动作电位精品.ppt

* * * * * * * * * * * * * * * * * * * * * * 多发性硬化症是一种奇特的神经系统疾病，多发于20～40岁的中青年人，病因仍不详。 　　对于为什么会产生这种髓鞘的病变则有许多不同的理论，一般认为这是一种自体免疫疾病，也就是说免疫系统错把髓鞘当成外来物质而加以破坏。个人体质或病毒都有可能促成这种免疫反应；有些证据表明，它是病毒慢性感染引起的，使对神经起绝缘作用的脊髓鞘受到损害，导致脑和脊髓的神经束产生错误的神经传导。但医学界还找不出那一种病毒可确定为此病的元凶。仍是一个谜。 　　虽然根治多发性硬化症的药物尚未被发现，但是对于控制病情及疾病所带来的后遗症仍有许多的治疗方法。对于疾病所带来的症状如僵硬、痉挛、疼痛、大小便机能失常等，合并药物及复健的治疗都可使症状改善。皮质类固醇可用来治疗急性的发作；有贝它干扰素对于减少复发的次数及复发时严重程度的报告。许多医师也发现，抱持着乐观态度的多发性硬化症患者，往往能享受更丰富的生活，及更容易得到症状的改善。 * * * * * * * * * Myelin and Saltatory Conduction Myelin (髓鞘) Schwann cells in the peripheral nervous system Oligodendroglia in the central nervous system Voltage-gated sodium channels are concentrated in the membrane of the nodes of Ranvier (郎飞结) In myelinated axones, action potentials skip from node to node (Saltatory conduction 跳跃式传导) Myelin and Saltatory跳跃式 Conduction In myelinated axones, action potentials skip from node to node (Saltatory conduction) 75 电流沿轴突流动得越远，在动作电位发生前膜的去极化程度越大，膜的传导速度就越快；髓鞘可以迫使电流在轴突内流动，这样增加了膜的传导速度；郎飞结处密集了很多电压门控钠通道，此部位发生离子跨膜运动从而产生动作电位。 Saltatory跳跃式 Conduction 自体免疫疾病，也就是说免疫系统错把髓鞘当成外来物质而加以破坏！ Chapter 4 The Action Potential PROPERTIES OF THE ACTION POTENTIAL The Ups and Downs of an Action Potentials Generation of an Action Potential The Generation of Multiple Action Potentials THE ACTION POTENTIAL IN THEORY Membrane Currents and Conductances The Ins and Outs of Action Potential THE ACTION POTENTIAL IN REALITY The Voltage-Gated Sodium Channel Voltage-Gated Potassium Channels Putting the Pieces Together ACTION POTENTIAL CONDUCTION Factor influencing conduction velocity ACTION POTENTIALS, AXONS, AND DENDRITES CONCLUDING REMARKS Spike-initiation zone (动作电位起始点). Only membrane that contains voltage-gated sodium channels is capable of generating action potential. Voltage-gated sodium channels The axons The dendrites The axons The cell bodies The part of the neuron where an axon originates from the soma, the axon hillock (轴丘), is often also called the spike-initiation zone (动作电位起始点). Figure 4.14 M