Musculoskeletal System: Muscle Structure & Function 🏋️‍♂️

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Ninja Nerds!
In this lecture, Professor Zach Murphy will present on the detailed structure and function of skeletal muscle. We begin by breaking down the organization of skeletal muscle from the macroscopic level—muscle belly, fascicles, and muscle fibers—down to the microscopic myofibrils, sarcomeres, and myofilaments. We explain the roles of actin, myosin, and associated proteins such as tropomyosin and troponin, as well as the structural proteins titin and nebulin, in maintaining sarcomere stability.

We then move into the functional aspects of muscle physiology, focusing on the sliding filament theory and how cross-bridge cycling produces contraction. The lecture explores the excitation-contraction coupling process, starting with motor neuron stimulation, neuromuscular junction signaling via acetylcholine, and the propagation of action potentials along the sarcolemma and T-tubules. This leads to calcium release from the sarcoplasmic reticulum and binding to troponin, allowing actin-myosin interactions.

We also discuss the differences between muscle fiber types—Type I (slow-twitch, oxidative) and Type II (fast-twitch, glycolytic)—and their roles in endurance versus power activities. Finally, we tie these structural and functional principles together by highlighting how ATP supply, calcium handling, and neural input determine muscle performance and fatigue.

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