Cell Physiology in Health and
Disease
Biol
o 2174
A ti potentials
Action
t ti l
Lecture 14
[email protected]
@
References
Animations references:
z http://www.blackwellpublishing.com/matth
http://www blackwellpublishing com/matth
ews/channel.html
z http://www.blackwellpublishing.com/matth
htt //
bl k ll bli hi
/ tth
ews/actionp.html
z Text references: as per lecture 13
z
Learning objectives
To understand the factor which contribute
to the direction and velocity
y of action
potential propagation
z To appreciate the diversity (or lack
thereof) of K+ and Na+ ion channel
subtypes
z
Initiation
z
z
All or none principle
Injected current must
depolarize the
membrane to
threshold for AP to be
generated
Source: wikipedia
Depolarization
p
p
phase
Resting State:
Voltage-gated Na+ channels – rest
Voltage-gated K+ - closed
Depolarization Phase
Threshold = -55
55 mV
Na+ activation gate open
Na+ channel
Extracellular
Na+
K+ channel
Cytosol
K+
Inactivation gate
+30
0
+30
0
-70
-70
Repolarizing
p
gp
phase
Repolarizing phase
Continued depolarization
Opens K+ channels
Closed Na+ inactivation gate
Repolarization continues
-K+ outflow restore resting
g membrane
potential
-K+ channels begin to close
-Na+ inactivation gates are opening
+30
0
+30
0
-70
-70
Hyperpolarization
yp p
+30
0
-70
z
z
Outflow of K+ is large enough to allow
the Em to drift closer to the EK of -90
mV.
As the voltage gated K+ channel closes
– Em returns to rest ((--70 mV)
Positive feedback cycle
Depolarization
Inward INa
Opens Na+
channels
Kandel
principles of
neural science
Recovery
yp
period
Pulse 1. to -15 mV,, activates and
inactivates rested Na+ channels
Pulse 2. It takes 12.5 ms of
recovery time for the second pulse
to produce an identical response
to the control pulse
Source: Hill
S
Hille, IIon channels
h
l off
excitable membranes
AP summary
z
http://www.blackwellpublishing.com/matth
ews/channel.html
Directionality?
What causes the
unidirectional
conduction of an
action potential?
Berne and Levy – principles
of Physiology
Myelin sheath
Velo
ocity (m/s)
120
myelinated
li t d
100
80
60
unmyelinated
40
20
0
0
5
10
15
Fibre diameter (um)
20
25
Nodes
Conduction of the action potential
Molecular cell biology - Lodish
AP conduction animation
z
http://www.blackwellpublishing.com/matth
ews/actionp.html
p
???
Currently, there are 116067 journal
articles on action potentials listed in the
Pubmed database
K+ channel diversity
KcNQ
Q channel mutation
Na+ channels – less diverse
Source: Ashcroft: - Ion
channels and disease
Source: Hille, Ion channels of excitable membranes
Na+ channel
mutation
Febrile convulsions &
generalized epilepsy
Source: Ashcroft: Ion channels and disease
Action potentials not only in
neurons
Source: Berne and levy: Principles of Physiology
Directionality
Again
..
http://www.vancouver.wsu.edu/fac/portfors/APs.pdf