Resting Membrane Potential

Question 1

In which direction is the membrane potential defined?

Answer 1

The inside compared to the outside of the cell.

Question 2

What is the standard unit for membrane potential?

Answer 2

millivolts

Question 3

How can ions move through a membrane?

Answer 3

They cannot diffuse and so the only way is through ion channels.

Question 4

List three properties of ion channels.

Answer 4

Selective, gated and allow rapid ion flow (when open)

Question 5

What is selective permeability?

Answer 5

This is the fact that the cell membrane is permeable to different ions depending on the different ion channels which are open.

Question 6

What ion is most responsible for setting up the resting membrane potential?

Answer 6

K+. It achieves this because there is an outward concentration gradient and an inward electrical gradient and so ions flow until these are equal and opposite.

Question 7

What is the use of the Nerst equation?

Answer 7

This allows us to calculate Ek or E for any ion which is the membrane potential if it is only permeable to that specific ion.

Question 8

Why is the resting membrane potential not equal to Ek?

Answer 8

There is a small leak of Na and Ca back into the cell.

Question 9

What is the resting membrane potential in cardiac muscle?

Answer 9

-80mV

Question 10

What cell type has a resting membrane potential of -70mV?

Answer 10

Nerve cells

Question 11

What is the resting membrane potential of skeletal muscle?

Answer 11

-90mV

Question 12

What is the resting membrane potential in smooth muscle cells?

Answer 12

-50mV

Question 13

Define depolarisation.

Answer 13

This is a decrease in the size of the membrane potential (so it moves closer to 0)

Question 14

What is repolarisation?

Answer 14

This is when the membrane potentIal becomes more negative and moves further away from threshold.

Question 15

Opening of which ion channels leads to hyperpolarisation?

Answer 15

Cl- and K+

Question 16

What ion channels need to open for a cell to depolarise?

Answer 16

Na+ and Ca2+

Question 17

Can channels allow more than one ion to pass through?

Answer 17

Yes. Nicotinic acetylcholine receptors are permeable to both Na+ and Ca2+. They do not allow anions to move through.

Question 18

Name three types of gating ion channels can exhibit.

Answer 18

Ligand gating, mechanical gating and voltage gating.

Question 19

What is synaptic transmission?

Answer 19

This is where a chemical transmitter is released from the pre synaptic cells and binds to receptors on the post synaptic membrane.

Question 20

What is fast synaptic transmission?

Answer 20

The receptor protein is an ion channel which opens when the transmitter binds.

Question 21

What happens at an excitatory synapse?

Answer 21

At these synapses, binding of the transmitter opens ion channels which cause depolarisation of the membrane. More transmitter leads to a greater response.

Question 22

What is the exciting post synaptic potential?

Answer 22

This is the change in potential of the post synaptic cell caused by the binding of transmitter and opening of ion channels.

Question 23

When a synaptic transmitter binds to a receptor which opens Cl- or K+ channels, what type of synapse is this?

Answer 23

Inhibitory as it leads to hyperpolarisation of the membrane and the potential moves further away from threshold.

Question 24

Give two examples of transmitters which act at inhibitory synapses

Answer 24

A-aminobutyric acid and glycine

Question 25

What is slow synaptic transmission?

Answer 25

This involves a messenger molecule (G protein) as the ion channel and the receptor are different molecules.

Question 26

Give two examples of slow synaptic transmission.

Answer 26

Direct G protein gating and gating via an intracellular messenger

Question 27

What is gating via an intracellular messenger?

Answer 27

This is where when the transmitter binds to the receptor this activates the G protein. This binds to enzymes which produces a signalling cascade and the the messenger binds to the channel or activates PKA which phosphorylates the channel.

Question 28

What is the difference in effect between direct G protein gating and gating via an intracellular messenger?

Answer 28

Direct G protein gating is a more localised effect whereas intercellular messengers affect the whole cell.

Question 29

What is the role of Na+/K+ ATPase in the membrane potential?

Answer 29

It has a very minor role and may add a few mV to the membrane potential.