动物生理学2细胞的基本功能下ppt课件

1、2.2.3.3 动作电位的传播动作电位的传播 propagation of AP 部分电流local circuit current是导致动作电位传导和阈下反响传播的缘由。动作电位传导去极化到达了阈电位阈下反响传播去极没有到达阈电位，不能产生动作电位的情况下，阈下反响可经过部分电流在短间隔内传播。前面讲过阈下反响是衰减传导的。影响动作电位传导速度的要素影响动作电位传导速度的要素神经和肌细胞具有电缆的某些特性rm/rin的比值越高，跨质膜的电流损失就越小，信号可以无明显衰减地经过电紧张性传送的间隔就越远。传导速度由细胞阻抗和电容决议传导速度由细胞阻抗和电容决议直径越大的细胞轴突axon传导速度越

2、快。这主要是由于细胞轴突直径增大时，胞质的纵向电阻越小，因此部分电流越大。只需少数动物采取增大轴突直径的战略来增大传导速度，如枪乌贼。在脊椎动物中，有些神经纤维外包裹着髓鞘myelin 5maiEli(:)n sheath ，这种神经纤维称作有髓神经纤维。 髓鞘化导致传导速度显著添加在有髓神经纤维，由于大量的膜缠绕着轴突，添加了有效膜阻抗，以致rm/rin增大。另外，具有髓鞘缠绕的膜较裸露轴突膜的电容要小得多，部分电流可以更快地使膜去极化。以上两要素均可增大传导速度。在有髓纤维，动作电位只在郎飞氏节(node of Ranvier) 处再生，双由于以上电学特性，动作电位可以以小的衰减和高的速度

3、由一个郎飞氏节传导至下一个郎飞氏节。这种传导称作腾跃式传导saltatory conduction2.2.3.4 缝隙衔接缝隙衔接 gap junction缝隙衔接也称作电突触，在中枢和外周神经系统中广泛存在，许多非神经细胞间也存在，如心肌等。在电突触中一个细胞的膜电位变化以电流的方式直接传送给另一个细胞。通常允许双向传送。 电紧张电位电紧张电位 被动被动 部分电位部分电位 少量离子通道开放，没有产生再生性循环少量离子通道开放，没有产生再生性循环 动作电位动作电位 产生再生性循环产生再生性循环 去极化的部分电位多是由于去极化电紧张电位和少量去极化的部分电位多是由于去极化电紧张电位和少量离子通道

4、开放产生的自动反响叠加而构成的。离子通道开放产生的自动反响叠加而构成的。 仍具有电紧张电位电学特征不表现仍具有电紧张电位电学特征不表现“全或无特征；全或无特征；在部分构成电紧张传播在部分构成电紧张传播Electrotonic propagation，范围不超越几个毫米范围不超越几个毫米 可以叠加可以叠加 summation总总和，包括和，包括spatial summation; temporal summation 2.2.4 部分电位部分电位 local potential空间总和时间总和2.2.5 可兴奋细胞及其兴奋性可兴奋细胞及其兴奋性2.2.5.1 excitation and exc

5、itable cells excitation 动作电位本身或动作电位产生的过动作电位本身或动作电位产生的过程程excitable cells 受刺激后能产生动作电位的细受刺激后能产生动作电位的细胞胞 including: neurons, muscle fibers, gland cells 2.2.5.2 Excitability and threshold stimulus stimulus 的参数有3 个，强度、时间、强度对于时间的变化率。 实验时普通用electrical stimulus，缘由是这三个参数都好控制。运用是普通采用方波。 threshold stimulus, thr

6、eshold intensity留意与threshold potnetial的区别刺刺 激激双刺激：双刺激： 强度强度1 1，波宽，波宽1 1 强度强度2 2，波宽，波宽2 2，波间隔，波间隔串刺激：强度，波宽，频率，串长串刺激：强度，波宽，频率，串长延续延续( (复复) )刺激：强度，波宽，频率刺激：强度，波宽，频率双刺激串刺激延续刺激 强度时间曲线 strength-duration curve: 引起组织excitation所需的电小刺激强度与该刺激的作用时间根本上是一个反比例关系。It强度时间曲线 固定刺激时间，可以引起兴奋的最小刺激强度称阈强度threshold intensity,

