UWL BIO 312 - Muscle contraction (3 pages)

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Muscle contraction

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Muscle contraction


Lecture notes describing the anatomy and physiology of muscular synapses, pharmacology of neuro-muscular interactions, as well as intro to muscle mechanics, motor unit, external muscle tension, load, isometric, isotonic, concentric, eccentric

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Lecture Note
University of Wisconsin-La Crosse
Bio 312 - Human Anatomy and Physiology I

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Bio 312 Lecture 20 Lecture Outline 1 Muscular contraction a Anatomy of synapses b Physiology of contraction c Pharmacology 2 Muscle Mechanics a Motor units b Types of contraction Muscular Contraction Neuromuscular junction where nerve cell axon synapses with skeletal muscle o Always excitatory somatic muscles are always nicotinic o Synapse in middle of muscle fiber for most uniform action potential throughout fiber Sarcoplasmic reticulum membranous sac surrounding every myofibril stores Ca2 when not stimulated o Releases calcium during stimulation o Active re uptake of calcium when relaxed Transverse tubules invaginations of sarcolemma that occur at regular intervals throughout sarcolemma o Rapidly conduct action potentials to interior of cell so all myofibrils can be activated simultaneously o Action potential passing down T tubule opens nearby calcium channels located on the sarcoplasmic reticulum flooding the area surrounding the myofibrils sarcoplasm with calcium ions o Extensiveness of the sarcoplasmic reticulum assures that when calcium is released it quickly reaches all areas of the myofibrils Role of Ca 2 ions in sarcoplasm o No calcium present means that tropomyosin blocks actin binding sites keeping cross bridges from binding to actin molecules o Raise in concentration of calcium ions rotates actin and revealing the binding sites allowing cross bridges to bind to actin and initiate contraction o Re uptake of calcium into S R causes tropomyosin to go back to blocking actin binding sites causing relaxation of the muscle Action potential initiates Excitation Contraction Coupling 1 Action potential generated and propagated along the sarcolemma and down the T tubule via voltage gated ion channels same as unmyelinated axon 2 Action potential triggers Ca 2 release from sarcoplasmic reticulum 3 Calcium ions bind to troponin removing the blocking action of tropomyosin exposing actin binding sites 4 Myosin cross bridges alternately attach to actin and detach pulling

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