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Membranes and Receptors > Session 3 - Resting membrane potential > Flashcards

Session 3 - Resting membrane potential Flashcards

1
Q

How is resting membrane potential measured?

A

-Micropipette containig conducting solution (KCl) inserted into cell membrane and records PD

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2
Q

What are the typical resting potentials of

i) Nerve cells
ii) Smooth muscle cells
iii) Cardiac and skeletal cells

A

i) -70mV
ii) -50mV
iii) -90mV

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3
Q

What enables membranes to be selectively permeable to ions?

A
  • Channel proteins within the membrane are permeable to one or a few species of ions
  • Enable ions to cross the PM via diffusion when they are open
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4
Q

How do ion channels differ from transporters?

A
  • When ion channels open there is rapid flow of ions down the electrochemical gradient
  • Transporters ping-pong molecules one at a time
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5
Q

What are ion channels which are open permanently in cell membranes called?

A

-Voltage-insensitive channels

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6
Q

What determines a cells selective permeability to ions?

A

-The number, type and selectivity of ion channels open within a membrane

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7
Q

What ion is the main determinant in RMP in most cells?

A

-K+

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8
Q

How does permeability to K+ set up the resting membrane potential?

A
  • Cells permeable to K+ at rest so it flows out of the cell down its concentration gradient
  • Anions cannot follow (as the cell is not permeable) so the inside becomes more negative relative to the outside (membrane potential)
  • This membrane potential opposes outward movement of K+ as a chemical gradient is established (negative inside attracts K+)
  • When the chemical gradient is equal and opposite to the electrical gradient of K+ an equilibrium is reached where there is no net movement of K+ and a negative membrane potential is maintained
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9
Q

Are large quantities of K+ involved in setting up the resting membrane potential?

A

-No, the amount of K+ that moves is very small and a slight efflux can maintain the RMP for a long time

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10
Q

What is the equilibrium potential of an ion?

A

-The membrane potential at which there is no net movement of ions across the membrane as the chemical gradient is = and opposite to the electrical gradient for that ion

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11
Q

What is the nernst equation?

A

-calculates the membrane potential at which there will be no net movement of ions given the intra and extracellular concentrations ie, calculates the equilibrium potential of an ion

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12
Q

If a cell was solely permeable to K+, what would be the resting membrane potential?

A

-Ek (approx. -95mV)

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13
Q

Which ions have a positive Ep?

A
  • Ena

- Eca

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14
Q

Which ions have a negative Ep?

A
  • Ek

- Ecl

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15
Q

What happens to the membrane potential if a cell is permeable to more than just K+?

A

-Permeability to all the ions contributes to the membrane potential

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16
Q

What happens to the membrane potential if the permeability to a particular ion increases?

A

-The membrane potential moves towards the equilibrium potential of that ion

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17
Q

How is a cells permeability to a particular ion increased?

A

-Open more ion channels for that ion

18
Q

Why does a cell, which is only permeable to K+ at rest, not have a resting potential of -95mV (Ek)?

A
  • Cells are not perfectly selective
  • Channels flicker open and closed
  • This allows for ions to leak down their concentration gradients into the cell
  • This leakage contributes to the RMP, deviating it from Ek
19
Q

What happens to the resting membrane potential during depolarisation?

A

-It becomes less negative (moves closer to 0/+ve)

20
Q

Does depolarisation=action potential?

A

-No, depolarisation can be a few mV as it doesnt always reach the threshold for an action potential

21
Q

What happens to the resting membrane potential during hyperpolarisation?

A

-Membrane potential becomes more negative and falls below RMP

22
Q

What happens to the membrane potential during repolarisation?

A

-Returns closer to the resting membrane potential

23
Q

Give examples of membrane potential involvement in signalling roles

A
  • Action potentials in nerve and muscle cells
  • Control of secretion of hormones and neurotransmitters
  • Transduction of sensory information to electrical activity by receptors
24
Q

What types of gating are ion channels controlled by?

A
  • Voltage-gated
  • Ligand-gated
  • Mechanical-gated (stretch receptors respond to membrane deformity)
25
Q

Where can synaptic trasmission occur?

A
  • Nerve:nerve
  • Nerve:muscle
  • Nerve:gland
  • Sensory:nerve
26
Q

What are the two types of synaptic transmission?

A
  • Fast

- Slow

27
Q

Describe fast synaptic transmission

A
  • The receptor is also an ion channel and binding of a ligand causes it to open
  • Eg NachR
28
Q

What is the main difference in slow synaptic transmission from fast synaptic transmission?

A

-The receptor and ion channel are separate in slow transmission

29
Q

What are the two types of slow synaptic transmission?

A
  • Direct G-protein gating

- Intracellular messanging

30
Q

How does direct G-protein gating slow synaptic transmission occur?

A
  • Ligand binds to receptor
  • G-protein dissociates from receptor and translocated to the ion channel where it binds to the channel causing it to open
31
Q

How does intracellular messaging slow synaptic transmission occur?

A

-Ligand binding initiates an enzymatic cascade throughout the cell which results in the channel opening

32
Q

Which is the fastest kind of slow-synaptic transmission?

A

-G-protein gated

33
Q

What is hyperkalaemia?

A

-Raised serum K+ conc above 6mM

34
Q

Does NaKATPase contribute to the resting membrane potential?

A

-NaKATPase is electrogenic as it pumps 3Na+ out for every 2K+ in, and thus it can contribute a few mV, however the contribution is minimal

35
Q

What is an Excitatory Post-Synaptic Potential?

A

-A membrane depolarisation caused by excitatory transmitters opening ligand-gated channels, causing the cell to be more permeable to Na+/Ca2+

36
Q

How does an EPSP differ from an AP?

A
  • Has a longer time course than AP

- Is a smaller depolarisation

37
Q

Give examples of excitatory transmitters

A
  • Acetylchline

- Glutamate

38
Q

What is an Inhibitory Post-Synaptic Potential?

A

-Hyperpolarisation caused by inhibitory transmitters opening ligand-gated channels, increasing permeability to K+ or Cl-

39
Q

Give examples of inhibitory transmitters

A
  • Glycine

- Gamma-aminobutyric acid (GABA- an a’a which acts as a ligand for Cl- channels)

40
Q

What does hyperpolarisation do to a membrane in terms of excitability?

A

-Decreased the excitability of a membrane

41
Q

What is a resting membrane potential?

A

-The electrical potential across a membrane generated by the distribution of ions in fluids inside and outside of the cell

Membranes and Receptors (13 decks)

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