Lecture 8- Changing membrane potential

Question 1

depolarisation

Answer 1

Depolarization

A decrease in the size of the membrane potential from its normal value

Cell interior becomes less negative
e.g. a change from – 70 mV to – 50 mV

Question 2

hyperpolarisation

Answer 2

An increase in the size of the membrane potential from its normal value

• *Cell interior becomes more negative
  e. g. a change from–70mVto–90mV**

Question 3

how do membrane potentials arise

Answer 3

as a result of selective ionic permeability

Question 4

changing selectivity to ions

Answer 4

will change membrane potential

Question 5

increasing membrane permeability to a particular ion moves the membrane potential

Answer 5

towards the equilibirum potential for that ion

Question 6

list the equilibrium potential for :

K+

Cl-

Na+

Ca2+

Answer 6

Question 7

opening of K+ or Cl- (moving eqilibrium potential towards Ek and Ecl)

Answer 7

will hyperpolarise

Question 8

opening Na+ or Ca2+ (moving equilibrium potential towards E_Na or E_Ca

Answer 8

channels will depolarise

Question 9

The contribution of each ion to the membrane potential will depend on

Answer 9

how permeable the membrane is to that ion

Question 10

some channels are less selective e.g.

Answer 10

nACHr at the NMJ

• allows both Na+ and K+ to enter (not anions)

Question 11

equation that can be used to understand selective permeability

Answer 11

GHK (Goldman-Hodgkin-Katz) equation

Question 12

nAChR at the NMJ

Answer 12

1. Have an intrinsic ion channel
2. Opened by binding of acetylcholine
3. Channel lets Na+ and K+ through, but not anions
4. Moves the membrane potential towards 0 mV, intermediate between ENa and EK
5. = depolarisation

Question 13

channels are often..

Answer 13

gated

Question 14

controlling gated channels

Answer 14

1. ligand gated
2. voltage gated
3. mechanical gated

Question 15

ligand gated channel

Answer 15

responds to binding of a chemical ligand (ACh)

Channels at synapses that respond to extracellular transmitters and intracellular messengers

Question 16

Voltage gate

Answer 16

responds to change in membrane potential

• Channels involved in AP

Question 17

mechanical gated

Answer 17

response to membrane deformation

• Mechanoreceptors e.g. hair cells

Question 18

synaptic conenction occur between (4 types of tissue)

Answer 18

1. Nerve cell – nerve cell
2. Nerve cell – muscle cell
3. Nerve cell – gland cell
4. Sensory cell – nerve cell

Question 19

how does a synapse work

Answer 19

a chemical transmitter released from the presynaptic cell binds to receptors on the postsynaptic membrane.

Question 20

two types of synaptic transmission

Answer 20

fast and slow

Question 21

example of fast synaptic transmission

Answer 21

Receptor protein is also an ion channel

Transmitter binding causes the channel to open

E.g. nicotinicACh

Question 22

example of slow synaptic transmission

Answer 22

GPCRs

• direct G-protein gating
• gating via an intracellular messenger

Question 24

fast synaptic tranmission can be separated into 2 branches

Answer 24

excitatory

inhibitory

Question 25

excitatory synapes

Answer 25

Open ligand gated channels that cause membrane depolarisation (e.g. permeable to sodium and calcium)

i. Ach binding
ii. Glutamate binding

Question 27

Inhibitory synapes

Answer 27

Open ligand gated channels that cause hyperpolarisation (permeable to potassium and chloride)

Membrane taken further away from action potential

i. Glycine binding
ii. GABA binding

Question 28

direct G-protein gating

Answer 28

G protein directly linked to channel- when ligand binds to G protein the channel will open

• Localised
• Quite rapid

Question 29

GPCR- gating via intracellular messenger

Answer 29

G protein causing enzyme to signal intracellular messages or protein kinases which activate channels to open

Question 30

what other factors can influence membrane potential?

Answer 30

• change in ion concentration
• electrogenic pumps

Question 31

Changes in ion concentration influencing membrane potential

Answer 31

Most important is extracellular K+ concentration (~4.5 mM normally)

Sometimes altered in clinical situations

Question 32

Acute hyperkalaemia-

Answer 32

brings resting potential closer to threshold- initially more excitable

In chronic hyperkalaemia, cells become less excitable

• Cannot reactivate sodium. Channels to keep opening- no AP
• Can alter membrane excitability, e.g. in heart – arrythmias

Question 33

electrogenic pumps (Na/K ATPase) influence on membrane potential

Answer 33

tiny affect

• One positive charge moved out for each cycle
• Contributes a few mV directly to the membrane potential, making it more negative

Question 34

Indirectly active transport of ions (Na/K ATPase) is responsible for

Answer 34

entire membrane potential, because it sets up and maintains the ionic gradient