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BRS - Neuro > Membranes + Action Potentials > Flashcards

Membranes + Action Potentials Flashcards

1
Q

What is voltage?

A

• Potential difference
• Unit = Volts
• Generated by ions to produce a charge gradient
(i.e. like a chemical battery)

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2
Q

What is current?

A
  • Unit = Amps

* Movement of ions due to a potential difference

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3
Q

What is resistance?

A
  • Unit = Ohms

* Barrier that prevents the movement of ion

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4
Q

How is membrane potential measured?

A
  1. A reference electrode is placed outside the cell. This is the zero-volt level
  2. Another electrode is placed inside the cell to measure a voltage difference that is negative compared with the outside
  3. All cells have a membrane potential.
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5
Q

What are ion channels?

A

Permeable pores in the membrane (ion channels) open and close depending on transmembrane voltage, presence of activating ligands or mechanical forces

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6
Q

Why are ion channels necessary?

A
  • Lipid (hydrophobic) cell membrane is a barrier to ion movement and separates ionic environment
  • The cell membrane can selectively change its permeability to specific ions
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7
Q

How can equilibrium potential be calculated?

A

Using the Nernst equation

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8
Q

What is the Nernst equation?

A

Too complicated, google it

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9
Q

What is the composition of ions like, intracellular vs. extracellular?

A 
Intracellular:
→ low Na
→ high K
→ high Ca2+
→ low Cl-
Opposite for extracellular
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10
Q

Why do membrane potentials not rest at Ek or ENa?

A

membranes have mixed K+ and Na+ permeability (but at rest K+&raquo_space; Na+)

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11
Q

What ions contribute to the value of real membrane potential?

A

Potassium, Chloride + sodium

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12
Q

What is the permeability of the membrane to each significant ion proportional to?

A

The size of each ion’s contribution

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13
Q

What is the purpose of the GHK equation?

A

More accurate way to describe membrane potential

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14
Q

What is the GHK equation?

A

Check notes

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15
Q

What happens when you increase the permeability of a membrane to a particular type of ion?

A

Shifts the membrane potential toward the reversal potential for that ion

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16
Q

What happens to membrane potential when Na channels open?

A

Shifts membrane potential towards sodium reversal potential → usually around 100 mv → therefore in positive direction

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17
Q

What happens to membrane potential when K channels open?

A

shifts the membrane potential toward about –90 mV (shifts the membrane potential in a negative direction, except when the membrane is hyperpolarised to a value more negative than the K+ reversal potential)

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18
Q

What happens to membrane potential when Cl channels open?

A

shifts the membrane potential toward about –70 mV (shifts toward the resting potential)

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19
Q

What is pertsynaptic potential?

A

temporary change in membrane potential produced by activation of a synapse by a single graded or action potential

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20
Q

What is equilibrium potential (E)?

A

Potential at which electrochemical equilibrium is reached

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21
Q

Why are Action Potentials important?

A

• Play a central role in cell-to-cell communication
• can activate intracellular processes
- in muscle cells, an AP is the first of a series of events leading to contraction
- in beta cells of the pancreas and AP stimulates insulin release

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22
Q

What does membrane permeability to ions depend on?

A

Conformational state of ion channels

23
Q

How is a resting membrane potential generated?

A

Uneven ion distribution due to impermeability of membrane to these ions = difference in ion concentrations = potential difference across membrane

24
Q

What is resting membrane potential for neuronal cells?

A

Negative change inside compared to outside = - 40 to-90 mv

25
Q

How is an action potential generated?

A

Through membrane depolarisation - opening of VGSC causes Na influx → generates impulse

26
Q

Why do VGSCs open before VGKCs?

A

Faster kinetics

27
Q

How is the membrane repolarised?

A

VGKSs open slowly as VGSCs start to open causing K+ efflux

28
Q

Why does hyper polarisation occur?

A

VGKCs are still open so membrane potential moves closer to K+ equilibrium

29
Q

What is an absolute refractory period?

A

Period of time where it’s impossible to evoke another action potential due to inactive state of VGSCs

30
Q

What is an relative refractory period?

A

Very strong stimulus (stronger than normal) is needed to evoke an action potential - some of the VGSCs have recovered

31
Q

What is the role of Na+/K+ ATPase during resting membrane potential?

A

Maintains resting potential - in its resting configuration pumps Na out of cell

32
Q

What is the role of Na+/K+ ATPase after an action potential?

A

Helps return membrane potential to resting value - in its active configuration na is removed from cell + K is moved into cell

33
Q

How does the action potential spread down the axon?

A

Through saltatory conduction.

34
Q

What is the purpose of myelin sheath?

A

High resistance + low capacitance prevents spread of AP - forces AP to jump

35
Q

What are the Nodes of Ranvier?

A

Small gaps between myelin intermittently placed along axon - AP has to jump from node to node

36
Q

What happens to the AP at the axon terminal?

A

Can no longer continue

37
Q

Why is an action potential an all or nothing event?

A

Once threshold potential is reached, a full sized AP is triggered

38
Q

What mainly restores the electrochemical equilibrium after an action potential?

A

Non-voltage gated ion channels

39
Q

Why does the action potential propagate down the length of the axon?

A

→ While one area of the axon is at peak AP, local current flow depolarizes adjacent area towards threshold
→ slight depolarization spreads and more VGSCs open + more N a rush in
→ old area is still returning to resting potential so depolarisation starts to happen at new adjacent area.

40
Q

What is continuous conduction?

A

Propagation along an unmyelinated axon

41
Q

What is saltatory conduction?

A

Propagation along an myelinated axon

42
Q

Why is continuous conduction slower than saltatory?

A

No jumping + more time spent waiting for all voltage-gated sodium channels to open, etc.

43
Q

What 2 factors affect conduction velocity?

A

→ axon diameter

→ myelination

44
Q

When are ion channels opened?

A

Membrane depolarisation

45
Q

What inactivates ion channels?

A

Sustained depolarisation

46
Q

What closes ion channels?

A

Hyperpolarisation or repolarisation

47
Q

What is passive propagation?

A

Only resting potassium channels open?

48
Q

What increases conduction velocity?

A

Lange diameter + myelinated axons

49
Q

What decreases conduction velocity?

A

reduced axon diameter (i.e. re-growth after injury), reduced myelination (e.g.
multiple sclerosis and diphtheria), cold, anoxia, compression and drugs (some anaesthetics)

50
Q

What are the 3 main factors that influence the movement of ions across the membrane?

A
  • Concentration of ion on both sides of the membrane,
  • the charge on the ion
  • the voltage across the membrane.
51
Q

Why is the K+ equilibrium potential negative (e.g. -70mV) and the Na+ equilibrium potential positive(e.g. +40mV) when both are positive ions?

A

more K+ inside the cell than outside so tend to flow out of the cell, while more Na+ outside the cell than in, therefore tend to flow into the cell. A potential of -70mV is needed to attract K+ and stop net outward flow, while a positive charge of +40mV is needed to repel Na+ from entering the cell.

52
Q

Which ion is important for the upstroke (rising portion) and which is important for the falling portion of the action potential? In which direction do these ions move?

A

The upstroke mediated largely by Na+ ions moving down their concentration gradient into the cell. The falling portion of the action potential dominated by K+ ions going down their concentration gradient and therefore exiting the cell

53
Q

What factors influence the speed of propagation of an action potential along an axon?

A

Larger axons have lower resistance, so ions move faster – conduction velocity is proportional to the square root of the axon diameter. There is a linear relationship between conduction velocity and myelin thickness

BRS - Neuro (10 decks)

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