Membrane Potential

Question 1

What is chemical potential?

Answer 1

concentration gradient

Question 2

What is electrical potential?

Answer 2

charge differential

Question 3

What is electrostatic potential?

Answer 3

cumulative forces that act on charged ions

Question 4

What causes a membrane potential?

Answer 4

asymmetrical distribution of charges across a semipermeable membrane

Question 5

What determines changes in membrane potential?

Answer 5

changes in permeability of membrane ion channels

Question 6

What is the equilibrium potential?

Answer 6

membrane potential that just opposes the chemical potential for a given ion across a semipermeable membrane

Question 7

What equation describes equilibrium potential for a given ion? Explain each variable

Answer 7

Nernst equation - 
R = universal gas constant
T = temperature
z = valence (+1 for Na and +2 for Ca)
F = Faraday's constant
[ion]o = conc of ions outside
[ion]I = conc of ions inside

Question 8

What are the approximate equilibrium potentials of potassium, sodium and chlorine?

Answer 8

potassium = -95mV
sodium = +65mV
chlorine = -64mV

Question 9

What determines resting membrane potential?

Answer 9

Na+/K+ ATPase and leak channels (K+ leak channels dominate, but small Na+ leak draws membrane potential toward it)

Question 10

What equation describes resting membrane potential?

Answer 10

Goldman-Hodgkin-Katz Equation:

Question 11

What is the physiological importance of resting membrane potential?

Answer 11

important for action potentials and heart beating

driving force for ion transport

Question 12

What is the medical importance of membrane potential?

Answer 12

inhibition of ion channels or too much leakage of ion channels can be deadly

Question 13

What is a graded potential?

Answer 13

local transient changes in membrane potential invoked by neurotransmitters

Question 14

What determines the intensity of a graded potential?

Answer 14

distance away from stimulus (further means smaller)

strength of stimulus (stronger means larger)

Question 15

What is EPSP?

Answer 15

excitatory post synaptic potential: depolarizes membrane

by signaling of ionotropic glutamate receptors that conduct Na+ or Ca2+

Question 16

What is EPP?

Answer 16

end plate potential - depolarizes membrane

by signaling of acetylcholine receptors that conduct Na+ and Ca2+

Question 17

What is IPSP?

Answer 17

inhibitory post synaptic potential - hyperpolarizes membrane

by signaling of GABA receptors that conduct Cl-

Question 18

What is the difference of function of GABA receptors during development?

Answer 18

developing neurons have high Cl- in the cell so GABA receptors depolarize the cell by letting Cl- out

Question 19

What is the threshold potential?

Answer 19

membrane depolarization needed to trigger an action potential

Question 20

What is the safety factor?

Answer 20

amount that a graded potential depolarizes a cell more than the threshold potential

Question 21

What is myosthenia gravis?

Answer 21

loss of acetylcholine receptors at EP so safety factor is lost
muscle can’t generate as many action potentials

Question 22

What is an action potential?

Answer 22

dynamic all or nothing changes in membrane potential

Question 23

Describe the sequence of events in an action potential.

Answer 23

1. ESPSs sum to reach threshold depolarization
2. voltage gated Na+ channels activate letting Na+ into the cell (MP to 35mV)
3. at 35mV, voltage gated K+ ion channels activate to repolarize cell (-90mV)
4. Na+ channels are inactivated after a short time and remain that way until repolarization of membrane
5. often overshoots, so cell has to depolarize to get to resting membrane potential

Question 24

What is the absolute refractory period?

Answer 24

the cell cannot undergo another action potential during this time

Question 25

What is the relative refractory period?

Answer 25

it would be very difficult to undergo another action potential during this time, requires a huge stimulus

Question 26

What are the phases of cardiac action potential?

Answer 26

Phase 0: depolarization, Na+ channels open
Phase 1: rapid repolarization, K+ channels open, Na+ inactive
Phase 2: plateau repolarization, L-type Ca+ channels open, prolonging repolarization
Phase 3: end repolarization, another type of K+ channel opens to tip balance

Question 27

What is long QT syndrome?

Answer 27

caused by drugs that impair K+ channels