Lec 3 - Mam Phys
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84 Terms
Question
Answer
What is the resting membrane potential (RMP)?
The electrical potential difference across the membrane of a resting cell.
What is the typical resting membrane potential of a neuron?
Approximately -70 mV.
Why is the resting membrane potential negative?
Because the inside of the cell is more negative than the outside.
What three factors determine the resting membrane potential?
Ion concentration gradients, membrane permeability, and the Na+/K+ ATPase.
Which ion has the greatest influence on resting membrane potential?
Potassium (K+).
Why does potassium have the greatest effect on resting membrane potential?
Because the membrane is much more permeable to K+ than Na+ at rest.
Which ion is more concentrated inside the cell?
Potassium (K+).
Which ion is more concentrated outside the cell?
Sodium (Na+).
Where is calcium (Ca2+) found in highest concentration?
Outside the cell.
Which negatively charged proteins remain inside cells?
Large intracellular anionic proteins.
Why can't intracellular proteins diffuse across the membrane?
They are too large and impermeable.
What is an electrochemical gradient?
The combined effects of concentration and electrical gradients.
What is the concentration gradient?
The difference in solute concentration across a membrane.
What is the electrical gradient?
The difference in electrical charge across a membrane.
What does the electrochemical gradient determine?
The direction ions move across the membrane.
What is equilibrium potential?
The membrane potential at which electrical and chemical forces are balanced.
What equation calculates equilibrium potential?
The Nernst equation.
What does the Nernst equation calculate?
The equilibrium potential for a single ion.
What happens when membrane potential equals an ion's equilibrium potential?
There is no net movement of that ion.
What equation predicts membrane potential using multiple ions?
The Goldman-Hodgkin-Katz equation.
Which ions are included in the Goldman equation?
Na+, K+, and Cl−.
Why is the Goldman equation more accurate than the Nernst equation?
It accounts for multiple ions and their relative permeabilities.
What is membrane permeability?
How easily an ion crosses the membrane.
What primarily determines membrane permeability?
The number of open ion channels.
What is membrane conductance?
A measure of how easily ions flow across the membrane.
How are permeability and conductance related?
Higher permeability results in higher conductance.
What happens when potassium permeability increases?
The membrane potential becomes more negative.
What happens when sodium permeability increases?
The membrane potential becomes less negative.
What is depolarization?
A membrane potential becoming less negative.
What is hyperpolarization?
A membrane potential becoming more negative.
What is repolarization?
The return toward resting membrane potential after depolarization.
What is the driving force on an ion?
The difference between membrane potential and the ion's equilibrium potential.
What determines the direction an ion moves?
Its electrochemical gradient.
Which direction does sodium move when sodium channels open?
Into the cell.
Why does sodium enter the cell?
Because both concentration and electrical gradients favor influx.
Which direction does potassium move when potassium channels open?
Out of the cell.
Why does potassium leave the cell?
Its concentration gradient is stronger than the electrical attraction inward.
Which pump maintains sodium and potassium gradients?
The Na+/K+ ATPase.
How many sodium ions does the Na+/K+ ATPase move?
Two K+ Three Na+ out.
How many potassium ions does the Na+/K+ ATPase move?
Two K+ in.
Does the Na+/K+ ATPase require ATP?
Yes.
Why is the Na+/K+ ATPase considered electrogenic?
It exports more positive charges than it imports.
How much does the Na+/K+ ATPase directly contribute to resting membrane potential?
Only a few millivolts.
What is the primary role of the Na+/K+ ATPase?
Maintaining long-term sodium and potassium gradients.
What happens if the Na+/K+ ATPase stops working?
Ion gradients gradually disappear.
Does membrane potential disappear immediately if the pump stops?
No, it dissipates gradually.
Which ion leak channels are most abundant at rest?
Potassium leak channels.
Why do potassium leak channels exist?
To establish resting membrane potential.
What is a leak channel?
An ion channel that is normally open.
Are voltage-gated sodium channels open at rest?
No.
What opens voltage-gated sodium channels?
Depolarization reaching threshold.
What opens voltage-gated potassium channels?
Depolarization.
Which opens faster during an action potential: voltage-gated Na+ or K+ channels?
Sodium channels.
Why do sodium channels produce rapid depolarization?
They open quickly and allow Na+ influx.
Why do potassium channels repolarize the membrane?
They allow K+ efflux.
What happens if extracellular potassium increases?
Resting membrane potential becomes less negative.
Why does hyperkalemia depolarize cells?
It reduces the potassium concentration gradient.
What happens if extracellular potassium decreases?
The membrane becomes more negative.
Why does hypokalemia hyperpolarize cells?
It increases potassium efflux.
Which ion's equilibrium potential is closest to resting membrane potential?
Potassium.
What is the approximate equilibrium potential for potassium?
About -90 mV.
What is the approximate equilibrium potential for sodium?
About +60 mV.
What is the approximate equilibrium potential for chloride?
About -70 mV.
Why is resting membrane potential closer to potassium's equilibrium potential?
Because resting membranes are much more permeable to K+.
What is capacitance?
The membrane's ability to store electrical charge.
What acts as a capacitor in cells?
The phospholipid bilayer.
What acts as resistors in the membrane?
Ion channels.
How does increasing membrane resistance affect ion flow?
It decreases current flow.
How does increasing conductance affect ion flow?
It increases current flow.
What happens to membrane potential when sodium conductance increases?
The membrane depolarizes.
What happens to membrane potential when potassium conductance increases?
The membrane hyperpolarizes or repolarizes.
What is the inside electrical charge relative to the outside at rest?
Negative.
Which side of the membrane has more sodium at rest?
Outside.
Which side has more potassium at rest?
Inside.
Which side has more calcium at rest?
Outside.
What is meant by selective permeability?
The membrane allows some ions to cross more easily than others.
Why is selective permeability essential?
It allows cells to establish membrane potentials.
What two forces always determine ion movement?
The concentration gradient and the electrical gradient.
What is meant by steady state?
Ion concentrations remain constant despite continuous ion movement.
How is steady state maintained?
By the Na+/K+ ATPase continually restoring ion gradients.
What is the difference between equilibrium and steady state?
Equilibrium has no net driving force; steady state requires energy to maintain constant conditions.
Which requires ATP: equilibrium or steady state?
Steady state.
Why is resting membrane potential important?
It provides the electrical foundation for action potentials and cell signaling.