7、 对应的刺激称阈刺激。强度大于阈强度的刺激称阈上刺激，subthreshold stimulus 强度小于阈强度的刺激称阈下刺激 suprathreshold stimulus。 2.2.5.3 The change of excitability after excitation当细胞在接受一次有效刺激产生action potential(excitation)的当时和以后一小段时间内兴奋性阅历一系列有次序的变化，然后恢复正常。依次是：绝对不应期、相对不应期、超凡期和低常期。 对于nerve and muscle cells, absolute refractory period: 0.52

8、 ms, relative refractory period: a few ms supranormal period and subnormal period 3050 ms 蛙的有髓神经纤维最多 500次s Na+通道的电压依赖性失活是呵斥不应期和细胞对刺激顺应的缘由。失活门在激活门开放后迅疾封锁。一旦Na+通道失活，它只能在膜电位恢复到或接近恢复到静息电位程度后才可以再次被激活。在绝对不应期，大量Na+离子通道被电压失活；在相对不应期的早期，一些Na+离子通道仍被电压失活被太缓慢去极化的细胞能够不会产生动作电位factors that affect the excitability o

9、f cells RP threshold potential Ca2+ concentration2.4 Contrction of muscle cells 肌肉组织Muscle横纹肌 striated muscle 平滑肌 smooth muscle 骨骼肌 skeletal muscle心肌 cardiac muscle随意肌voluntary muscle2.4.1 striated muscle 2.4.1.1 Transmission at neuromuscular junction Traditionally, synapse has been reserved for neu

10、ron-to-neuron contacts, and junction is used more broadly for contacts between any excitable cells. However, with the realization that synapses and other junctions operate by similar mechanisms, the distinction in terminology has seemed less important, and synapse is often used losely to connote neo

11、ron-effector organ junction as well as those between neorons. The axon terminal and muscle cell are seperated by 60 nm synaptic cleft. The presynaptic terminals are filled with thousands of 50-nm-diameter synaptic vesicles and many mitochondria. A muscle fiber many centimeters long may have an end -

12、plate reegion only 100 to 500 m long. A few vertebrate muscles have more than one end-plate region innervated by different motoneurons, but most muscle fibers have only a single endplate innervated by one axon.Structure of neuromuscular junctionNeuromuscular TransmissionNeuromuscular transmission be

13、gins when:1) An AP propagating down the axon invades and depolarizes the presynaptic terminal region. This causes:2) A flow of Ca2+ into the boutons through voltage-activated Ca2+ channels. The elevated Ca2+ triggers:3) The fusion of synaptic vesicles with pre-synaptic membrane specializations and t

14、he release of packets or quanta of transmitter (Ach) into the cleft.These are the pre-synaptic events. Post-synaptic Events of Neuromuscular Transmission:4) ACh diffuses across the cleft. This takes time (up to several hundred s).5) ACh binds to Nicotinic Acetylcholine receptors in the post-synaptic

15、 membrane, opening monovalent cation channels.6) Channel opening depolarizes the post-synaptic membrane, creating an endplate potential (EPP).7) EPPs spread passively to the excitable muscle membrane.8) Voltage-activated Na+ channels open giving rise to a muscle AP.9) Termination of the transmission

16、 process occurs via hydrolysis of ACh by acetylcholinesterase present in the junction.Please note:End-plate potential is not a “all or none typeIt can cause action potential of the excitable muscle membrane 筒箭毒，银环蛇毒可以阻断神经肌肉接头处的传送 2.4.1.2 The structure of striated musclemyofibril and sarcomeres:kmiIs

17、otropic (等方性的等方性的 band (I band) or light bandanisotropic band (A band) or dark bandmyosin myofilament 粗肌丝粗肌丝actin myofilament 细肌丝细肌丝sarcotubular systemtransvers tubules (T tubules)Sarcoplasmic reticulum, SR( a special type of smooth ER found in smooth and striated muscle )Juctional SR or terminal ci

