M&R The resting membrane potential

Question 1

How can the resting membrane potential be measured? and what are the range of values found?

Answer 1

A microelectrode filled with a conducting solution penetrates the cell membrane and measures the voltage inside the cell relative to the outside.

Animal cells RP is -20 – -90mv
Cardiac and skeletal RP is -80 – -90mV
Nerve Cells RP is -50 – -75mV

Question 2

How is the resting potential established?

Answer 2

The types of channels open on the cell membrane makes the cell selectively permeable to certain ions which determines the resting potential.

Open K+ channels dominate the membrane ionic permeability at rest - the membrane is SELECTIVELY PERMEABLE to K+.

The Nernst equation lets you work out the equilibrium potential for any ion.

If the cell was selectively permeable to K+ alone the RP would equal Ek (-90mV), however there are other ions, so the RP is less negative at -70mV.

Question 3

What is the equilibrium potential of an ion?

Answer 3

The potential at which there is no net movement of the ion

Question 4

Define depolarisation

Answer 4

A decrease in the size of the membrane potential from its normal value - the inside of the cell becomes LESS NEGATIVE
Opening Na+ or CA2+ channels causes depolarisation

Question 5

Define hyperpolarisation

Answer 5

An increase in the size of the membrane potential from its normal value - the inside of the cell become MORE NEGATIVE
Opening K+ or Cl- channels causes hyperpolarisation

Question 6

What is the role of changing membrane potentials?

Answer 6

1. Action potentials
2. Triggering muscle contraction
3. Control of hormone and neurotransmitter secretion
4. Transducing sensory info to electrical activity via receptors

Question 7

How is the membrane potential changed?

Answer 7

Increasing membrane permeability to a particular ion moves the membrane potential towards the equilibrium constant for that ion

Question 8

What are the different types of gated channels?

Answer 8

1. Ligand gating
   Channel opens/closes in response to binding of ligand
   e.g. Channels at synapses
2. Voltage gating
   Channel opens/closes in response to changes in membrane potential
   e.g. Channels involved in action potentials
3. Mechanical gating
   Channel opens/closes in response to membrane deformation
   e.g. carotid sinus stretch receptors

Question 9

Give an example of fast and slow synaptic transmission

Answer 9

Fast synaptic transmission - the receptor protein is also an ion channel e.g. Ach receptors

Slow synaptic transmission - the receptor and channel are separate proteins (direct G-protein gating or gating via a intracellular messenger)

Question 10

Explain how ligand gating can give rise to synaptic potentials

Answer 10

Excitatory synapses - excitatory transmittors cause depolarisation resulting in an Excitatory Post-Synaptic Potential. Longer duration than AP, more transmitter = greater depolarisation
e.g Ach, Glutamate

Inhibitory synapses - inhibitory transmitters cause hyperpolarisation resulting in an Inhibitory Post-Synaptic Potential
e.g. Glycine, GABA