Chapter 2 Electrical signals of nerve cells

細胞內的電位記錄 玻璃電極，直徑 小於 1 um 刺激電極 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

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

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

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

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

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

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

Intracellular recording replace cytoplasm large synapse

The ionic basis of the resting membrane potential K+

The ionic basis of action potential

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

Chapter 3 Voltage-dependent membrane potential

Ionic currents across nerve cell membrane How the increase in Na + permeability occurs? Voltage clamp method: Kenneth Cole, 1940s

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

Squid neuron: E Na = 55 mV

To test whether the early current is Na + or not

Toxins that poison ion channels: tetrodotoxin Na + tetraethylammonium ions K +

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

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

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

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

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

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

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

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

Two types of voltage- dependent channels

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

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