肌细胞的收缩功能PPT.ppt

粗肌丝、横桥与细肌丝的关系 Pulling thin filaments inward by the bend of cross bridges is directed toward the center of the thick filament. Each thick filament is surrounded by six thin filaments, all the which are pulled inward simultaneously through cross-bridge cycling during muscle contraction. 从神经元动作电位到肌纤维收缩-----(1) 1. Action potential is initiated and propagates in motor neuron axon. 2. Action potential triggers release of Ach from axon terminals at neuromuscular junctions. 3. Ach binds to receptor sites on motor end plate in muscle fiber, opening Na+,K+ ion channel. 从神经元动作电位到肌纤维收缩-----(2) 4. More Na+ moves into the fiber at the motor end plate than K+ move out, depolarizing the membrane, producing the end-plate potential (EPP). 5. Local currents depolarize the adjacent plasma membrane to its threshold potential, generating an action potential that propagates over the muscle fiber surface and in to the fiber along T tubles. 从神经元动作电位到肌纤维收缩-----(3) 6. Action potential in T tubules triggers release of Ca2+ from lateral sacs of SR. 7. Ca2+ binds to troponin（肌钙蛋白） on thin filaments, causing tropomyosin（原肌球蛋白） to move away from its blocking position and thus uncovering cross-bridges binding sites on actin（肌纤蛋白）. 从神经元动作电位到肌纤维收缩-----(4) 8. Energized myosin cross-bridges （高能肌球蛋白横桥） on the thick filaments bind to actin（肌纤蛋白）.（横桥之所以处于高势能状态, 是因其头部具有ATP酶活, 并可将与其结合ATP分解成ADP和无机磷酸而贮能.） 9. Cross-bridge binding triggers release of energy stored in myosin（肌球蛋白）, producing a movement of each cross bridge. 此时ADP和无机磷酸便与横桥分离 10. 在ADT分离点， ATP binds to myosin（肌凝蛋白）, breaking linkage between actin（肌纤蛋白）and myosin and thereby allowing cross bridges to dissociate from actin.(横桥头部与ATP结合后，其对肌纤蛋白的亲和力降低，使其与纤动蛋白解离）。 11. ATP bound to myosin is split by myosin ATPase, transferring energy to myosin cross bridge once again.（结合到横桥头部的ATP被ATP酶分解，又把能量贮存在横桥） 从神经元动作电位到肌纤维收缩-----(5) 从神经元动作电位到肌纤维收缩-----(6) 12. Cross bridges repeat steps 8 to 11, producing movement of thin filaments past thick filaments.