L3: resting membrane potential - Levy

Question 1

membrane resting potential in most human cells is near…

Answer 1

-70 mV

Question 2

a reduction in resting potential is called ___

Answer 2

depolarization

Question 3

a “graded” response is…

Answer 3

proportional to the stimulus

Question 4

an action potential is initiated when the local potential reaches…

Answer 4

threshold depolarization

Question 5

roughly how big is the gap in a synapse

Answer 5

~20 nm

Question 6

T/F an action potential propagates without decrement

Answer 6

true

Question 7

T/F a local potential propagates without decrement

Answer 7

false - a local potential diminishes over distance

Question 8

why is an action potential said to be a “stereotyped electrical signal” ?

Answer 8

the amplitude and shape is always the same

Question 9

how does the nervous system code the strength of a stimulus?

Answer 9

frequency of impulses

magnitude is always the same regardless of strength

Question 10

how does the nervous system code the duration of a stimulus?

Answer 10

length of action potential train
(repeated action potentials over time.. the length of a single action potential is always the same regardless of duration)

Question 11

one way nervous system codes strength of stimulus is frequency of impulses, what is another way?

Answer 11

activation of more sensory fibers

Question 12

I = zFJ

Answer 12

current carried by an ion = valence x faraday x flux

Question 13

cell resting potential depends upon the __ and __of different ions across the membrane

Answer 13

• concentration gradients

- permeabilities

Question 14

ECF   Cytoplasm     (mEq/L)
K+
Na+
Cl-
Ca2+

Answer 14

ECF   Cytoplasm     (mEq/L)
K+        4         150
Na+    145         12
Cl-      112         10
Ca2+    2           10^-4

Question 15

@ physiologic temperature equilibrium potential =

Answer 15

E = 61/z log (Cout/Cin)

Question 16

if the nerve cell were only permeable to K+, one would expect a membrane potential of…

Answer 16

equilibrium potential for K+ = -96 mV

EK+ = 61 log (4/150) = -96 mV

Question 17

how do voltage gated channels work?

Answer 17

+ and - charged amino acid residues on the channel change conformation when a voltage is applied

Question 18

what kind of channel gate is “mechano receptive” ?

Answer 18

stretch-gated channels

Question 19

driving force of K+ across a membrane =

Answer 19

DF = Vm - Ek+

Question 20

I = g (V - E)

Answer 20

ion current = conductance x driving force

Question 21

at equilibrium:
(V - E) for Na+ > (V - E) for K+
yet I K+ = I Na+, how?

Answer 21

I K+ = I Na+
g (V-E) = g (V-E)
for Na+, (V-E) is higher but g is lower

Question 22

oubain (or digitalis) is a drug that blocks…

Answer 22

blocks the Na+ K+ ATPase

so depolarization can be observed

Question 23

T/F the Na+ K+ ATPase causes the resting membrane potential

Answer 23

false - the resting membrane potential is caused mostly by K+ leak channels, modified by Na+ leak channels, and then maintained slightly more polarized by the Na+ K+ ATPase. to explain: concentrations of cations and anions on the same sides of the membrane are macroscopically electroneutral. a small outward leak of K+ (most permeable) causes the equilibrium potential near -96 mV. inward Na+ leak channels (less permeable) depolarize slightly (say ~ - 60 mV), and the Na+ K+ ATPase repolarizes slightly to typical -70 mV resting potential.

Question 24

at rest, is a nerve cell more permeable to K+ or Na+ ?

Answer 24

10x more permeable to K+

at rest

Question 25

T/F the resting membrane potential is a weighted sum of the equilibrium potentials, and will lie closest to the equilibrium potential for the ion with the greatest conductance

Answer 25

true

Question 26

what is the math expression for resting membrane potential as a weighted sum of equilibrium potentials

Answer 26

Vm = sum (gi Ei) / sum gi
Vm = (g1E1 + g2E2 + ...) / (g1 + g2 + ...)

Question 27

ion current across membrane is related to…

Answer 27

conductance (g) and driving force (V-E)

Question 28

at electrochemical equilibrium, how are ion currents, conductances, and driving forces related to each other

Answer 28

I1 + I2 + I3 +… = sum I = 0
g1(Vm-E1) + g2(Vm-E2) + g3 (Vm-E3) +..= sum I = 0
Vm = (g1E1 + g2E2 + …) / (g1 + g2 + …)
Vm = sum (gi Ei) / sum gi

Question 29

how is the Na+ K+ ATPase pump “electrogenic”

Answer 29

K+K+ in
Na+Na+Na+ out
generates an electric potential

Question 30

what substance is a specific blocker of the Na+ K+ ATPase pump

Answer 30

oubain

Question 31

accounting for both passive ion flux and active pump current, how is membrane potential calculated

Answer 31

Vm = [ sum (gi Ei) / sum gi ] + (Ia / sum gi)

where Ia = active pump current

Question 32

accounting for both passive ion flux and active pump current, at electrochemical equilibrium, how are ion currents, conductances, and driving forces related to each other

Answer 32

Ia + I1 + I2 + I3 +… = Ia + sum I = 0
I a + g1(Vm-E1) + g2(Vm-E2) + … = Ia + sum I = 0
Vm = (Ia + g1E1 + g2E2 + …) / (g1 + g2 + …)
Vm = [ Ia + sum (gi Ei) ] / sum gi
where Ia = active pump current

Question 33

does Vm hyperpolarize or depolarize if K+ is added to ECF?

Answer 33

depolarizes (ususally, unless gK increased)

• must add Cl- along with extracellular K+ to maintain macroscopic electroneutrality. thus concentration gradient down, less flux across K+ leak channels, smaller polarization and Veq
• -if raising K+ increases gK+ by opening more K+ channels, then cell may hyperpolarize instead

Question 34

Which of the following statements is correct?
A. Increasing the extracellular K+ concentration will cause the membrane to hyperpolarize.
B. Increasing the Na+ conductance of the leak channels will cause the membrane potential to hyperpolarize.
C. If Cl- is at equilibrium, increasing gCl will cause an increase in the net movement of ions through the membrane leak channels.
D. Increasing the intracellular Na+ concentration will increase the Na-K ATPase activity.
E. Blockage of the Na-K pump with ouabain will cause the membrane potential to hyperpolarize

Answer 34

D. Increasing the intracellular Na+ concentration will increase the Na-K ATPase activity