Membrane Potentials

Question 1

Membrane potential

Answer 1

The potential difference between the inside and outside of a cell (measured in millivolts: mV).

Question 2

Membrane potential of extracellular fluid

Answer 2

0 mV by definition

Question 3

Microelectrode

Answer 3

• Fine glass pipette
• Tip diameter < 1 μm
• Can penetrate cell membrane
• Filled with conducting solution (KCl)

Question 4

Animal cell resting membrane potential

Answer 4

-20 to -90 mV

Question 5

Cardiac and skeletal muscle cell resting membrane potential

Answer 5

-80 to -90 mV

Question 6

Nerve cell resting membrane potential

Answer 6

-50 to -75 mV

Question 7

Effect of -70 mV membrane potential

Answer 7

Outward chemical gradient exceeds inward electrical gradient resulting in net efflux of K+ ions.

Question 8

Effect of -90 mV membrane potential

Answer 8

Equilibrium potential- chemical and electrical gradients equal but opposite- no net flow of K+.

Question 9

The Nernst equation

Answer 9

Ek = (61/z)log([K+]o/[K+]i
Ek: membrane potential at which K+ at eqm
z: valency (+1 for K+)
[K+]o,[K+]i: concentrations

Question 10

Setting up the resting potential

Answer 10

• Open K+ channels dominate membrane ionic permeability at rest
• At eqm no net movement of K+ but -ve membrane potential
• Resting membrane potential arises as membrane more permeable to K+ at rest than other ions

Question 11

Depolarisation

Answer 11

• Decrease in the size of membrane potential from normal value
• Cell interior less negative

Question 12

Hyperpolarisation

Answer 12

• Increase in the size of membrane potential from normal value
• Cell interior more negative

Question 13

Effect of increasing membrane permeability to a particular ion

Answer 13

Membrane potential moves towards the equilibrium potential for that ion

Question 14

Equilibrium potential for K+ (Ek)

Answer 14

-90 mV

Question 15

Equilibrium potential for Cl- (Ecl)

Answer 15

-70 mV

Question 16

Equilibrium potential for Na+ (Ena)

Answer 16

+70 mV

Question 17

Equilibrium potential for Ca2+ (Eca)

Answer 17

+120 mV

Question 18

Movement of Na+ ions

Answer 18

Na+ moves into the cell to move Vm closer to Ena

Question 19

Movement of K+ ions

Answer 19

K+ moves out of the cell

Question 20

Movement of Cl- ions

Answer 20

Cl- moves into cell (has a -ve charge)

Question 21

Ligand gating

Answer 21

Channel opens or closes in response to binding of a chemical ligand e.g. channels at synapses that respond to extracellular transmitters.

Question 22

Voltage gating

Answer 22

Channel opens or closes in response to changes in membrane potential e.g. channels involved in action potentials.

Question 23

Mechanical gating

Answer 23

Channel opens or closes in response to membrane deformation e.g. channels in mechanoreceptors.

Question 24

Where can synaptic connections occur between?

Answer 24

nerve cell - nerve cell
nerve cell - muscle cell
nerve cell - gland cell
sensory cell - nerve cell

Question 25

Basic synaptic mechanism

Answer 25

Chemical transmitter released from presynaptic cell binds to receptors on postsynaptic membrane.

Question 26

Excitatory synapses

Answer 26

• Excitatory transmitters open ligand-gated channels that cause membrane depolarisation
• Permeable to Na+, Ca2+ or cations in general
• Resulting change called excitatory post-synaptic potential (EPSP)
• Excitatory transmitters include acetylcholine, glutamate

Question 27

Inhibitory synapses

Answer 27

• Inhibitory transmitters open ligand-gated channels that cause hyperpolarisation
• Permeable to K+ or Cl-
• Resulting change called inhibitory post-synaptic potential
• Inhibitory transmitters include glycine, ɣ-aminobutyric acid

Question 28

Factors that influence membrane potential

Answer 28

1. Changes in ion concentration
   - most important extracellular K+ conc (~5mM)
2. Electrogenic pumps - Na+/K- ATPase
   - contributes very little to potential
   - one +ve charge moved out per cycle

Question 29

Significance of active transport of ions on membrane potential

Answer 29

Indirectly responsible for entire membrane potential, because it sets up and maintains ionic gadients.