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BDS2 LA Symposium > Action Potential Mechanisms > Flashcards

Action Potential Mechanisms Flashcards

1
Q

what is a resting membrane potential?

A

a potential difference that exists across the membrane of all cells

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2
Q

what is the resting membrane potential range for cells?

A

20-90mV

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3
Q

how does the ICF compare to the ECF

A

the inside (ICF) is NEGATIVE with respect to the outside (ECF)

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4
Q

what are the charges found within the ICF and ECF?

A

equal numbers of positive and negative charges in the ECF and ICF

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5
Q

if there are equal numbers of +ve and -ve charges in the ECF and ICF, why is there a difference in overall charge?

A
  • the charges on each side of the membrane are not evenly distributed
  • on the periphery of the ICF, the charges that lie there are negative
  • on the edge of the ECF, the charges that lie there are positive
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6
Q

what does the resting. membrane potential arise from?

A

arises from the separation of charges on either side of the membrane

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7
Q

what is the resting membrane potential determined by?

A
  • diffusion of K+ from cell interior through K+ channels*****
  • the sodium/potassium pump also contributes by moving unequal amounts of Na and K
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8
Q

where are Na+ ions found?

A

mainly in the ECF

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9
Q

where are K+ ions found?

A

mainly in the ICF

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10
Q

where are Cl- ions found?

A

mainly in the ECF

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11
Q

how does the ‘resting’ membrane differ with respects to Na+ and K+ ions?

A
  • the ‘resting’ membrane is impermeable to Na+

- the ‘resting’ membrane is very permeable to K+

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12
Q

what does diffusion of K+ ions out of the cell cause?

A
  • an excess of negative charge inside the cell

- the potential gradient arising from diffusion is the ‘resting membrane potential’

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13
Q

how does the Na+/K+ pump contribute to the RMP?

A
  • small traces of Na+ leak into cells

- the pump moves 3 Na+ outwards and 2 K+ inwards

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14
Q

when sodium is moved out of the cell and potassium is moved in using the pump, is this process passive or via active transport?

A

active transport

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15
Q

what is meant by active transport?

A

movement of ions that requires energy

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16
Q

how can the membrane potential be altered?

A

by applying an electric current to the cell (a ‘stimulus’)

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17
Q

what is the membrane potential ‘threshold’, after which depolarisation occurs?

A

around -55mV

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18
Q

what occurs once the membrane potential ‘threshold’ is reached?

A
  • large depolarisation occurs
  • opening of voltage-gated Na+ channels
  • the MP ‘overshoots’ zero, so that the polarisation is reversed
  • the action potential starts
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19
Q

what is the ‘rising’ phase of the action potential caused by?

A
  • Na+ influx through voltage gated Na channels
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20
Q

what is the ‘falling’ phase of the action potential caused by?

A
  • K+ efflux through voltage gated K channels
21
Q

what occurs at around 35mV?

A
  • Na+ channels shut (h gate closes)
  • K+ channels open
  • K+ leaves the cell, making the MP more negative
22
Q

what are ion channels?

A
  • transmembrane proteins
23
Q

what type of ion channels exist in cells?

A
  • gated channels

- ion selective (specific) channels

24
Q

what types of gated ion channels are there?

A
  • ligand

- voltage

25
Q

what is the AP down stroke?

A

the ‘recovery’ phase

- refractory period in the Na+ channels

26
Q

how can the AP event be described?

A
  • an ‘all or nothing’ event

- amplitude is independent of stimulus

27
Q

what is the refractory period of a neuron?

A
  • period of inexcitability

- after an AP is initiated, the neuron cannot generate another AP until the first has ended

28
Q

why does the refractory period occur?

A

it occurs due to the inactivation of voltage-gated sodium channels

29
Q

what are the consequences of the refractory period?

A
  • limits maximum firing frequency of action potentials in axons
  • ensures unidirectional propagation of APs
  • prevents summation of APs
30
Q

what is unique about the cardiac AP?

A

it lasts as long as the ventricular contraction

31
Q

how do action potentials travel?

A

APs travel along the axon as waves of depolarisation

32
Q

how does the axon diameter effect the AP?

A

the speed of the action potential increases with the axon diameter

33
Q

what can increase the speed of an AP in a smaller neuron?

A
  • myelination which forms an insulating layer, reducing leakage of current from axon
34
Q

what are glial cells?

A

cells that form myelin

35
Q

what type of glial cells form myelin in the PNS?

A
  • Schwann cells
36
Q

what type of glial cells produce myelin in the CNS?

A

oligodendrocytes

37
Q

what are the short unmyelinated specialised sections of the axon better known as?

A

Nodes of Ranvier

38
Q

what is meant by saltatory conduction?

A

when an electrical impulse skips from node to node down the full length of an axon

39
Q

what is the epineurium?

A

the outermost layer of dense, connective tissue that surrounds a peripheral nerve

40
Q

what is the perineurium?

A
  • protective sheathe that surrounds a nerve fascicle

- it bundles together axons that target the same anatomical region

41
Q

what is the perineurium composed of?

A

mostly fibroblasts

42
Q

what is the endoneurium?

A

a layer of delicate connective tissue that surrounds the myelin sheathe of each myelinated nerve fibre

43
Q

are A fibres myelinated or unmyelinated?

A

myelinated

44
Q

what type of nerve fibres are unmyelinated?

A

C fibres

45
Q

what is the function of A-beta fibres?

A

mechanoreception

46
Q

what are the functions of A-delta fibres?

A
  • mechanoreception
  • thermoreception (cold)
  • nociception
  • chemoreception
47
Q

what is the function of C fibres?

A
  • mechanoreception
  • thermoreception (hot and cold)
  • nociception
48
Q

what type of fibres is the pulp composed of?

A

mostly unmyelinated C fibres

BDS2 LA Symposium (5 decks)

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