Membrane Potential and Action Potentials Flashcards

1
Q

Ion Flux

A

The number of molecules that cross a unit area per unit of time ( number of particles )

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2
Q

Voltage ( potential difference )

A

Generated by ions to produce a charge gradient

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3
Q

Current ( amps)

A

Movement of ions due to a potential difference

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4
Q

Resistance

A

Barrier that prevents the movement of ions

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5
Q

What are changes in membrane potential caused by

A

Ion transporters

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6
Q

When is an electrochemical equilibrium achieved

A

When electrical force prevents further diffusion across the membrane . So when the concentration gradient exactly balances the electrical gradient .

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7
Q

What does the Nernst equation tell you

A

The equilibrium potential ( E)

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8
Q

What is R in the Ernst Equation

A

Gas constant ( 8.31)

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9
Q

What is T in the Ernst Equaton

A

Temperature in Kelvin ( 37 degrees or 310K)

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10
Q

What is z on the Ernst Equation

A

Charge on the ion ( eg. -1 for Cl - etc)

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11
Q

What is F in the Ernst Equation

A

Faradays number - charge per mol of ion

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12
Q

What do you do to the Ernst equation when calculating

A

Assume T = 37 degrees or 310 K
Convert natural log to common log
State E in mV
Male compartment 2 the inside and 1 outside

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13
Q

X 2 and X1 in Ernst Equation

A

X2 is the intracellular ion conc and X 1 is theextra cellular ion conc

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14
Q

Typical concentrations of sodium

A

150 mmol outside and 10 mmol inside

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15
Q

Typical concentrations of potassium

A

5 mmol outside and 150 mmol inside

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16
Q

The version of the Ernst equation we need

A

E = -61/z x log ( X inside /X outside )

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17
Q

Why do membrane potentials not rest at E k or Ena

A

Because there are always some channels open at all times

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18
Q

What does the GhK questions do

A

Describes the resting membrane potential ( look at the examples on OneNote )

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19
Q

What is the supposed membrane potential supposed to be

A

A typical membrane resting potential is -70 mmol and not -90 mmol which is Ek as some of the other ion channels are always open . As even at rest, the membrane has some finite permeability to some Na + and so the membrane potential is higher

20
Q

Typical concentrations of Cl-

A

110 extra cellular and 5 intracellular

21
Q

What does depolarisation mean

A

Membrane potential moves towards 0 mV

22
Q

What does repolarisation mean

A

Membrane potential decreases towards the resting potential

23
Q

Overshoot

A

When membrane potential becomes more positive

24
Q

What does hyperpolarisation mean

A

When membrane potential decreases beyond resting potential

25
Q

What are graded potentials

A

They have decrement all speed and strength and they occur at synapses and in sensory receptors , they also contribute to initiating or preventing action potentials

26
Q

Action potentials and graded potentials

A

Actions potentials occur when a graded potentials reaches a threshold for the activation of Na + channels resulting an ‘all or nothing’ principal

27
Q

Where do action potentials occur

A

Excitable cells ( mainly neurone and muscle cells but also in some endocrine tissues)

28
Q

What does the permeability of ions depend on in action potentials

A

Permeability depends on conformational state of ion channels, they are opened by membrane depolarisation , inactivated by sustained depolarisation and closed by membrane hyperpolarisation / repolarisation

29
Q

Changes in membrane potential during the action potential are due to

A

Ion channels and not pumps . The sodium potassium potential manga is the concentration gradient on which the movement of the ion depends on

30
Q

Phase 1 of action potential

A

Resting membrane potential . Permeability for potassium ions are greater than sodium ions, the membrane potential is nearer the equilibrium potential for potassium ( -90mV) than that for sodium ( +72mV)

31
Q

Phase 2 depolarising stimulus

A

The stimulus depolarises the membrane potential and moves it in the positive direction towards the threshold

32
Q

Phase 3

A

Upstroke .starts at threshold potential, sodium channels open quickly and potassium channels open slowly , so potassium is moving out less than sodium is entering and membrane potential moves towards the sodium equilibrium potential

33
Q

Phase 4 repolarisation

A

The sodium ion channels close and sodium entry stops and potassium ion channels opens and remains open so membrane potential moves towards the potassium equilibrium potential

34
Q

At the start of repolarisation

A

Absolute refractory period , activation gate is open but inactivation gate is closed in sodium so new action potential cannot be triggered even with very strong stimulus

35
Q

Later in repolarisation

A

Absolute refractory period continues and so the activation and inactivation gates are closed

36
Q

After hyperpolarisation

A

At rest the potassium channels are still open and so potassium continues to leave the cell down the electrochemical gradient . Membrane potential moves closer to the potassium equilibrium - some voltage gated potassium channels then close . Membrane potential returns to resting potential

37
Q

After hyperpolarisation what happens to sodium channels

A

Relative refractory period and so the inactivation gate is open and a stronger than normal stimulus is required to trigger an action potential

38
Q

What affects how quickly the graded potential decays away from the site of initiation

A

Internal diameter of the axon
Internal resistance of axon
How well the axon is insulated

39
Q

Where are voltage gated channels mostly located

A

Nodes of Ranvier

40
Q

What affects the conduction velocity

A

Axon diameter and myelinated
Large diameter , myelinated axons travel very quickly while small diameter non myelinated axons travel slower.
Cold anoxia compression and drugs ( anaesthetics ) also decrease conduction velocity . Reduced myelination can be due to multiple sclerosis and diphtheria)

41
Q

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

A

Concentration of ion on both sides of the membrane, the change of the ion and the voltage across the membrane

42
Q

Why is potassium ion equilibrium negative and sodium positive when they are both positive ions

A

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

43
Q

Which ion is imp for the upstroke and which is imp for the falling portion of the action potential ?

A

The upstroke is mediated by the sodium ions moving down their conc gradient into the cell . The falling portion of the action potential is by potassium ions going down their conc gradient and exiting the cell

44
Q

What factors influence the speed of propagation of an action potential along the 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 the conduction velocity and myelin thickness

45
Q

What causes a graded potential

A

Local changes in ionic conductance ( e.g. synaptic or sensory that produces a local current) that spreads along a stretch of membrane becoming smaller