what state your body is in. If you have just eaten, you are in the fed state, and the sugars you absorbed in the digestive system travel to the liver, where they are converted into glycogen. The pancreas releases insulin to stop the release of glucagon. The amino acids, fatty acids, and glucose are sent to body cells to be stored as adipose tissue. If a person consumes and does not expend the energy stored in the form of fat, said fat will accumulate, causing obesity. Obesity can lead to many health complications, one of which is diabetes. Diabetes is a disruption in fuel metabolism. Diabetes can be one of two forms: Type I diabetes or Type II. Type I occurs when insulin is not correctly produced by the body, and those who are diagnosed are dependent on insulin shots. Insulin is a hormone that allows glucose to be absorbed into cells, triggering the migration of Glut4 receptors to the outside of the cell membrane, which allow glucose to enter the cell. This only affects 5-10% of all people with diabetes. The more common form of diabetes is Type II, which occurs when the body is insulin-resistant, meaning that insulin's intended effects do not work in the body. If not correctly managed, diabetes can be deadly. My grandfather had Type II diabetes, and my brother was pre diabetic until he changed his lifestyle.

Insulin's effect on Glut4 receptors in cells. Exercise also
triggers the movement of the Glut4 receptors.

The main struggle I had this unit was missing the Fuel Metabolism lecture. The printed handout had run out by the time I went to get one, so I had to write the whole thing by hand, which muddled the information, and also meant I don't have some diagrams in my notebook. I also realized that it was incredibly complex, and I am still slightly confused on exactly what some terms mean. In regards to my New Year goals, I am doing mas o menos. I completely forgot that we had a temp check, and at that point I still had not done my Fuel Metabolism notes, so that went poorly. I wish I had taken initiative and done them earlier. However, I am eating much healthier, and I've eliminated my snacking habit. Now I stick to my 3 wholesome meals a day, with one small snack before I go to work. Having a job and being a second semester senior is a catch 22; now that it is competition season, I have increasing obligations and commitments to my students, (including rhinestoning over 45 costumes...) and I have to continue to do well in school while juggling changing social aspects.