Moving our limbs seems like a relatively simple task. Whether it’s pickingupacupof tea or taking a walk, the process of movement appears instant and without much thought. However, beneath the skin, our skeletal muscle cells are undergoing an extensive process to simply lift a finger. Skeletalmuscleshangonour bones like biological babushka dolls: within each layer of the tissue smaller versions are revealed. At the core of each muscle fiber are rod structures called myofibrils. Within these filaments are two all-important proteins called actin and myosin. It’s their attraction to one another that is responsible for the contracting and relaxing of muscles. However, it’s only after a chain reaction of molecules is released throughout the tissue that the pair are allowed to come together. These proteins interact in what is known as the sliding filament model or theory. The actin and myosin, with the aid of released calcium and a molecule, called adenosine triphosphate (ATP), contract a section of the myofibrils called the sarcomere. When the calcium and ATP are used up the pair of proteins unbind, releasing the sarcomere from contraction and allowing the muscle to relax. As this cycle continues our muscles are able to animate our bodies. The collective tissue pulls the muscle together, then connective tissue called tendons, which grip the surrounding bone, follow suit. When the muscle contracts the two attached bones are pulled together and thus produce movement.
The heart is arguably one of the most important muscles in our body. Typically beating between 60 and 100 times a minute in an adult, it continuously contracts and relaxes to circulate blood around the body, without ever tiring. However, the structure of the cardiac muscle is unique to this vital organ. Though similar to skeletal muscle cells, cardiac cells are more extensively branched and connected via intercalated discs. These discs allow the cardiac muscle cells to move like a wave rather than in a linear motion as skeletal muscle cells do. This wave motion is what allows the heart to become a pump. Though there is a need for electrical impulses to cause contraction, heartbeats are controlled by the autonomic nervous system (ANS), whereby electrical signals activate muscle cells without conscious thought.
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