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BDS2 BAMS > Action Potential > Flashcards

Action Potential Flashcards

1
Q

whats is the potential difference across

A

the membrane of all cells

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2
Q

what is the range for resting membrane potential

A

20 - 90mV

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3
Q

what is more negative - intracellular or extracellular fluid

A

intracellular fluid is more negative than extracellular fluid

Equal numbers of +ve and –ve charges in ECF and ICF

But, ion/charge distribution is ‘polarised’

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4
Q

what is the intracellular membrane charge

A

negative

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5
Q

what is the extracellular membrane charge

A

positive

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6
Q

is the resting membrane potential natural

A

no

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7
Q

3 key ions in the ICF and ECF

A

sodium Na+

potassium K+

chloride Cl-

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8
Q

sodium ions in ECF compared to ICF

A 
ECF= 145mM
ICF= 15mM
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9
Q

potassium ions in ECF compared to ICF

A

ECF= 4mM

ICF=150mM

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10
Q

Chloride ions in ECF compared to ICF

A

ECF=110mM

ICF= 10mM

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11
Q

the resting membrane potential causes which ion to want to move in and which ion to want to move out of the cell

A

sodium wants to move into the cell (higher conc in ECF)

potassium wants to move out of the cell (high conc in ICF)

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12
Q

what do substances need to be in order to move across the membrane

A

hydrophillic

so ions cannot diffuse (only small leak)

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13
Q

sodium concentration gradient

A

Na+ high concentration in ECF flows down concentration gradient to ICF

Into cell

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14
Q

potassium concentration gradient

A

K+ high concentration in ICF flows down concentration gradient to ECF

Out of cell

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15
Q

what is the ‘resting’ membrane potential impermeable and very permeable to

A

impermeable to Na+

very permeable to K+

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16
Q

what is the diffusion potential and what ion creates this

A

Diffusion of K+ leaves excessive positive charge inside cell compared to the ECF

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

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17
Q

what is the RMP mainly due to

A

diffusion of K+ from cell interior through K+ channels

The small amount of Na+ that leaks into the cell is expelled by the Na+/K+ pump

The Na+/K+ pump also contributes by
- exchanging unequal numbers of Na+ and K+

The Na+/K+ pump is ‘electrogenic’
- ATP required

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18
Q

action of Na+/K+ pump

A

The pump moves 3 Na+ outwards and 2 K+ inwards

‘electrogenic’
- ATP needed

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19
Q

what is the process of action potential

A

Process of bringing from RMP to inverted arrangement and back

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20
Q

what is the threshold for action potential

A

-55mV

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21
Q

what is the rising phase of action potential due to

A

Na+ influx through voltage gated Na+ channels

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22
Q

what is the falling phase of action potential due to

A

K+ efflux

voltage gated K channels

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23
Q

what are ion channels

A

Transmembrane proteins

Aqueous channel through membrane

Gated opening:

  • Ligand e.g. Ca channels usually
  • Voltage e.g. Na and K channels usually
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24
Q

what are voltage gated ion channels opened by

A

Specific voltages open and close the channel

Ion selective (specific):

  • Na+ channel
  • K+ channel
  • Ca++ channel
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25
Q

can an ion channel have more than one gate

A

yes

e.g. Na channel has 2 gate arrangement

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26
Q

first stage of AP after stimulus applied

A

lead to depolarisation is sufficient strength

MP moves towards the ‘threshold’

gated ion channels are closed

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27
Q

what happens when the MP reaches the ‘threshold’

A

cause Na+ voltage gated channels to open (both)

Na+ influx
- more depolarisation

more Na channels recruited throughout influx leads to greater level of depolarisation

K+ channels remain closed

28
Q

what causes the MP to overshoot 0mV after reached above threshold

A

all sodium channels are opened

so maximum Na+ influx

29
Q

what happens when MP reaches +35mV

A

Na+ channels shut
- inactivation (‘h’ gate closes)

