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Chapter 2 Electrical signals of nerve cells

Chapter 2 Electrical signals of nerve cells. 刺激電極. 細胞內的電位記錄. 玻璃電極，直徑 小於 1 um. 記錄電極. Hyperpolarization Depolarization Threshold potential. 離子的流動如何造成電訊號? 1. Create different ionic concentrations across cell membrane 2. Membranes are selectively permeable to ions.

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Chapter 2 Electrical signals of nerve cells

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  1. Chapter 2 Electrical signals of nerve cells

  2. 刺激電極 細胞內的電位記錄 玻璃電極，直徑 小於 1 um 記錄電極 Hyperpolarization Depolarization Threshold potential

  3. 離子的流動如何造成電訊號? 1. Create different ionic concentrations across cell membrane 2. Membranes are selectively permeable to ions

  4. Electrochemical equilibrium: electricity & concentration gradient 只對K+通透的膜 濃度差十倍時 膜電位差為 58 的倍數

  5. 單一離子平衡電位的計算方式 • Nernst equation: EX = RT/zF ln [X]2/[X1] • = 58/z log [X]2/[X1] • z is the electrical charge • EK = 58 log 1/10 • = -58 mV • side 2 is a reference compartment, defined as 0 potential

  6. 問題 1. Side 1: [Na+] = 1 mM Side 2: [Na+] = 10 mM 2. Side 1: [Ca2+] = 1 mM Side 2: [Ca2+] = 10 mM 3. Side 1: [Cl-] = 10 mM Side 2: [Cl-] = 1 mM 4. Side 1: [K+] = 100 mM Side 2: [K+] = 1 mM

  7. 答案 1. ENa = 58/1*log 10/1 = 58 mV 2. ECa = 58/2*log 10/1 = 29 mV 3. ECl = 58/-1*log 1/10 = 58 mV 4. EK = 58/1*log 1/100 = -116 mV

  8. 膜電位對離子流動的方向及大小的影響 p42 • Connect a battery across the two sides to make side 1 more negative than side 2 • Side 1 = -58 mV, no net K+ ion flow • Side 1 more negative than -58 mV, K+ ion will flow form side 2 to side 1

  9. Electrochemical equilibrium in a multi-ion environment 1. Permeability p43 2. Goldman equation

  10. Intracellular recording replace cytoplasm large synapse

  11. The ionic basis of the resting membrane potential 若休息膜電位對 K+ 的通透性最好，則改變細胞外K+ 濃度將影響膜電位

  12. The ionic basis of action potential 移除Na+同時影響了上升速度及強度

  13. Action potential form and nomenclature Frog motor neuron Cell body Squid giant axon axon Cell body Inferior olive Purkinje Hodgkin & Katz 尚無法證實 membrane 是如何改變 其 permeability 以 generate action potential

  14. Chapter 3 Voltage-dependent membrane potential

  15. Ionic currents across nerve cell membrane • How the increase in Na+ permeability occurs? • Voltage clamp method: Kenneth Cole, 1940s 2. 1. 4. 3.

  16. Alan Hodgkin & Andrew Huxley, 1940s 當膜電位改變時，是否有離子進出細胞膜？ Capacitive current: voltage clamp 輸入的電流

  17. Squid neuron: ENa = 55 mV

  18. To test whether the early current is Na+ or not

  19. Toxins that poison ion channels: tetrodotoxin Na+ tetraethylammonium ions K+ 證明造成這兩種離子通透性改變的機制， 是互相獨立的。

  20. Toxins that poison ion channels 減緩Na+ channels inactivation 降低 threshold

  21. Two voltage-dependent membrane conductances • V = IR = I * 1/g = I/g • Ix = gV = g (Vm-Ex) • Conclusions: • (1) both Na+ and K+ conductances are voltage-dependent Fig. 3.6

  22. (2) the Na+ and K+ conductances change over time

  23. Reconstruction of the action potential Rate of depolarization falls: (1) electrochemical driving force of Na+ decreases (2) Na+ conductance inactivates (3) K+ conductance increase

  24. Until Na+ conductance inactivation Restore the membrane potential to the resting level by inactivate K+ channels

  25. Threshold: (1)the point at which the amount of heat supplied exogenously = the amount of heat that can be dissipated (2) Na+ inflow = K+ outflow

  26. Long-distance signaling by means of action potentials Passive current flow: current leak neurons are poor conductors than a wire

  27. How do action potentials propagate along such a poor conductor? (1) the amplitude of AP (2) the time delay of AP Conduction velocity

  28. Two types of voltage-dependent channels

  29. Voltage-dependent channels close AP propagation: (1) passive flow (2) active flow by voltage- dependent channels Refractory period (1) the number of AP/ time (2) propagate back

  30. Increased conduction velocity as a result of mylination Improve passive flow, increase velocity: (1) increase diameter, decreases the internal resistance (2) increase insulation Mylination: CNS oligodendrocyte PNS Schwann cells

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