Week 1 Pacemaker Cells Flashcards

1
Q

Myogenic action potentials

A

action potentials created in heart muscle

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2
Q

Pacemaker cells

A

produce action potentials that allow the heart to beat

do not have a normal resting potential like other cells

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3
Q

where are pacemaker cells found

A

in three places - SAN, AVN, purkinje network/bundle of His

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4
Q

pacemaking ability by location

A
  1. SAN - highest rate of AP generation
  2. AVN - slower than SAN, not enough alone
  3. bundle of His/purkinje - very low contributor
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5
Q

what channels are found in pacemaker cells

A

no sodium channels
have funny channels

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6
Q

what are funny channels

A

Unique sodium channels found in pacemaker cells

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7
Q

what are contractile cells

A

99% of cardiac muscle cells
function in mechanical work of pumping

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8
Q

pacemaker cells process

A

membrane potential slowly depolarises or drifts between action potentials (pacemaker potential)
until threshold is reached
when an action potential is fired

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9
Q

ion movement for pacemaker potential

A
  1. increased inward Na+ current
  2. decreased outward K+ current
  3. increased Ca2+ current
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10
Q

why are funny channels different to normal channels

A
  • activated by hyperpolarisation (more negative membrane) rather than depol (less negative membrane)
    at the end of repol of the prev AP
  • membrane potential immediately moves toward threshold again after an AP - slow leak of inward Na+
  • outflow of K+ ions gradually declines
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11
Q

Lowest membrane potential of funny channels

A

-60mv

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12
Q

Threshold of funny channels

A

-40mv

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13
Q

Peak of funny channels

A

10mv

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14
Q

Adrenaline signal cascade

A
  1. Binds onto channel receptors
  2. G proteins activate enzyme
  3. Enzyme turns ATP to cAMP
  4. Affects protein kinase
  5. cAMP opens calcium and funny channels
  6. Sodium and calcium enter cell
  7. Speeds up the heart
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15
Q

Specialised CONDUCTIVE cells

A

Pacemaker cells

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16
Q

Specialised CONTRACTILE cells

A

Cardiomyocytes

17
Q

Conduction system is surrounded by

A

Fibrous collagenous tissue

18
Q

Gap junctions function

A

To allow APs to flow to neighbouring cells

19
Q

Evidence of gap junctions

A

Antibody stain - fluorescent labelling technique
Added to connexin - protein that makes gap junctions

20
Q

Function of the cardiac skeleton

A
  1. Structure - for muscles to hold onto
  2. Valves - prevent back flow
  3. Non conductive = APs don’t leave conductive tissue, APs don’t travel straight from atria to ven (there is a pause)
21
Q

L type calcium ion channels

A

Normal myocardial contractility

Activated when threshold is reached

Causes large Ca2+ influx - potential becomes more positive

22
Q

T type calcium ion channels

A

Found in conducting and pacemaker cells

23
Q

Effect of L type Ca ion channels

A
  • long term
  • allow Ca2+ in
  • causes depolarisation
  • myosin heads can bind with actin filaments
24
Q

Channels only in pacemaker cells

A

Funny sodium channels
T type calcium channels

25
Q

Channels only in cardiomyocytes

A

Regular sodium channels

26
Q

Channel found in both cardiomyocytes and pacemaker cells

A

L type Ca2+ channels

But open longer in cardiomyocytes = constant Ca2+ flow

Long plateau in cardiomyocyte depol membrane

27
Q

Action of regular Na+ channels in cardiomyocytes

A

Act quickly
Steep change in membrane potential
Open and close quickly

28
Q

Hyperpolarisation

A

More negative

29
Q

Depolarisation

A

Less negative

30
Q

what is TTX

A

tetrodotoxin

ttx binding to sodium channels physically stops sodium ion flow through the channel

ttx does NOT affect pacemaker cells

31
Q

what is repolarisation

A

DECREASE in voltage

K+ efflux (more negative cell)

32
Q

what is depolarisation

A

INCREASE in voltage

Na+ influx (more positive cell)

33
Q

K+ channels

A

K+ leaves the cell

34
Q

Na+ channels

A

Na+ enters the cell

35
Q

L type calcium channels

A

Ca2+ influx
long term
slow activation

36
Q

T type calcium channels

A

activated at lower voltage
fast activation

37
Q

evidence suggest that SAN in small mammals

A

are relatively large - from superior to inferior vena cava

38
Q

what is ivabradine

A

a drug that prolongs action potential