![Page 1: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/1.jpg)
Monday April 9, 2014.
Nervous system and biological electricity II
1. Pre-lecture quiz2. A review of resting potential and Nernst equation3. Goldman equation4. Action potential
![Page 2: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/2.jpg)
Information flow through neurons
Nucleus
DendritesCollectelectricalsignals
Cell bodyIntegrates incoming signalsand generates outgoingsignal to axon
AxonPasses electrical signalsto dendrites of anothercell or to an effector cell
![Page 3: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/3.jpg)
Neurons form networks for information flow
![Page 4: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/4.jpg)
![Page 5: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/5.jpg)
Animation of resting potential
• https://www.youtube.com/watch?v=YP_P6bYvEjE
![Page 6: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/6.jpg)
Outside of cell
Inside of cell
Microelectrode 0 mV
– 65 mV
K channel
Increasingly negative charge inside the neuron
Increasing [K+] outside the neuron
Equilibrium!
![Page 7: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/7.jpg)
![Page 8: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/8.jpg)
at 20° C
The Nernst equation can be used to calculate the equilibrium potential of a given ion
Inside cell Outside cell
[K+] 400 mM 20 mM
[Na+] 50 mM 440 mM
[Cl-] 51 mM 560 mM
![Page 9: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/9.jpg)
Squid have axons about 1,000 X wider than humans. This allowed them to do the early experiments that provided critical insights into how neurons work.
Andrew HuxleyAlan Hodgkin
![Page 10: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/10.jpg)
Squid Neuron - ContinuedImportant Point #1: They measured actual membrane potential (E-membrane) for the squid axon.
voltage meter
SW
nerve1mm diameter
axon0.1mm diameter
Emembrane-measured = -65 mV
![Page 11: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/11.jpg)
Squid Neuron - ContinuedImportant Point #2: They measured the concentrations of Na+, K+, and Cl- inside thesquid neuron and outside of it.
voltage meter
SW
nerve1mm diameter
axon0.1mm diamter
Emembrane-measured = -65 mV
In Out
[K+] 400 mM 20 mM
[Na+] 50 mM 440 mM
[Cl-] 51 mM 560 mM
![Page 12: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/12.jpg)
Squid Neuron - ContinuedImportant Point #2: They measured the concentrations of Na+, K+, and Cl- inside thesquid neuron and outside of it.
In Out
[K+] 400 mM 20 mM
[Na+] 50 mM 440 mM
[Cl-] 51 mM 560 mM
What is the predicted membrane potential based on each of these ions?
To answer . . . we simplify the Nernst equation to the following for Na+ and K+.
[ ]58 *log
[ ]membrane
outE mV
inside
For Cl-, we alter the ratio due to the negative charge (valence). The formula is the following . . .
Remember: -log (x) = log (1/x)
![Page 13: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/13.jpg)
What's the e-membrane potential based on K+?
In Out
[K+] 400 mM 20 mM
[Na+] 50 mM 440 mM
[Cl-] 51 mM 560 mM
[ ]58 *log
[ ]membrane
outE mV
inside
A. -75mVB. +75 mVC. -173mVD. -1.3 mVE. +173mV
![Page 14: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/14.jpg)
Squid Neuron - ContinuedImportant Point #2: They measured the concentrations of Na+, K+, and Cl- inside thesquid neuron and outside of it.
Emembrane-measured = -65 mV
In Out
[K+] 400 mM 20 mM
[Na+] 50 mM 440 mM
[Cl-] 51 mM 560 mM
Emembrane -K+ = -75 mV
E membrane -Na+ = 55 mV
Emembrane- Cl- = -60 mV
Predicted E-membrane from Nernst
Measured E-membrane
![Page 15: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/15.jpg)
Squid Neuron - SolutionSolution: We need a way to consider the effects of all 3 ions on the membrane potential. Will the sum of these predicted values equal the measured membrane potential?
