Unit 8 Reflection

We ended last unit, the skeletal system, talking about joints. We had a nice transition to this unit, the muscular system, by beginning with synovial joints and their different movements, including gliding, angular, rotation, and special movements. In addition to different types of movement, there are also different types of synovial joints. These are planar, hinge, pivot, condyloid, saddle, and ball and socket joints. Examples of those would be the carpals in the wrist, the knee, the neck, the fingertips, the thumb, and the hip, respectively.

We then transitioned into learning about muscles, beginning with their basic characteristics. Muscles have many different purposes, such as maintaining posture, moving bones, stabilizing joints, and generating heat. As we learned earlier in the year (It feels like just yesterday), muscles can be classified as smooth, skeletal, or cardiac. Smooth movement generally controls involuntary movement, while skeletal controls voluntary movement. Cardiac muscle is located in the heart. Muscles must have one or a combination of these characteristics: contractibility, extensibility, elasticity, and excitability. Fascia holds the muscle together by wrapping around each muscle fiber as well as bundles of fibers, and finally surrounding the entire muscle. A muscle is anchored at its origin site. It stays still and while the rest of the muscle moves so that the insertion side can contract towards the origin site. Muscles work conversely: when one muscle contracts, another must relax. The contracting muscle is called the prime mover, and the relaxing muscle is the antagonist. The English Major in me likes that name. In addition to these two muscles, a synergist muscle works to prevent unnecessary movements, while fixator muscles anchor and stabilize the site of origin of the prime mover. Muscles are characterized and classified according to their location and their function. 

In order to understand how muscles worked, we needed to examine them on a microscopic level. This is the most remarkable part about muscles. Let us go in order from larger to smaller. The whole muscle is made up of muscle fibers, also known as myofibrils, which are comprised of sarcomeres. Within each sarcomere, there are two protein filaments, actin and myosin, that are arranged to overlap. These sarcomeres contract as individual units, causing the entire muscle to contract also. The process of muscle contraction is as follows: a motor neuron sends an action potential to the muscle, which stimulates the release of Acetylcholine, which then binds to the receptors located on the muscle membrane. This activates a second action potential, which triggers the release of Ca2+, which attaches to troponin on a TT complex, changing its shape. By changing the shape, the TT complex can pull away from the myosin-binding site on the actin, and ATP attaches to the head of the myosin. When the ATP splits into ADP and P, which energizes the head and makes it swing forward in an energized state. The P detaches so that the head can reattach to the myosin-binding site on the actin. When the ADP detaches, the head returns to a resting state and swings backward. This continues until the action potential stops and CA2+ is no longer being released. 

When we exercise, our muscles utilize different types of twitch fibers. These are the slow twitch, fast twitch a, and fast twitch b. The slow twitch is dependent on oxygen and stores little glycogen, and it is red in color. It is the slowest to fatigue, which makes it effective for long exercise. Fast twitch a fibers are also oxygen dependant, but they store a lot of glycogen and are pink in color. Fast twitch b fibers require no oxygen and therefore need no blood vessels, which is why they are white in color. These are helpful for short, intense bursts of exercise. Examine the effects of stretching on muscles in this analysis of an article that I did previously, here.

My personal favorite of this unit was learning about muscles on a microscopic level. I had no idea that these sarcomeres even existed. It was pretty mindblowing to learn about. Our bodies are like little factories! In other personal news, 20 Time is coming to a close, which is a bittersweet ending to a very enjoyable project. Hayley and I had a lot of fun despite our rocky start. We are in contact with a non-profit who would be delighted to receive our donation. My heart is happy that we are raising awareness and providing help to a cause very dear to me. My New Years Goals have been going okay in regards to school, however, I am still missing the Chicken Dissection Lab, but I plan on making that up with Hayley soon. 

Works Cited
https://upload.wikimedia.org/wikipedia/commons/thumb/6/6e/Sarcomere.svg/500px-Sarcomere.svg.png
https://en.wikipedia.org/wiki/Muscle_contraction