Passive and active properties of membranes Flashcards Preview

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Flashcards in Passive and active properties of membranes Deck (73):
1

What is denoted as "Vm"?

The plasma membrane potential

2

What is the membrane potential?

The potential produced by the separation of opposite charges (cation and anions across the membrane)

3

Define "cations"?

Ions that are positive in charge

4

Define "anions" ?

Ions that are negative in charge

5

How can you test and record the membrane potential of a cell?

Measured as the difference in potential between the tip of a micro electrode inserted into the cell and the electrode outside the cell.

6

What is the Vm for many nerve cells?

-65mV (indicates that the potential inside is negative with respect to the outside)

7

Relationship between Vm and cell types?

Vm varies considerably between cell types.

8

What two things determines the membrane potential?

1. Selective permeability 2. Concentration gradients

9

Define "selective permeability"?

The membrane is selective at transporting certain ionic species across the membrane

10

Define "concentration gradients"?

The differences in concentration between the other to the inside of the cell to specific ions

11

How is the resting membrane potential brought about?

The diffusion of ions down their concentration gradients generates an electrical potential across the membrane.

12

Consider the following picture. Describe what will happen to the ions in respect to movement and why that is?

There is an unequal concentration of both the cation and anion across the membrane. Selective permeability: The bilayer is impermeable to both of these ions. Concentration gradient: Charges are equal in both sides. No movement occurs!

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13

Consider the following picture. Describe what will happen to the ions in respect to movement and why?

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The membrane contains potassium selective ion channels that are open constitutively. K travels down its concentration gradient (A cannot). Charge separation and a potential across the membrane develops.

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14

Consider the following picture. Describe what will happen to the ions in respect to movement and why?

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Positive charge develops across the membrane: causing K to be attracted back into the cell (due to electrical gradients). When energy in the conc gradient is equal and opposite in electrical gradient-> no net movement of K.

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15

Define "Ek"?

The equilibrium potential for K

16

How are large changes in membrane potential brought about?

Actually only involves minuscule changes in ion concentration in the ECF and ICF.

17

Define "ECF" ?

Extracellular fluid.

18

Define "ICF"?

Intracellular fluid.

19

What electrical device is the membrane working as?

A capacitor. An electrical device that stores charge.

20

Define "equilibrium potential"?

Concentration difference across the membrane for an ion.

21

What does the Nernst equation calculate?

The equilibrium potential (Eion)

22

What is the Nernst equation?

Eion= RT/zF. ln [Ion]o/[ion]i

23

What does "R" stand for in the nernst equation?

Universal gas constant 8.314J/K/mol

24

What does "z" stand for in the Nernst equation?

Ionic valence. eg. K+ therefore z=+1.

25

What does "F" stand for in the Nernst equation?

Faraday constant. 9.649x10^4

26

Do the work example of the Nernst equation!

----

27

What is the sodium conc in the ECF? (nerve cell)

141mM

28

What is the sodium conc in the ICF? (nerve cell)

10-12mM

29

What is the potassium conc in the ECF? (nerve cell)

3.3mM

30

What is the potassium conc. in the ICF? (nerve cell)

120-140mM

31

What is the calcium conc. in the ECF? (nerve cell)

1mM

32

What is the calcium conc. in the ICF? (nerve cell)

10^-4 mM

33

What is the chloride conc. in the ECF? (nerve cell)

125mM

34

What is the chloride conc. in the ICF? (nerve cell)

5-10mM

35

What is the resting passive movement of sodium ions in a nerve cell?

Inward. Causing depolarisation

36

What is the resting passive movement of calcium ions in a nerve cell?

Inward. Causing depolarisation.

37

What is the resting passive movement of potassium ions in a nerve cell?

Outward, Causing hyperpolarisation.

38

What is the resting passive movement of chloride ions in a nerve cell?

Inwards (usually) Causing hyperpolarisation (usually).

39

What ions are the membrane potential depend upon and why them specifically?

K, Na and Cl. Because the neuronal membrane at rest is permeable to all ions other than these specific ions.

40

What equation is used to calculate the Vm?

Goldmann-hodgkin-katz equation

41

Define Goldmann-Hodgkin-Katz equation?

