Changing Membrane Potentials

Question 1

Give examples of how changes in membrane potentials are used.

Answer 1

Action potentials in nerve and muscle cells
Triggering and control of muscle contraction
Control of secretion of hormones and neurotransmitters
Transduction of sensory information into electrical activity by receptors
Postsynaptic actions of fast synaptic transmitters

Question 2

Define depolarisation.

Answer 2

A decrease in the size of the membrane potential from its normal value. This means that the membrane potential becomes less negative and therefore the cell interior becomes less negative.

Question 3

Define hyperpolarisation.

Answer 3

An increase in the size of the membrane potential from its normal value. This means that the membrane potential is more negative and therefore also the cell interior is more negative.

Question 4

How can the membrane potential be changed?

Answer 4

By changing the selective ionic permeability of an ion. For example increasing the membrane permeability for K+ means that K+ will leave the cell due to the concentration gradient. This will make the cell interior more negative and therefore cause hyperpolarisation.

Question 5

How can you increase the membrane permeability for an ion?

Answer 5

By opening channels.

Question 6

How does the membrane permeability relate to the equilibrium potential?

Answer 6

Increasing membrane permeability for an ion shifts the membrane potential towards the equilibrium potential of the ion.

Question 7

What will happen if you open channels for K+?

Answer 7

Hyperpolarisation and MP will move towards -95mV.

Question 8

What will happen if you open channels for Cl-?

Answer 8

Cl- will move into the cell. Cause hyperpolarisation and MP will move towards -96mV.

Question 9

What is the equilibrium potential of sodium?

Answer 9

+70 mV

Question 10

What is the equilibrium potential of Ca2+?

Answer 10

+122 mV

Question 11

What will happen if you open channels for sodium?

Answer 11

Sodium will enter the cell and cause depolarisation and MP will move towards Ena which is +70mV.

Question 12

What will happen if you open channels for Ca2+?

Answer 12

Calcium will enter the cell and cause depolarisation and MP will move towards Eca which is +122mV.

Question 13

Give an example of a channel that is not perfectly selective.

Answer 13

Nicotinic acetylcholine receptors with their channels are not perfectly selective to Na+. Also Ca2+ and K+ can pass through.

Question 14

Why can’t Cl- pass through the nicotinic acetylcholine receptor channel?

Answer 14

Because the pore is negative, it would not work.

Question 15

What is the consequence of the nicotinic acetylcholine receptor channel letting Na+ and other cations in?

Answer 15

An increased permeability for those ions means that depolarisation will occur and move the membrane potential towards 0mV. An intermediate between Ena and Ek

Question 16

What types of gating are there?

Answer 16

Ligand gated
Voltage gated
Mechanical gated

Question 17

How are ligand gated channels regulated?

Answer 17

By a signalling messenger (ligand)

Also by intracellular messengers like IP3

Question 18

How are voltage gated channels regulated?

Answer 18

The channels either open or close in response to changes in the membrane potential and therefore involved in action potentials.

Question 19

What is fast synaptic transmission?

Answer 19

When the receptor protein is also an ion channel.

Question 20

What is slow synaptic transmission?

Answer 20

When the receptor protein and the channel are two separate proteins.

Question 21

Give examples of synaptic transmissions. Where do they occur?

Answer 21

Nerve to nerve cell
Nerve to muscle cell
Nerve to gland cell
Sensory to nerve cell

Question 22

What is excitatory post-synaptic potential?

Answer 22

When a transmitter opens a ligand-gated channels that causes membrane depolarisation. It brings the membrane potential closer to the threshold for action potential.

Question 23

Give examples of transmitters that are responsible for EPSP.

Answer 23

Acetylcholine and glutamate

Question 24

What is inhibitory post-synaptic potential?

Answer 24

Inhibitory transmitters that open ligand-gated channels that cause hyperpolarisation. It takes the membrane potential further away from the threshold for action potential.

Question 25

Give examples of transmitters that are responsible for IPSP.

Answer 25

Glycine and GABA

Question 26

Give examples of slow synaptic transmission.

Answer 26

Direct g-protein gating.
Gating via an intracellular messenger by GPCR and a signalling cascade. An example can be adrenaline binding to b1-adrenoceptors in the heart.

Question 27

What other factors can influence membrane potential?

Answer 27

Changes in the ion concentration. For example increasing plasma concentration of K+ will lead to an influx of K+ into the cell and therefore depolarisation. This makes the cell more excitable.
Electrogenic pumps like Na+K+ATPase..