THE ACTION POTENTIAL · THE ACTION POTENTIAL Objectives: Understand the electrical underpinnings of...
Transcript of THE ACTION POTENTIAL · THE ACTION POTENTIAL Objectives: Understand the electrical underpinnings of...
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