Membrane Potentials

Question 1

What is the concentration of K+ inside and outside of the cell and what is the equilibrium constant?

Answer 1

Outside (small 5)
Inside (large 150)
E(k+)= -91

Question 2

What is the concentration of Na+ outside and inside the cell and what is the equilibrium constant?

Answer 2

145 Outside
12 Inside
+66 E(Na+)

Question 3

Which ion channel has the greatest influence on disrupting resting membrane potential? What would have a smaller influence?

Answer 3

Great: Potassium Leak channels

Small: Na-K ATPase

Question 4

What are the charges on the inside and outside of the cell?

Answer 4

Positive on outside and negative inside

Question 5

What is the largest factor of resting membrane potential ?

Answer 5

Permeability of potassium ions, allowed by potassium leak channels

Question 6

What are two important things about the Na/K ATPase channel?

Answer 6

3Na ions are transferred out, while 2K ions are transferred inside,

uses ATP

Question 7

what is the typical muscle (cardiac/skeletal) resting membrane potential?

Answer 7

-80 to -90 mV

Question 8

What is smooth muscle normal resting membrane potential?

Answer 8

-60 mV

Question 9

What is neurons normal resting membrane potential?

Answer 9

-60 to -70 mV

Question 10

What two forces act on ions to develop the membrane potential? What is both together called?

Answer 10

diffusion forces (chemical gradients/concentration)
electrostatic forces (electrical gradients)

both together are electrochemical force

Question 11

What is equilibrium potential (Eion)?

Answer 11

membrane potential when elctrical and chemical forces are equal, no further movement occurs (not resting membrane potential)

Question 12

nerst equation to calculate equilibrium potential

Answer 12

61.5/z(charge of ion) x log[x out]/[xin]

Question 13

How do you calculate the driving force?

Answer 13

Resting membrane potential (Vm) - equilibrium potential (Ex) = driving force

Question 14

What does the driving force represent?

Answer 14

it takes into accound electrical and chemical forces to predict movement of ions

Question 15

if IONin > IONout (less than one) what will the log be?

if IONin < IONout (greater than one) what will the log be?

if IONin = IONout (0) what will the log be?

Answer 15

1. log will be negative
2. log will be positive
3. log will be zero

Question 16

What is the membrane impermeable to?

Answer 16

Calcium!

Question 17

What happens when extracellular K+ is low and the RMP is more negative?

Answer 17

It is further away from the threshold, so more difficult to depolarize cell (hyperpolarized)

Question 18

What happens when extracellular K+ is high and RMP is more positive?

Answer 18

It is closer to the threshold, and is easier to depolarize the cell

Question 19

What do cardiac glycosides inhibit?

Answer 19

Na/K ATPase allowing positive change inside membrane

Question 20

What is polarization?

Answer 20

deviation from 0mV

Question 21

What is depolarization?

Answer 21

when membrane potential becomes less negative

Question 22

What is hyperpolarization?

Answer 22

when membrane potential becoms more negative

Question 23

what is repolarization?

Answer 23

when membrane potential is returning towards resting membrane potential

Question 24

What are the 3 key properties of action potentials?

Answer 24

All-or-none

propagating or self/reinforcing

non-decremental (looks the same everywhere)

Question 25

If there is a small stimulus (graded potentials), will it spread further and quicker on a large or small diameter axon?

Answer 25

Large axon, will not do action potential unless large stimulus.

Question 26

What are the different phase for 
resting
depolarization
repolarization
hyperpolarization

Answer 26

resting: phase 4
depolarization: phase 0
repolarization: phase 3
hyperpolarization: refractory period

Question 27

What happens during depolarization (phase 0)?

Answer 27

voltage gated Na+ channels open activation gate rapidly, and close inactivating gate after minimal delay, causes large positive influx, stopping at +30mV (NA CHANNELS NEED TO BE RESET TO CAUSE AP AGAIN)

Question 28

What happens during repolarization (phase 3) ?

Answer 28

voltage gated K+ channels open slowly, and K+ leak channels bring K+ back into cell to get back to negative RMP

Question 29

What happens during hyperpolarization (refractory period)?

Answer 29

voltage gated K+ channels stay open too long, causing excess K+ and negative charge, making it more difficult to stimulate a subsequent actionpotential

Question 30

What occurs in the absolute refractory period?

Answer 30

Na channels are either open or the inactivation gate is closed and cannot reopen (NA channels not reset so no AP can be generated)

Question 31

What occurs in relative refractory period?

Answer 31

all Na channels have been reset (inactivation gate is open and activation gate is closed), action potential may be initiated, but requires a stronger stimulus b/c of hyperpolarization

Question 32

Na permeability during an action potential rapidly increases and decreases, what does K+ permeability do?

Answer 32

Slowly increases and decreases

Question 33

As extracellular concentration of potassium decreases, the resting membrane potential becomes more negative. As extracellular concentration of potassium increases, the resting membrane potential becomes…?

Answer 33

it becomes more positive

Question 34

What occurs during hypokalemic periodic paralysis?

Answer 34

dips in blood K+ levels, membrane is hyperpolarized, harder to reach threshold

Question 35

What occurs during hyperkalemic periodic paralysis?

Answer 35

Excess levels of K+ in blood, closer to threshold, any stimulus makes AP