L10 - resting and action potential

Question 1

define equilibrium potential for an ion

Answer 1

the membrane voltage that a cell needs to be at to prevent movement of that ion down its concentration gradient

Question 2

what does E stand for? eg Ek or Ena

Answer 2

equilibrium potential (of potassium or sodium)

Question 3

what will stop K+ from leaving cell

Answer 3

if the inside is very negative

Question 4

what will stop Na+ entering cell

Answer 4

if inside is very positive

Question 5

value of Ek

value of Ena

Answer 5

-90mV

+50mV

Question 6

what is Vm

Answer 6

resting membrane potential

Question 7

why is the Vm closer to Ek than Ena

Answer 7

because the membrane is about 50x more permeable to K

Question 8

what happens to Vm when a membrane becomes more permeable to an ion?

Answer 8

the ion drives Vm towards its equilibrium potential (by moving down conc gradient)

Question 9

what is the equation for driving force of an ion?

Answer 9

Vm - Eeq

resting mem potential - equilibrium potential of ion

Question 10

what is driving force of:
K
Na
what does this mean?

Answer 10

K =  +20mV forcing K+ out of cell 
Na =    -120mV forcing Na into cell

at rest,
there is a force of +20mV trying to push K out
and
a force of -120mV trying to push Na in

Question 11

what does the Goldman Hodgkin Katz equation do

Answer 11

considers relative permeabilities of ions to calculate Vm

Question 12

what is the Goldman Hodgkin Katz equation

Answer 12

Vm = 58mV x log ( Pk [K+out] / Pk [K+ in] + Pk[Na out] / Pk[Na in] )

Question 13

why is driving force on sodium greater than on K

Answer 13

because it is less permeable to Na

Question 14

how is an action potential generated

Answer 14

1. depolarisation causes Vm increase towards Ena (gets more positive)
2. when threshold is reached Na+ channels open causing an Na influx making inside more positive (+ve feedback)
3. peak
4. Na channels snap shut

Question 15

describe repolarisation

Answer 15

1. depolarisation causes slow opening of K+ channels
2. K+ efflux out
3. Vm goes back towards Ek

Question 16

how does an action potential propagate along a neuron

Answer 16

1. during depolarisation the section of the neuron that is depolarised becomes positive (inside) and the rest of the neuron is -ve inside
2. +ve is attracted to -ve, so the AP conducts to these -ve areas

Question 17

what is balanced in the equilibrium membrane potential of an ion

Answer 17

electrical force and osmotic force

Question 18

what is capacitance

Answer 18

membranes ability to store charge on either side of the membrane

Question 19

what does nernst equation tell us

Answer 19

the membrane potential that will stop the movement of the ion down its conc gradient

Question 20

what is permeability (related to this topic)

what is conductance (related to this topic)

Answer 20

the ease at which ions cross the membrane

how many ions get through the membrane