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LA Symposium > Action Potentials > Flashcards

Action Potentials Flashcards

1
Q

what is the resting membrane potential

A

about -70mV

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2
Q

the ICF or the ECF more negative?

A

ICF

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3
Q

which ion is most abundant in the ECF?

A

Na

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4
Q

which ion is most abundant in the ICF?

A

K

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5
Q

which ion can move through the membrane more?

A

K

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6
Q

how is the resting membrane potential brought about?

A

potassium diffuses OUT of the cell which leaves an excess of -ve charges inside the cell. The potential gradient that arises from this is the resting membrane potential

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7
Q

what does the sodium potassium pump do?

A

move 3Na out and 2K in

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8
Q

does the sodium potassium pump require energy?

A

yes as it moves the ions from a low to high concentration

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9
Q

what is the threshold voltage during the AP?

A

-55mV

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10
Q

what is the rising phase during the action potential due to?

A

Na+ influx through voltage gated Na channels

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11
Q

what is the falling phase during the action potential due to?

A

K+ efflux through voltage gated K channels

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12
Q

what type of protein is an ion channel?

A

transmembrane protein

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13
Q

how many gates does the sodium channel have?

A

2 - H and M

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14
Q

what is the action of the sodium gates?

A

the channel opens when the M gate opens as H gate is already open. The channel closes when the H gate closes (refractory period)

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15
Q

at resting membrane potential what is the state of the Na gate?

A

H gate open, M gate closed

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16
Q

at the threshold until hyperpolarisation what is the state of the Na gate?

A

M gate and H gate open

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17
Q

at the refractory stage what is the state of the Na gate?

A

M gate open, H gate closed

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18
Q

how many gates are there for K

19
Q

what is the first step of the AP?

A

stimulus applied - depolarisation - MP moves towards threshold, gated ion channels closed

20
Q

what is the second step of the AP?

A

MP reaches threshold (-55mV) - Na channels start opening, Na influx, more depolarisation, K+ channels still closed

21
Q

what is the third step of the AP?

A

all Na channels open, maximum Na influx, MP overshoots 0mV

22
Q

what is the fourth step of the AP?

A

MP reaches +35mV - Na channels shut, inactivation, H gate closes, K+ channels open and K+ efflux begins

23
Q

what is the fifth step of the AP?

A

AP downstroke (recovery phase) - Na+ channels shut, refractory period, K+ channels open, K+ efflux continues

24
Q

what is the sixth step of the AP?

A

MP returns to resting level, ion channels return to resting state (H gate open, M gate closed), excitability restored

25
Q

what happens at the threshold of the AP?

A

voltage gated Na channels open, Na+ diffuse in, further depolarisation, positive feedback involved

26
Q

what happens at the peak of the AP?

A

Na+ channels close, voltage gated K+ channels open, K+ diffuse out - repolarisation

27
Q

what is the refractory period

A

after an AP is initiated the neuron cannot generate another AP until the first one has ended (period of inexcitability)

28
Q

what is the refractory period due to?

A

inactivation of the voltage gated sodium channels (H gate closed)

29
Q

what are the consequences of the refractory period?

A

limits maximum firing frequency, ensures unidirectional propagation of action potentials, prevents summation of AP, prevents summation of contractions in cardiac muscle

30
Q

describe AP propagation

A

AP set up in one section of axon, depolarises adjacent part, AP regenerated further along, it moves along the axon as waves of depolarisation

31
Q

what increases AP propagation?

A

myelination and large axons

32
Q

what does myelination do?

A

increases speed of AP propagation for given diameter of axon, forms an insulating layer which reduces leakage of current from axons

33
Q

what is myelin laid down by?

A

glial cells

34
Q

what are the spaces where the myelin sheath is interrupted called?

A

Nodes of Ranvier

35
Q

what occurs at the nodes of Ranvier?

A

axon membrane is exposed to ECF and ion flow can occur

36
Q

what is saltatory conduction

A

AP jumps from one node of Ranvier to the next which increases speed so fewer regeneration steps meaning more rapid AP propagation

37
Q

what is the tissue layer surrounding axons?

A

endoneuron

38
Q

what layer protects a bunch of axons?

A

perineuron

39
Q

what layer protects lots of bunches of axons?

40
Q

what do A beta fibres do?

A

mechanoreceptors

41
Q

what do A delta fibres do?

A

mechanoreceptors, thermoreceptors, nociceptors, chemoreceptors

42
Q

what do C fibres do?

A

mechanoreceptors, thermoreceptors, nociceptors

43
Q

are tooth fibres myelinated or unmyelinated?

A

most are unmyelinated as when myelinated fibres move closer to odontoblasts they lose myelination

LA Symposium (7 decks)

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