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Phys Lect 7

QuestionAnswer
____ 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