What Happens When You Stretch?

For homework, I read an article called "What Happens When You Stretch."

When a muscle is stretched, it is the sarcomere (basic unit of contraction in a muscle fiber) that stretches first. Then, after all the sarcomeres in a muscle are fully stretched, the connective tissue around the muscle start to stretch also. Fibers in the connective tissue line up along the force of tension, realigning any disorganized fibers -- I have heard something along these lines before, and it's nice to have than information confirmed. Stretching affects many different parts of the muscles from  intrafusal muscle fibers (those that contain myofibrils) to extrafusal muscle fibers (muscle spindles) to
proprioceptors (mechanoreceptros, or nerve endings from the muscular system). All these different parts of a muscle -- and different parts of those parts -- interact to create the stretch reflex, which tries to resist the muscle lengthening, and the lengthening reflex, which occurs when the stretching passes a certain point and stops the stretched muscle from contracting. The article also talks about how stretching can be made more effective by contracting the opposites and relaxing the synergists of the muscle being stretched. This explains why when we do certain stretches in certain ways, for example keeping our leg straight when we stretch our quads.

I chose 3 phrases that I felt held the most meaning:

• "[Stretching] helps to realign any disorganized fibers in the direction of the tension. This realignment is what helps to rehabilitate scarred tissue."
• I remember hearing about this a long time ago, but never really found out if it was true until now. I also find it interesting that stretching can help rehabilitate scarred tissue -- does that mean people with damaged muscles can do stretches to help them heal?
• "Some sources suggest that with extensive training, the stretch reflex of certain muscles can be controlled so that there is little or no reflex contraction in response to a sudden stretch."
• It's interesting to me that reflexes can be trained out of somebody. I have heard of certain responses being conditioned into people, but I didn't know you could condition an innate response out of someone. However, this also sounds a bit dangerous, since the reflex of a muscle to contract is there to stop the muscle from overstretching and becoming damaged, and removing it seems like a bad idea (nature has gone through all this trouble to make sure it's there in the first place, so it's probably quite important).
• "[Y]ou can get a more effective stretch by inducing the antagonists to relax during the stretch due to the contraction of the agonists. You also want to relax any muscles used as synergists by the muscle you are trying to stretch."
• This explains why we do certain stretches certain ways, and why coaches and PE teachers are so adamant that you follow their directions in stretches. It also explains why a stretch done properly "feels better" than one that is not done well.

Saving Endangered Species: 20 Time Project, Week 2

Last week we started our 20 Time projects. 20 Time is when a teacher gives about 20% of his or her class time for his or her students to pursue their own projects that interest them. My 20 Time project is on endangered species, specifically, which endangered species are extremely important to the ecosystem (keystone species), yet are not well known, and how can I raise awareness about these species?

To answer these questions, I want to build a website where I talk about various endangered species in order to raise awareness about them. I also want to design t-shirts for each species, which I can also use to raise awareness as well as raise funds to donate to organizations that help endangered species.

Every week, I want to research a new organism, create a page for it on my website, and create a new t-shirt design for it. I will measure my progress by how many webpages I create, how many people visit my website, and eventually how many people buy my t-shirts.

Unit 6 Reflection: The Skeletal System

In this unit, we learned about the skeletal system. The essential questions from this unit were:

• What are the microscopic and macroscopic characteristics of the skeletal system?
• How do disorders of the skeletal system affect different types or parts of bones?
• What are the effects of vitamins, cells, and the environment on bone density?
• How does a bone repair itself after being fractured?
• What are the defining characteristics of different types of joints?

The macroscopic features of bones include the diaphysis (shaft), which surrounds a hollow medullary cavity, and the proximal and distal epiphyses (flared ends). Compact, or cortical bone, is the smooth, dense bone, while spongy bone is more porous, with cross-hatching supports called trabeculae that help the bone resist stress. There are also two types of bone marrow stored in the bones: red, which produces blood cells and is found in spongy bone, and yellow, which stores energy as fat and is found in the medullary cavity.

At the microscopic level, osteons are what make up bone. They are cylinder-shaped weight-bearing units that run parallel to a bone's axis. They are made of tubes within tubes called lamellae between which are tiny spaces called lacunae, which hold osteocytes (mature bone cells that maintain bone). They also have a central canal that holds nerves and blood vessels to support all of the cells in the bone.

anatomy of a bone (Wikipedia)

Bones are assembled into skeletons, which can be divided into the axial and appendicular skeleton. The axial skeleton is made of the bones along the axis of a body: skull, ribs, sternum, and vertebrae. The appendicular skeleton includes all the rest of the bones, which are attached to the axial skeleton. Bones can also be classified by shape: long, short, flat, and irregular. To help us learn about the skeleton, we did a lab where we dissected an owl pellet, classified the bones we found in it, and tried to assemble them into a skeleton.

