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FunMed Physiology > Action Potentials > Flashcards

Action Potentials Flashcards

1
Q

Where is the membrane potential charge

A
  • This is only present in the cell membrane no the whole cell
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2
Q

where does the paracrine signalling act

A
  • Act locally
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3
Q

what does the paracrine system include

A

ncludes neural; neurotransmitters(NT) released from nerves

  • Some neurotransmitters can also be hormones such as adrenaline
  • Also directed coupled cells via gap junctions (electrical and chemical coupling) such as cardiac and smooth muscle
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4
Q

Where does the endocrine system secrete

A
  • Hormones released into the blood
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5
Q

What is the resting membrane potential

A

-70mv

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6
Q

what creates the negative voltage resting potential inside the cell

A
  • at rest there is a small conductance(leakage of potassium ions down its concentration gradient (potassium ions to leave the cell) this creates a negative voltage which is the resting potential inside the cell
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7
Q

What is the difference in distribution between the intracellular fluids and the extracellular fluids

A
  • in the inside Na+ 15nM, K+ 150mM, CL- 10nM, A- (protein)100nM
  • in the outside NA+ 150nM, A- 0.2nM, K+ 5mM, Cl- 120mM
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8
Q

what would happen if the membrane is completely permeable

A
  • if the membrane was complelety permeable then the natural concentration would be equal and we would not have this unequal distribution
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9
Q

How can ions move across the membrane

A
  • passive ionic diffusion - leak channels
  • facilitated diffusion
  • active ionic diffusion
  • gibbs-donnan equilibrium effect
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10
Q

what is passive diffusion for

A

leaks channels – this is mainly for water and gases, ions are usually to big

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11
Q

how does facilitated diffusion work

A

– pass down the channel, these are the leak channels, open all the time allow the passage of the ion down its concentration gradient, allows sodium to pass down pass through the open channel and get into the inside of the cell, opposite

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12
Q

How does active ionic diffusion work

A

– use energy move it against the concentration gradient, carrier channels move the ion against its concentration gradient, this is the sodium potassium ATPase, this moves sodium and potassium against its concentration gradient, sodium is pumped out from the inside of the cell

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13
Q

How does the Gibbs donnas equilibrium effect work

A

presence of charged impermeable ion(such as a protein this gets trapped inside the cell) on one side of a membrane (intracellular) which results in an asymmetric distribution of permeant charged ions, has negative charge, means that we have to balance the two negative charges with positive charges to create an electronetural situations on the inside and the outside of the cell

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14
Q

how does sodium enter through the cell membrane

A

Low intracellular Na+ compared to extracellular Na+ concentration so Na+ enters the cell by passive transport through non-gated (always open) Na+ channels.

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15
Q

what is the rate of sodium entry matched by

A

The rate of Na+ entry is matched by the active transport of Na+ out via Na+/K+ ATPase pump. This transports NA+ and K+ ions against their concentration gradient. The net result is intracellular Na+ is maintained low, even though Na+ continually enters

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16
Q

how is potassium moved across the membrane

A

Passive exit of K+ through non-gated K+ channels is matched by the active entry of K+.

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17
Q

what is the major contributor to the resting potential

A

sodium potassium pump is the major contributor

18
Q

what is the 3 effects of the sodium potassium pump

A
  • makes Na+ concentration high in extracellular space and low in intracellular space
  • makes K+ concentration high in intracellular space and low in extracellular space
  • Result = extracellular space has positive voltage with respect to intracellular space
19
Q

what does the sodium potassium pump do

A
  • Pump exchanges 3 Na+ ions from intracellular space for 2 K+ ions from extracellular spaces – contributes -4mV to resting membrane potential
20
Q

How is the membrane potential generated

A
  • More potassium leak channels then sodium, this moves the potassium out
  • Fewer sodium channels moving sodium in
  • Large negative charged proteins trapped in the cell
  • Sodium and potassium pumps move 3 Na+ out for 2 K+ in - main thing that establishing the resting potential membrane, as it moves against the concentration gradient and against the electrochemical gradient
  • All result in the inside being slightly more negative than the outside
  • Measure in volts
  • -70mv
21
Q

