Discuss how cellular structures, including the plasma membrane, specialized endoplasmic reticulum, cytoskeletal elements, and mitochondria, function together in the contraction of skeletal muscle cells.

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Discuss how cellular structures, including the plasma membrane, specialized endoplasmic reticulum, cytoskeletal elements, and mitochondria, function together in the contraction of skeletal muscle cells.


The plasma membrane of a muscle cell (the sarcolemma) is an excitable membrane, meaning that it can propagate an action potential. You need to explain how the membrane and transverse tubules (T tubules) propagate the action potential.

The specialized endoplasmic reticulum of a muscle fiber (i.e., muscle cell) is called the sarcoplasmic reticulum. It stores Ca2+ (calcium ions). When released, the calcium ions cause contraction; when actively transported back into the sarcoplasmic reticulum, the dropping levels of calcium ions in the cytoplasm cause muscle contraction to cease.

The cytoskeletal elements refers to the microfilaments, made of actin, and the associated proteins, such as myosin. Together, these various proteins form units called sarcomeres; these are the functional units of muscle cells. They are what contract, thereby causing the muscle cell, and ultimately the muscle, to shorten.

The mitochondria provide the ATP needed for the cycling involved in muscle contractions.

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