Action potentials

Question 1

what is the RMP of a neuron

Answer 1

-65 mV

Question 2

what is the RMP determined by (2 main factors)

Answer 2

primarly permeable to K+ via leak channels (K+ flowing at rest)

K+ is more concentrated inside than outside

Question 3

what is the permeability of an ion proportional to

Answer 3

how many ion channels are open for that ion

Question 4

rank Cl-, K+, and Na+ from most to least permeable at rest

Answer 4

K+ (1.0) —> Cl- (0.45) —> Na+ (0.04)

Question 5

4 steps of an AP

Answer 5

1. all v-gated channels closed (RMP)
2. small amount of Na+ enters the neuron, MP becomes more positive, more v-gated Na+ channels open (depolarisation)
3. Na+ channels begin to inactivate while slower K+ channels open, MP becomes more negative (repolarisation)
4. Most v-gated channels closed but K+ leak channels and some v-gated still open, MP more negative than RMP because K+ is more permeable than at rest

Question 6

which blocker blocks Na+ (hodgkin and huxley)

Answer 6

tetrodotoxin (puffer fish)

Question 7

which blocker blocks K+ (hodgkin and huxley)

Answer 7

tetraethylammonium (sea snails)

Question 8

how did hodgkin and huxley know sodium was entering the cell

Answer 8

when sodium was removed, there was no more inward current

Question 9

how do APs propagate

Answer 9

spreads down axon like a wave in one direction

Question 10

why do APs only move in one direction

Answer 10

Na+ channels are inactive for a brief moment after AP so AP can’t propogate back

Question 11

why are active APs slower than passive diffusion

Answer 11

APs are slow because of gates but passive diffsion is insufficient because they decay

Question 12

how does passive diffusion effect voltage at neighbouring locations

Answer 12

voltage decays exponentially due to leaking ions

Question 13

what is saltatory conduction

Answer 13

AP jumping donw the axon from node of ranvier to node of ranvier

fast under myelin, slow AP, fast under myelin, slow AP

Question 14

3 factors that affect conduction velocity

Answer 14

membrane capacitance (stickiness)

membrane resistance (leakiness)
axoplasmic resistance (ion resistance to flow)

Question 15

how does membrane capacitance negatively affect conduction velocity in axons

Answer 15

high membrane capacitance (sticky)

small distance between + and - ions inside and outside = strong force
ions sticking to the sides decreases conduction velocity

Question 16

how does membrane resistance negatively affect conduction velocity in axons

Answer 16

low membrane resistance (hard to hold ions inside)

leak channels for K+ and Na+/K+ pumps

Question 17

how does axoplasmic resistance negatively affect conduction velocity in axons

Answer 17

high axoplasmic resistance - axons are thin

resistance for ion to flow (4 lanes of traffic on a 2 lane highway)

Question 18

how did invertebrates increase conduction velocity

Answer 18

larger diameter axons = decreased axoplasmic resistance

Question 19

how did vertebrates increase conduction velocity

Answer 19

adding myelin

increases membrane resistance (leakiness) by plugging leak channels
decreases membrane capacitance (stickiness) by increasing the distance from inside to outside