03-18 Introd; Resting Membrane Potentials

Question 1

What is the RMP for an SKM cell?

Answer 1

-90mV

Question 2

What is ohm’s law?

Answer 2

V = IR (voltage = current X resistance)

or

I = GV (current = conductance X voltage)

Question 3

units of current

Answer 3

amperes (A) = 1 coulomb of charge/sec

Question 4

units if potential different (E)

Answer 4

volts

Question 5

units of work

Answer 5

joules (1 joule is amt of work req’d to move 1 coulomb of charge across a 1 volt difference

Question 6

units of resistance (R)

Answer 6

measured in ohms (also 1/G)

Question 7

units of capacitance (C)

Answer 7

farads

Question 8

What is the capacitor in neurons?

Answer 8

the lipid bilayer of the plasma membrane

Question 9

What is the conductance (G) pathway in neurons?

Answer 9

ion channels

Question 10

What are the resistors (R) in neurons?

Answer 10

ion channels are also resistors b/c flow through them is limited by the size of the pore (re-call the R = 1/G)

Question 11

What are the major classes of ion channels?

Answer 11

1. leak channels
2. voltage-gated
3. ligand-gated
4. mechanosensory

Question 12

How much energy is req’d by ion channels to allow flux through them?

Answer 12

none, flux through ion channels is PASSIVE; they conduct orders of magnitude more ions through per second than pumps

Question 13

Give examples of where mechanosensory channels are located.

Answer 13

Pacinian corpuscles

Question 14

For a vertebral spinal cord neuron, compare and contrast the intracellular vs. extracellular concentration of Na+

Answer 14

Out = high (117mM)
In = lower (30mM)

Question 15

For a vertebral spinal cord neuron, compare and contrast the intracellular vs. extracellular concentration of K+

Answer 15

Out = low (3mM)
In = high (90mM)

Question 16

For a vertebral spinal cord neuron, compare and contrast the intracellular vs. extracellular concentration of Cl-.

Answer 16

Out = low (4mM)
In = high (117mM)
(think opposite of Na+)

Question 17

For a vertebral spinal cord neuron, compare and contrast the intracellular vs. extracellular concentration of “Anions-.”

Answer 17

Out = high (116mM)
In = none (0mM)

Question 18

Which channels are predominantly responsible for the maintenance of the negative RMP?

Answer 18

leaky K+ channels (not voltage- or ligand-gated; constitutively open at rest)

Question 19

What class of channels do leaky K+ channels belong to? What are some examples?

Answer 19

tandem-pore domain channels; they have names like TREK, TRAAK, TWIK, TASK, etc.

Question 20

When measuring current through a single pore (with patch-clamp technique) or across a whole membrane, what is the graphing convention for tracing (i.e. how does a tracing looking showing a flux of positive ions)?

Answer 20

flow of positively charged ions is downward deflection

Question 21

What are some examples of the intracellular anions that contribute to negative charge balance?

Answer 21

impermeable groups: phosphates on nucleic acids

Question 22

The intracellular concentration of K is much higher than the extracellular conc., and the intracellular anions that balance its positive charge in the cell are two big to follow it out the leaky channels. Since you have these constitutively-open, leaky K+ channels, why doesn’t the cell just waste all of its K+?

Answer 22

The resulting (-) charge inside the cell due to anions that are two big to follow K+ outside the cell pulls the K back into the cell.

Question 23

What is the point at which equilibrium is reached between the chemical gradient push of K+ out of the cell equals the electrical gradient push of K+ back into the cell?

Answer 23

The Equilibrium Potential (Eion)—there’s NO net flow of ions at this point. That is in SUMMATION of all the different ions, however.

Question 24

What is the equation to calculate the Eion?

Answer 24

The Nernst Equation!

Eion = (RT/zF)*ln([ion_in]/[ion_out])

Question 25

What is the Nernst equation for monovalent cations (like K+) at 37°C (body temp)?

Answer 25

E_k+ = 61*ln([ion_in]/[ion_out])

Question 26

Compare and contrast ion channels and pumps

Answer 26

Channels-always open, passive diffusion through them, large # ions can flow through fast (high flux)

Pumps-no pore so not always open, usually requires energy (e.g. ATPase, or conc grad of another ion), slower (low flux)

Question 27

What is the most important ion pump in neurons? How much energy does it use?

Answer 27

Na+/K+ ATPase; uses 20-40% of total brain’s energy requirement; 70% electrically active neuron’s energy requirement!

Question 28

What is the ratio of the Na+/K+ ATPase? What does the mean in terms of electroneutrality?

Answer 28

3Na+out/2K+in therefore ELECTROGENIC

Question 29

What is ouabain? Mechanism?

What another example in this drug class still used?

Answer 29

a cardiac glycoside poison that blocks Na+/K+ ATPase activity—>incr [Na+ in]—>upreg Na+/Ca2+ exchanger—>incr intracellular [Ca2+]—>ionotropically increases contraction

**in this situation the Na+/Ca2+ exchanger is operating in the opposite direction

**Digoxin is still used

Question 30

How sensitive are neurons to changes in membrane potential?

Answer 30

Very, even a 1-2mV ∆ can have big consequences

Question 31

What is RDP?

Answer 31

rapid-onset dystonia parkinsonism

• hereditary mutation in Na+/K+ ATPase
• leads to dystonic spasms in limbs, speech, swallow balance
• occurs after stressful event
• can cause seizures

Question 32

Myotonia Congenita

Answer 32

SKM Cl- channel mutation

• examples include Thomsen’s and Becker’s
• delayed relaxation after voluntary mov’t—>stiffness and/or weakness
• myotonic goats