细胞的基本功能3-2008

1、Summary of Membrane ReceptorsFig 2Fig 3安静时膜对K+有permeability； K的电化学驱动力：K有向细胞外扩散的动力膜两侧的离子浓度梯度膜两侧的电位差形成的电位梯度；为细胞膜保持膜内较膜外为负的基础K+外流Na+内流膜内外离子浓度梯度的维持：Na+ K+ pump影响静息电位的主要因素：膜内、外K+浓度差；膜对K+和Na的相对通透性；NaK泵活动的水平。Fig 膜通透性：膜通透性：膜允许某种物质从膜的一侧转移到另一侧的能力膜电导膜电导 (G)：膜运送带电离子，形成离子电流的能力电压钳（电压钳（voltage clamp）：又叫电压固定）：又叫电压固

2、定原理：原理：欧姆定律 V=IR；膜电导 (G) = 1/膜电阻 (R) 跨膜离子电流 (I) = V/R = VG; 只要固定膜电位 (V), 测出的跨膜电流 (I) 的变化，既可反应膜通透性的改变工具药：工具药： Na+通道阻断剂河豚毒 (tetrodotoxin, TTX) K+通道阻断剂 四乙基胺 (tetraethylammonium, TEA)膜片钳膜片钳 (patch clamp) 是一种记录膜结构中单一通道的开放和关闭，测量单通道离子电流I和电导G的技术 Fig电压钳（voltage clamp）和膜片钳 (patch clamp)的应用 FigAction potential

3、 (AP) 和门控通道和门控通道 膜对膜对Na、K通透性发生变化而形成。通透性发生变化而形成。AP 原理：原理：depolarizationNa+内流 (Na+ ion channel) repolarizationK+外流 (K+ ion channel)AP和细胞兴奋性的变化和细胞兴奋性的变化绝对不应期：绝对不应期：兴奋性兴奋性0，Na通道失活状态通道失活状态相对不应期：相对不应期：阈上刺激才引起兴奋，阈上刺激才引起兴奋，Na通道尚未恢复正常通道尚未恢复正常超常期：超常期：阈下刺激既可引起兴奋，阈下刺激既可引起兴奋，Na通道恢复正常通道恢复正常低常期：低常期：阈上刺激才引起兴奋，阈上刺激才

4、引起兴奋，Na通道恢复正常，但通道恢复正常，但Na泵活动增强，泵活动增强，超极化状态超极化状态FigFigSummary:膜的 depolarization Na+ channel打开Na+内流 Na+ equilibrium potentialFigNa+ channel关闭K+ channel延迟开放repolarizationAfter hyperpolarization voltage gated channel 在膜电位返回resting potential 之后才开始关闭FigFigCytosolExtracellularfluidCation +Anion -VoltmeterA

5、nion -Anion -Anion -Cation +60- 0 + 0 -Er = 70 - 75 mV- 0 +DiffusionInsideOutside(a) Developing membrane potentialmVCell90DiffusionChargeInsideOutsideCell(b) Electrochemical equilibriummVPotassium ionOrganic anion- 0 +-StimulatorAxonMicroelectrodeInside axonCROOvershootStimulus appliedTime (msec)Aft

6、er-hyperpolarizationgKgNaRepolarizationDepolarizationVm(mV)OvershootCLOSEDOPEN(a) Ion channel(b) Voltage-gated channel(c) Ligand-gated channelResting state-90 mVVoltage-gated sodium ion channelActivation state-60+30mVInactivation state+30-90mVVoltage-gated potassium channelOpen+30-90mVClosed-90+30mV

7、Na+ channelsK+ channels1. Resting state2. Depolarization3. Depolarization4. RepolarizationThresholdRestingRestingRestingRestingRestingThresholdThresholdThresholdThreshold5. HyperpolarizationStimulus appliedTime (msec)gKgNaVm(mV)少量少量Na 通道开放通道开放大量大量Na 通道开放通道开放Na 通道关闭，通道关闭，K通道完全开放通道完全开放K通道延迟开放通道延迟开放Na

8、K泵运转泵运转After-hyperpolarizationRepolarizationDepolarizationK通道持续开通道持续开放放Stimulus#1Stimulus#2 (stronger)Time (milliseconds)Note the changes in threshold potential and AP amplitudeNon-refractoryperiodRelative Refractory Period (RRP)Absolute Refractory Period (ARP)Action Potential (AP)ThresholdThreshold

9、Membrane Potential (mV)AxonhillockShort Time ConstantTimeLong Time ConstantThresholdTimeMembrane potential at axon hillock (mV)Membrane potential at axon hillock (mV)AxonhillockTime Single excitatory postsynaptic potentialThresholdMembrane potential at axon hillock (mV)AxonhillockTime Single excitat

10、ory postsynaptic potentialThresholdMembrane potential at axon hillock (mV)AxonhillockTime Simultaneous excitatory postsynaptic potentialThresholdMembrane potential at axon hillock (mV)ABCDESinkSourcePropagationPropagationNodes of Ranviert1t2t3t4Sink SourceSink SourceSink SourceSink SourceSink SourceSink Source Sink SourceSink SourceUNMYELINATED AXONAction potential generated at each succeeding adjacent membrane segmentMYELINATED AX