Lab 6 Action Potential

Question 1

RMP and where is more negative?

Answer 1

-70, more negative on the inside

Question 2

depolarization and cause

Answer 2

• voltage is less negative, Na+ enters

Question 3

hyperpolarization and cause

Answer 3

voltage is more negative, K+ keeps leaving or Cl- enters

Question 4

stimulated neuron meaning

Answer 4

neuron where Na+ LGIC are open (EPSP generated)

Question 5

EPSP cause and NT

Answer 5

Na+ LGIC open and Na+ enters causing depolarization, Ach on nicotinic and glutamat e

Question 6

IPSP cause and NT

Answer 6

Cl- LGIC opens and Cl- enters causing hyperpolarization, GABA in brain and glycine in spine

Question 7

4 phase of action potential and causes

Answer 7

• EPSP/ graded potential caused by Na+ entering through LGIC
• steep depolarization by Na+ entering through VGIC
• steep repolarization by K+ leaving through K+ VGIC
• after hyperpolarization by K+ still leaving

Question 8

overall story of action potential generation

Answer 8

NT binds to Na+ LGIC opening it –> Na+ enters causing wave of depolarization going to axon hillock –> Na+ VGIC open causing depolarization and Na+ enters –> K+ VGIC open and K+ leaves causing repolarization –> K+ keeps leaving causing hyperpolarization –> Na+/K+ pump restores RMP

Question 9

absolute refractory period

Answer 9

• no AP possible

- all Na+ VGIC are inactive closed and must go back to active closed before they can open again

Question 10

relative refractory period

Answer 10

• AP possible if strong enough stimulation (more frequent or greater duration)
• K+ hyerpolarization makes it hard for threshold to be reached

Question 11

equilibrium potential meaning

Answer 11

• if no other ion present around cell besides the one being examined and measure the voltage
• balance of electrical and chemical gradient across cell

Question 12

why RMP closer to equilibrium potential of K+

Answer 12

membrane more permeable to K+ due to leakage channels

Question 13

equilibrium potential of K+ and Na+

Answer 13

K+ = -90 = 
Na+ = +66

Question 14

action potential vs graded potential

• amplitude
• max depolarization
• summation
• refractory period
• initial stimulation

Answer 14

• all or none vs graded
• +40 vs 0
• no summation vs yes summation
• refractory period vs no refractory period
• Na+ VGIC vs Na+ LGIC

Question 15

summation meaning and temporal vs spatial summation

Answer 15

• summation = graded potentials can add up or cancel each other out
• temporal = higher frequency of graded potential
• spatial = graded potential from multiple presynaptic neurons add up

Question 16

2 ways intensity is encoded

Answer 16

1) increased frequency of AP

2) recruitment of more neurons to fire in a nerve

Question 17

all or none meaning and relation to different magnitudes of EPSP

Answer 17

• AP happens or doesnt happen

- if EPSP too weak = no AP, if EPSP stronger AP generated, stronger EPSP generates same AP

Question 18

E, gNa, gK meaning

Answer 18

E = membrane potential 
gNa = Na conductance / movement across membrane 
gK = K+ movement across membrane

Question 19

normal neuron at time 0

why gNa < gK

Answer 19

E = -63

gNa < gK because increased permeability to K+ due to leakage channels

Question 20

normal neuron at after hyper-polarization - what is the expected E value

Answer 20

E more negative then -63

Question 21

Na+ poison name and mechanism, common drug name

- effect on AP and why?

Answer 21

tetrodotoxin blocks Na+ VGIC

• no AP because no depolarization can be created
• lidocaine works the same way

Question 22

K+ channel poison

• effect on AP and why
• name of poison

Answer 22

• cannot repolarize completely since K+ VGIC dont work
• some repolarization due to leakage channel and Na+/K+ pumps
• tetraehtyl ammonia

Question 23

hypernatremia

• E at rest and why
• overall magnitude of impact

Answer 23

• more Na+ outside, slightly less negative RMP, very small impact in general

Question 24

hyponatremia

• E at rest and why
• affect on AP and why

Answer 24

• less Na+ outside, RMP is slightly more negative

- weaker AP because less Na+ available to rush in

Question 25

mild hypoklemia - effect on E - effect on after hyperpolarization

Answer 25

- less K+ outside, K+ leaves cell and RMP is more negative | - after hyperpolarization is more negative since steeper gradient for K+ to rush out

Question 26

mild hyperkalemia - effect on E - effect on gradient - effect on AP - relation to lethal injection

Answer 26

- more K+ outside, K+ enters cell and makes RMP less negative - gradient is weaker - AP generate one after the other by one stimulus - K+ lethal injection causes seizures and cardiac arrhythmia

Question 27

severe hypo and hyper kalemia and why

Answer 27

- both = no AP - hypo = less K+ in blood, K+ leaves causing hyperpolarzation of RMP that is so negative threshold can never be reached - hyper = more K+, inside of cell has lot of K+ so RMP less negative, Na+ VGIC open once then stay inactive (not sure why)

Question 28

second stimulus after relative refractory period

Answer 28

normal AP generated

Question 29

second stimulus during relative refractory period but is weak

Answer 29

no AP generated because stimulus is not strong enough small spike due to EPSP

Question 30

second stimulus during relative refractory period but is strong

Answer 30

AP generated but it is weaker due to K+ hyperpolarization