Contrary to popular belief, bones do not require just calcium to grow. They also need vitamin K, which can be found in animal-based foods, and vitamin D, which the skin can make when exposed to sunlight. Vitamin D is especially important, since it is needed to absorb calcium so that the calcium can be used to make bones stronger. Severe vitamin D deficiency can lead to rickets, the softening of bones to the point where they may become crooked. Lack of calcium can exacerbate osteoporosis, where the bones become more porous and brittle.

Bone fractures can be classified into many different types. A greenstick, or incomplete, fracture occurs when the bone does not break all the way through. A fissured, or hairline, fracture is a incomplete fracture along the axis of the bone. A comminuted fracture is when the bone breaks into three or more pieces. A transverse fracture crosses a bone perpendicular to its axis, an oblique fracture crosses a bone at an angle, and a spiral fracture occurs when a large twisting force breaks the bone. Simple, or closed, fractures are those that do not puncture the skin, whereas compound, or open, fractures are when the end(s) of the fractured bone(s) break the skin.

After a bone breaks, bone cells called osteoclasts, which build up new bone, and osteoblasts, which break down old bone can repair the bone. Osteoclasts and osteoblasts are also used in bone remodeling, such as when a bone is growing.

 

bone remodeling

Bones attach together at joints, which can be classified by function (syn-, amphi-, and di-arthroses) or by structure (fibrous, cartilagenous, and synovial). Synarthroses are immoveable, amphiarthroses are slightly moveable, and diarthroses are freely moveable. When most people think about joints, like the elbow or the knee, they are thinking about synovial joints, which are diarthrotic. Sutures in the skull are an example of a fibrous synarthrotic joint.

I learned a lot of new things this unit, but there are still a few things I wonder about. For example, if the bone marrow in the medullary cavity is just fat, then is the bone marrow fancy restaurants serve really just fat? What happens to the bone marrow of starving people? Does the body utilize the energy stored in the fat there, and what does this mean for the bones? I would also be interested in learning more in detail about the other types of joints, not just synovial joints.

So far, I have been reaching my New Year's goals of getting eight hours of sleep everyday and not procrastinating on studying for my tests. I hope to continue to keep fulfilling these goals throughout the rest of the year.

2016.02.22 Owl Pellet Lab

Today we dissected an owl pellet to study the bones inside. Using a probe and forceps, we broke apart an owl pellet, separated the bones from the fur, categorized them, then tried to identify the organism that was in the pellet.

our owl pellet

After studying the bones in our owl pellet, we concluded that the organism in our pellet was a shrew. We determined by comparing our bones with an identification chart. In particular, we used the skull, mandible, and tibia and fibula to determine that our organism was a shrew. Our organism's skull and mandible resembled the skull and mandible of the shrew in the diagram; furthermore, the skull was 14 mm long and the mandible was 10 mm long, the average lengths of a shrew's skull and mandible. Also, the fused-together tibia and fibula (bottom-right-most bone in the picture on the right below) resembled the tibia and fibula of the shrew in the identification chart.

some bones from the pellet

bones sorted in a chart

Compared to a human skeleton, our shrew skeleton had the same basic parts: skull, vertebral column, ribs, and limbs. These bones all fit in pretty much the same way, and they all perform the same function a human's skeleton does. Some of the bones, like the skull, are made of several fused-together parts, just like a human's.

However, compared to a human skeleton, a shrew skeleton has many differences. For example, the skull and mandible of a shrew are shaped very differently from the skull and mandible of a human. Also, a shrew's pelvis is shaped very differently from a human's (it is longer), since a shrew crawls around on all four feet while a human walks upright. A shrew's tibia and fibula are fused together, where as a human's tibia and fibula are separate bones.

Unit 5 Reflection: The Digestive, Endocrine, and Lymphatic Systems

In this unit, we learned about the digestive, endocrine, and lymphatic systems. The essential questions for this unit were:

• How are the functions of the digestive system fulfilled by the structures of the alimentary canal and accessory digestive organs?
• How does the body use certain molecules and biochemical pathways to meet its energy demands?
• How is diabetes a disruption in fuel metabolism?
• How do glands use hormones to control various activities of the body?
• What is the role of the lymphatic structures in the body's defenses and circulation?

