Action Potentials and Related Concepts

Question 1

Action potential outline

Answer 1

-90 mV is the resting potential
-65 mV is the approx. threshold value, sodium channel becomes activated
depolarization continues until +35 mV
sodium channels close 10,000ths of a second
potassium ion channels open, efflux of potassium
repolarization overshoots -90 mV: (refractory period, no additional impulse can be initiated)

Question 2

myelination

Answer 2

1. main lipid is sphingymyelin

2. allows 100X less loss of ions and requires little energy for repolarization

Question 3

diameter of axon is directly proportional to its speed

Answer 3

large cross section = more pathways for potential to take

Question 4

Orthodromic

Answer 4

direction of AP

axon to synapse

Question 5

antidromic

Answer 5

direction of AP

synapse to axon

Question 6

absolute refractory period

Answer 6

period during which a second action potential cannot be elicited even with a strong stimulus

Question 7

relative refractory period

Answer 7

stronger than normal stimulus can cause action potential

Question 8

Why is there a potential difference across the membrane?

Answer 8

it’s due to the immediately dichotomous distribution of ions across a membrane

Question 9

Nernst equation

Answer 9

used to determine the diffusion potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane: measures potential one ion at a time

Question 10

Which equation is used to determine the diffusion potential that opposes the net potential of another ion? what about more than one ion?

Answer 10

the nernst

the goldman equation

Question 11

nernst formula

Answer 11

z(61.5) * log (Outside ion/Inside ion) = EMF

z represents valence

Question 12

Equilibrium potential versus Diffusion potential

Answer 12

equilibrium potential refers to the electrical force driving ions across one permeable membrane versus ions from the other direction

“equilibrium will be reached when the electrical force driving chloride ions out of the left hand compartment exactly balances the concentrational force driving chloride ions of the right hand compartment”

in short, equilibrium is achieved when both the electrical forces and the force of concentration differentials

Question 13

Electrical neutrality

Answer 13

the sume of cations must equal the sum of anions

Question 14

Donnan (Gibbs-Donnan) Equilibrium

Answer 14

electrical potential must balance concentration gradients of both ions

Question 15

Which equation would you use to solve for the electrical potential of the sodium potassium pumps?

Answer 15

the donnan equilibrium

Question 16

resting potential of potassium ALONE versus sodium ALONE

Answer 16

potassium is around -94 mV, sodium is around +61 mV

Question 17

when do voltage gated ion channels “open” during the process of initiating an action potential

Answer 17

between -70 and -50 mV the sodium channels open