THE ACTION POTENTIAL

Objectives:

Understand the electrical underpinnings of the action poten

Differentiate between voltage-time, current-time and currvoltage relations

Understand the electrical underpinnings of the action poten

Understand the general equation for macroscopic membrancurrent

Know the Nernst equation and the approximate concentratof Na+ and K+ ions inside and outside of cardiac cells

Superior

Vena CavaSA Node

Atrium

AV Node

Purkinje

Tricuspid Valve

Mitral Valve

Ventricle

ECGP

PR QRS

Q

R

S

T

Sir Andrew Fielding Huxley

&

Sir Alan Hodgkin

Cambridge University

Winners of the1963 Nobel Prize

for Physiology.

Axon Action Potential

IC = C dE/dt

Itot = IC + Iionic

Late = K+ curre

TEA sensitive

Early = Na+ cu

TTX sensitive

gK

gNa

gNagK

mV

30 ms

Na+

in

K+

out

IK = gK (Et - EK)

INa = gNa (Et - ENa)

gK = IK

(Et - EK)

gNa = INa

(Et - ENa)

+

+

+

Outside

Inside

‘pore’

‘gate’

Voltage-gated Ion Channel

Outside

Inside

Sodium ionTetrodotoxin (TT

+

+

+

Outside

Inside

Potassium ionTetraethylammonium (TE

N

C2H5

C2H5

C2H5C2H5

+

+

+

+

Single-channel currents recorded from membra

of denervated frog muscle fibres.

Neher E, Sakmann B

Nature 260, 799-802, 1976

Nobel Prize 1991

pA = 10-12 A or 1/1,000,000,000,000th of an Amp

Or

1,000,000 ions per second per channel