Title: Generator Potentials, Synaptic Potentials and Action Potentials All Can Be Described by the Equivale
1Generator Potentials, Synaptic Potentials and
Action Potentials All Can Be Described by the
Equivalent Circuit Model of the Membrane
PNS, Fig 2-11
2Equivalent Circuit Model of the Neuron
The Nerve (or Muscle) Cell can be Represented by
a Collection of Batteries, Resistors and
Capacitors
3Equivalent Circuit of the Membrane andPassive
Electrical Properties
- Equivalent Circuit of the Membrane
- What Gives Rise to C, R, and V?
- Model of the Resting Membrane
- Passive Electrical Properties
- Time Constant and Length Constant
- Effects on Synaptic Integration
- Voltage-Clamp Analysis of the Action Potential
4Ions Cannot Diffuse Across the Hydrophobic
Barrier of the Lipid Bilayer
5The Lipid Bilayer Acts Like a Capacitor
Vm Q/C
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?Vm ?Q/C
?Q must change before ?Vm can change
6Capacitance is Proportional to Membrane Area
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7The Bulk Solution Remains Electroneutral
PNS, Fig 7-1
8Electrical Signaling in the Nervous System
isCaused by theOpening or Closing of Ion
Channels
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The Resultant Flow of Charge into the Cell Drives
the Membrane Potential Away From its Resting Value
9Each K Channel Acts as a Conductor (Resistance)
PNS, Fig 7-5
10Ion Channel Selectivity and Ionic Concentration
Gradient Result in an Electromotive Force
PNS, Fig 7-3
11An Ion Channel Acts Both as a Conductor and as a
Battery
RT Ko
ln
EK
zF Ki
PNS, Fig 7-6
12All the K Channels Can be Lumped into One
Equivalent Structure
PNS, Fig 7-7
13An Ionic Battery Contributes to VM in Proportion
to the Membrane Conductance for That Ion
14When gK is Very High, gKEK Predominates
15The K Battery Predominates at Resting Potential
gK
16The K Battery Predominates at Resting Potential
gK
17This Equation is Qualitatively Similar to
theGoldman Equation
18The Goldman Equation
Vm RTln (PKKo PNaNao PClCl-i)
ln
Vm
zF (PKKi PNaNai PClCl-o)
19Ions Leak Across the Membrane atResting Potential
20At Resting Potential The Cell is in
a Steady-State
Out
In
PNS, Fig 7-10
21Equivalent Circuit of the Membrane andPassive
Electrical Properties
- Equivalent Circuit of the Membrane
- What Gives Rise to C, R, and V?
- Model of the Resting Membrane
- Passive Electrical Properties
- Time Constant and Length Constant
- Effects on Synaptic Integration
- Voltage-Clamp Analysis of the Action Potential
22 Passive Properties Affect Synaptic Integration
23Experimental Set-up forInjecting Current into a
Neuron
PNS, Fig 7-2
24Equivalent Circuit for Injecting Current into Cell
PNS, Fig 8-2
25If the Cell Had Only Resistive Properties
PNS, Fig 8-2
26If the Cell Had Only Resistive Properties
?Vm I x Rin
27If the Cell Had Only Capacitive Properties
PNS, Fig 8-2
28If the Cell Had Only Capacitive Properties
?Vm ?Q/C
29Because of Membrane Capacitance,Voltage Always
Lags Current Flow
t Rin x Cin
t
PNS, Fig 8-3
30The Vm Across C is Always Equal toVm Across the R
Out
?Vm ?Q/C
?Vm IxRin
In
PNS, Fig 8-2
31Spread of Injected Current is Affected by ra and
rm
?Vm I x rm
32Length Constant l vrm/ra
PNS, Fig 8-5
33 Synaptic Integration
PNS, Fig 12-13
34Receptor Potentials and Synaptic Potentials
Convey Signals over Short DistancesAction
Potentials Convey Signals over Long Distances
PNS, Fig 2-11
351) Has a threshold, is all-or-none, and is
conducted without decrement2) Carries
information from one end of the neuron to the
other in a pulse-code
The Action Potential
PNS, Fig 2-10
36Equivalent Circuit of the Membrane andPassive
Electrical Properties
- Equivalent Circuit of the Membrane
- What Gives Rise to C, R, and V?
- Model of the Resting Membrane
- Passive Electrical Properties
- Time Constant and Length Constant
- Effects on Synaptic Integration
- Voltage-Clamp Analysis of the Action Potential
37Sequential Opening of Na and K Channels
Generate the Action Potential
Rising Phase ofAction Potential
Falling Phase ofAction Potential
Rest
Na Channels Open
Na Channels Close K Channels Open
Voltage-Gated Channels Closed
Na
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38A Positive Feedback Cycle Generates theRising
Phase of the Action Potential
Open Na Channels
Inward INa
Depolarization
39Voltage Clamp Circuit
Voltage Clamp 1) Steps 2) Clamps
PNS, Fig 9-2
40The Voltage Clamp Generates a Depolarizing Step
by Injecting Positive Charge into the Axon
Command
PNS, Fig 9-2
41Opening of Na Channels Gives Rise to Na
Influx That Tends to Cause Vm toDeviate from Its
Commanded Value
Command
PNS, Fig 9-2
42Electronically Generated Current Counterbalances
the Na Membrane Current
Command
g I/V
PNS, Fig 9-2
43Where Does the Voltage ClampInterrupt the
Positive Feedback Cycle?
Open Na Channels
Inward INa
Depolarization
44The Voltage Clamp Interrupts thePositive
Feedback Cycle Here
Open Na Channels
Inward INa
Depolarization
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