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3. ICPP > 4.2 Changing Membrane Potential > Flashcards

4.2 Changing Membrane Potential Flashcards

1
Q

Define depolarisation.

A
  1. Membrane potential becomes LESS NEGATIVE

2. E.g. -70mV => -50mV

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2
Q

Define hyperpolarisation.

A
  1. Membrane potential becomes MORE NEGATIVE

2. E.g. -70mV => -90mV

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3
Q

What are changes in membrane potential caused by?

A

Changes in activity of ion channels

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4
Q

What does increasing the membrane permeability to a particular ion do to the membrane potential?

A

Moves it toward the equilibrium potential for that ion

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5
Q

What does opening Na+ or Ca2+ channels do?

A

The ions rush in causing membrane potential to become less negative so DEPOLARISATION

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6
Q

What does opening K+ channels do?

A

K+ move out, membrane potential becomes more negative, HYPERPOLARISATION

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7
Q

What does opening Cl- channels do?

A

Cl- move into cell, membrane potential becomes more negative, HYPERPOLARISATION

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8
Q

What is conductance? Where is it useful?

A

Contribution of each ion to the membrane potential depends on how permeable the membrane is to that ion.

As real cell membranes have imperfect selectivity (channels open for >1 type of ion)

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9
Q

Give an example of a channel that is less selective than ones for Na+, K+, Cl-, Ca2+ only.

A
  1. Neuromuscular junction - neurone releases ACh
  2. 2 bind to Nicotinic Acetylcholine Receptors on muscle membrane (these have an intrinsic ion channel!)
  3. Channel lets Na+, Ca2+ in and K+ out
  4. Results in depolarisation and moving membrane potential towards 0 (an intermediate between ENa and Ek)
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10
Q

What are channels that can open and close called? Give three types.

A

Gated

  1. Ligand gated (ligand binds cause open/close)
  2. Voltage gated (changes in MP cause it to open/close)
  3. Mechanical gated (membrane deformation cause open/close)
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11
Q

Give example of mechanical gated channel.

A

Hair cells in inner ear

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12
Q

What channels are involved in fast synaptic transmission?

A

Ion channels

Transmitter binding causes the channel to open

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13
Q

What is an excitatory post synaptic potential (EPSP)?

A

Excitatory transmitter
Open ligand gated channels
Na+, Ca2+
Cause membrane DEPOLARISATION

The change in MP is called an EPSP

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14
Q

What are the characteristics of an EPSP?

A

Excitatory post synaptic potential

  1. Longer time course than an AP
  2. Graded with amount of NT
  3. E.g. Acetylcholine, glutamate, dopamine
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15
Q

What is an inhibitory post synaptic potential (IPSP)?

A 
Inhibitory transmitter
Open ligand gated channels 
K+, Cli- 
Cause membrane HYPERPOLARISATION 
E.g. Glycine, gamma-aminobutyric acid(GABA)

The change in MP is called an IPSP

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16
Q

What channels are involved in slow synaptic transmission?

A
  1. G-protein gated
    - localised
    - rapid
  2. Gating via intracellular messengers
    - throughout cell
    - amplification by cascade
17
Q

Factors that influence membrane potential

A
  1. Changes in ion conc

2. Electrogenic pumps (e.g. Na/K ATPase - one +ve charge moved out each time)

18
Q

Give three properties of cardiac ion channels.

A
  1. Selectivity
    - permeable to single type of ion based on physical configuration
  2. Voltage-sensitive gating
    - specific membrane potential ranges cause specific channels to open/close as MP changes during de/depolarisation
  3. Time-dependence
    - some ion channels e.g. Na+ configured to close a fraction of a second after opening, then cannot be opened until MP back to resting levels
19
Q

Describe phase 4 (the resting phase) in cardiomyocytes

A
  1. Resting potential in cardiomyocyte - -90mV
  2. Due to instant outward leak of K+ through inward rectifier channels
  3. Na+, Ca2+ channels closed at resting MP
20
Q

Describe phase 0 (depolarisation) in cardiomyocytes

A
  1. AP triggers in pacemaker/neighbouring cardiomyocyte causing MP to depolarise a little
  2. Fast Na+ channels open one by one and leaks into cell further depolarising
  3. MP approached -70mV where threshold potential reached causing more channels to open
  4. Rapid depolarisation to 0mV then slightly above (overshoot) for a transient period of time
21
Q

What is threshold potential?

A

Point at which enough fast Na+ channels have opened to generate a self-sustaining inward Na+ current

22
Q

Describe phase 1 (early depolarisation) in cardiomyocyes.

A
  1. MP now slightly positive

2. Some K+ channels open briefly, outward flow of K+ returns MP to approx 0mV

23
Q

Describe phase 2 (the plateau phase) of cardiomyocytes

A
  1. L-type(long opening) Ca2+ are still open, influx of Ca2+ (small constant inward current)
  2. Delayed rectifier K+ channels - K+ leaks out down its conc gradient
  3. These two are electrically balanced so MP maintained at plateau just below 0mV
24
Q

Describe phase 3 (repolarisation) in cardiomyocytes.

What pumps are invovled in recovering normal transmembrane ionic concentration gradient of Na+, Ca2+, K+

A
  1. Ca2+ channels gradually inactivated
  2. Persistent outflow of K+ now exceeding inward Ca2+
  3. MP brought back towards resting potential of -90mV
  • Na+ Ca2+ exchanger
  • Ca2+ ATPase
  • Na+ K+ ATPase
25
Q

Cardiomyocytes mV overview

A 
-90mV resting
Depolarise to above 0mV 
Small repolarise to 0mV
Plateau at about 0mV
Hyperpolarise to -90mV

Note. L-type Ca2+ channels open when MP is greater than -40mV and causes a small but steady influx of Ca2+ down conc gradient

3. ICPP (15 decks)

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