Note: the chloride is inverted due to its negative ionic valence.

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42

What ion permeability is dominant in setting Vm for a nerve cell?

Potassium.

43

Why is the potassium dominant in setting Vm?

As potassium ion channels are open at rest. Therefore membrane drive towards Ek.

44

What happens to Vm when other ion channels are open?

The membrane potential is driven towards the specific ion equilibrium constant.

45

Define "Ion channels" and the role they play in movement?

Protein complexes that span the lipid bilayer to forma central pathway that allows rapid flow of selected ions.

46

How many states does an ion channel exist in?

Open Closed Additional conformations Cycling between them.

47

Name the 3 different gated types of ion channel?

1. Voltage-gated ion channels (Affected by membrane voltage). 2. Ligand gated ion channels (Affected by chemical substances) 3. Physical stimuli (eg. mechanical, thermal)

48

Name the two channels that are responsible for the action potential?

1. Voltage-activated sodium channels (depolarisation) 2. Voltage-activated potassium channels (hyperpolarisation)

49

Describe the different parts of the Action potential in neurones?

Upstroke -> overshoot -> downstroke -> undershoot.

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50

Define "action potential"?

Brief electrical signals in which the polarity of the nerve cell membrane is momentarily reversed.

51

How is the action potential propagated along a long distance?

Propagate along nerve cell axons with constant magnitude and velocity allowing signalling over long distances

52

When is AP generated?

When threshold is reached. All or nothing

53

What type of axon does a squid have?

A giant axon. Used to give the squid a big burst of energy in need to swim away quickly

54

What is the ion movement during an action potential?

Potassium channels are open at rest. Sodium channels start to open causing more and more to open. Eventually the sodium channels start to move into its inactive form. Potassium channels start to open again.

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55

Define what terodotoxin does (TTX)?

Blocks sodium channels from opening.

56

Define what tetrathylammonium (TEA)?

Blocks potassium channels from opening

57

What is the time frame that the sodium and potassium open by membrane depolarisation?

Sodium channels activated rapidly Potassium what a delay.

58

How is the sodium channels self-reinforcing?

Once a few channels are activated it causes a depolarisation inside the cell causing further channels to open and causing further depolarisation. Positive feedback.

59

How is the potassium channels self-limiting?

Outward movement of potassium causes depolarisation which turns off the stimulus from opening the channels. Negative feedback

60

What happens during the refractory period in respects to sodium channels?

The channels initially open in response to depolarisation. They enter a non-conducting state (inactivation) during maintained depolarisation.

61

What is needed for the sodium channels to enter the closed state?

Repolarisation is needed.

62

How many different gates does sodium channels have?

2 gates. Inactivation and activation gate.

63

Difference between closed state and inactivated state?

The inactivation gate is closed for the inactivation state while in the closed state its the activation gate that is closed

64

Define the "absolute refractory period"?

No stimuli (no matter how strong) can cause a second AP. All sodium channels are inactivated.

65

Define the "relative refractory period"?

A stronger stimuli than normal is needed to elicit a second AP.

66

Why will the electrical signals decay along the membrane?

The membrane is leaky therefore passive signals do not spread far from their site of origin due to current loss across the membrane.

67

Name 2 ways on how to stop the decay along the membrane to make it more efficient?

1. Increase axon diameter 2. Add an insulating material (myelin)

68

Aa axons properties: Diameter? Myelinated? Conductance? What type of receptor?

Large diameter. Thickly myelinated High conductance Proprioceptors of skeletal muscle.

69

Ab axons properties: Diameter? Myelinated? Conductance? What type of receptor?

Large/medium diameter. Moderately myelinated Moderate conductance Mechanoreceptors of skin

70

Ad axons properties: Diameter? Myelinated? Conductance? What type of receptor?

Small/medium diameter. Thinly myelinated. Moderate conductance. Pain, temperature.

71

C axons properties: Diameter? Myelinated? Conductance? What type of receptor?

Small diameter. No myelination. Low conductance. Temperature, pain, itch

72

Conductance in myelinated axons?

The action potential "jumps" from one node of Ranvier to the next. Only at the Node of Ranvier can the AP leak out.

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73

How are messages relayed between neurones?

By chemical synaptic transmission.