Membrane Potential

Question 1

Define the two parts in electrochemical gradient.

Answer 1

1. Chemical gradient(concentration gradient) due to difference in concentration across the membrane.
2. Electrical gradient due to membrane potential.

Question 2

How does electrical potential difference or voltage arise?

Answer 2

When charges are separated by distance.
Deeper explanation: the force of attraction between the charges separated by a distance is a form of potential energy known as an electrical potential difference. Electrical potential difference is measured by units called volts.

Question 3

How does the separation of charge across the membrane arise? 2 main concepts, 2 side concepts.(only worry about main)

Answer 3

Main:
1. Membranes of cells have leak channels
2. Na+ & K+ concentration gradients between the ICF and ECF established by the Na+/K+ ATPase.
Side:
1. Ions are very hydrophilic so the hydrophobic core of the bilayer prevents ions, removing across it. (Membrane acts as insulator)
2. The bilayer is only about 3 nm thick. There is still a strong force of attraction between the charges.

Question 4

What is normal charge or ICF and ECF in the body?

Answer 4

Both are electron Neutral always!(unless something is wrong). The only uneven distribution of charge is right at the cell membrane.

Question 5

What is the equilibrium potential for K+ in normal human? What about concentration?

Answer 5

-90mV.
ICF [150mM]
ECF [5mM]

Question 6

What is the equilibrium potential for Na+? What about general concentrations?

Answer 6

+60mV.
ICF [15mM].
ECF [145mM].

Question 7

What is the equilibrium potential for Cl-? What about general concentrations?

Answer 7

-63mV
ICF [10mM]
ECF [108 mM]

Question 8

Define equilibrium potential and what it means.

Answer 8

The voltage that equals the force of the concentration gradient, stopping net diffusion.
Ex. If positive ion has positive Eq. Potential: means cell needs to be more positive for equilibrium, meaning the chemical gradient is driving the positive ions into the cell, and you need a positive ICF environment to stop attracting more positive ions into the cell.

Question 9

What is the Nernst equation?

Answer 9

The Nerst equation determines the equilibrium potential for a single ion based on its concentration gradient.
(Actual cells have leak channels for several different ions.)

Question 10

What is the equilibrium potential for Ca++? What about general concentrations?

Answer 10

+128mV.
ICF [0.0001mM]
ECF [1.5 mM]
Note: calcium has a vanishing small concentration in the ICF. This allows, small puffs of calcium inside the sale to be effective signals.

Question 11

What does the Goldman-Hodgkin-Katz equation show?

Answer 11

Determines the membrane potential for a cell that is permeable to multiple ions.
Shows that the effect of an ion membrane potential is a function of its concentration gradient, and its relative membrane permeability.
(Like a weighted average, weighed on relative permeability(bottom of division), averaged on the concentration gradients (top of division).

Question 12

Given a typical resting membrane potential is -70 mV, which ion is the membrane most permeable to? Why?

Answer 12

K+.
Because potassium equilibrium potential equals -90 mV, which is the closest out of the four options, meaning it has the most leak channels. Because all ions want to reach equilibrium, so the one with the most leak channels wins.
(Cells have leak channels for both sodium and potassium but typically they are about 40 times more permeable to potassium.)

Question 13

What sets the resting membrane potential for any cell?

Answer 13

The relative number of Na+ and K+ leak channels. (Sometimes Cl- too).

Question 14

What is the membrane potential of neurons?

Answer 14

-70mV

Question 15

What is the membrane potential of skeletal muscle cells?

Answer 15

-90mV

Question 16

What does this mean: Cells have leak channels for both sodium and potassium, but they are about 40 times more permeable to K+

Answer 16

This means that the resting membrane potential is close to (but not the same as), the K+ equilibrium potential.

Question 17

What does this mean: A very small number of ions need to move across the membrane in order to establish the resting membrane potential.

Answer 17

Consider the concentration gradient as fixed. even though ions move to generate membrane potential, it is a tiny number compared to the total number of ions in the ICF and ECF.

Question 18

What does this mean: The Na+/K+-ATPase establishes and maintains the concentration gradient for Na+ and K+

Answer 18

Even though the pump is electrogenic (changes charge), the resting membrane potential is caused by the concentration gradient and relative permeabilities of the ions.

Question 19

What do cells use for signaling? (Hint: Voltage)

Answer 19

Changes in Membrane potential.

Question 20

What do cells use for signaling? (Hint: Voltage)

Answer 20

Changes in Membrane potential.

Question 21

Define depolarization.

Answer 21

Membrane potential (Vm) becomes less negative. (Positive!)

Question 22

Define hyperpolarization.

Answer 22

Membrane potential (Vm) becomes more negative.

Question 23

What ion permeability changes cause depolarization in cells? (3)

Answer 23

1. Increasing sodium permeability. Na+
2. Increasing calcium permeability. Ca++
3. Decreasing potassium permeability. K+

Question 24

What ion permeability changes caused hyperpolarization in the cell? (2)

Answer 24

1. Increasing potassium permeability. K+
2. Increasing chlorine permeability. Cl-

Question 25

Is hyperpolarization or depolarization excitatory?

Answer 25

Depolarization. (Makes line go higher on graph towards action potential voltage)

Question 26

For neurons, what are open channels?

Answer 26

Leak channels: they establish resting membrane potential.

Question 27

For temperature gated and mechanically gated channels in neurons, what is the “gate”?

Answer 27

Receptor potentials in afferent(sensory) neurons.

Question 28

For voltage gated channels, what is the “gate”?

Answer 28

Action potentials

Question 29

For chemically gated channels, what is the gate?

Answer 29

Synaptic potentials.