For muscles to contract, the muscle fiber creates tension within itself. This tension is brought up by the action of myosin and actin cross-bridging sequence. Contraction in muscles generally means the generation of tension by the muscles with the help of neurons (Starr, Beverly 108). “The sliding-filament theory of muscle action” explains the movement of filaments resulting in relaxation and contraction of muscles. There are two types of filaments in the muscles; the thin filaments and the thick filaments. A group of overlapping thick and thin filaments forms up the sarcomeres. The thin and the thick filaments in the sarcomeres glide over one another which shortens the length of the sarcomere (Starr, Beverly 108). The heads of the myosin interact with the filaments of the actin causing them to slip over each other.
Myosins utilize energy in the form of ATP in bending and pulling the actin causing the muscle to contract. This is a six-step process that starts with the intake of calcium ions by the myosin resulting in the exposure of binding sites on myosin. Once the binding sites are exposed, myosin binds to actin in order for sliding to take place. The myosin is full of energy in the form of ATP at this point. The third step involves myosin grabbing actin and pulling it generally known as power stroke. The next step begins with ATP binding. At this stage, myosin is deficient in energy. More ATP is bound to myosin head. This ATP will be utilized in the next power stroke. This is followed by ATP hydrolysis to release energy in the myosin. This gives myosin a high-energy state. The final stage involves the transfer of calcium ions into the sarcoplasmic reticulum (SR). This happens at the end of signaling from the nervous system that causes muscles to contract. At this point, calcium is taken back to the SR. The muscle relaxes stopping the contraction of the muscle. The above process repeats itself causing contraction and relaxation of the muscles.
ATP is very important in muscle contraction. Muscles require a lot of energy for contraction. ATP is a product of the breakdown of food substances. The amount of ATP stored in the muscles is not enough for contraction processes. This problem is conquered by the conversion of creatine phosphate groups to ADP and finally ATP, which is found in the muscles (Starr, Beverly 112). The ATP formed is used as a source of energy for the contractions. The creatine phosphate in the muscles is sufficient to complement ATP provision before it is provided via respiration and glycolysis in the muscle cells once oxygen is available. “Muscles breakdown glucose releasing energy in the presence of oxygen, this process is called aerobic respiration” (Starr, Beverly 112). In the absence of oxygen supply from the lungs to the muscle tissue, oxygen is supplied from the oxygenated myoglobin. This is a protein that stores oxygen. The muscles, therefore, have their oxygen storage. ATP is thus very important in the determination of the characteristic expansion and contraction of the muscles. ATP determines how long the muscle will hold a contraction, how far the contraction will go, and the force that will accompany the contraction. This explains why muscles suffer from fatigue if the glycogen and oxygen stored in the muscles are used up. Extreme fatigue happens when the anaerobic breakdown of food takes place in the muscles to release ATP. This is normally due to the accumulation of lactic acid generated by anaerobic respiration in the muscle tissues.
Works Cited
Starr, Cecie, and Beverly McMillan. Human Biology. 9th ed. Stamford, Connecticut, U.S.: Cengage Learning. 2012. Print.