The digestive system consists of the alimentary canal (also known as the gastrointestinal track), a long, coiled tube that runs through the body and is open at both ends, and the accessory organs to the alimnetary canal. The organs of the alimentary canal are, in order, the mouth, pharynx, esophagus, stomach, small intestine, large intestine, anal canal, and anus. These organs either digest (break down) food or absorb (take in) nutrients from the food. Assisting them are the liver, gallbladder, and pancreas, which make and store enzyme that help with digestion.

the digestive system (Wikipedia)

The endocrine system is the system of glands in the body that release hormones that affect the body. Hormones can be steroid (lipid-soluble) or non-steroid (non-lipid-soluble) and act like "keys" to "unlock" a certain result or action from a cell. The many glands of the endocrine system include the pituitary, thyroid, parathyroid, and adrenal glands and the pancreas. Each one releases one or more different hormones that regulate different parts of the body.

the endocrine system (Wikipedia)

The lymphatic system is a system of vessels that run parallel to the circulatory system's blood vessels and contain a plasma-like fluid call lymph. This lymph comes from liquid lost by the circulatory system or from tissues, and the lymphatic system's job is to return it to the circulatory system. The lymphatic system is also very closely related to the immune system, as there are areas where lymph vessels congregate, called lymph nodes, which host a huge number of immune cells, ready to attack any foreign invader that might be in the lymph. The lymphatic system also includes the thymus, tonsils, and spleen, which are also involved in the immune response.

the lymphatic system (Wikipedia)

One of the themes of this unit is balance. One of the systems we learned about, the endocrine system, is especially all about balance. It makes sure that there is enough of each hormone in the bloodstream at any given time so that homeostasis is properly maintained. The hormones released by the glands of the endocrine system can regulate fluid retention, metabolism, protein synthesis, mineral levels in the skeletal system, heart rate, blood pressure, respiration, and many more. If this delicate hormone balance is upset, it can spell disaster for the body. In this unit we also learned about diabetes, which occurs when the body cannot properly regulate the level of glucose in the bloodstream. This may be because the body cannot produce insulin (type I diabetes) or because the body stops responding to insulin (type II diabetes).

During this unit, we did one lab, the digestive system lab. I thought the lab was very interesting, since it let me see firsthand just how long the digestive system really is. I had always known that the digestive system is very long in the way that one knows a strand of DNA is long, but doesn't actually realize it until one holds it in one's hand.

I would have loved to learn more about the lymphatic system, which most people don't know much about. I am also interested in the different hormones of the endocrine system and how exactly they affect different parts of the body.

At the beginning of this semester I set some New Year's goals, which were to get more sleep and to study for exams earlier. So far, I have gotten more sleep but not as much as I had wanted to (8 hours). However, I am reviewing the material I have learned every day, accomplishing my second goal. I will continue to work on my first goal and hopefully reach it by the deadline I set for myself (February).

2016.01.05 Digestive System Lab

Today, we made a measured the length of our digestive system. The main organs of the digestive system are the mouth, the esophagus, the stomach, and the small and large intestines. We used different colors of ribbon to represent each organ in the digestive system. I chose blue ribbon to represent the mouth, green to represent the esophagus, pink to represent the stomach, white string to represent the small intestine, and red to represent the large intestine. Then I tied all the pieces together, resulting in a very long string, representing the length of my digestive system.

lengths and color of strings I used

all the string I used

The length of my digestive system turned out to be 8.336 meters. In comparison, my height is 1.524 meters, which means that my digestive system is almost 6 times my height. In order to fit such a long organ system in my body, it must be folded over and over again (especially the small intestine, which is the longest organ in the digestive system).

I though that it takes about 2 days for food to move through the entire digestive system. After searching online, I found that it takes a little less than 2 days (30-40 hours) for food to move through the entire digestive system, which is pretty close. Factors such as the composition of the food, gender, and stress levels all can affect the amount of time it takes for food to move through the digestive tract.

Digestion is the breaking down of food into little pieces (nutrients), while absorption is the taking in of these nutrients by the body. Digestion occurs in the mouth and stomach, while it is the intestines that absorb nutrients from the digested food.

New Year's Goals

I have set some goals for 2016:

• I will get at least 8 hours of sleep everyday. To do this, I will manage my time better, such as by allocating a specific amount of time for everything I do, so that I do not waste any time and have more time to sleep. I will achieve this goal within by February.
• I will start studying for tests earlier. After every class, I will review what I have just learned, instead of just studying for tests the night before. This will allow me to retain information better, as well as give me less exam-related stress. Next time I have an exam, I won't be cramming, and I won't be losing any sleep by staying up later to study for a test.

