1. Action Potentials in Different Nerve Membranes
AP = A membrane potential change caused by a flow of ions through
ion channels in the membrane
Intracellular Recording
Two Points, Ea and Eb
Conduction Velocity (cv) =
Probagation time/distance
between a and b
Node of Ranvier:
Depolarize then Spike
Motoneuron, Squid Axon:
Shocked away from a
Latency is distance
Traveled.
Conduction Velocity but
Not Channel Conductance is Temperature Dependent

2. Hermann’s Cable Theory: Passive spread of APs
Similar to a Leaky Telegraph Cable
Re = extracellular membrane resistance
Ri = cytoplasmic membrane resistance
Rm = variable dependent upon channel gating
that causes change in emf
Cm = membrane as parallel plate capacitor
“These two elements may be just different aspects of the same
membrane mechanism” Cole and Curtis 1938

3. Action Potentials: 1, Underlying ionic basis = Na and K channels
All or none
Propagated by passive spread of electrotonic currents
Restriction of ion channel expression – Example Node of Ranvier and Saltatory Conduction
Nav1.6 and Kv1.2 (See Plate 1)
Ion channels have no thresholds for activation. AP 15% TH
Code is not in the width or height of the AP – Information code = The Frequency

4. Voltage-clamp Electrophysiology – Approach is Preparation
Dependent – Best Biophysical Technique to Study
Ion Channel Activity
E’ = recording electrode
I” = current injecting electrode
FBA = feedback amplifier
(Px changes can be rapid and FBA
with high freq. response has to
readjust the current injection
constantly )
Principle: Vc is set by investigator
Simultaneously Acts as a
Voltage Sensor (E’) and Current
Injector (I’)
Best Utility for These 3:
Two Microelectrode
Suction Pipette
Patch Clamp
Im = Ii + Ic = Ii +Cm dE dt

5. First Recordings of Current by Hodgkin, Huxley, and Katz
Ionic Theory of Membrane Excitation
Classical Biophysics Period ( )

6. The Independence Relation: First recognized that current
could be separated into components carried by different
ions.
First to use the approach of Ion Substitution
1. Observed Biphasic
Current when
Hyperpolarized.
2. Choline Chloride for
Nao
3. Algebraic Difference
To Derive the INa

7. HH Model to Determine the H Infinity Curve for Na Channel Inactivation
Activation: rapid process that opens Na channels during a depolarization
Inactivation: process that closes Na channels during a depolarization; must
repolarize membrane to release channels from inactivated state
Recovery from Inactivation Curves

8. Why are there MANY different types of of Na and K channels even within
the same species but across different tissues/organs?

9. All V-gated Ion Channels – Glycosylation, esp. eukaryotic
Na Channels
Alpha, Beta1, Beta 2
Ca Channels
Alpha1, alpha2, beta, gamma, delta
K Channels
4 Alpha Beta
All V-gated Ion Channels –
Glycosylation, esp. eukaryotic
Principle and Auxillary subunits
a. Principle:
toxin-binding sites
S4 voltage sensor
pore
gate
selectivity filter
b. Auxillary
membrane trafficking to the PM
alteration of inactivation
3. Protein-protein interactions

10. External Ion Channel Pore Blockers to Isolate gNa vs. gK

11. Armstrong’s Experiments: Internal TEA Block
Incoming K flux knocked out TEAi, therefore must be
A Pore! Flux rate determined as 600 ions/millisecond.

12. Myelination allowed increase conduction velocity of APs through
Saltatory Conduction across the Nodes of Ranvier
Localization of Ion Channels: Nav1.6 and Kv1.2 (See Plate 1)
Tau = Rm x Cm
How did invertebrate
organisms increase
conduction velocity?
What is the evolutionary
advantage of myelin?

13. Do Current Biophysical Properties Deliniate a Different Gene?
Human gene names = all capital letters
Non-human mammalian = lower case
Gene names are always in italics