Session 4 (Resting Membrane Potential + Changing The Membrane Potential)

Question 1

What is membrane potential?

Answer 1

The magnitude of an electrical charge that exists across a plasma membrane

Question 2

What is used to measure a membrane potential?

Answer 2

A glass microelectromechanical (pipette)

Question 3

What do you fill your glass pipette with when measuring membrane potentials?

Answer 3

A conducting solution (ie KCl)

Question 4

What causes a membrane potential to be set up?

Answer 4

The membranes selective permeability

Question 5

How is a membrane potential set up?

Answer 5

At rest K+ channels are open, allowing K+ to flow OUT (down its conc gradient), other anions (-ive ions) cannot follow.
-ive charge builds up inside cell, K+ therefore don’t want to leave as much and a equilibrium is reached.
K+ wants to leave because of conc gradient but wants to stay because of electrical gradient

Question 6

What is Ex?

Answer 6

The equilibrium potential of a given ion (x)

Question 7

What does z mean in the following equation?:

Ex=61/Z.log([x]o/[x]i)

Answer 7

Z means valency (charge on ion)

Question 8

If a membrane potential is set up as a result of K+ ions moving, why is the membrane potential not -95mV, which is Ek?

Answer 8

Because the membrane is not perfectly selectable for K+ ions, some other channels are open.

Question 9

What happens if [K+]o increases?

[x]o means concentration of ion outside of cell

Answer 9

Ek becomes more positive therefore membrane potential becomes more positive

Question 10

What will opening Na+ and/or Ca2+ channels do?

Answer 10

Depolarise cell

Question 11

What will opening K+/Cl- channels do?

Answer 11

Hyperpolarise cell (or repolarise, depending on the context)

Question 12

What is Px?

Answer 12

The relative permeability coefficient for each of a given ion (x)

Question 13

What underlies the overall selectively of a cell membrane?

Answer 13

The number of open channels of different types (eg ligand/voltage/mechanical)

Question 14

What channels are used for fast synaptic transmission?

Answer 14

Ligand gated ion channels

Question 15

What do depolarising transmitters cause?

Answer 15

Excitatory postsynaptic potentials (EPSP)

Question 16

Name an excitatory transmitter (3)

Answer 16

ACh, Glutamate, Dopamine

Question 17

Name an inhibitory transmitter (2)

Answer 17

Glycine, GABA

Question 18

What do hyper-polarising transmitters cause?

Answer 18

Inhibitory post synaptic potentials (IPSP)

Question 19

Why is slow synaptic transmission slow?

Answer 19

Because the receptors and the channels are separate proteins

Question 20

Give an example of a protein receptor involved in slow synaptic transmission

Answer 20

GPCRs

Question 21

What are the 2 types of slow synaptic transmission that involve a GPCR? Explain the methods

Answer 21

Direct G protein gating (receptor caused G protein to activate channel- localised and quite rapid)

Gating via an intracellular messenger (GPCR activates enzymes involved in signalling cascade, secondary messenger activates channel- throughout cell, amplification by cascade)

Question 22

Define ‘hyperpolarising’

Answer 22

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

Question 23

Define ‘depolarising’

Answer 23

A decreasing of the size of the membrane potential from its normal value (cell interior becomes less negative)

Question 24

What changes membrane potentials?

Answer 24

Changes in activity of ion channels

Question 25

What is conductance?

Answer 25

How permeable a membrane is to a given ion