How do you measure the charge across a membrane

A
  • voltmeter
  • a recording electrode is inserted into the cell and a reference electrode is inserted outside the cell
  • by comparing the charge measured by these two electrodes
  • transmembrane voltage is determined
22
Q

what is a nearest equation

A
  • Em=61.5log [concentration]0/[concentration]
23
Q

what does the nerst equation measure

A
  • Potential across the cell membrane at which the net diffusion of ions across the cell membrane due to the concentration gradient stops
  • Relates Em the membrane potential to the concentration gradient
24
Q

whats the constant for potassium

A

61.5

25
Q

whats the constant for chloride

A

-61.5

26
Q

what is the temperature for a monovalent cation

A

37 degrees

27
Q

what is the relative permeability

A

• Relative permeability
• P K+ : P Na+ = 50 -100:1
• The neuron plasma membrane is 100 times more permeable to K+ than Na+
– More passive leak channels for K+ and bigger diameter than Na+ leak channels

28
Q

what cells have electrical activity

A

nerve and muscle cells

29
Q

what are action potentials

A
  • Rapid changes in voltage across the membrane are called action potentials
30
Q

what are action potentials due to

A
  • Due to presence of voltage dependent ion channels – there are two of them, sodium and potassium
31
Q

where are the voltage dependent ion channels found

A

axonal and axon hillock

- trigger region as if this region is activated then you will get generation of an action potentials

32
Q

what are the two types of channels

A

sodium and potassium ion channels

33
Q

describe the voltage sensitive sodium channel how it opens and how it closes

A
  • Activation gate which is closed in the resting state, this activation gate is opened in response to depolarisation, it opens very fast at less than 0.1ms, allows 6000 sodium ions into cell
  • Inactivation gate, this is the gate that is open in the resting state, it closes in response to depolarisation, closes slowly (around 1ms after depolarisation)

after repolarisation the channels return to a resting state

  • Depolarisation opens both activation and closes the inactivation gate, but as the inactivation gate closes more slowly sodium ions enter before the inactivation gate closes
  • After the inactivation gate is closed the activation gate closes a bit after
34
Q

describe how the voltage sensitive potassium channels work

A
  • Open in response to depolarisation but open slower than sodium channels close
  • They stay open during the entire depolarisation and stay open longer than the sodium pumps,
  • Increase the potassium concentration greater than resting potassium concentration
  • Produce repolarisation and undershoot called hyperpolarisation when we are repolarising the membrane
35
Q

how does the overview of the action potential work

A

Stage 1 resting state
- All gated sodium and potassium channels are closed (sodium activation gates closed, inactivate gate is open)
Stage 2 depolarisation
- Depolarisation opens the sodium channel open, activate gate opens very quickly
- 6000 sodium ions go down the concentration gradient
Stage 3 repolarisation
- Inactivate sodium channel closes blocks further entry
- Potassium channel open and it is now able to leave the cell
stage 4 Hyperpolarization
- Potassium channels remain open
- Sodium channels are resetting - resting potential goes below -70mV because potassium leaves the cell and no Na+ move in, Na/K pumps then restore resting potential

36
Q

describe the all for nothing law

A
  • All or nothing threshold this means that either the depolarisation doesn’t reach the threshold therefore no action potential is generated or it reaches threshold and this elicits an action potential that is always the same
  • Threshold for an action potential is reached when the opening voltage gated sodium channels stimulate other channels to open in a positive feedback loop
  • As the stimulus increases then more action potentials take place in a certain period of time
37
Q

what are the 2 levels of refractory period

A
  • absolute and relative
38
Q

describe absolute refractory period

A

– cannot open regardless of the size of the applied stimulus,
1-2ms long
- no channels inactive
– due to inactivated sodium ions, absolute refractory period contributes to the all or none properly this makes it impossible fro action potentials during this period

39
Q

describe the relative refractory period

A
  • before the closure of potassium channels PK+ is large, therefore larger stimulus is needed to make PNA+ > PK+,
  • Increased threshold,
  • 3-15ms
  • due to continued outward diffusion of sodium ions
  • makes it possible to encode information by converting the strength of a stimulus into the frequency of action potentials – suprathreshold graded potential can produce a higher number of action potentials within a given period – stronger stimulus, higher frequency

explanation
- sodium channels now reset but potassium still leaking out of the cells which makes it more negative and therefore need a strong stimulus to reach a threshold

40
Q

How do local anaesthetics work

A
  • Binds to a specific site on the intracellular side of the receptor
  • Has the greater affinity for sodium channel in activated state and slows its reversion to the resting state so refractory period is increased
  • Resting membrane potential unaltered at sodium channels are not blocked and Na/K channel still works
    what does this mean
  • they bind to open voltage gated sodium ion channels
  • allows them to become inactivated
  • prevents them returning to resting state
  • so prevent voltage gated sodium ion channels from reopening and producing any subsequent action potentials
41
Q

Numbers 1 to 4

A 
1 = resting 
2= depolarisation 
3= depolarisation 
4= hyperpolarisation

FunMed Physiology (10 decks)

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