17). AI Membrane Potentials & Ion Gradients Practice Flashcards

A comprehensive set of 60 practice flashcards testing membrane potentials, driving forces, equilibrium potentials, ion concentrations, and passive flux predictions based on the lecture material.

What creates the chemical driving force for an ion across a biological membrane?

A difference in ion concentration across the membrane.

What two factors determine the electrical force acting on an ion?

Membrane voltage and ionic charge.

In which direction does a concentration gradient drive an ion?

From higher to lower concentration.

A negatively charged intracellular environment electrically attracts which type of ions?

Cations.

If the cell interior is negative, in which direction does the electrical force on $\text{Cl}^-$ generally point?

Outward.

Which phrase describes the combined influence of electrical and chemical gradients?

Electrochemical driving force.

Why can an ion move against its concentration gradient through an open channel?

The electrical gradient may outweigh its chemical gradient.

For $\text{Na}^+$ in a typical resting cell, which direction do both the concentration and electrical gradients favor?

Inward.

Which force opposes outward $\text{K}^+$ diffusion from a typical resting cell?

Electrical attraction of $\text{K}^+$ toward the negative interior.

How do ion channels facilitate ion movement without directly hydrolyzing ATP?

They allow passive movement down an electrochemical gradient.

What is the definition of membrane potential ($V_m$)?

The voltage inside the cell relative to the outside.

What is an ion's equilibrium potential?

The $V_m$ at which its electrical and chemical forces balance.

Which equation calculates an individual ion's equilibrium potential?

The Nernst equation.

What is an ion's net passive movement when the membrane potential equals that ion's equilibrium potential?

Zero.

If extracellular $\text{K}^+$ increases while intracellular $\text{K}^+$ stays constant, what happens to $E_{\text{K}}$?

It becomes less negative.

If extracellular $\text{Na}^+$ increases while intracellular $\text{Na}^+$ remains fixed, what happens to $E_{\text{Na}}$?

It becomes more positive.

Which quantity is zero for an ion at electrochemical equilibrium?

Net electrochemical driving force.

What is the value of an ion's equilibrium potential ($E_{\text{ion}}$) if its inside and outside concentrations are equal?

$0\,\text{mV}$ for that ion.

What is the physical meaning of $V_m = -70\,\text{mV}$?

The cell interior is $70\,\text{mV}$ more negative than outside.

Which equation estimates $V_m$ using the relative permeabilities of several ions?

The Goldman-Hodgkin-Katz equation.

Which ion is typically more concentrated inside a mammalian cell?

$\text{K}^+$.

Which ion is typically more concentrated outside a mammalian cell?

$\text{Na}^+$.

Where is the concentration of free $\text{Ca}^{2+}$ generally much higher relative to the cytosol?

Outside the cell.

How does $\text{Cl}^-$ concentration compare across the membrane for a typical mature neuron?

It is higher outside than inside.

What is a common resting membrane potential for a neuron?

Approximately $-70\,\text{mV}$.

What is a typical equilibrium potential for $\text{K}^+$ ($E_{\text{K}}$) in a neuron?

Approximately $-90\,\text{mV}$.

What is a typical equilibrium potential for $\text{Na}^+$ ($E_{\text{Na}}$) in a neuron?

Approximately $+60\,\text{mV}$.

What is a typical equilibrium potential for $\text{Ca}^{2+}$ ($E_{\text{Ca}}$) in a cell?

Approximately $+120\,\text{mV}$.

What is an illustrative equilibrium potential for $\text{Cl}^-$ ($E_{\text{Cl}}$) in many mature neurons?

Approximately $-70\,\text{mV}$.

Between $\text{K}^+$ and $\text{Na}^+$, which sides of the membrane normally feature their respective high concentrations?

$\text{K}^+$ inside; $\text{Na}^+$ outside.

Why is the resting membrane potential ($V_m$) often closer to $E_{\text{K}}$ than to $E_{\text{Na}}$?

Resting membranes are commonly more permeable to $\text{K}^+$ than $\text{Na}^+$.

Which membrane proteins provide much of the resting membrane permeability to $\text{K}^+$?

$\text{K}^+$ leak channels.

What primary transport mechanism maintains the major resting $\text{Na}^+$ and $\text{K}^+$ gradients over time?

$\text{Na}^+/\text{K}^+\text{-ATPase}$.

How many $\text{Na}^+$ ions does the $\text{Na}^+/\text{K}^+\text{-ATPase}$ export per cycle?

