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Cell physiology and pharmacology > Lecture 9- The action potential > Flashcards

Lecture 9- The action potential Flashcards

1
Q

3 features of an AP

A

1) All or nothing (only occurs if threshold is reached) 2) Non-overlapping 3) Unidirectional

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2
Q

AP are different in

A

different structures

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3
Q

if a stimuli does not depolarise the membrane above the threshold…

A

the AP will not fire down the hillock of the axon

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4
Q

hillock of axon

A

The axon hillock is the last site in the soma where membrane potentialspropagated from synaptic inputs are summated before being transmitted to the axon

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5
Q

when cells are depolarised which channels are open

A

sodium

-moves Vm (membrane potential) closer to ENa

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6
Q

when the cell is polarising the …… are open

A

potassium

  • moves Vm back to Ek
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7
Q

Vm

A

membrane potential

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8
Q

voltage clamp

A

enables membrane currents to be measured overtime at a set membrane potential

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9
Q

Time course of conductance changes during an action potential

A

During the course of an action potential, the permeability to different ions changes considerably.

At the beginning of an AP Na+ conductance is high and K+ conductance is low. Mid way through the AP Na+ conductance considerably reduces and K+ conductance increases. By the end of the AP when the cell is at resting potential, the conductance of both sodium and potassium will be 0.

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10
Q

Summary of sodium and potassium channel activity during AP

A
  1. Summary of sodium and potassium channel activity during AP
  2. NaV (voltage gated) channels open
  3. Na+ influx into cell
    • Positive feedback to trigger opening of other NaV channels
  4. Membrane depolarisation
  5. At ENa NaV channels inactivate and KV channels open
    • Na+ influx stops
    • K+ efflux
  6. Membrane repolarises
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11
Q

Is Na/K ATPase pump involved in the repolarisation of the AP?

A

NO

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12
Q

the refractory period is the

A

Recovery period after AP has fired- the amount of time it takes for an excitable membrane to be ready for a second stimulus.

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13
Q

during the refractory peroid

A

New AP will not fire

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14
Q

types of refractory period

A

ARP- absolute refractory period

RRP- relative refractory period

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15
Q

absolute refractory period

A

Is the period of time during which a second action potential ABSOLUTELY cannot be initiated, no matter how large the applied stimulus is (i.e. during active AP).

Nearly all Na+ channels are in inactivated states

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16
Q

relative refractory period

A

Is the interval immediately following the Absolute Refractory Period during which initiation of a second action potential is INHIBITED, but not impossible. As voltage-gated potassium channels open to terminate the action potential by repolarizing the membrane, the potassium conductance of the membrane increases and the K+ ions move out of the cell and bring the membrane potential closer to the equilibrium potential for potassium and this can lead to membrane hyperpolarization.

Na+ channels are recovering from inactivations- excitability returns to normal as the number of channels in the inactivated state decreases and as the number of open voltage KV channels closing increases

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17
Q

inacgtivated voltage channels

A

cannot open

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18
Q

active voltage gated channels

A

may not be open, but have the potential to

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19
Q

hyperpolarisation

A

Occurs when the membran potential becomes more negative than the normal resting potential.

Until K+ conductance returns to the resting value, a greater stimulus will be required to reach the threshold for another AP

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20
Q

what marks the end of the relative refractory period

A

Return of equilibrium resting potential

  • Ek
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21
Q

molecular properties of votlage gated Na+ channel

A
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22
Q

molecular properties of votlage gated K+ channel

A
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23
Q

different types of cells have

A

different conduction velocities

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24
Q

the larger the axon the

A

the lower the cytoplasmic resistance and the higher the conduction velocity

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25
Q

classes of peripheral axons (6)

A

Aα

Aβ

Aγ

A𝛿

B

C

26
Q

which class of peripheral axon has the created conduction velocity

A

Aα- widest

27
Q

Which class of peripheral axons has the smallest conduction velocity

A

C- narrowest

28
Q

what type of fibres are Aα

A

sensory fibres fron muscle spindles, motor neurone to skeletal muscle

29
Q

what type of peripheral axon is A𝛿

A

sensory fibre from pain and temp receptors (sharp localised pain)

30
Q

what type of peripheral axon is B

A

preganglionic neurones of the autonomic nervous sstem (myelinated)

31
Q

what type of peripheral axon is C

A

sensory fibres from pain, temp and itch receptors (diffuse pain)

32
Q

local current theory

A

Injection of current into an axon will cause the resulting charge to spread along the axon and cause an immediate local change in the membrane potential.

A change in MP in one part can spread to adjacent areas of the axon

33
Q

conduction velocity is determined by

A

how far along the axon these local currents can spread

34
Q

name 3 properties of an axon that leads to high conduction velocity

A
  • High membrane resistance
  • Low membrane capacitance
  • Large axon diameter- leads to low cytoplasmic resistance
35
Q

capacitance, C, is simply the

A

ability to store charge

  • property of the lipid bilayer
36
Q

high capacitance

A

voltage changes more slowly in response to a current injection- decrease in spread of local current

37
Q

low capacitance

A

increase conduction velocity

38
Q

membrane resistance dpends on the number of

A

ion channels open

39
Q

low resistance

A

the more ion channels open and more loss of the local current across the membrane

40
Q

high resistance

A

increase conductance- change in voltage spreads further along the axons

41
Q

what can increase conduction velocity of a neurone

A

myelination

42
Q

effect of myelination

A

reduce capacitance and increase the resistance of the axonal membrane

43
Q

which types of neurones are myelination - larger or smaller diameter?

A

larger e.g. motorneurons

44
Q

what process does myelination faciliate

A

saltatory conduction

45
Q

what is the myelin sheath made out of in the peripheral NS

A

schwanna cells

46
Q

what is myelin sheath made out of in the CNS

A

oligodendrocytes

47
Q

density of sodium channels in myelinated neruones

A

high density in nodes of ranvier- quick conduction of AP

48
Q

density of sodium channels along non-myleinted axon

A

evenly distributed

49
Q

structure of mylelin sheath

A

Layers of Schwann cells tightly folded around each other

  • Shwanna cells surround the outside of the neurone
50
Q

saltatory conudction

A

Myelin sheath acts as a good insulator causing local circuit currents to depolarise the next node above threshold and initiate an action potential

Action potnetial “jumps “from node to node allowing much faster conduction velocity- AP only occurs at nodes.

51
Q

what occurs when demyelination happens

A

Action potential threshold cannot reach threshold in regions of demyelination and stop saltatory conduction

52
Q

what is the most common demylinating disease

A

multiple sclerosis

53
Q

multiple sclerosis causes

A

all CNS nerves to become demyelinated

54
Q

what is a less common demyelinating disease of the CNS

A

Devic’s disease

55
Q

Devic’s disease

A

demylination of optic and spinal cord nerves only

56
Q

demylinating disease of the PNS

A
  • Landry-Guillain-Barre syndrome
  • Charcot-Marie-Tooth disease
57
Q

name two widely used anaesthetics

A

lidocaine and procain

58
Q

local anaesthetics can be

A

protonated or unprotonated

  • unprotonated can pass the membrane
59
Q

anaesthetics work by

A

blocking Na+ channels

Easier when the channel is open and have a higher affinity to inactivated state of Na+ channel

60
Q

how does lidocaine act as a loacl anaesthetic

A

Act by binding to and blocking Na+ channels

This stops AP from occurring

61
Q

Local anaesthetics block conduction in nerve fibres in the following order:

A
  • Small myelinated axons
  • Non-myelinated axon
  • Large myelinated axon

Cell physiology and pharmacology (20 decks)

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