ActionPotentials / V-gated Channels

Question 1

Four phases of an action potential (in order)

Answer 1

1) Rising Phase
2) Overshoot Phase
3) Falling Phase
4) Undershoot Phase

Question 2

Which channel type gates faster? voltage gated Na or K?

Answer 2

Na+

Question 3

Is there an inactivation mechanism for voltage-gated K+ channels?

Answer 3

No

Question 4

Cause of the absolute refractory period

Answer 4

inactivation of voltage-gated Na+ channels

Question 5

Cause of the relative refractory period

Answer 5

activation of voltage-gated K+ channels

Question 6

Toxins which block voltage-gated Na+ channels (2)

Answer 6

Tetrodotoxin and Saxitoxin

Question 7

Drug categories which block/inactivate Na+ channels (3)

Answer 7

1) local anesthetics
2) some antiarrhythmics
3) some antiepileptics

Question 8

Toxin used for treating multiple sclerosis, blocking voltage-gated K+ channels

Answer 8

4-aminopyridine

Question 9

Toxins/Drugs (3) affecting voltage-gated K+ channels. Block delayed rectifier channel pore.

Answer 9

1) Tetraethylammonium (TEA)
2) 4-aminopyridine
3) some ions (barium, cesium)

Question 10

What is the affect of blocking voltage-gated K+ channels on action potentials.

Answer 10

Increases the duration of the action potential and shortens the refractory period. Enhance action potential initiation.

Question 11

How are action potential conducted in unmyelinated axons?

Answer 11

The action potential is regenerated at each segment along the length of the axon

Question 12

Name for the flow down an axon “ahead” of the action potential, depolarizing next segment to threshold

Answer 12

capacitive current

Question 13

Structural area where voltage-gated Na+ channels are densely clustered in myelinated axons

Answer 13

Nodes of Ranvier

Question 14

Areas of voltage-gated K+ channel concentration in myelinated axons

Answer 14

Juxtaparanodal region

Question 15

Where are juxtaparanodal regions situated in relations to Nodes of Ranvier?

Answer 15

Off to the sides of the node, with the paranode sandwiched in between

Question 16

How does the internodal membrane in myelinated axons affect the length constant?

Answer 16

Very high Rm increases the length constant.

Question 17

How does the internodal membrane in myelinated axons affect the time constant?

Answer 17

Time constant = (resistance) x (capacitance)

Decreased capacitance due to the thick membrane balances out the increased membrane resistance. Slight decrease in time constant.

Question 18

Why do demyelinating disease affect either the central OR peripheral axons?

Answer 18

CNS axons are myelinated by oligodendrocytes instead of Schwann cells in the PNS. So there’s a different pathology.

Question 19

Demyelination has what mechanism of action

Answer 19

Exposes voltage-gated and leak K+ channels, decreasing the Rm and then also length constant.

Question 20

What is the typical cause for acquired (as opposed to inherited) channelopathies?

Answer 20

Autoimmune

Question 21

Main pore-forming subunit in voltage-gated ion channels

Answer 21

alpha subunit

Question 22

Voltage-gated ion channels have how many alpha subunits (either homo or heterotetramers)

Answer 22

four

Question 23

How many transmembrane segments are in each alpha subunit of voltage-gated ion channels?

Answer 23

six

Question 24

Lines the pores of voltage-gated ion channels. Controls ion selectivity and permeability of channel.

Answer 24

Pore-loop (P-loop). In between transmembrane segments S5 and S6

Question 25

The S4 segment of voltage-gated ion channels. Contains positively charged amino acids (arginine, lysine)

Answer 25

Voltage-sensor

Question 26

Where might there be an inactivation particle on voltage-gated K+ channels?

Answer 26

N-terminal

Question 27

When are HVA Ca2+ channels activated?

Answer 27

High voltage activated during action potentials.

Question 28

When are HVA Ca2+ channels activated?

Answer 28

Low voltage activated so they activate somewhere between resting potential and action potential threshold.

Question 29

Myotonia, periodic paralysis and GEFS (generalized epilepsy with febrile seizures) are examples of…

Answer 29

Channelopathies

Question 30

Auxiliary subunits of voltage-gated ion channels

Answer 30

Beta, gamma, etc..

Question 31

Inheritance pattern of periodic paralysis

Answer 31

autosomal dominant (patients will have both mutated and normal voltage-gated sodium channels)

Question 32

What’s wrong with mutated voltage-gated sodium channels in periodic paralysis?

Answer 32

They inactivate slowly. Hyperkalemia (high blood/extracellular potassium) may play a role in this.

Question 33

Target L-type HVA channels on vascular smooth muscle (used to control hypertension) specifically.

Answer 33

Dihydropyridine calcium channel blockers