L3 - Membrane Potential

Question 1

What is the input zone of a nerve cell?

Answer 1

dendrites/cell body

Question 2

What is the trigger zone of a nerve cell?

Answer 2

axon hillock

Question 3

What is the conducting zone of a nerve cell?

Answer 3

axon

Question 4

What is the output zone of a nerve cell?

Answer 4

axon terminals

Question 5

Which cations are more concentrated in extracellular fluid?

Answer 5

calcium and sodium

Question 6

What is the equilibrium potential of K+?

Answer 6

-90 mV

Question 7

What is the equilibrium potential of Na+?

Answer 7

+60 mV

Question 8

What is the equilibrium potential of Cl-?

Answer 8

-63 mV

Question 9

What is the equilibrium potential of Ca2+?

Answer 9

+137 mV

Question 10

What is the resting membrane potential?

Answer 10

membrane potential of non-excitable cells at “rest”

Question 11

What allows for&raquo_space;90% of resting membrane potential?

Answer 11

passive diffusion of K+ and Na+ down their concentration gradients

Question 12

What allows for «10% of resting membrane potential?

Answer 12

Na+/K+ pump (active transport)

as this pump maintains Na+ and K+ gradients it has indirect effect to maintain RMP

Question 13

How many Na+ and K+ ions does the Na+/K+ pump exchange?

Answer 13

three Na+ out and two K+ in

Question 14

What causes a membrane potential?

Answer 14

near the cell membrane separated charges are responsible for creating a membrane potential (most of the fluid in the cell is electrically neutral)

Question 15

Are cells more permeable to Na+ or K+? Are potassium ions able to leave quicker than sodium ions enter?

Answer 15

cells are more permeable to potassium

therefore potassium ions are leaving quicker than sodium ions are entering

Question 16

Why is the equilibrium potential of K+ negative?

Answer 16

this is because a negative charge is required to keep K+ ions from leaking out into the extracellular fluid
K+ ions are at much higher concentrations inside the cell in comparison to outside the cell and are, therefore, driven to leak out into the extracellular fluid as a result of diffusion

Question 17

Why is the equilibrium potential of Na+ positive?

Answer 17

this is because a positive charge is required to keep Na+ ions from entering into the cell
Na+ ions are at much higher concentrations outside the cell in comparison to inside the cell and are, therefore, driven to enter the cell as a result of diffusion

Question 18

What will ultimately determine the value of the resting membrane potential?

Answer 18

determined by which occurs at a higher rate: Na+ influx, or K+ efflux
K+ efflux > Na+ influx because there are more K+ leak channels than Na+ leak channels in the membrane
thus resting membrane potential sits around -70mV, closer to the equilibrium potential for K+

Question 19

In the living body, is Na+ in the ECF and ICF in equilibrium or is it not in equilibrium?

Answer 19

is not in equilibrium

Question 20

Resting cell membranes are most permeable to…

Answer 20

K+

Question 21

What are the methods by which Na+ and K+ enter and leave the cell?

Answer 21

Na+ leak channels, K+ leak channels and Na+/K+ pumps

Question 22

What happens to the resting membrane potential of a cell if the extracellular K+ concentration increases?

Answer 22

it becomes more positive

Question 23

What happens to the resting membrane potential of a cell if the K+ leak channels are blocked?

Answer 23

it becomes more positive because only sodium ions are going to be moving into the cell

Question 24

What happens to the membrane potential of a cell that suddenly becomes more permeable to Na+?

Answer 24

it becomes more positive

Question 25

What is the Nernst potential of an ion?

Answer 25

the potential level across the cell membrane that exactly opposes net diffusion of the ion through the membrane

Question 26

What determines that magnitude of the Nernst potential and what is the formula for this equation?

Answer 26

determined by the ratio of the concentrations of that specific ion on the two sides of the membrane
E = V(in) - V(out) = RT/zF x In[C]out/[C]in