Changing Membrane Potential

Question 1

What happens during depolarisation?

Answer 1

Na+ Ca2+ channels open, becomes less negative

Question 2

Describe repolarisation

Answer 2

Na+ and ca2+ channels close – K+ channel opens moves out

Question 3

What is hyperpolarisation?

Answer 3

K+ / Cl- channels remain open after potential reaches resting level = more negative -70mV to -90mV

Question 4

What is conductance?

Answer 4

permeability the membrane is to a particular ion and therefore the contribution the ion has on membrane potential

Question 5

What are channels that open and close called? Give examples

Answer 5

Gated

1. Ligand: chemical neurotransmitters, intracelular messengers
2. Voltage: change in MP
3. Mechanical: membrane deformation

Question 6

What is an example of the mechanical gated channel?

Answer 6

Mechanical Gating Hair cells in the inner ear

Question 7

What channels are involved in fast synaptic transmission?

Answer 7

Ions channel; nAChR

Question 8

What channels are involved in slow synaptic transmission?

Answer 8

G-protein gated or intracellular messengers

Question 9

Which membrane potential only involves ion channels?

Answer 9

In the heart

Question 10

Outline how ligand gated channels can give rise to synaptic potential

Answer 10

Excitatory transmitter = open ligand-gated = membrane depolarisation Na+, Ca2+ = change in membrane potential = excitatory post-synaptic potential (EPSP)

Inhibitory transmitter = open ligand-gated = hyperpolarisation K+, Cl- = change in membrane potential = inhibitory post-synaptic potential (IPSP)

Question 11

How are changes in membrane potential caused?

Answer 11

changes in the activity of ion channels

Question 12

Whats is the GHK (goldman-hodgkin-katz) equation?

Answer 12

calculates MP from many ions

Question 13

What are the properties of cardiac ion channels?

Answer 13

1. Selectivity: only permeable to single type of ion
2. Voltage-sensitive gating: specific MP required to open channels
3. Time-dependence: some channels close VERY quickly, only open after back to resting MP

Question 14

Outline an AP in a cardiomyocyte

Answer 14

1. AP arrives = Na+ channels open, Na+ inward = depolarisation
2. -70mV = threshold is reached, all Na+ channels open = MP to 0mV
3. L-type Ca2+ channels open when mV greater than -40mV = inward
4. Slight overshoot = mV above 0, Na+ channels close
5. Slight +ve mV = K+ open = outward = returns mV to 0mV
6. Ca2+ inward balanced with K+ outward = plateau
7. Ca2+ channels inactivate but K+ still outward = mV back to -90

Question 15

What pumps restore normal transmembrane ionic conc?

Answer 15

sarcolemmal Na+ Ca2+ exchanger
Ca2+ ATPase
Na+ K+ ATPase

Question 16

Give 2 examples of excitatory neurotransmitters

Answer 16

ACh, dopamine

Question 17

What is summation?

Answer 17

When the amount of excitable or inhibitory transmitters exceeds the other to give an overall response