musclefibers肌肉纤维.PPT

Muscle Muscle cells Myofibrils Sarcomeres Thick + thin filaments Myosins (+titin) + actins (+troponin+tropomysin) The deadly South American arrowhead poison curare 南美箭毒 binds strongly to nicotinic Ach receptors, but it does not open their ion channels and acetylcholinesterase does not destroy 破壞 it Therefore, although the motor nerves still conduct normal action potentials and release Ach, there is no resulting EPP and contraction ? can cause death by asphyxiation 窒息 Some organophosphates 有機磷酸鹽類, which are the main ingredients in certain pesticides 殺蟲劑 and nerve gases 神經毒氣 ? inhibit acetylcholinesterase ? Ach ? ? a maintained EPP ? cannot generate action potentials because the voltage-gated Na+ channel become inactivate, which requires repolarization to reverse Thus, the muscle does not contract in response to subsequent nerve stimulation, and the result is skeletal muscle paralysis 骨骼肌麻痺 and death from asphyxiation 窒息 Botulinum toxin肉毒桿菌毒素 (botulism 肉毒桿菌病) is an enzyme that breaks down a protein required for the binding and fusion of Ach vesicles with the plasma membrane of the axon terminal ? Ach ? p292-293 Disruption of neuromuscular signaling Mechanisms of single-fiber contraction The force exerted on an object by a contracting muscle 肌肉收縮作用 在物體上的力量 is known as muscle tension 肌肉張力, and the force exerted on the muscle by an object (usually its weight) 物體作用在肌肉 上的力量 is the load 負重 ? tension load are opposing 相反方向 When a muscle develops tensions but does not shorten (or lengthen), the contraction is said to be isometric (constant length) 等長收縮 A contraction in which the muscle shortens, while the load on the muscle remains constant, is isotonic (constant tension) 等張收縮 A lengthening contraction 伸長收縮 occurs when an unsupported load on a muscle is greater than the tension the cross-bridges are generating The mechanical response of a single muscle fiber to a single action potential is known as a twitch 單次收縮；抽動