Lecture 7- Resting Potentials

Question 1

how can the membrane potential be measured

Answer 1

• Use voltmeter and microelectrode inside and outside the cell - When both electrodes on the outside- voltmeter= 0 - When the microelectrode penetrates inside the cell the potential will be negative

Question 2

phospholipid bilayer are permeable to

Answer 2

small uncharged molecules and very impermeable to charged ions

Question 3

what changes the permeability of the phospholipid bilahyer

Answer 3

membrane proteins e.g. protein channels that enable ions to cross the cell membrane

Question 4

membrane potential is defined as

Answer 4

the electrical charge that exists across a membrane

Question 5

units of membrane potential

Answer 5

mV

Question 6

resting membrane potential range from

Answer 6

-20 to -90mV

Question 7

skeletal muscle resting potential

Answer 7

-90mV

Question 8

cardiomyocytes resting potential

Answer 8

-80mV

Question 9

nerve cells resting potential

Answer 9

-70mV

Question 10

smooth muscle resting potential

Answer 10

-50mV

Question 11

ion channels make the whole membrane

Answer 11

selectively permeable to ions

Question 12

which channels dominate the membrane ionic permeability at rest

Answer 12

potassium

Question 13

when do sodium channels open

Answer 13

during depolarisation

Question 14

resting potential =

Answer 14

equilibrium potnetial of potassium (EK)

Question 15

how is the equilibrium potnetial of potassium (resting potential) set up?

Answer 15

Chemical diffusion and electrical gradients

1) Chemical diffusion: Potassium flows out of the cell down its concentration gradient via diffusion

2) Electrical gradient: causes potassium to flow back in due to the negativity created by K+ initially leaving the cell down its conc gradient (and also intracellular anions)

When these forces are equal and opposite- no net movement of potassium - negative membrane potential due to anions

Question 16

the Nerst equation can rearranged to

Answer 16

calculate the membrane potential at which [K+] ([any ion]) will be in equilibrium, given the outside and inside K+

Question 17

resting potential of potassum

Answer 17

potassum dominates resting membrane permea bility

Ek= -95mV

Question 18

Why is the resting ptoential of a cell - 70mV and not -95mV

Answer 18

Sodium and calcium channels leak sodium and calcium into the cell, diminishing the negative potential to -70mV

• Na+ and K+ channels normally closed- voltage sensitive
• Occasionally flicker into open conformation and then close again
• Depolarising the membrane

Question 19

why do different cell types have different resting potnetials

Answer 19

In some cells the number of sodium, calcium and chloride (would make more negative)channels are higher or lower- different cells have different resting potentials e.g. smooth muscle cells must have lots of sodium and calcium channels

Question 20

Na/K ATPase and resting potential

Answer 20

K + channels dominate the resting membrane permeability (not the Na/K+ ATPase)

Leaves negative potential inside cell- but only a tiny change

*predominant potential set by channels and not ATPase*

Question 21

Role of Na/K+ ATPase

Answer 21

Leaves negative potential inside cell- but only a tiny change

Creates gradient for sodium and potassium to cause movement of ion