MnR S3 - Resting Membrane Potential

Question 1

Define membrane potential

Answer 1

Potential differences across the plasma membrane as the voltage inside the cell relative to the outside

Question 2

How can resting potential be measured?

Answer 2

• Using a microelectrode

- Fine glass micropipette containing conducting solution penetrates the cell membrane

Question 3

What is the resting potential of skeletal muscle?

Answer 3

• 90mV

Question 4

What is the resting potential of nerve cells?

Answer 4

-70mV

Question 5

What gives the cell membrane selectivity?

Answer 5

Ion channels

Question 6

How are ion channels controlled?

Answer 6

Ligand gating - opened or closed by binding of chemical legends which may be intracellular or extracellular

Voltage gating - opened and closed by changes in membrane potential

Question 7

How is resting membrane potential set up?

Answer 7

• Open K+ channels at rest means potassium diffuses out of the cell down its concentration gradient set up by the Na+-K+-ATPase
• Anions inside the cell cannot follow so cell becomes negatively charged on the inside
• The electrical gradient opposes the chemical gradient and an equilibrium is formed

Question 8

What is an equilibrium potential of an ion?

Answer 8

Membrane potential at which there is no net movement of that ion as the electrical and diffusional forces balance

Question 9

What equation can be used to calculate the equilibrium potential?

Answer 9

Nernst equation

Question 10

Why is the resting potential often less negative than Ek (equilibrium potential for potassium)?

Answer 10

Open K+ channels dominate the resting permeability of many cells so resting potential is close to Ek, however he membrane is not perfectly selective and so other types of channels may be open allowing ions to move in

Question 11

What is depolarisation?

Answer 11

Decrease in membrane potential so inside of cell becomes less negative. This occurs over a longer time period than an action potential.

Involves movement of Na+ and Ca2+

Question 12

What is hyperpolarisation?

Answer 12

Membrane potential increases and inside of cell becomes more negative

Involves movement of K+ and Cl-

Question 13

What would be the effect of increasing extracellular K+?

Answer 13

Make Ek more positive and so membrane potential would also become more positive

(The concentration gradient is less steep so less K+ leaves the cell)

Question 14

What is an excitatory postsynaptic potential?

Answer 14

Change in membrane potential that occurs in excitatory fast synaptic transmission when depolarising transmitters open Na+ and Ca+ and other cation channels

Question 15

What is an inhibitory postsynaptic potential?

Answer 15

Change in membrane potential that occurs in inhibitory fast synaptic transmission when hyperpolarising transmitters open K+ or Cl+ channels

Question 16

What are the two mechanisms of slow synaptic transmission?

Answer 16

• Direct G-protein binding

- Gating via intracellular messenger

Question 17

Outline the difference between G-protein binding and gating via intracellular messenger for slow synaptic transmission

Answer 17

Direct G-protein binding is rapid and localised

Gating via an intracellular messenger is across the whole cell membrane and involves G-protein binding to an enzyme which initiates a signalling cascade via an intracellular messenger or protein kinase

Question 18

How do fast and slow synaptic transmission differ?

Answer 18

Fast - receptor protein is also an ion channel

Slow - receptor protein and ion channel are separate proteins

Question 19

What is the resting potential of cardiac muscle?

Answer 19

-80mV