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CSC1005 - Integrated Human Physiology > Action Potentials > Flashcards

Action Potentials Flashcards

1
Q

Define action potential:

A
  • Fundamental unit of information in the nervous system

- short lasting event in which the electrical membrane potential of cell readily rise and falls

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2
Q

What cells do action potentials occur in?

A
  • Neurons
  • Muscle cells
  • Cardiac cells
  • Endocrine cells
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3
Q

Define action potential:

A

The difference in electric charge across a cell membrane

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4
Q

What resting potential do electrically excitable cells tend to be?

A

-40 to -90 mV

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5
Q

What do we call cells at their resting potential?

A

polarised

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6
Q

What do we call cells which are more positive than their resting potential?

A

Depolarisation

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7
Q

What do we call cells which are more negative than their resting potential?

A

Hyperpolarisation

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8
Q

How does a potential difference across a cell membrane arise relating to k+ ion?

A

From an in balance of k+ ions inside the cells than the outside

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9
Q

Finish the sentence:

Excitable cells must have a ….

A

negative (hyperpolarised) resting potenial

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10
Q

What do impermeable membranes mean relating to chemical gradient?

A

Cannot exist

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11
Q

What is an electrochemical equilibrium?

A

When the ions are balanced

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12
Q

What is an opposing electrical gradient?

A

Chemical gradient increasing whilst electrical gradient is decreasing

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13
Q

What can stop all k+ ions reaching a chemical equilibrium?

A

an opposing electrical gradient

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14
Q

What is another name for opposing electrical gradient?

A

-Reversal potential

or

-Nernst potential

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15
Q

What is a reversal potential?

A

Membrane potential where the chemical and electrical gradients of an ion across a biological membrane are in equilibrium

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16
Q

What is the net flow of ions across a membrane at reversal potential?

A

No net flow

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17
Q

What does the Nernst equation show?

A

Equilibrium potential of an ion dependent on intra and extra cellular concentrations

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18
Q

What is the Nernst equation?

A

Ex = RT/zF ln [X]out/[X]in

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19
Q

What does R mean in the Nernst equation?

A

The universal gas constant

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20
Q

What does Ex mean in the Nernst equation?

A

The equilibrium potential

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21
Q

What does T mean in the Nernst equation?

A

The temperature in Kelvin

22
Q

What does z mean in the Nernst equation?

A

The valence of the ion

23
Q

What does F mean in the Nernst equation?

A

The Farady constant

24
Q

What does [X]out mean in the Nernst equation?

A

Concentration of ion outside cell

25
Q

What does [X]in mean in the Nernst equation?

A

Concentration of ion inside cell

26
Q

What is the universal gas constant equal to?

A

8.3145 JK-1mol-1

27
Q

What is the temperature in Kelvin equal to at 37C?

A

310.15K

28
Q

What is the faraday constant equal to?

A

96485 C mol-1

29
Q

During depolarisation of membrane potential what opens?

A

Voltage-gated Na+ channels open

30
Q

What does voltage-gated Na+ channel-mediated depolarisation trigger?

A

A chain reaction

31
Q

When is a chain reaction triggered?

A

At an action potential threshold

32
Q

Describe an action potential:

A
  • Na+ flow into cell due to depolarisation opening voltage-gated Na+ channels
  • Result in a region of positive charge across the membrane
  • Local depolarisation causes Na+ channels nearby to open
  • More Na+ ion can flow into cell
  • Voltage-gated K+ channels also activated by depolarisation (much more slowly)
  • K+ leave the cell
  • Na+ channel inactivates
  • More voltage-gated K+ channels open causing hyperpolarisation
  • Resting membrane potential re-established
33
Q

Finish the sentence:

Voltage-gated Na+ channels rapidly…

A

inactivate after activation

34
Q

Finish the sentence:

Due to depolarisation voltage-gated K+ channels activate more…

A

Slowly than voltage-gated Na+ channels

35
Q

Is electrical resistance within an axon higher or lower in thinner axons?

A

Higher

36
Q

What is meant bu a higher electrical resistance in thinner axons?

A

Slower conduction of signal

37
Q

What do myelin sheath do?

A

Insulate the axon from negative external charge

38
Q

What are the effects on electrical transmission due to myelin sheath?

A

Faster transmission

39
Q

Can myelinated axon store some of the charge?

A

Yes

40
Q

What acts as signal boosters to prevent storage of charge?

A

Nodes of Ranvier

41
Q

What are at Nodes of Ranvier?

A

Highly density of volt-gated Na+/K+ channels

42
Q

How does a Nodes of Ranvier work?

A

When a propagating action potential reaches the Node a new action potential is initiated

43
Q

What is the action at the Nodes of Ranvier called?

A

Saltatory conduction

44
Q

What makes up myelin sheath in PNS?

A

Schwann cells

45
Q

What makes up myelin sheath in CNS?

A

Oligodendrocytes

46
Q

What initiates an action potential?

A
  • Anything which causes a depolarisation beyond action potential threshold
  • Under physiological conditions normally generated by ion channels
47
Q

What are different types o d ion channels which can generate an action potential?

A
  • Voltage-activated
  • Extracellular-activated (Ligand/light/heat/cold -activated)
  • Intercellular-activated
  • Stretch-activated
48
Q

Describe the role of action potential in synaptic transmission:

A
  • Action potential reaches presynaptic neurones
  • Ca2+ enter voltage-gated Ca2+ channels
  • Causing Na+ neurotransmitters to be released across the synapse
  • Na+ reaches postsynaptic neuron and initiated a new action potential
49
Q

Is the size of action potential does change what does?

A

The number of frequency

50
Q

Why is it important to calculate the equilibrium potential?

A

If we know what ion channel is permeable to, we can predict what opening that channel will do to the membrane potential

CSC1005 - Integrated Human Physiology (18 decks)

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