30: Membrane Potentials

Question 1

Ion concentrations: which are higher in ICF? ECF?

Answer 1

ICF: high K
ECF: high Na, Cl, Ca

Question 2

Na concentration in ECF and ICF

Answer 2

ECF: 140 mEq/L
ICF: 12 mEq/L

Question 3

K concentration in ICF and ECF

Answer 3

ECF: 3 mEq/L
ICF: 120mEq/L

Question 4

Diffusion potential

Answer 4

Voltage difference generated across a membrane when an ion diffuses down its concentration gradient

Question 5

What is the driving force for diffusion potential?

Answer 5

Concentration gradient

Question 6

Diffusion equilibrium for an Un-charged substance (ex: sucrose)

Answer 6

Only need to consider concentration gradient, not the electrical force

Question 7

Which ions make the greatest contribution to resting membrane potential

Answer 7

Those with the highest permeability (AKA high conductance = drives Em towards equilibrium potential)

Question 8

Resting membrane potential value

Answer 8

-70mV

Question 9

Channel status at resting membrane potential

Answer 9

Na + K channels closed

Question 10

What happens to channels with depolarization

Answer 10

1. Na activation gate opens
2. Na inactivation gate closes a lil after
3. K gates open around the peak

Question 11

What causes depolarization phase?

Answer 11

Na influx into cell

Question 12

Overshoot of AP

Answer 12

Membrane potential overshoots zero - becomes briefly positive

Question 13

Channels in repolarization

Answer 13

Na closed, K open

Question 14

Undershoot of AP

Answer 14

Membrane potential undershoots resting, transiently becomes more negative

Question 15

Absolute refractory period following AP

Answer 15

Inactivation gate of Na gate is closed - no amount of depol can cause AP

Question 16

Relative refractory period of AP

Answer 16

AP can be evoked, but not only with a greater than normal depolarization (threshold is higher)

Question 17

When is the Na Channel activation gate closed

Answer 17

When Em is = or more negative than resting membrane potential

Question 18

Is inactivation gate of Na channel open or closed during resting membrane potential?

Answer 18

Open

Question 19

Where does K move during repolarization of AP?

Answer 19

K moves out of cell

Question 20

Saltatory conduction

Answer 20

AP leaping along myelinated axon from one Node of Ranvier to the next

Question 21

Most common demyelination disease of CNS

Answer 21

Multiple Sclerosis

Question 22

Three things that occur in AP with loss of myelin sheath

Answer 22

1. Decrease in membrane resistance
2. Local currents decay more rapidly
3. Failure to conduct AP due to insufficient number of Na channels on internodal segments

Question 23

Symptoms of MS

Answer 23

Weakness in LEs, numbness, parasthesia, blurred vision, pain with eye movement

Question 24

Accommodation

Answer 24

When a nerve or muscle cell is stimulated at a sustained depolarized level -> never reaches AP because depol will open activation gates, but also closes inactivation gates and opens K gates

Question 25

What conductance is highest in accommodation?

Answer 25

K conductance (only gate that remains open)

Question 26

Hyperkalemia: two phases

Answer 26

1. Muscle spasms: due to increased K causing depolarization

2. Prolonged weakness: accommodation occurs due to prolonged depol from K

Question 27

What happens with hypokalemia in skeletal muscle?

Answer 27

Cell becomes hyperpolarized -> impaired ability for APs -> muscle weakness

Question 28

Periodic paralysis in hypokalemia

Answer 28

Rare neuromuscular disorder with sudden generalized weakness attacks

Question 29

What triggers periodic paralysis in hypokalemia?

Answer 29

Vigorous exercise, stress, high carb meals (often with a delay of several hours), increase in blood epi or insulin

Question 30

Why do epi and insulin increases cause periodic paralysis in hypokalemia?

Answer 30

They cause movement of K into cells

Question 31

Lidocaine mechanism of action

Answer 31

Blocks Na channels -> AP cannot occur