Parts of a Sarcomere

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Describe all the parts of a sarcomere and their respective functions. The parts of a sarcomere can be detailed once the sarcomere is explained. Myofibrils are cylindrical structures that carry out contraction of the muscle. These muscle structures are composed of individual cylindrical subunits called sarcomeres. Sarcomeres are myofilaments that are contractile, repetitious functional units in muscle (Martini & Nath, 2009, p. 298). These myofilaments are the smallest operational/functional unit in the muscle. Even with these being small, they still have thick and thin filaments, stabilizing proteins for the thick and thin filaments, and proteins which regulate interactions of the thin and thick filaments. Starting with the outside of the sarcomere, there is the sarcolemma. Sarcolemma is the plasma membrane of skeletal muscle cells. Sarcolemma extends to separate the sarcomeres. T tubules (transverse tubules) which are responsible for allowing the flow of calcium into the sarcoplasmic reticulum (SR) invaginate the sarcolemma. The sarcolemma is not only for protection, but is also a means of communication for nerve impulses that cause the muscle to contract. Longitudinal tubules or myofilaments connect the T tubules to the sarcolemma. Bundled longitudinal myofilaments that are in an ordered arrangement are called myofibrils. The points at which the longitudinal tubules connect the T tubules onto the sarcolemma are triad junctions. The triad has a T tubule which is called terminal cisternae. Mitochondria are in between myofibrils and sarcolemma. The sarcoplasmic reticulum (SR) is specialized endoplasmic reticulum (ER) membrane of each skeletal muscle cell that surrounds the sarcomere. SR is responsible for the storing and providing the calcium that is required for muscle contraction (Martini & Nath, 2009, p. 298). Looking at the sarcomere section of a myofibril, there are noticeable colorations (striations), lines, and bands. See page 299 for the visualization. The...
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