生理學(xué)課件：細(xì)胞興奮性和生物電

1、Membrane potentials膜電位,Objectives,To understand the shape and form of the action potential and understand how it arises in terms of the changes in the underlying Na+ and K+ channels To explore how action potentials are conducted in axons and how this is affected by myelin,Electrocardiogram ECG（心電圖）,

2、Electroencephalogram EEG（腦電圖）,Electromyogram EMG（肌電圖）,Extracellular Recording（細(xì)胞外記錄）,Intracellular Recording（細(xì)胞內(nèi)記錄）,Opposite charges attract each other and will move toward each other if not separated by some barrier.,Only a very thin shell of charge difference is needed to establish a membrane pote

3、ntial.,Resting membrane potential（靜息電位）,A potential difference across the membranes of inactive cells, with the inside of the cell negative relative to the outside of the cell Ranging from 10 to 100 mV,Depolarization occurs when ion movement reduces the charge imbalance.,A cell is “polarized” becaus

4、e its interior is more negative than its exterior.,Overshoot refers to the development of a charge reversal.,Repolarization is movement back toward the resting potential.,Hyperpolarization is the development of even more negative charge inside the cell.,（極化）,（去極化）,（超極化）,（復(fù)極化）,（超射）,chemical driving f

5、orce,electrical driving force,The Nernst Equation: K+ equilibrium potential (EK) (37oC),R=Gas constant T=Temperature Z=Valence F=Faradays constant,（鉀離子平衡電位）,Begin: K+ in Compartment 2, Na+ in Compartment 1; BUT only K+ can move.,Begin: K+ in Compartment 2, Na+ in Compartment 1; BUT only Na+ can move

6、.,Ion movement: Na+ crosses into Compartment 2; but K+ stays in Compartment 2.,Mammalian skeletal muscle cell -95 mV-90 mV Frog skeletal muscle cell -105 mV-90 mV Squid giant axon -96 mV-70 mV,Ek Observed RP,Difference between EK and directly measured resting potential,Goldman-Hodgkin-Katz equation,

7、Electrogenic Hyperpolarizing,Role of Na+-K+ pump:,Establishment of resting membrane potential: Na+/K+ pump establishes concentration gradient generating a small negative potential; pump uses up to 40% of the ATP produced by that cell!,Origin of the normal resting membrane potential,K+ diffusion pote

8、ntial Na+ diffusion Na+-K+ pump,Action potential（動(dòng)作電位）,Some of the cells (excitable cells) are capable to rapidly reverse their resting membrane potential from negative resting values to slightly positive values. This transient and rapid change in membrane potential is called an action potential,Neg

9、ative after-potential,Positive after-potential,Spike potential After-potential,A typical neuron action potential,Electrotonic Potential（電緊張電位）,The size of a graded potential (here, graded depolarizations) is proportionate to the intensity of the stimulus.,Graded potentials can be:EXCITATORYorINHIBIT

10、ORY (action potential(action potential is more likely)is less likely),The size of a graded potential is proportional to the size of the stimulus.,Graded potentials decay as they move over distance.,Graded potentials decay as they move over distance.,Local response（局部反應(yīng)）,Not “all-or-none” （全或無(wú)） Elect

11、rotonic propagation: spreading with decrement（電緊張性擴(kuò)布） Summation: spatial 585-587 Biochem J 1911, 5 (6-7).,1835-1910,He wrote “The striking contrast between potassium and sodium with respect to this modification (wrt refractoriness) is of great interest.because, from the chemical point of view, it wo

12、uld be quite unlooked for in two elements apparently so akin”,Ringer found that in excess potassium the period of diminished excitability is increased, and frequnecy of heart beats diminishes.,A rather somber application note: Death by lethal injection,Lethal injection is used for capital punishment

13、 in some states with the death penalty. Lethal injection consists of (1) Sodium thiopental (makes person unconscious), (2) Pancuronium/tubocurare (stops muscle movement), (3) Potassium chloride (causes cardiac arrest).,It seems a bit sick, but we can understand how this works from what we know about electrical signalling. Recall that,This explains what Sydney Ringer observed in frog hearts in 1882!,SUMMARY,Resting potential: K+ diffusion potential Na+ diffusion Na+ -K+ pump Graded potential Not “all-or-none” Electrotonic propagation Spatial and temporal summation,Action pot