The human body is very interesting. In muscles you could spend a least 5 or ten minutes just explaining what something is and what it is made up of. At least that it how a muscle is. A muscle is broken up into compartments. The whole muscle is surround by the Epimysium. Inside, there are sections of muscles surrounded by the Perimysium. Inside that, are the single muscle fibers. In between the fibers there is the Endomysium. All of which help the muscle to form bundles, making it stronger. But why are these bundles able to contract and ultimately get shorter in length? This is because each fiber is made out of individual strands called myofibrils. The myofibrils are striped. They have a Dark area called the A band and a light area called the I band. In the whole thing there are thick and thin filaments.
A section holding both from z disc to z disc is called a sarcomere. The main thing that causes movement is the sarcomere. The thick filament contain ATP which is needed for contraction and the thin filament is made of material that helps keep the myosin heads binding to only the active site. The form is so important because it makes sure that the body is able to move and then reset to move again and so forth so there isn't something happening out of place.
There are multiple steps that happen in nanoseconds to create movement in the muscle. The motor neuron generates an action potential. It then releases Acetylcholine (ACh) which crosses the synapse and binds to it receptors on the sarcolemma. Temporarily the sarcolemma becomes more permeable so that Sodium can rush into the cell and Potassium can rush out. This change in electrical current causes the action potential to travel to the T-Tubule. Next Calcium leaves the Sarcoplasmic Reticulum and goes into the cytoplasm. The Calcium ends up binding to troponin, which then changes shape. The Shape change causes the Tropomyosin to move off of the binding sites on the actin. This draw in the myosin heads to bind to the actin. And the muscle contracts due to the sliding filament theory which has the myosin heads pull the actin together. This process is fast but as it goes, it requires energy. It requires ATP in the Sodium Potassium pump, the cocking myosin heads and when the muscle resets and the crossbridge detaches. So therefore there has to be a way to get energy to go through this process. There are multiple ways get energy. One process is called glycolysis. This process occurs in the cytoplasm and doesn't require oxygen. It breaks down glucose into pyruvic acid. There is also the Krebs cycle that is a process that goes from ATP or adenosine triphosphate to ADP or adenosine diphosphate. This cycle and electron transport chain can produce 36 ATP but it is slow and require oxygen. What is most important about all these processes is that in all of them there it is a cycle. That means that the body will never change how it gets energy and wont run out of material to do so because it recycles the material.
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