Week 1: Resting Membrane Potential Flashcards
List the components of the intracellular and extracellular fluids that are important for neuronal function.
Water (a polar solvent); ions (Na+, K+, Cl-, Ca2+); proteins (intracellular)
Describe the basic structure of the cell membrane, and the protein components that are embedded within it, particularly ion channel proteins and ion pumps
The phospholipid membrane has two layers with outward facing a polar “heads” and inward facing nonpolar hydrocarbon “tails”. It has membrane proteins in it, some which span the phospholipid bilayer. Special proteins, which exhibit ion selectivity and gating are key to neuronal function.
What are the physicochemical factors that influence the movement of ions in solution?
The concentration gradient and the electrical field.
Define current.
Movement of electrical charge (I).
Measured in amps
Ionic current - flow of charged ions
Define potential (voltage).
Electrical potential, difference in charge between anode and cathode.
Define conductance, and resistance.
Conductance (g) - measured in seimens, number of ions (or e-) available to carry a charge, and how easily they can move through space (e.g. if channels open).
Resistance is inverse of conductance.
What is Ohm’s Law?
V = IR
Ix = V.gx
Current = Voltage x conductance
What value you would expect for the resting membrane potential of a neuron?
-65mV
How would you measure the resting membrane potential of a neuron?
Using a microelectrode which was grounded in the extracellular fluid.
Which of the following does resting membrane potential depend on? (Select all that apply):
a. composition of salt solutions on either side of membrane
b. oxygen and carbon dioxide simple diffusion
c. composition of membrane itself
d. properties of proteins that span membrane
a. composition of salt solutions on either side of membrane
c. composition of membrane itself
d. properties of proteins that span membrane
What is needed to generate a steady electrical potential across a membrane
ionic concentration gradient for a particular ion
selective permeability of membrane to that ion
What does current depend on? (what is it proportionate to)
Voltage (potential difference) and conductance
What is the difference between monovalent and divalent ions?
a. Monovalent ions are positively charged, divalent ions are negatively charged
b. Monovalent ions are negatively charged, divalent ions are positively charged
c. Monovalent ions are have a charge of one, divalent ions have a charge of two
d. Monovalent ions are Na+ and Ca2+, divalent ions are Cl- and K+
c. Monovalent ions are have a charge of one, divalent ions have a charge of two
Which of the following is not a feature of proteins?
a. Alpha carbon
b. Amino group
c. A variable group (R)
d. A carboxyl group
e. A nitrate group
e. A nitrate group
What two conditions are necessary for ion movement by diffusion to occur?
Channels permeable to ions
Concentration gradient
What does the Nernst equation tell us, and what does it take into consideration?
Calculates the exact value of the equilibrium potential for each ion in mV
Takes into consideration:
• Charge of the ion
• Temperature
• Ratio of the external and internal ion concentrations
What does the Goldman Equation take into account?
Goldman-Hodgkin-Katz (GHK) equation takes into
account the relative permeabilities of all major ions
What drives ion movement by diffusion?
Diffusion
driven by ionic concentration gradient
Which of the following is NOT true?
a. Cations are positive
b. Cathodes are negative
c. Anions are positive
c. Anions are positive
Which of the following are true regarding channel proteins? (Select all that apply.)
a. They contain polar R groups and nonpolar R groups
b. They contain polar R groups which are hydrophobic
c. They sit on the surface of the cell membrane
d. They exhibit ion selectivity and gating
e. They have extracellular and intracellular regions
f. They are gated
a. They contain polar R groups and nonpolar R groups
d. They exhibit ion selectivity and gating
e. They have extracellular and intracellular regions
b and c and f are wrong: they span entire membrane, and polar = hydrophilic; some are gated some aren’t
What is equilibrium state?
A state where there is no net movement of ions. Diffusion and electrical forces are equal.
What is the difference between ion transporters and ion channels?
a. Ion transporters shown ion selectivity while ion channels do not
b. Ion transporters are gated while ion channels are not gated
c. Ion channels use ATP while ion transporters use glucose
d. Ion channels allow ions to diffuse down concentration gradient, while ion transporters actively move ions against their concentration gradients
d. Ion channels allow ions to diffuse down concentration gradient, while ion transporters actively move ions against their concentration gradients
What does the y Na+/K+ pump (Na/K ATPase) do?
It maintains ionic gradients by transporting 3x Na+ out of the cell and 2x K+ into the cell, using ATP.
Describe the structure of K+ channel.
4 protein subunits together to form pore, Pore loop amino acid chain
makes channel selective for
K+ ions
What drives ion movement by electricity through membrane channels?
Electrical field
driven by transmembrane potential
