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

HyperpolarizationDepolarizationThreshold potential

離子的流動如何造成電訊號 ?

1. Create different ionic concentrations across cell membrane2. 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: 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

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

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 environment1. Permeability p432. Goldman equation

Intracellular recording replace cytoplasmlarge synapse

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

The ionic basis of action potential

移除N

a+

同時影響了上升速度及強

度

Squid giant axonFrog motor neuron

axon Cell bodyCell body

Inferior olive Purkinje

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

1.2.

3.

4.

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: ENa = 55 mV

To test whether the earlycurrent is Na+ or not

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。

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

• Ix = gV = g (Vm-Ex)

• 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 levelby 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 oligodendrocytePNS Schwann cells