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Foundations 2 > Membrane Potentials I and II > Flashcards

Membrane Potentials I and II Flashcards

1
Q

What is the typical membrane potential of a cell?

A

-60 mV

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2
Q

two basic functions of membrane potentials

A

storage of energy

generation of action potentials for communication

driving force behind influx of calcium

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3
Q

extracellular/intracellular concentrations of Na+

A

145/10 mM

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4
Q

extracellular/intracellular concentrations of K+

A

5/140 mM

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5
Q

extracellular/intracellular concentrations of Cl-

A

116/4

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6
Q

causes of membrane potential

A

membrane is selectively permeable to K+

K+ leaks out of cells down its concentration gradient

leakage of K+ leaves a net negative charge inside the cell and a net positive charge outside

this generates an electric field, which opposes the opposite of K+

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7
Q

ionic equilibrium potential

A

the membrane potential at which there is no net flux of the ion across the membrane

different for each type of ion

due to a balance of electrical and chemical forces

defined by the Nernst equation

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8
Q

Nernst equation

A

Ei = (RT)/(zF)ln[(Ciout)/(Ciin)]

R = Gas constant (8.314)

T = temperature in K

z = number of elementary charges of the ion in question

F = Faraday constant (96,485)

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9
Q

Nernst potential for Na+

A

+67mV

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10
Q

Nernst Potential for K+

A

-84 mV

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11
Q

Nernst potential for Cl-

A

-84 mV

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12
Q

Nernst potential for Ca2+

A

+125 mV

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13
Q

Goldman-Hodgkin-Katz equation

A

sum of equilibrium potentials for major ions

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14
Q

What maintains the membrane potential?

A

the Na+/K+ ATPase moves 3 Na+ and 2 K+ in per cycle

resting potential occurs when ATPase activity counter-balances the passive fluxes

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15
Q

How quickly does potential across a passive membrane change? Why?

A

exponentially because the membrane acts as a resistor and a capacitor

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16
Q

Equivalent Circuit Model

A

modeling a membrane as a capacitor and a resistor (conductor) in parallel

17
Q

conductance equation

A

Gion = Iion/(RP - Eion)

18
Q

equation to calculate resting membrane potential using the electric circuit model

A
19
Q

equation to calciulate membrane potential in terms of permeability

A
20
Q

permeability

A

a measure of how many channels are open, does not depend upon ion concentrations

21
Q

response time

A

rate of change of Vm

has a delay due to Cm

time constant = Rm x Cm

22
Q

stimuli that can alter membrane potential

A

natural an artificial stimuli

23
Q

natural stimuli

A

neurotransmitters

hormones

toxins

24
Q

artificial stimuli

A

elevated extracellular K+ concentrations

intracellular Na+ injection

pharmaceutical agens that are analogs of natural stimuli

25
Q

action potential

A

a membrane depolarization that reaches a theshold and elicits additional depolarization without further stimulation

26
Q

properties of an action potential

A

rapid, transient depolarization of the membrane potential that exceeds 0 mV and is followed immediately by a rapid hyperpolarization

during of aobut 1-100 msecs

27
Q

absolute refractory period (ARP)

A

the short period of time after an action potention where a second one cannot be evoked

28
Q

relative refractory period (RFP)

A

the period of time from the end of the absolute refractory period to the time when new action potentials can be generated

29
Q

Why does the Na+ permeability of the membrane change with depolarization?

A

Due to the opening of depolarization-gated Na+ channels

activation of Na+ channels produces a regenerative increase in Vm

30
Q

What gives rise to the rapid fall of the action potential?

A

the opening of potassium channels that allows efflux of potassium

slightly slower than sodium channels

leads to the hyperpolarization of the membranes because it makes the membrane much more permeable to potassium than sodium

31
Q

drugs that modify or block action potentials

A

Na+ channel blockers

k+ channel blockers

Ca2+ channel blockers

Foundations 2 (33 decks)

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