Exam #1: Membrane Potential

Question 1

Is the intracellular concentration or extracellular concentration higher for K+?

Answer 1

Intracellular

Question 2

Is the intracellular concentration or extracellular concentration higher for Na+?

Answer 2

Extracellular

Question 3

Is the intracellular concentration or extracellular concentration higher for Cl-?

Answer 3

Extracellular

Question 4

Is the intracellular concentration or extracellular concentration higher for Ca++?

Answer 4

Extracellular

Question 5

Will the chemical driving force for K+ tend to push the ion into the cell or out of the cell?

Answer 5

Out

*Note that chemical force on an ion is only due to the chemical concentration gradient; charge nor membrane potential affect the direction of the chemical force.

Question 6

Will the chemical driving force for Na+ tend to push the ion into the cell or out of the cell?

Answer 6

In

*Note that chemical force on an ion is only due to the chemical concentration gradient; charge nor membrane potential affect the direction of the chemical force.

Question 7

Will the chemical driving force for Cl- tend to push the ion into the cell or out of the cell?

Answer 7

In

*Note that chemical force on an ion is only due to the chemical concentration gradient; charge nor membrane potential affect the direction of the chemical force.

Question 8

Will the chemical driving force for Ca++ tend to push the ion into the cell or out of the cell?

Answer 8

In

*Note that chemical force on an ion is only due to the chemical concentration gradient; charge nor membrane potential affect the direction of the chemical force.

Question 9

How does Ek+ change if the extracellular concentration of K+ is raised? What if it is lowered?

Answer 9

Remember that Ek+, or the electrochemical equilibrium, is the voltage where the chemical & electrical driving forces balance each other with no net movement of ions.

• Normal= -95mV
• Increase ECF K+ & Ek+ will be less negative
• Decrease ECF K+ & Ek+ will be more negative

Question 10

How does ENa+ change if the extracellular concentration of Na+ is raised? What if it is lowered?

Answer 10

Remember that ENa+, or the electrochemical equilibrium, is the voltage where the chemical & electrical driving forces balance each other with no net movement of ions.

• Normal= +70mV
• Increase ECF Na= ENa+ will be more positive
• Decrease ECF Na= ENa+ will be less positive

Question 11

How does the membrane potential change if the extracellular concentration of K+ is raised? What if it is lowered?

Answer 11

• Resting membrane potential is primarily determined by K+. - Thus, raising the ECF concentration of K+ will make the resting membrane potential less negative.
• Decreasing ECF concentration of K+ will make resting membrane potential more negative.

Question 12

How does the membrane potential change if the extracellular concentration of Na+ is raised? What if it is lowered?

Answer 12

• Elevated ECF Na+ would make the resting membrane potential more positive, but remember that Na+ contributes less than K+
• Diminished ECF Na+ would make the resting membrane potential less positive

Question 13

How does membrane potential change if the membrane permeability is changed?

Answer 13

The greater an ion’s permeability, the greater the “presence” it holds in determining Vm; i.e. more permeability= Vm close to the Ex of that ion.

Question 14

What is the role of the Na+-K+ Pump in maintaining cell membrane potential?

Answer 14

• The Na+/K+ Pump is electrogenic
• 3x Na+ Out
• 2x K+ In
• Thus, the sodium-potassium pump maintains the membrane potential & cell volume

Question 15

Hyperkalemia

Answer 15

Higher than normal ECF concentration of K+

Question 16

Hypokalemia

Answer 16

Lower than normal ECF concentration of K+

Question 17

Hypernatermia

Answer 17

Higher than normal ECF concentration of Na+

Question 18

Hyponatremia

Answer 18

Lower than normal ECF concentration of Na+

Question 19

Hypercalcemia

Answer 19

Higher than normal ECF concentration of Ca++

Question 20

Hypocalcemia

Answer 20

Lower than normal ECF concentration of Ca++

Question 21

What is depolarization?

Answer 21

Membrane becomes more negative outside

Question 22

What is hyperpolarization?

Answer 22

Membrane becomes more negative inside

Question 23

What is membrane potential due to?

Answer 23

Separation of electrical charges across the membrane

Question 24

How did the charges get separated?

Answer 24

1) Active transport of ions through the cell membrane

2) Diffusion of ions through selectively permeable membrane

Question 25

How is membrane potential measured? By convention what is the outside of the cell considered to be? What does that mean for the inside of the cell?

Answer 25

• Membrane potential is measured by placing electrodes in & outside the cell, then measure potential with a voltmeter
• Outside of the cell is 0 volts by convention
• Thus, inside of the cell is always negative relative to the outside of the cell

Question 26

If the membrane potential is negative, which direction will the electrical force draw positive ions? What about negative ions?

Answer 26

• Cations drawn IN

- Anions pushed OUT

Question 27

If a positive ion moves out of a cell, what happens to the membrane potential?

Answer 27

More negative

Question 28

If a positive ion moves into a cell, what happens to the membrane potential?

Answer 28

More positive

Question 29

Write the Nernst Equation. What does the Nernst Equation tell us?

Answer 29

• Value of membrane potential that would prevent any net diffusion of the ion
• Thus, strength of the chemical force on the ion

Question 30

What is the principle of electroneutrality?

Answer 30

Any macroscopic region of a solution must have equal numbers of positive & negative charges.

Question 31

Write the Goldman-Hodgkin-Katz equation.

Answer 31

N/A

Question 32

What are the differences between the Nernst & Goldman equations?

Answer 32

Nernst=

• Equilibrium potential
• Single ion
• Permeability is NOT a factor

Goldman=

• Multiple ions
• Permeability is a factor

Question 33

What is Quabain?

Answer 33

• Sodium-potassium pump inhibitor

- Causes the cell to lose its membrane potential

Question 34

At rest, does Ca++ contribute to resting membrane potential?

Answer 34

No, the membrane is impermeable to Ca++