Session 3

Question 1

How is the membrane potential measured?

Answer 1

Using a voltmeter with an extracellular electrode and fine glass pipette microelectrode that impales the cell, around which the membrane reforms. A KCl/other conducting solution is used

Question 2

Which animal cells generally have the largest (most negative) resting potentials?

Answer 2

Cardiac and skeletal muscle cells, ~-80 to -90mV

Question 3

What is the range of animal cell membrane potentials at rest?

Answer 3

All negative; ~ -20 to -90mV range

Question 4

Which ion channels dominate the membrane ionic permeability in most cells at rest?

Answer 4

Voltage in sensitive K+ channels

Question 5

How does the resting membrane potential arise?

Answer 5

Membrane is selectively permeable to K+ (voltage in sensitive); there is an outward concentration gradient, but an inward electrical gradient; the equilibrium potential of K+ is about -95mv, but the membrane potential is closer to -70mV as the membrane is not perfectly selective (leak)

Question 6

How do smooth muscle cells achieve a lower resting potential of around -50mV?

Answer 6

The membrane has a lower selectivity for K+; there is increased contribution from other channels

Question 7

How do skeletal muscle cells achieve a more negative resting potential of around -90mV?

Answer 7

Cl- channels are open

Question 8

What is the equilibrium potential?

Answer 8

The charge at which the electrical and concentration gradients of an ion balance so that there is no net driving force on K+ across the membrane

Question 9

How can the equilibrium potential be calculated?

Answer 9

By using the Nernst equation

Question 10

What is ‘depolarisation’?

Answer 10

A decrease in the size of the membrane potential from its normal value; cell interior becomes less negative – not necessarily positive, just closer to 0

Question 11

What is ‘hyperpolarisation’?

Answer 11

An increase in the size of the membrane potential from its normal value; the cell interior becomes more negative

Question 12

How are changes in the membrane potential brought about?

Answer 12

Changing the activity of ion channels

Question 13

What is the Goldman-Hodgin-Katz equation?

Answer 13

Theoretical equation that takes into account permeabilities of important ions when calculating a theoretical membrane potential; it also depends on the number of channels open

Question 14

Which ions do nicotinic acetylcholine receptors allow through their intrinsic channel?

Answer 14

Na+ and K+ (and Ca2+; they are anionic)

Question 15

What are three mechanisms of gating of channel?

Answer 15

Ligand gating, voltage gating, mechanical gating

Question 16

What is mechanical gating?

Answer 16

Channels open in response to membrane deformation; e.g. channels in mechanoreceptors, carotid sinus

Question 17

What is the difference between fast and slow synaptic transmission?

Answer 17

Fast: receptor protein is also an ion channel (conformational change)
Slow: receptor and ion channel are separate proteins

Question 18

What is the difference between excitatory synapses and inhibitory synapses?

Answer 18

Excitatory open channels causing membrane depolarisation (Na+/Ca2+), inhibitory open channels that cause hyperpolarisation (K+/Cl-)

Question 19

Which transmitters cause ‘EPSP’s?

What are ‘EPSP’s?

Answer 19

Excitatory postsynaptic potential; longer time course than AP, graded with amount of transmitter; Ach, glutamate

Question 20

Which transmitters cause ‘IPSP’s?

What are ‘IPSP’s?

Answer 20

Inhibitory post-synaptic potential; longer course than AP; transmitters include glycine and GABA

Question 21

What are two mechanisms of slow synaptic transmission?

Answer 21

Direct G-protein gating, gating via intracellular messenger (cascade)

Question 22

What are electrogenic pumps?

Answer 22

Carrier proteins, that can slightly alter the membrane potential; example is Na+ pump