lecture 5

Question 1

what does P refer to in the GHK equation

Answer 1

relative permeability

Question 2

what type of transporter is most I’m portent to action potentials

Answer 2

ion channels- much faster than transporters

Question 3

what happens if the permeability of an ion is increased

Answer 3

• the membrane potential will approach (but not go —–beyond) the equilibrium potential for that ion
• current will flow to move the membrane potential close to Eion

Question 4

what happens if the permeability of an ion decreases

Answer 4

the membrane potential will be less influenced by the ion whose permeability was reduced

Question 5

what is ionic current

Answer 5

amount of ionic current for any given ion is proportional to the permeability (force driving it across the membrane)

Question 6

current equation for ionx

Answer 6

I ionx= G ionx (E ionx - V m)

Question 7

what is the driving force

Answer 7

E ion x - V m

difference between equilibrium potential and membrane potential

Question 8

what is positive feedback action potential propagation

Answer 8

more current allows more voltage gated channels to open which makes more current which open more channels

Question 9

why are APs all or none

Answer 9

there is a threshold (voltage at which neuronal will go into positive feedback loop of sodium channels opening causing a inward current and depolarizing membrane further)

Question 10

what are someproblems in the textbook diagram of an action potential

Answer 10

the peak will not actually reach E Na because there are other ions contributing
disregards leak channels

Question 11

how can you measure the current being generated if it is constantly changing

Answer 11

voltage clamp technique - keeps voltage at a certain number

Question 12

what does the current flow for each ion species depend on

Answer 12

1. the force driving the ions, which = the difference between the voltage at the moment and the equilibrium potential
2. the conductance (through membrane) for that ion, which = the number of open channels * the single channel conductance (I ionX = Gx (Vm - Ex)

Question 13

what makes up a current profile

Answer 13

early: inward
late: outward

Question 14

K channel propbability

Answer 14

don’t all open at the same time or stay open for same amount of time- individual entities with probabilistic opening
increases with increased voltage and time

Question 15

Na channel speed

Answer 15

quick to open and quick to close

Question 16

K channel speed

Answer 16

slow to open and stay open until V is returned to negative potential

Question 17

Na functional states

Answer 17

after membrane potential returns to -ve value the inactivation gate takes a msec to relax back to non block

Question 18

K functional state

Answer 18

transitions from open to closed only takes a few sec after membrane is no longer depolarized

Question 19

when does Na channel go from inactivated to closed

Answer 19

when the membrane is hyper polarized

Question 20

when is the refractory period (channels_

Answer 20

when the K channel is slow to close and the Na channel is inactivated

Question 21

conductance

Answer 21

depolarization increases Na and K conductances

Question 22

action potential (channels)

Answer 22

result of fast acting inward Na that turns off even tho membrane is depolarized and slow acting K conductance that persists
Na inactivation and K persitence