Thin filaments are made of actin troponin tropomyosin

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Thin filaments are made of actin, troponin, & tropomyosin The myosin-binding site on each actin molecule is covered by tropomyosin in relaxed muscle The thin filaments are held in place by Z lines. From one Z line to the next is a sarcomere.
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The Proteins of Muscle - Titin Titan anchors the thick filament to the M line and the Z disc. The portion of the molecule between the Z disc and the end of the thick filament can stretch to 4 times its resting length and spring back unharmed. Role in recovery of the muscle from being stretched.
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Other Structural Proteins The M line (myomesin) connects to titin and adjacent thick filaments. Nebulin, an inelastic protein helps align the thin filaments. Dystrophin links thin filaments to sarcolemma and transmits the tension generated to the tendon .
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Sliding Filament Mechanism of Contraction Myosin cross bridges pull on thin filaments Thin filaments slide inward Z Discs come toward each other Sarcomeres shorten.The muscle fiber shortens. The muscle shortens Notice :Thick & thin filaments do not change in length
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Chemical Synapses Action potential reaches end bulb and voltage-gated Ca 2+ channels open Ca 2+ flows inward triggering release of neurotransmitter Neurotransmitter crosses synaptic cleft & binds to ligand-gated receptors the more neurotransmitter released the greater the change in potential of the postsynaptic cell Synaptic delay is 0.5 msec One-way information transfer
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Neuromuscular Junctions Synapse is region where nerve fiber makes a functional contact with its target cell (NMJ) Neurotransmitter released from nerve fiber causes stimulation of muscle cell (acetylcholine) Components of synapse synaptic knob is swollen end of nerve fiber contains vesicles filled with ACh motor end plate is region of muscle cell surface has ACh receptors which bind ACh released from nerve acetylcholinesterase is enzyme that breaks down ACh & causes relaxation schwann cell envelopes & isolates NMJ
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The Neuromuscular Junction
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10_10
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How Does Contraction Begin? Nerve impulse reaches an axon terminal & synaptic vesicles release acetylcholine (ACh) ACh diffuses to receptors on the sarcolemma & Na+ channels open and Na+ rushes into the cell A muscle action potential spreads over sarcolemma and down into the transverse tubules SR releases Ca 2+ into the sarcoplasm Ca 2+ binds to troponin & causes troponin- tropomyosin complex to move & reveal myosin binding sites on actin - the contraction cycle begins
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Excitation - Contraction Coupling All the steps that occur from the muscle action potential reaching the T tubule to contraction of the muscle fiber.
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Contraction Cycle Repeating sequence of events that cause the thick & thin filaments to move past each other.
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