Three.

How many $\text{K}^+$ ions does the $\text{Na}^+/\text{K}^+\text{-ATPase}$ import per cycle?

Two.

Why is the $\text{Na}^+/\text{K}^+\text{-ATPase}$ designated as electrogenic?

It exports one net positive charge per cycle.

If membrane permeability to $\text{Na}^+$ increases substantially at rest, how does $V_m$ respond?

It depolarizes toward $E_{\text{Na}}$.

If membrane permeability to $\text{K}^+$ increases substantially at rest, toward which value does $V_m$ move?

It moves toward $E_{\text{K}}$.

What is the physiological definition of hyperpolarization?

$V_m$ becomes more negative.

What is the physiological definition of depolarization?

$V_m$ becomes less negative or more positive.

When $V_m$ equals $E_{\text{ion}}$, what effect does opening a selective channel have on that ion's movement?

There is no net passive flux of that ion.

For a cation, in which direction does passive movement tend to go when $V_m$ is more positive than $E_{\text{ion}}$?

Outward.

For a cation, in which direction does passive movement tend to go when $V_m$ is more negative than $E_{\text{ion}}$?

Inward.

For an anion such as $\text{Cl}^-$, in which direction does passive movement tend to go when $V_m$ is more positive than $E_{\text{Cl}}$?

Inward.

For an anion such as $\text{Cl}^-$, in which direction does passive movement tend to go when $V_m$ is more negative than $E_{\text{Cl}}$?

Outward.

If $V_m = -70\,\text{mV}$ and $E_{\text{K}} = -90\,\text{mV}$, opening selective $\text{K}^+$ channels causes net flux in which direction?

Net $\text{K}^+$ efflux.

If $V_m = -70\,\text{mV}$ and $E_{\text{Na}} = +60\,\text{mV}$, opening selective $\text{Na}^+$ channels causes net flux in which direction?

Net $\text{Na}^+$ influx.

If $V_m = -70\,\text{mV}$ and $E_{\text{Ca}} = +120\,\text{mV}$, opening selective $\text{Ca}^{2+}$ channels causes net flux in which direction?

Net $\text{Ca}^{2+}$ influx.

If $V_m = -50\,\text{mV}$ and $E_{\text{Cl}} = -70\,\text{mV}$, opening selective $\text{Cl}^-$ channels causes net flux in which direction?

Net $\text{Cl}^-$ influx.

If $V_m = -90\,\text{mV}$ and $E_{\text{Cl}} = -70\,\text{mV}$, opening selective $\text{Cl}^-$ channels causes net flux in which direction?

Net $\text{Cl}^-$ efflux.

Do typical equilibrium potentials have fixed, identical values across all biological cells?

No, typical equilibrium potentials are approximate and vary by cell type and conditions.

What is the stoichiometric ratio of $\text{Na}^+$ exported to $\text{K}^+$ imported by the $\text{Na}^+/\text{K}^+\text{-ATPase}$ pump?

$3\,\text{Na}^+$ exported to $2\,\text{K}^+$ imported.

Under what condition is the net electrochemical driving force acting on a specific ion equal to zero?

When the membrane potential ($V_m$) is equal to that ion's equilibrium potential ($E_{\text{ion}}$).

When an ion's electrical force is equal in magnitude and opposite in direction to its chemical force, what state has it achieved?

Electrochemical equilibrium.

Why does a chemical driving force naturally move ions down a concentration gradient?

Because diffusion naturally drives substances from higher to lower concentration.

How can open passive channels permit ion movement against a concentration gradient without ATP consumption?

A sufficiently strong electrical gradient can outweigh the chemical gradient.

If a resting neuron at $V_m = -70\,\text{mV}$ undergoes an increase in $\text{K}^+$ permeability, does the cell depolarize or hyperpolarize toward $E_{\text{K}} = -90\,\text{mV}$?

It hyperpolarizes.

If a resting neuron at $V_m = -70\,\text{mV}$ experiences an increase in $\text{Na}^+$ permeability, does the cell depolarize or hyperpolarize toward $E_{\text{Na}} = +60\,\text{mV}$?

It depolarizes.

Why does a negatively charged cell interior exert an outward electrical force on $\text{Cl}^-$?

The negative intracellular charge repels negatively charged anions outward.

Why does a negative resting membrane potential favor the inward movement of cations electrically?

Opposite charges attract, drawing positively charged cations into the negative intracellular environment.