Emembrane-measured = -65 mV
In Out
[K+] 400 mM 20 mM
[Na+] 50 mM 440 mM
[Cl-] 51 mM 560 mM
Emembrane -K+ = -75
E membrane -Na+ = 55
Emembrane- Cl- = -60
Emembrane-sum= -80
Predicted E-membrane from Nernst
Measured E-membrane
![Page 16: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/16.jpg)
[ ] [ ] [ ]58 *log
[ ] [ ] [ ]
K o Na o Cl i
membrane
K i Na i Cl o
P K P Na P ClE mV
P K P Na P Cl
at 20° C
The Goldman Equation extends the Nernst Equation to consider the relativepermeabilities of the ions (P): Ions with higher P have a larger effect on Emembrane
Calculating the total resting potential – the Goldman Equation
Permeabilities change during an action potential and how this allows neurons to “fire”.
![Page 17: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/17.jpg)
More key points on equilibrium & membrane potential
• The equilibrium potential for an ion is the voltage at which the concentration and electrical gradients acting on that ion balance out.
• The Nernst equation is a formula that converts energy stored in a concentration gradient to the energy stored as an electrical potential. This is calculated independently for each ion.
• The Goldman equation calculates a membrane potential by combining the effects of key individual ions.
![Page 18: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/18.jpg)
The Action Potential Is a Rapid Change in Membrane Potential
1. Depolarization phase
2. Repolarization phase
3. Hyperpolarization phase
Resting potential
Threshold potential
![Page 19: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/19.jpg)
Outside of cell
Inside of cell
Microelectrode 0 mV
– 65 mV
K channel
Increasingly negative charge inside the neuron
Increasing [K+] outside the neuron
Equilibrium!
![Page 20: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/20.jpg)
Voltage-gated sodium channels allow the action potential to occur
• https://www.youtube.com/watch?v=ifD1YG07fB8
![Page 21: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/21.jpg)
Voltage-gated channels
How voltage-gated channels work
At the resting potential, voltage-gated Na+ channels are closed.
Conformational changes openvoltage-gated channels whenthe membrane is depolarized.
Two important types:1.) Na+ voltage gated channels2.) K+ voltage gated channels
![Page 22: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/22.jpg)
Patch Clamping Allows Researchers to Record from Individual Channels
Currents through isolated channels can be measured duringan action potential.
Na
+ infl
ow K
+ outflow
Inwardcurrentfrom Na+
channels
Outwardcurrentfrom K+
channels
![Page 23: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/23.jpg)
Resting Potential - Both voltage gated Na+ and K+ channels are closed.
![Page 24: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/24.jpg)
Initial Depolarization - Some Na+ channels open. If enough Na+ channels open, then the threshold is surpassed and an action potential is initiated.
![Page 25: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/25.jpg)
Na+ channels open quickly. K+ channels are still closed.
PNa+ > PK+
![Page 26: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/26.jpg)
Na+ channels self-inactivate, K+ channels are open.
PK+ >> PNa+
![Page 27: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/27.jpg)
Emembrane ≈ E K+
PK+ > PK+ at resting state
![Page 28: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/28.jpg)
Resting Potential - Both Na+ and K+ channels are closed.
![Page 29: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/29.jpg)
![Page 30: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/30.jpg)
Action Potentials Propagate because Charge Spreads down the Membrane
PROPAGATION OF ACTION POTENTIAL
NeuronAxon
1. Na+ enters axon.
2. Charge spreads;membrane“downstream”depolarizes.
Depolarization atnext ion channel
3. Voltage-gatedchannel opens inresponse todepolarization.
![Page 31: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/31.jpg)
![Page 32: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/32.jpg)
![Page 33: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/33.jpg)
![Page 34: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/34.jpg)
Action Potentials Propagate Quickly in Myelinated Axons
Action potentials jump down axon.
Nodes of Ranvier Schwann cells (glia)wrap around axon,forming myelin sheath
Axon
Schwann cell membranewrapped around axon
Action potential jumpsfrom node to node
![Page 35: Monday April 9, 2014. Nervous system and biological electricity II 1. Pre-lecture quiz 2. A review of resting potential and Nernst equation 3. Goldman](https://reader031.vdocument.in/reader031/viewer/2022032702/56649cc35503460f9498c975/html5/thumbnails/35.jpg)
Wider axons have higher conduction velocities.
Myelinated axons have higher conduction velocities.