Sheep Heart Dissection Video Tutorial

After we finished our sheep heart dissection, we made a video explaining the parts of the heart, their functions, how the blood flows through the heart, and how the heart beats. The video is below and can also be found on YouTube here and here:

2015.11.01 Sheep Heart Dissection

Today we dissected a sheep's heart. We were able to observe all the structures on the outside and inside the heart. As we studied the heart we answered questions that our teacher gave to us. The answers are below, and the question numbers are in parentheses ().

On the outside of the heart is the pericardium, a two-layered membrane sac that protects the heart and secretes a fluid that lubricates the heart to reduce friction. It also keeps the heart together as it continuously contracts and relaxes (1).

There are many blood vessels that connect to the heart. Blood vessels that take blood from the heart to the body are called arteries. Blood vessels that take blood from the body to the heart are called veins. Arteries are more elastic than veins, and their walls are thicker and contain more smooth muscle than the walls of veins. This lets the arteries expand and contract under the pressure that the heart exerts against the artery walls as it pumps blood (2).

The inside of the heart is divided into four chambers, two atria and two ventricles. The four chambers are divided into left and right. Each side (left or right) has one atrium and one ventricle. The right side of the heart pumps blood only to the lungs, so it is not as large and muscular as the left side of the heart, which pumps blood to the whole body. The right side of the heart contains deoxygenated blood, while the left side of the heart contains oxygenated blood (12).

The atria are the superior chambers that receives blood from the veins and pumps it into the ventricles. On top of each atrium is a dogear-like pouch that increases the blood volume of the atria so they can receive more blood from the veins (3). Since the atria only have to pump blood to the ventricles, their walls are not as thick and muscular as the walls of the ventricles, which have to pump blood to the lungs or to the whole body (4).

The atria are separated from the ventricles by atrioventricular valves, which prevent blood in the ventricles from flowing back into the atria when the ventricles contract. The atrioventricular valves, which are the tricuspid and bicuspid (mitral) valves, are "anchored" by the chordae tendinae, which are long fibers that trail off the valve, and the papillary muscle, which attach the chordae tendinae to the wall of the ventricle. This makes sure the valves close properly and keeps the valves from swinging backwards into the atria so that blood does not leak backwards into the atria. If valves are not anchored properly, blood could leak backwards instead of going where it needs to go, which could cause health problems like fatigue, swelling, or heart palpitations (irregular heartbeat) (7).

drawing of the tricuspid valve, showing the chordae tendinae and papillary muscle (6)

drawing of the bicuspid (mitral) valve, showing the chordae tendinae and papillary muscle (8)

The semilunar valves are the valves that separate the ventricles from the arteries that leave the heart. Just like the atrioventricular valves, they prevent blood from flowing backwards. The semilunar valves prevent blood flow back into the ventricles and keeps the blood flowing in the arteries away from the heart (9).

drawing of aortic semilunar valve (11)

Valve failure on different sides of the heart has different effects. If valvular heart disease occurs on the right side of the heart, swelling in the feet and ankles occurs because blood that is pumped into the right ventricle by the right atrium does not stay in the right ventricle. Instead, it flows back into the right atrium, backing up the blood flow and not letting blood from the body flow into the right atrium. As a result, blood collects in the feet and ankles, causing them to swell up (10a).

If valvular heart disease occurs on the left side of the heart, the body would not be able to get as much blood. Body cells would not get as much oxygen, which would cause fatigue. This is because blood in the aorta that is supposed to be pumped to the body by the left ventricle instead flows back into the left ventricle and does not go to the body (10b).

At the very end of the dissection, we made a frontal cut through the heart to separate the anterior (front) and posterior (back) sides. This way we were able to see all the structures inside the heart.

drawing of interior of heart (13)

Unit 3 Reflection: The Circulatory System

Unit 3 was about the circulatory system and the respiratory system. The essential questions of this unit included:

• What are the major features of the circulatory system?
• What are the structures of the heart and their functions?
• What are the (dys)functions of the blood vessels?
• What are the different components of blood and what are their functions?
• What are heart attacks and strokes? What causes them, how are they identified, and how are they treated?
• What are the functions of the respiratory system?

The circulatory system is a fluid-filled network of tubes throughout the body. It is made of several major components: the heart, which pumps the fluid through the system; the blood vessels, which carry the fluid through the system; and the blood, which is the actual fluid. There are also several accessory organs to the circulatory system: the lungs, which exchange carbon dioxide in the blood for oxygen; the kidneys, which remove excess waste and water from the blood; and the intestines, which absorb nutrients and water from digested food into the blood.

