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Esdin LS 2 Lec 5 Muscles

Motor neuron muscle fibers 13 42113 neuromuscular

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Unformatted text preview: es & SR Ryanodine receptor Lateral sac releases calcium T tubule Lateral sacs Ca2+ T tubule DHPR dihydropyridine receptor What Triggers Ca Release? Motor neuron Muscle fibers 13 4/21/13 Neuromuscular Junction action potential reaches axon terminal and NTs released Axon terminal Sarcolemma Neurotransmitter T-tubules Muscle cell Myofibril T-Tubules & SR Ryanodine receptor Lateral sac opens when connected to DHPR T tubule physically linked when action potential travels down Lateral sacs Ca2+ T tubule DHPR 14 4/21/13 Neuromuscular Junction action potential Axon terminal Ca2+ Neurotransmitter (ACh) VGSC Sarcolemma N a+ Muscle cell ACh receptor ionotropic What Causes Ca Release? •  The action potentials at the axon terminal stimulate the release of acetylcholine (ACh) •  ACh binds to ACh receptors activating them, causing Na+ entry into the cell AChR opens, Na influx •  Na+ depolarizes the membrane end plate potential, muscular AP AP travels down t-tubule, activates DHPRs 15 4/21/13 What Causes Ca Release? end plate potential •  EPP causes an action potential in the muscle cell •  The action potential travels down the sarcolemma then dip into the T-tubules •  The action potential activates DHPR •  DHPR activates ryanodine receptors leading to Ca2+ release calcium coming out is going to the calcium binding site on the troponin T-Tubules & SR Ryanodine receptor Lateral sac T tubule Lateral sacs Ca2+ T tubule DHPR 16 4/21/13 Where Does Ca Go? •  The calcium ions released bind to troponin •  Troponin, which is bound to tropmyosin slides away from the actin exposing the binding site of myosin •  Myosin binds to actin sliding filament hypothesis: the calcium binding, troponin rolls off, myosin binding sites on actin exposed Muscle Contraction AP in axon terminals lead to NT release EPP leads to AP T-tubule AP causes Ca2+ release Ca2+ binds to troponin Myosin binds to actin 17 4/21/13 Cross Bridge Cycle Myosin is ready for the next cycle Detachment occurs relaxes Pi ADP happens until calcium not available different ATP New ATP binds ATP ATP ATP being hydrolyzed actin Pi ADP Binding of myosin to actin loses affinity for ADP ADP is released Power stroke ADP ADP Pi Pi is released dissociating myosin bends the actual contraction Cross Bridge Cycle •  ADP & Pi are initially bound to the cross bridge of the the myosin (energized state) •  When actin is exposed, myosin binds to actin •  Pi unbinds from...
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