Unit 8 Reflection

This unit was primarily about the muscular system and the movements that we make. We began this unit by learning about the different synovial joint movements. Some movements that we went over included flexion, which decreases the angle between articulating bones, and extension, which increase the angle between articulating bones. We also learned the six synovial joints: plantar, hinge, pivot, condyloid, saddle, and ball and socket. I studied the ACL in the knee in particular when completing build a better joint project. Plantar joints are flat and slightly curved joints that are commonly found in feet. Hinge joints are convex surfaces where one bone fits into the concave of another. Pivot joints are rounded or pointed surface of one bone that articulates with a ring formed partly by a ligament. Condyloid joints are convex oval-shaped projections of one bone that fit into the concave oval-shaped depression of another bone. A saddle joint is when the articular surface of one bone is saddle-shaped, while the articular surface of the other bone fits into the saddle like a rider on a horse. A ball and socket joint is when a ball like surface of one joint fits into the cup like depression of another bone.

We also learned about the different properties of muscles and their functions. Muscles have four main functions: movement of bones and fluid, body posture and position, stabilizing joints, and heat generation. The properties of muscles are contractility, which is the ability to shorten when stimulated; excitability, which is the ability to receive and respond to stimuli; extensibility, which is the ability to be stretched; and elasticity, which is the ability to recoil to resting length. All muscles have at least one origin, which is the immovable end of a muscle, and one insertion, which is the end of the muscle that moves towards the origin. Muscles are classified by their function. The prime mover causes a desired action, while the anatagonist relaxes when the prime mover contracts. The synergist helps the prime mover by reducing unnecessary movements. Fixators help stabilize the origin of the prime mover. We also went over some commonly known muscles such as the biceps brachii, which flexes the elbow joint, and the triceps brachii, which extends the elbow joint. We were able to examine many of these muscles for ourselves when we did our chicken dissection.

Each muscle fiber is composed of myofibrils and sarcomeres. Muscles contract with the sliding filament theory. To signal a muscle contraction, nerves send impulses to the muscle fibers, resulting in Ca+ being released. The Ca+ binds to the receptors on the fiber, causing the myosin-binding sites to be open. The opening of these binding sites allows the myosin to slide the muscle into contraction, with the help of ATP. There are three different types of muscle fibers: Slow twitch, fast twitch a, and fast twitch b. Slow twitch fibers are generally found in long distance runners since they contract at a slower rate and can last longer. They are dependent on blood for oxygen and nutrients so they are red. Fast twitch a fibers contract at a much faster rate and are relatively fatigue resistant due to their relatively high blood flow capacity. On the other hand, fast twitch b fibers fatigue quickly because of their low blood flow capacity. When an individual exercises, their muscles can either go through hypertrophy, where cells increase in size/volume due to myofibrils, or hyperplasia, where cells remain the same size, but increase in number.

Muscle contractions are classified into four different groups. In concentric contractions, the muscle is actively shortening, while in eccentric contractions, the muscle is actively lengthening. Isometric contractions are when the muscle is actively held at a fixed length. An example of an isometric contraction is holding a plank. Lastly, passive stretching is when the muscle passively lengthens.

I want to learn more about what happens during a muscle cramp or twitch. I know that cramps have something to do with calcium, so maybe they occur due to low levels of calcium during a muscle contraction, causing the whole muscle to get stuck in a contraction. I have grown as a student through the different activities and labs that we do in class. For example, through the chicken dissection, I was able to identify different muscles on an actual chicken that I eat on a regular basis. It really showed me the complexities of something that seems so simple. I have been doing a good job in one half on my new years goal in that I have really been relating what I am learning to my everyday life. This whole unit has helped me understand my own body better and the reasons behind some of my physical therapy exercises. I am also doing pretty well on the eating healthier part of my goal. I think that will be very important for me as I continue recovering from my knee surgery. And of course I am still unable to move around well so the exercising part of my goal will probably have to be taken out.