L3: resting membrane potential - Levy Flashcards

1
Q

membrane resting potential in most human cells is near…

A

-70 mV

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2
Q

a reduction in resting potential is called ___

A

depolarization

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3
Q

a “graded” response is…

A

proportional to the stimulus

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4
Q

an action potential is initiated when the local potential reaches…

A

threshold depolarization

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5
Q

roughly how big is the gap in a synapse

A

~20 nm

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6
Q

T/F an action potential propagates without decrement

A

true

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7
Q

T/F a local potential propagates without decrement

A

false - a local potential diminishes over distance

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8
Q

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

A

the amplitude and shape is always the same

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9
Q

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

A

frequency of impulses

magnitude is always the same regardless of strength

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10
Q

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

A

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

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11
Q

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

A

activation of more sensory fibers

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12
Q

I = zFJ

A

current carried by an ion = valence x faraday x flux

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13
Q

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

A
  • concentration gradients

- permeabilities

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14
Q
ECF   Cytoplasm     (mEq/L)
K+
Na+
Cl-
Ca2+
A
ECF   Cytoplasm     (mEq/L)
K+        4         150
Na+    145         12
Cl-      112         10
Ca2+    2           10^-4
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15
Q

@ physiologic temperature equilibrium potential =

A

E = 61/z log (Cout/Cin)

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16
Q

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

A

equilibrium potential for K+ = -96 mV

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

17
Q

how do voltage gated channels work?

A

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

18
Q

what kind of channel gate is “mechano receptive” ?

A

stretch-gated channels

19
Q

driving force of K+ across a membrane =

A

DF = Vm - Ek+

20
Q

I = g (V - E)

A

ion current = conductance x driving force

21
Q

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

A

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

22
Q

oubain (or digitalis) is a drug that blocks…

A

blocks the Na+ K+ ATPase

so depolarization can be observed

23
Q

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

A

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.

24
Q

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

A

10x more permeable to K+

at rest

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
true
26
what is the math expression for resting membrane potential as a weighted sum of equilibrium potentials
``` Vm = sum (gi Ei) / sum gi Vm = (g1E1 + g2E2 + ...) / (g1 + g2 + ...) ```
27
ion current across membrane is related to...
conductance (g) and driving force (V-E)
28
at electrochemical equilibrium, how are ion currents, conductances, and driving forces related to each other
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
29
how is the Na+ K+ ATPase pump "electrogenic"
K+K+ in Na+Na+Na+ out generates an electric potential
30
what substance is a specific blocker of the Na+ K+ ATPase pump
oubain
31
accounting for both passive ion flux and active pump current, how is membrane potential calculated
Vm = [ sum (gi Ei) / sum gi ] + (Ia / sum gi) | where Ia = active pump current
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
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
33
does Vm hyperpolarize or depolarize if K+ is added to ECF?
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
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
D. Increasing the intracellular Na+ concentration will increase the Na-K ATPase activity