Topic 3 - NERVOUS SYSTEM I (Neuronal Physiology - AP)

Question 1

action potential

• a nerve ______
• large change in what?
• initiated where?

Answer 1

• a nerve impulse (signal)
• large change in membrane potential that propagates along an axon with no change in intensity
• initiated at trigger zone
  
  • e.g. axon hillock of multipolar neurons and bipolar neurons, just past dendrites of unipolar neurons

Question 2

study diagram (Ask teacher first)

Question 3

phases of action potential:

name the 3 phases

Answer 3

1. depolarization phase
2. repolarization phase
3. after-hyperpolarization phase (below RMP)

Question 4

phases of the action potential:

depolarization phase

1

1. 2. as gates open, more Na+ diffuses in (further increasing MP ⇒causes even more Na+ gates to open (a positive feedback mechanism)
2. Na+ diffuses in, causing depolarization to +30mV (inside of membrane becomes positive)

Answer 4

voltage-gated Na+ channels respond to membrane potential change (ex. GP) and open - greatly increases Na+ permeability

Question 5

phases of the action potential

depolarization phase

2

1. voltage-gated Na+ channels respond to membrane potential change (ex. GP) and open - greatly increases Na+ permeability
2. 3. Na+ diffuses in, causing depolarization to +30mV (inside of membrane becomes positive)

Answer 5

as gates open, more Na+ diffuses in (further increasing MP ⇒causes even more Na+ gates to open (a positive feedback mechanism)

Question 6

phases of the action potential

depolarization phase

3

1. voltage-gated Na+ channels respond to membrane potential change (ex. GP) and open - greatly increases Na+ permeability
2. as gates open, more Na+ diffuses in (further increasing MP ⇒causes even more Na+ gates to open (a positive feedback mechanism)
   3.

Answer 6

Na+ diffuses in, causing depolarization to +30mV (inside of membrane becomes positive)

Question 7

phases of the action potential:

repolarization phase

1

1. 2. voltage-gated K+ channels are open (increased permeability) therefore K+ diffuses out (positive charges (K+ move out - decreases MP)

Answer 7

Na+ channels close, become inactivated (decreased Na+ permeability) ⇒ Na+ movement returns to resting levels

Question 8

phases of the action potential:

repolarization phase

2

1. Na+ channels close, become inactivated (decreased Na+ permeability) ⇒ Na+ movement returns to resting levels
   2.

Answer 8

voltage-gated K+ channels are open (increased permeability) therefore K+ diffuses out (positive charges (K+ move out - decreases MP)

Question 9

phases of the action potential

after hyperpolarization phase (below RMP)

1

1. 2. Na+ channels are reactivated - can respond to stimuli

Answer 9

K+ channels are slow to close

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Question 10

phases of the action potential

after hyperpolarization phase (below RMP)

2

1. K+ channels are slow to close
   2.

Answer 10

Na+ channels are reactivated - can respond to stimuli

Question 11

phases of the action potential

what happens once K+ channels closes?

Answer 11

membrane potential returns to RMP

Question 12

note: ATPase always working to maintain ingredients

Question 13

how many action potentials does it take to cause a measureable change in [ion] in the cell?

Answer 13

10,000s