announcements tutorial next thursday, oct 9 –submit questions to me mid-term schedule go vote!
TRANSCRIPT
![Page 1: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/1.jpg)
Announcements
• Tutorial next Thursday, Oct 9– Submit questions to me
• Mid-term schedule
• Go vote!
![Page 2: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/2.jpg)
• Today– Action Potential Conduction
• Next Lecture– Synaptic Transmission
![Page 3: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/3.jpg)
Action Potential Conduction
Axon hillock
Region of neuron where AP usually starts
![Page 4: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/4.jpg)
Action Potential Conduction
Why are Action Potentials needed?1. First look at current flow without APs.
2. Second look at current with APs
![Page 5: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/5.jpg)
Passive Current Flow
Recordvoltage
Inject current
axon
![Page 6: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/6.jpg)
axon
voltage
distance
0.63V0
0Length constant
V= Vo – 0.63Vo
Inject current
Recordvoltage
![Page 7: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/7.jpg)
Passive Current
1. Current decays very rapidly along the length of an axon
2. The length constant is the distance over which the potential drops to 63% of the highest value
3. Typical length constants range only from
1-5 mm
![Page 8: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/8.jpg)
Length Constant
• Depends on:
1. Resistance across the membrane (‘leakiness’)
2. Longitudinal resistance to current flow (varies with axon diameter)
![Page 9: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/9.jpg)
Passive Current FlowInject current
axon
Membrane Resistance
Longitudinal Resistance
![Page 10: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/10.jpg)
Action Potential Conduction
Recordvoltage
Stimulate Action Potential
axon
![Page 11: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/11.jpg)
Action Potential Conduction
1. APs constant amplitude at all points along the axon
![Page 12: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/12.jpg)
Na+Inject current
![Page 13: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/13.jpg)
Na+Inject current
![Page 14: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/14.jpg)
Sequence of Events leading to AP propagation
1. Stimulus opens Na+ channels & cause AP
2. Depolarizing current flows down the axon
3. Local depolarization opens Na+ channels
downstream & initiate a new AP
4. Na+ channels close (inactivate) & K+ channels open
5. Local depolarization opens Na+ channels
downstream and initiate a new AP
![Page 15: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/15.jpg)
Na+Inject current
![Page 16: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/16.jpg)
Conduction Velocity
Recordvoltage
Inject current
axon
Measure distance betweenrecording sites
Measure time between APs
![Page 17: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/17.jpg)
distanceconduction velocity=
time
1. Axon diameter2. Myelination
Small unmyelinated 0.5 m/sLarge myelinated 120 m/s
![Page 18: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/18.jpg)
Myelinated nerve
Myelin Formed by: Schwann cells (periphery)Oligodendrocytes (central)
Node of Ranvier
![Page 19: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/19.jpg)
Myelin
![Page 20: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/20.jpg)
MyelinNa+
Saltatory conduction
![Page 21: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/21.jpg)
Myelin
Myelin increases speed of conduction by:
1. Increasing membrane resistance• Reduces ‘leakiness’ length constant
2. Voltage-gated channels only at Node of Ranvier
• APs generated only at the Node
![Page 22: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/22.jpg)
Mulitple Sclerosis
• Demyelination of axons– Impaired AP conduction– Symptom depends on nerves affected
• Optic nerve blindness• Motor nerves weakness or paralysis
![Page 23: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/23.jpg)
Summary & Key Concepts
1. Currents flow passively down axon• decay described by length constant
2. Action potentials propagation due to sequential opening of Na+ channels in response to local depolarization
3. Conduction velocity determined by axon diameter and myelination - length constant
4. Myelin trans-membrane resistance and Na+ channels only at Nodes
• Saltatory conduction
![Page 24: Announcements Tutorial next Thursday, Oct 9 –Submit questions to me Mid-term schedule Go vote!](https://reader035.vdocuments.us/reader035/viewer/2022062322/56649e895503460f94b8db0f/html5/thumbnails/24.jpg)
Sample Question
• AP conduction velocity will increase following an increase in the electrical resistance of the:
A. Axon membrane
B. Node of Ranvier
C. Schwann cell