lecture 4 membrane potential

Question 1

what is equilibrium potential

Answer 1

when flow of ions (current) due to concentration gradient of an ion is exactly counterbalanced by the current due to the electrical gradient across the membrane

Question 2

what is the nerst equation used to calculate

Answer 2

the membrane potential at which an ion’s fixed concentration gradient is in equilibrium

Question 3

how do you calculate the nerst potential

Answer 3

60/valence charge of ion
* log (concentration out/concentration in)

Question 4

what is resting potential

Answer 4

what value a cell’s membrane potential is when it’s at rest

Question 5

how are glial cells different from neurons relative to ion channels

Answer 5

leak k+ channels are the only ion selective channels

Question 6

what two potentials are equal in glia cells

Answer 6

membrane potential and potassium equilibrium potential

Question 7

what does depolarizing mean

Answer 7

membrane potential is getting more positive, going toward positive values

Question 8

what does hyperpolarizing mean

Answer 8

membrane potential is getting more negative toward negative values

Question 9

goldman hodgkins katz equation function

Answer 9

how to figure out the resting potential when multiple ions are permeable (such as in neurons)

Question 10

are na and cl permeable in glial cells

Answer 10

no, the permeability is negligible so the ghk equation isn’t helpful in glia cells

Question 11

why is there a sodium potassium pump

Answer 11

maintains k+ and na+ concentrations

Question 12

where does most of energy neurons produce go

Answer 12

na/k pump, because as they move the ions against their concentration gradient they create energy

Question 13

when is an ion in equilibrium

Answer 13

at its nerst potential, because flow inward and outward are equal

Question 14

when is an ion in a steady state

Answer 14

with ghk, where the inward and outward currents are equal but may be carried by different ions

Question 15

what is the pump used in the na k pump made of

Answer 15

atpase, which uses energy by breaking down atp to adp

Question 16

what is resting potential

Answer 16

what value a cell’s membrane potential is when it’s at rest (-70)

Question 17

how do glia cells differ from neurons membrane poential

Answer 17

in glia cells, leak k+ channels are the only ion selective channels

Question 18

what is the membrane potential of glia cells equal to

Answer 18

potassium equilibrium potential

Question 19

what does ghk stand for

Answer 19

goldman hodkins katz

Question 20

what is the ghk equation used for

Answer 20

used for calculating resting potential when multiple ions are permeable

Question 21

what is the ghk equation

Answer 21

60*log {(permeability of ion concentration in/permeability of ion concentration out) + (permeability of ion concentration in/permeability of ion concentration out) + (permeability of ion concentration in/permeability of ion concentration out)

Question 22

why are there k leak channels

Answer 22

the leak channels bring excitable neurons back to stable state (restores equilibrium and brings back normal potential)

Question 23

what are the positive cations

Answer 23

k, na, ca

Question 24

what are the negative anions

Answer 24

cl, a (impermeant cellular proteins)

Question 25

why is the na k pump electrogenic

Answer 25

it creates a stronger electrical gradient by moving them against their concentration gradient, increasing energy and allowing atp to be made and used

Question 26

what factors allow ions to move in and out of cells

Answer 26

1) concentration gradient
2) electrical gradient/membrane potential
3) ion selective channels

Question 27

what gradients are in equilibrium at the equilibrium potential of an ion

Answer 27

chemical and electrical gradient

Question 28

What two gradients are in balance when an ion is said to be at its equilibrium potential

Question 29

Draw a graph of neuron’s cell membrane potential as a function of changing extracellular
potassium concentration (and how it differs from the graph of a glial cell)

Question 30

Recall the equilibrium potentials of potassium, sodium, and chloride and know which way
each would flow in a resting neuron

Question 31

Be able to apply the Nernst and GHK equations and know when to use which equation

Question 32

If a membrane is permeable to all ions, ion flow will eventually ______.

Answer 32

reach equilibrium

Question 33

What makes the cell membrane permeable to specific ions?

Answer 33

ion specific channels

Question 34

The Nernst equation calculates each ion’s equilibrium potential based on its _____.

Answer 34

both charge and ratio

Question 35

Glial cells are normally permeable to ______.

Answer 35

just K+

Question 36

If the concentration of a cation is higher on the outside of the neuron compared to the inside, the equilibrium potential will be _____ .

Answer 36

positive

Question 37

At a typical neuronal resting potential, the net movement of potassium ions through leak channels _____.

Answer 37

is outward

Question 38

The equation used to calculate membrane potential when there are multiple permeant ions is called the _____ equation.

Answer 38

Goldman, Hodgkin, Katz

Question 39

Resting potential

Answer 39

the membrane potential of a cell when it is just
chilling (no synaptic or action potential activity)

Question 40

Membrane potential

Answer 40

is a measure of the difference in the number of
positive versus negative charges inside a cell

Question 41

Write out the narrative for what it means for sodium to have an equilibrium
potential of +60 mV
(15mM inside and 150mM outside)

Answer 41

Imagine a cell with no channels and no membrane potential (i.e. it’s at 0 mV) but the outside
of the cell has 10-fold more sodium (Na+) than the intracellular cytosol. Now, let’s allow the
cell to have open sodium channels (i.e. it becomes permeable to Na+). Na+ will move down its
concentration gradient (outside to inside) until the membrane potential becomes +60mV
inside. At that membrane potential (and only that potential) the now positively charged inside
membrane potential will repulse enough of the high concentration of Na+ outside to stop the
net flow inward so that the movement of Na+ inward and outward are equal and opposite: in
equilibrium, that is, the chemical gradient (high outside) is counterbalanced by the electrical
gradient (high pos. inside). (Please remember the number of ions that move is so small that
the concentrations inside and out hardly change at all).

Question 42

how do capacitors in electric
circuits work

Answer 42

Charge of membrane potential
is “stored” on the membrane
where the excess charges in the
cell (typically too many anions)
are aligned with ions of the
opposite charge on the other
side of the nonconductive lipid
bilayer (the dielectric)

Question 43

In a neuron at normal resting physiological conditions, the resting potential is a) the same, b)
more hyperpolarized, or c) more depolarized than in a glial cell? Why?

Answer 43

A typical neuron is more depolarized than a glial cell. This is because a neuron at rest is permeable to
sodium and chloride in addition to potassium, while a glial cell is typically permeable only to potassium. The
equilibrium potentials for both sodium and chloride are more positive (depolarized) than the equilibrium
potential for potassium, so the flow of those ions make the membrane depolarized compared to EK. The
exact values can be calculated using the GHK equation

Question 44

What is the equilibrium potential of Ca++ ions? How does that compare to the equilibrium
potential for potassium? If the extracellular concentration of Ca++ is lower than K+, why is the
equilibrium potential for one positive and the other negative?

Answer 44

ECa = = 30mV*log (2/0.0002)= 120 mV
EK, = -80.6 mV (Calculated in #2). ECa is much more positive (depolarized) than the value for EK
The ratio and not the absolute value of the concentration sets the Nernst potential, and since the outside
concentration is much higher, the reversal potential for Ca is positive