18、sternaTriad(the T-tubule and its two terminal cisternae form a triad)The structure of striated muscle2.4.1.3 Mechanism of muscle contraction2.4.1.4 Excitation-contraction (EC)coupling T-tubules conduct signal APs into the cell Depolarization of T-tubule causes calcium release from SR Calcium activat

19、ion of contraction Relaxation occurs as a result of the active transport of Ca2+ into the SR by the Ca2+ pump on the SR membrane 2.4.1.5 影响横纹肌收缩效能的要素影响横纹肌收缩效能的要素 isometric contraction 等长收缩等长收缩 Tension in the muscles increases The muscle is unable to shorten isotonic contraction 等张收缩等张收缩 Myofilaments

20、 are able to slide past each other during contractions The muscle shortensPreloadPreloadInitial lengthSingle twitch tension is determined by length of sarcomereAfterloadContractility肌肉收缩才干(Contractility)是指与负荷无关的决议肌肉收缩效能的肌肉本身的内在特性。与多种要素有关，如： Ca2+ concentration of cytosol ATPase activity of myosin The

21、 level of other related proteinsThe variation of contractility is important for cardiac muscleThe force of skeletal muscle are affected by Number of motor units recruitedFrequency of stimulation SummationForce and the number of motor units recruitedFrequency of stimulation Simple twitch, summation,

22、tetanusIndividual muscle fibers respond to a single stimulus in an all or none fashion-simple twitchSlide 6.26bCopyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings Anaerobic glycolysis (continued) This reaction is not as efficient, but is fast Huge amounts of glucose are needed Lac

23、tic acid produces muscle fatigueFigure 6.10bSlide 6.25Copyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings Aerobic Respiration Series of metabolic pathways that occur in the mitochondria Glucose is broken down to carbon dioxide and water, releasing energy This is a slower reaction

24、that requires continuous oxygenFigure 6.10cSlide 6.27Copyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings When a muscle is fatigued, it is unable to contract The common reason for muscle fatigue is oxygen debt Oxygen must be “repaid to tissue to remove oxygen debt Oxygen is require

25、d to get rid of accumulated lactic acid Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less骨骼肌可以根据收缩速度被分为快肌和慢肌骨骼肌可以根据收缩速度被分为快肌和慢肌 骨骼肌可以根据其收缩速度被分为两种根本类型：快肌(fast twitch)和慢肌(slow twitch)。 虽然有些肌肉几乎只含有快肌纤维或慢肌纤维，大多数肌肉是由这两种肌纤维混合而成的。但是另一方面，一个运动单位典型地只含有一种类型的肌纤维。因此，骨骼肌往往同时

26、含有快肌运动单位和慢肌运动单位。 在人体，快肌纤维直径较大，具有高的酵解才干和低的氧化才干。与此相反，慢肌纤维典型地具有较小的直径，具有较高的氧化才干和较低的酵解才干。 这个代谢活动的根本差别是与慢肌纤维的抗疲劳特性相吻合的。与此相比，快肌纤维那么易于疲劳。 由于肌纤维疲劳特性的这种差别，在肌肉收缩的过程中，首先被募集的是慢肌纤维，然后才是快肌纤维。 慢肌纤维较小的直径也使得细胞的外表积体积比例得以提高，因此提高来自血液的氧和代谢物质的分散及摄取才干，并有利于抗疲劳特性的提高。 慢肌较高的氧化才干也表如今其由于丰富的血红蛋白、线粒体以及丰富的血管供应而构成的红色外表。与此相比，快肌由于更多地依赖无氧代谢，看上去显得惨白。 决议肌纤维种类的一个重要要素是支配神经的类型。这个概念可以经过将支配神经进展互换的实验得到验证。在这个实验中，当原先支配慢肌运动单位的运动神经元被接到快肌纤维，会使快肌运动单位肌纤维的氧化才干加强，收缩速度降低，并表达慢肌肌球蛋白异构体。类似地，将慢肌纤维接上支配快肌运动单位的运动神经元，慢肌运动单位肌纤维的特性也会转化成快肌纤维的特性，包括快肌肌球蛋白的合成。 2.4.2 Smooth Muscle Distribute widely throughout the body and is more