1	Motor mechanisms
2	Keywords (reading p. 1080-1086) Bundle, fiber, myofibril, sarcomere Z-line, thick filament, thin filament Actin, myosin, sliding filament model Molecular basis for filament movement Troponin, tropomyosin Sarcoplasmic reticulum Integration of synaptic signals neurotransmitters
3	Motor mechanisms Create movement Can be cilia, flagella, contractile proteins, muscles Will focus on skeletal muscle Muscle of vertebrates that is under voluntary control
4	Structure of skeletal muscle Bundle Fiber Myofibril sarcomere
5	Features of muscle cells # of nuclei- multinucleate; formed by fusion of embryonic cells length - this results in very long cells
6	Sarcomere Structure gives muscle a striated appearance Z line, thick filaments (myosin), thin filaments (actin)
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8	Sliding-filament model of muscle contraction
9	Thick and thin filaments slide past each other
10	At maximal contraction, there is no space at end of thick filament, thin filaments overlap
11	Molecular basis for movement of filaments against each other
12	ATP bound, head retracted and unattached
13	Hydrolysis of ATP cocks head
14	Myosin head attaches to actin filament
15	Release of ADP + P_i causes a further conformational change pushing against the actin filament
16	Binding of ATP to myosin head causes dissociation from actin filament
17	Cycle repeats and sarcomere shortens
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19	toughness Young muscle fibers smaller in diameter less actin/myosin per fiber Elastin cross links, not broken by heating Collagen does melt with cooking but older collagen is less gelatin-like and more highly crosslinked Muscles that are worked harder are tougher
20	meatiness Meatiness results from muscle fibers, aromas result from fats Heat breaks down to amino acids, short aa chains, sugars, fatty acids, nucleotides and salts. Further heating results in rxns creating aromatic compounds. Red fibers contain more materials that will generate flavors
21	aging Initially before 2.5 h will be tender, then rigor mortis Ageing can increase flavor and tenderness for up to 1 month. Enzymes: proteins to savory aa’s; glycogen to glucose, ATP to IMP, fats to aromatic fatty acids Calpains and cathepsins break apart proteins including collagen.
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24	Control of muscle contraction by Ca⁺⁺ Tropomyosin- blocks the myosin binding sites on the actin filament when muscle is at rest Troponin complex-binds calcium and controls the position of tropomyosin
25	At rest, myosin cannot bind because sites are covered by tropomyosin
26	During muscle contraction Ca⁺⁺ levels rise. Ca⁺⁺ binds to troponin which then pulls tropomyosin way from the binding sites
27	What triggers the Ca⁺⁺ rise that induces muscle contraction?
28	[Ca⁺⁺] regulated by the sarcoplasmic reticulum
29	Structure of the sarcoplasmic reticulum T tubules - are a network of the fiber plasma membrane that goes deep into the muscle fiber. This allows transmission of the action potential into the fiber
30	Sequence of events leading to muscle contraction Motor neuron releases acetylcholine Depolarization of the muscle fiber membrane results in action potentials Action potentials trigger release of Ca⁺⁺ from the sarcoplasmic reticulum Increased Ca⁺⁺ allows actin and myosin to slide against each other
31	Characteristics of other muscle types: Cardiac muscle - found only in the heart, striated, gap junctions allow direct electrical signaling between cells Smooth muscle - involuntary muscle, meshwork of actin and myosin, can contract more (greater shortening), but with less tension.