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Phys Lect 7
| Question | Answer |
|---|---|
| ____ is essential for intercellular communication | Propagation of APs |
| is the conduction of electrical current through an excitable cell active or passive? | Both. The current travels passively, but since the cell is leaky channels need to be actively opened (actively regenerated). |
| Actively depolarizing a membrane causes? | passive propagation of that current in both directions. The passive propagation triggers active AP regeneration in neighboring Na+ channels on the membrane. |
| Why don't AP cause retrograde depolarization since the current passively travels in both directions? | Becuase the retrograde Na+ channels are still in the absolute refractory period (INACTIVATED) and can not be re-activated. Therefore the AP only moves Anterograde down the axon. |
| How do internal resistance (Ri) and membrane resistance (Rm) influence the conduction velocity? | If Rm > Ri then velocity will be faster due to less leakiness from the axon. If Ri > Rm then velocity will be slower because the current will leak out of the axon. |
| What are 4 ways to increase conduction speed (based on resistance)? | 1.Increased Rm. 2.Decreased Ri. 3.Increased Axonal radius. 4.Increased space constant (Lambda). **Because the farther the current passively travels, the quicker depolarization occurs downstream. |
| The space constant is proportional to? Inversely proportional to? | Proportional: 1.Axonal Radius. 2.Rm. Inversely Proportional to: 1.Ri. **Larger space constant = faster velocity. |
| By what mechanism does myelination increase conduction velocity? | Since it is ~300 layers of lipid membrane, it drastically increases Rm thus increasing the space constant. |
| Which impacts conduction velocity more, myelination or axonal radius? | Myelination of an axon with 1/100th the radius is still 2-4 X faster. |
| Why does increasing an axon's radius increase the speed of conduction? | It directly increases the space constant. |
| Where is the only spot on a myelinated axon that active regeneration of an AP can occur? | Nodes of Ranvier. |
| a | contain a high density of Na+ channels, and represent the site at which the action potential is regenerated in a myelinated axon |
| Why do demyelination diseases lead to slower conductance? | With the loss of myelin, the Rm of the axon will decrease, allowing more of the current to leak out and the space constant to decrease. Therefore after a certain point, the current decays without being regenerated and the signal dies off. |
| symptoms of demyelination: | 1.Malcoordination. 2.Loss of balance. 3.muscle weaknes. |
| Guillain-Barre Syndrome | Demyelination of the PNS. |
| Multiple Sclerosis | Demyelination of hte CNS. |
Created by:
WeeG
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