Changing Membrane Potential

Question 1

What are some examples of when membrane potentials are changed?

Answer 1

Action potentials, triggering of muscle contraction, control of secretion of hormones and neurotransmitters, transduction of sensory information into electrical activity by receptors and postsynpatic actions of fast synaptic transmitters

Question 2

What is depolarisation?

Answer 2

A decrease in the size of the membrane potential from its normal value, cell interior becomes less negative

Question 3

What is hyperpolarisation?

Answer 3

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

Question 4

What will change membrane potential

Answer 4

Changing the selectivity between ions

Question 5

What does increasing membrane permeability to a particular ion do?

Answer 5

Moves the membrane potential towards the equilibrium potential for that ion

Question 6

What is the equilibrium potential for K+?

Answer 6

Ek = -95 mV

Question 7

What is the equilibrium potential for Na+?

Answer 7

Ena = +70 mV

Question 8

What is the equilibrium potential for Cl-?

Answer 8

Ecl = -96 mV

Question 9

What is the equilibrium potential for Ca2+?

Answer 9

Eca = +122 mV

Question 10

The opening of which channels will cause hyperpolarisation?

Answer 10

Opening of K+ or Cl- channels

Question 11

The opening of which channels will cause depolarisation?

Answer 11

Opening of Na+ or Ca2+ channels

Question 12

What are nicotinic acetylcholine receptors opened by and what do they let through?

Answer 12

Opened by binding of acetylcholine (x2)
Channel lets Na+ and K+ through, but not anions
Moves the membrane potential towards 0 mV - intermediate between Ena and Ek

Question 13

What are the types of gating?

Answer 13

Ligand gating, voltage gating and mechanical gating

Question 14

What is an example of mechanical gating?

Answer 14

Hair cells in the inner ear

1. K+ channel closes in cuticular plate
2. Membrane depolarises
3. Ca2+ channel opens
4. Vesicles containing neurotransmitter (dopamine or dynorphin) fuse with BM close to afferent nerve
5. Neurotransmitter binds to receptor on post-synpatic plate and generates action potential that goes to CNS for interpretation

Question 15

Where do synaptic connections occur?

Answer 15

Between:
nerve cell-nerve cell
nerve cell-muscle cell
nerve cell-gland cell
sensory cell-nerve cell

Question 16

In fast synaptic transmission, the receptor protein is also what?

Answer 16

Also an ion channel, transmitter binding causes channel to open

Question 17

What do excitatory transmitters do?

Answer 17

Open ligand gated channels that cause membrane depolarisation. Can be permeable to Na+, Ca2+ and sometimes cations in general

Question 18

What is the resulting change in membrane potential caused by excitatory transmitters called?

Answer 18

Excitatory post-synaptic potential (EPSP)

Question 19

What are some excitatory transmitters?

Answer 19

Acetylcholine, glutamate, dopamine

Question 20

What do inhibitory transmitters do?

Answer 20

Open ligand-gated channels that cause hyperpolarisation, permeable to K+ or Cl-

Question 21

What are some inhibitory transmitters?

Answer 21

Glycine, GABA

Question 22

In slow synaptic transmission, are the receptor and channel separate proteins?

Answer 22

Yes

Question 23

What are the two basic patterns seen in slow synaptic transmission?

Answer 23

1. Direct G protein gating (localised, rapid)

2. Gating via intracellular messenger (throughout cell, amplification by cascade, isn’t confined to cell membrane

Question 24

What can influence membrane potential?

Answer 24

1. Changes in ion concentration (most important is extracellular K+ concentration which is 4.0 mM)
2. Electrogenic pumps

Question 25

How is the active transport of ions indirectly responsible for the entire membrane potential?

Answer 25

It sets up and maintains the ionic gradients that generate the resting membrane potential

Question 26

What are some properties of cardiac ion channels?

Answer 26

1. They are only permeable to a single type of ion
2. A specific MP range is required for a particular channel to be open/close
3. Some ion channels are configured to close a fraction of a second after opening and cannot be opened again until MP is back to resting levels

Question 27

What is the resting potential in a cardiomyocyte?

Answer 27

-90mV due to a consntant outward leak of K+ through inward rectifier channels

Question 28

When do L type Ca2+ channels open?

Answer 28

When the MP is greater than -40mV and cause a small but steady influx of Ca2+ down its concentration gradient