Topic 2:3

Question 1

Absolute RP

Answer 1

For a period of 1-2 msec after first AP, all voltage gated Na+ channels are inactive and cannot be opened
This produces an absolute refractory period- 1-2msec after one AP, second cannot be produced
Threshold to produce an AP is infinite during this period after one AP

Question 2

relative RP

Answer 2

6-7msec after, as different voltage-gated Na+ channels start recovering at different rates

Question 3

Start of RRP

Answer 3

Only small number of channels
Opening results only in small influx of Na+ before channels again inactivate
So if you want a full AP where the Em reaches +30mV, you can’t do it unless provide lots of current
The start of the RRP, the threshold for an AP is very high

Question 4

Middle of RRP

Answer 4

Still not all of them but more
If you want a full AP, provide some current to combine with the charge from this amount of Na+ Ions flowing into cell
The middle of RRP, effective threshold is not as high as at start

Question 5

End of RRP

Answer 5

All Channels open
Usual influx of Na+ before they inactivate again
Can raise the Em to +30mV without current
By the end of RRP, effective threshold for a full sized AP is back to normal levels

Question 6

AP flow

Answer 6

passive electrotonic spread of current

Question 7

AP travel unidirectional

Answer 7

The current from a point producing an AP does flow backwards into regions that had just previously produced an AP
But remember that during an AP, the voltage gated Na+ channels became refractory
So since they are now refractory, it means that although there is current flowing back into those regions of the axon, they will not be able to produce an AP
This current will simply leak out over time

Question 8

reduce AP leaking

Answer 8

increase axon diameter: changes the ratio between the resistance to current flow down the neuron vs resistance to current flow across the neuron
Decreased leakage decreases number of times AP has to be produced
As diameter increases, CV also increases
myeline sheathes around axons, decreasing leakiness and decreasing number of APs that have to be produced to transmit information along the nerve and therefore speeding up the CV

Question 9

AP propagation in myelinated neurons

Answer 9

saltatory conduction

Question 10

demyelinating disorders

Answer 10

destruction of myelin (autoimmune diseases like multiple sclerosis, Guillain-Barre syndrome)

Question 11

dismyelinating disorders

Answer 11

abnormality in the make up of the myelin (genetic diseases like adrenoleukodystrophy)