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Muscles

Muscles . Skeletal muscle organization and how it contracts. Vertebrate Skeletal Muscle. Contract/relax: antagonistic pairs w/skeleton Muscles: bundle of…. Muscle fibers: single cell w/ many nuclei consisting of…. Myofibrils: longitudinal bundles composed of….

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Muscles

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  1. Muscles • Skeletal muscle organization and how it contracts

  2. Vertebrate Skeletal Muscle • Contract/relax: antagonistic pairs w/skeleton • Muscles: bundle of…. • Muscle fibers: single cell w/ many nuclei consisting of…. • Myofibrils: longitudinal bundles composed of…. • Sarcomere: repeating unit of muscle tissue, composed of…. • Z lines~sarcomere border this gives “striated” appearance in muscle

  3. Sliding-filament model • Theory of muscle contraction • Sarcomere length reduced • Z line length becomes shorter • Actin and myosin slide past each other (overlap increases) but their length stays the same

  4. Actin-myosin interaction • 1- Myosin head breaks down ATP to ADP and inorganic phosphate (Pi); termed the “high energy configuration” with ADP and phosphate attaching to the head. (GRABBING ON) • 2- Myosin head binds to actin; termed a “cross bridge” • 3- Releasing ADP and (Pi), myosin relaxes sliding actin; “low energy configuration” (PULLS THE ACTINS FROM BOTH SIDES TO BE CLOSER) • 4- Binding of new ATP releases myosin head (LET GO) • 5- This ATP is broken down (See #1)

  5. Muscle contraction regulation, I • Relaxation: tropomyosin protein blocks myosin binding sites on actin • Contraction: calcium is released from ER of muscle cell due to action potential from neurons. It binds to troponin complex; tropomyosin changes shape, exposing myosin binding sites. MAKES SLIDING FILAMENT POSSIBLE

  6. Muscle contraction regulation, II • Calcium (Ca+)~ Must be present • Sarcoplasmic reticulum~ a specialized endoplasmic reticulum (ER) in muscle that stores and releases Ca. • Stimulated by action potential in a motor neuron • Ca+ then binds to troponin allowing this to go forward

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