K+ channels open
- K+ efflux begins

reverse of process stop Na movement and start movement of K

30
Q

what occurs in the AP downstroke and refractory phase

A

‘recovery’ phase

Na channels shut
- the refractory period

K+ channels open so efflux continues

31
Q

what happens after the refractory phase when the MP returns to resting state

A

ion channels return to resting state

  • Na+ H gate opens after refractory period so M gate closed
  • K+ gate closed

excitability restored

32
Q

what gate is responsible for the refractory period

A

Na+ H gate

33
Q

what is the purpose of the refractory period

A

ensure signal moves unidirectionally

the neuron cannot generate another AP until the first one has ended

34
Q

what happens when the -55mV threshold is reached

A

AP is all or none, cannot add together APs

no need to alter stimulus as will travel through neuron once triggered

35
Q

what happens at the AP threshold

A

voltage-gated Na+ channels open

  • Na+ diffuse in leads to further depolarisation

Positive feedback involved here

36
Q

what happens at AP peak

A

Na+ channels close; voltage-gated K+ channels open;

K+ diffuse out causes repolarisation

Return to resting membrane potential

37
Q

what is the period of in-excitability post AP called

A

refractory period

38
Q

what is the sequence of opening and closing of Na+ gates in AP

A

M gate closed in first phase

Then both open

Then H gate in second phase (refractory period)

39
Q

where a sodium gates positioned

A

they are intracellular

40
Q

what are 4 consequences of the refractory period

A

Limits maximum firing frequency of action potentials in axons

Ensures unidirectional propagation of action potentials

Prevents summation of action potentials

Prevents summation of contractions in cardiac muscle – the cardiac AP lasts as long as the ventricular contraction

41
Q

how does an AP travel through a neuron

A

AP in one section of axon sets up longitudinal current flow
- This depolarises adjacent ‘resting’ parts of the axon

The AP is regenerated further along the axon

More current flows, and the next region of axon is activated

Action potentials travel along the axon as waves of depolarisation

  • Crawling through axon
  • Travelling waves of depolarisation
42
Q

what is the effect on AP diameter on the speed of AP propagation

A

the speed of AP propagation increases with axon diameter

43
Q

large axons compared to small axons conduction s speed

A

large axons conduct impulses more rapidly than small ones

44
Q

what is the issue with smaller thinner axons and propagating AP

A

they are more fragile

less membrane for AP to work

45
Q

why does myelinated axons require more energy

A

made of 1000s of Schwann cells
- Each need fed and maintained to survive

more efficient to have unmyelinated if don’t need speed

46
Q

what is the role of myelination

A

Myelination increases speed of AP propagation for a given diameter of axon

47
Q

what is a myeline sheath made of on an axon

A

consists of many layers of cell membranes wrapped round the axon

Myelin laid down by glial cells (Scwann Cells)

48
Q

what lays down myeline

A

glial cells (Schwann Cells)

49
Q

what is the physical role of myelin

A

forms an insulating layer, reducing leakage of current from axon
- rather like lagging a hot water pipe

50
Q

what are the interruptions in myeline sheath called

A

Nodes of Ranvier

51
Q

what is the role of Nodes of Ranvier

A

axon membrane is exposed to the ECF, and ion flow can occur

where the AP is
- need space so can jump from one node to next

52
Q

what type of conduction occurs in myelinated axons

A

saltatory conduction

53
Q

how is the propagation speed greater for myelinated axons compared to unmylinated

A

In myelinated nerve, the passive currents spread further along the axon

There are fewer regeneration steps per unit length of axon
- high concentration of channels at node (unmyelianted has same amount but more spaced)

Thus, the AP propagates more rapidly than in unmyelinated axons

54
Q

what covers myeline

A

types of connective tissue membrane

55
Q

what is the name of the connective tissue which covers the bunch of axons

A

perineurium

- has BV around it

56
Q

what surrounds the perineurium (bunch of axons) and BVs

A

the epineurium

57
Q

what are the connective tissue membranes that surround axons made of

A

lipid layers

Structure with high concentration of lipids
- Fat pads
Blood vessels

58
Q

can nerves have different types of axons in it

A

yes

- can have myelinated and unmyelinated in one aggregation

59
Q

myelination of alpha beta nerves

A

myelinated

60
Q

myelination of alpha delta nerves

A

myelination of

61
Q

myelination of C fibres

A

unmyelinated

62
Q

role of alpha beta nerves

A

mechanoreceptors

63
Q

role of alpha delta nerves

A

mechanoreceptors
thermoreceptors (cold)
nociceptors
chemoreceptors

64
Q

role of C fibres

A

mechanoreceptors
thermoreceptors (hot and hot)
nociceptors (pain)
autonomic symp system

65
Q

what happens to myelinated axons as they enter tooth pulp

A

lose myelination

66
Q

what is the effect of myelination of LA acting

A

lack of myelination means LA works faster on axon

BDS2 BAMS (54 decks)

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