We learned about different parts of the heart in detail in this unit. To help us learn about the heart's structure, we went outside, drew a diagram of the heart on the ground, and made a video explaining the path a red blood cell takes through the heart.

Our diagram (top) and video (left) of the heart

I also drew a diagram of the heart by myself to help me learn about the heart. This was after we had learned more about the structures of the heart and their functions, so it is more accurate (the papillary muscle in the above diagram is incorrectly labeled).

my diagram of the heart

All this drawing of the heart helped us prepare for our sheep's heart dissection, which was very interesting and let us see what an actual heart looked like. There was some fat on the heart, which we did not really expect because diagrams of the heart don't really depict fat, and the anatomy of the heart was a little bit different since it wasn't a human heart.

anterior (front) view of sheep's heart (where's the inferior vena cava!?)

heart cut lengthwise (the way most heart diagrams are drawn)

We also learned about blood vessels. There are three main kinds of blood vessels: arteries, which take blood from the heart to the body; veins which take blood from the body to the heart; and capillaries, which connect the two. Arteries are the ones that expand and contract as the heart beats (this is how you feel you pulse). Veins have valves in them that prevent blood from flowing backwards (e.g. blood in your leg has to flow against gravity to get back to your heart). The capillaries are where the exchange of nutrients, wastes, and gasses actually occur.

In the blood vessels flow the blood, which is made of plasma and cells. Plasma itself is made of water and dissolved solutes. Blood cells include red blood cells, which carry oxygen, and white blood cells, which are part of our immune system and help fight infections. There are many different kinds of white blood cells, including neutrophils, basophils, eosinophils, lymphocytes (B-cells and T-cells), and monocytes (which mature into macrophages). Blood also contains platelets, which help the blood clot if you get cut.

What we learned about heart diseases tied into our past unit about health. Mostly we learned about atherosclerosis (the buildup of plaque, or fatty material, in the blood vessels) and aneurysms (the weakening of a blood vessel wall due to blood getting in between the layers of the wall and making it swell up). Atherosclerosis is caused by chronic inflammation; excess sugars, omega-6, and LDL ("bad") cholesterol; and too little HDL ("good") cholesterol. When little microtears form in the blood vessel wall, this excess LDL becomes stuck in the wall. If there is too little HDL to clean it up, white blood cells think that the body is under attack, come to engulf the LDL, and become stuck as well. This forms a plaque in the artery that restricts blood flow. A blood clot can form around the plaque and cut off blood flow entirely. If this happens in a coronary artery that provides blood to the heart muscle, it is called a heart attack. If this happens in the brain, it is called a stroke (strokes can also be caused by aneurysms). Good nutrition lowers your risk of atherosclerosis (since atherosclerosis is caused by excess sugars, omega-6, and LDL) and therefore the diseases associated with it. Exercising, managing stress, and controlling your weight also prevents atherosclerosis.

We also learned about the respiratory system, since it is connected to the circulatory system (oxygen-poor blood is pumped from the heart to the lungs to exchange carbon dioxide for oxygen, then returns back to the heart to be pumped to the rest of the body). Air enters the respiratory system through the nose, then travels down the pharynx (throat), larynx (voice box), trachea (windpipe), bronchus, broncial branches, and finally into the lungs. The lungs themselves are made of tiny air sacs called alveoli, which are covered with capillaries and are where the actually gas exchange takes place. Breathing in occurs when the diaphragm contracts and flattens out from its relaxed, curving-upward state (this is interesting; I didn't know about how the diaphragm actually moved down before), and the intercostals (muscles between the ribs) contract and pull the ribcage out.

This unit was a pretty good unit for me, since I understood what was taught in class. I felt more comfortable with this unit's material than with last unit's on health; I suppose I am better at learning about the larger things that I can see and feel than I am at learning about the little things that I can't really see for myself. The active studying method that we discussed in class also helped, especially relating concepts to each other by drawing concept maps.

active studying

 Last unit we made a chart of health goals. My goals were to:

• eat seafood at least three times a week.
• exercise at least three times a week.
• sleep at least eight hours every day.

So far, I have achieved the eating and the exercise goals. These were pretty easy since my whole family likes to eat seafood, and whenever I wanted to exercise I would just go run with my friends on the cross-country team. However, now that the cross-country season is over, I need to find time during the weekends to exercise with my family or convince some friends to run with me after school (most of them don't really want to run after the season is over), since I don't like to exercise alone. I also have to work harder on getting eight hours of sleep daily. I get eight hours of sleep during the weekends now, but sometimes during the weekdays I stay up later doing homework. I can manage my time better and spend less time lying around so that I can finish my homework earlier and go to sleep earlier.