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Semester 2 - Membranes and Receptors areen > Session 3 - What is a membrane potential? > Flashcards

Session 3 - What is a membrane potential? Flashcards

1
Q

What is a membrane potential?

A

Membrane potential: the potential difference across a cell’s plasma membrane

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2
Q

How do you measure membrane potential?

A
  1. Micropipette/ microelectrode, connected to voltmeter, penetrates the cell membrane
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3
Q

When membrane potential is measured, what is it expressed as?

A
  1. Membrane potentials expressed as voltage of inside of a cell relative to the outside
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4
Q

What is animal cell range of membrane potential?

A

Animal cell range: -20 to -90 mV

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5
Q

What is skeletal and cardiac muscle range of membrane potential?

A

Skeletal & cardiac muscle: -80 to -90 mV

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6
Q

What is nerve cells membrane potential?

A

Nerve cells: -50 to 75 mV

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7
Q

How is a membrane potential set up?

A

Membrane potentials are set up because the membrane is selectively permeable to different ions due to transmembranous channel proteins.

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8
Q

Give three characteristics of ion channels

A

Monspecificity
Gating
A high rate of ion flow

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9
Q

What is monospecificity of ion channels?

A

Channels that let through one (or a few) ion species

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10
Q

What is gating of an ion channel?

A

Channel can bbe open or closed by a conformational change in the protein molecule

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11
Q

What is special about the high rate of ion flow through an ion channel?

A

It is always down the electrochemical gradient for the ion

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12
Q

Depending on which channels are open…

A

The resting membrane can be selectively permeable to certain ion species

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13
Q

What is the intracellular and extracellular ion conc of Na+

A

Na+
Intracellular ~10mM
Extra cellular -145mM

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14
Q

What is the intracellular and extracellular ion conc of K+

A

Intracellular - 160 mM

Extracellular - 4.5 mM

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15
Q

What is the intracellular and extracelular ion conc of Cl-?

A

Intracellular - 3mM

Extracellular - 114mM

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16
Q

What is A- in cell ion terminology?

A

Represents anions other than Cl-, including phosphate, amino acids and charged groups on proteins

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17
Q

What is the intracellular concentration of A-? What is the extracellular?

A

167 mM intracellular

40mM extracellular

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18
Q

How is a membrane potential generated?

A
  1. K+ channels open \ membrane selectively permeable to K+
  2. K+ diffuse out of cell down the concentration gradient
  3. Anions can’t follow \ cell is negatively charged on the inside with respect to the outside
  4. This membrane potential will oppose outward movement of K+ \ system comes into equilibrium
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19
Q

What is the equilibrium potential?

A

Equilibrium potential: the membrane potential at which the electrical and diffusion forces balance one another out so that there is no further net movement of an ion

20
Q

What is the unit of measurement used in the Nernst equation

A

mV

21
Q

What is theoretical membrane potential if the membrane was 100% permeable to K+?

A

-94.6 mEquilibrium potential: the membrane potential at which the electrical and diffusion forces balance one another out so that there is no further net movement of an ion

22
Q

What does the Nernst equation calculate?

A

The potassium equilibrium potential

23
Q

CHECK EQUATIONS IN WORKBOOK

A

DONE?

24
Q

Why is the true membrane potential around 75mV rather than 94.6 mV?

A

selectively permeable to K+. In reality the cell is also permeable to other cations such as Na+ and Ca2+ which move into the cell and make the membrane less negative

25
Q

Define depolarisation

A

Depolarization: decrease in membrane potential so that inside of the cell becomes less negative

26
Q

Define hyperpolarisation

A

Hyperpolarisation: increase in membrane potential so that the inside of the cell becomes more negative

27
Q

How can membrane permeability for a particular ion be increased?

A

By opening its channels

28
Q

How does depolarisation occur?

A

Opening of Na+ and Ca2+ channels

29
Q

How does hyperpolarisation occur?

A

Opening of K+ or Cl- channels

30
Q

K+ is postive, why does opening its channels hyperpolarise the cell?

A

Because higher intracellular conce, lower extracellular - Moves out of cell

31
Q

What does increasing selective permeability of an ion cause?

A

The membrane potential is pushed towards the equilibrium potential for that ion

32
Q

What two things could have occured if there is a depolarisation of cell membrane potential (must outline two DIFFERENT mechanisms)

A

Permeability of membrane to Na+ increases
Ions enter cell
Inside more +’ve>depolarisation

A-
Ions leave cell
Inside more +’ve > depolarisation

33
Q

What happens if selective permeability of membrane to Cl- increases?

A

Inside more -‘ve, hyperpolarisation (reduced membrane excitability

34
Q

What happens if selective permeability of membrane to K+ decreases?

A

Inside more +’ve > depolarisation

increased membrane excitability

35
Q

Give five roles of membrane excitation

A
  1. Actions potentials in nerve and muscle cells
  2. Triggering and control of muscle contraction
  3. Control of secretion of hormones and neurotransmitters
  4. Transduction of sensory information into electrical activity by receptors
  5. Postsynaptic actions of fast synaptic transmitters
36
Q

How can we control channel activity?

A

How can we control channel activity? Ligand, mechanical (membrane deformation) or voltage gating

37
Q

What is ligand gating

A

The channel is opened (or closed) by binding of a chemical ligand, which may be an extracellular transmitter or an intracellular messenger

38
Q

How does voltage gating work?

A

The channels opens or closes in response to changes in the membrane potential

39
Q

What is fast synaptic transmission?

A
  • Receptor protein is also an ion channel
  • Transmitter binding causes the channel to open
  • Change in membrane potential:
40
Q

What is an excitatory synapse and how is the action potential caused?

A

· Excitatory transmitters open ligand gated channels that cause depolarization

· Resulting change is called an Excitatory post-synaptic potential (EPSP) – relatively long to ensure that voltage sensitive channels have sufficient time to open

· Transmitters include: acetylcholine, glutamate

41
Q

How does a fast inhibitory synapse work?

Name two neurotransmitters which stimulate it

A

· Hyperpolarization

· Inhibitory post-synaptic potential (IPSP)

· Transmitters include: glycine, g-aminobutyric acid (GABA)

42
Q

What are two mechanisms of slow synaptic transmission?

A
  1. Direct G-protein gating

2. Gating via intracellular messenger

43
Q

How does direct G-protein gating work?

A
  • Localized and quite rapid

* NT binding causes G-protein dissociation > binds to ion channel > ion channel opens

44
Q

How does gating via intracellular messenger work?

A
  • NT binding causes G-protein dissociation > binds to enzyme effector > which initiates a signaling cascade > intracellular messenger binds to ion channel > ion channel opens
45
Q

What does digoxin do

A

It sabilizes the heart

Semester 2 - Membranes and Receptors areen (15 decks)

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