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cardiovascular > control of cardiac muscle > Flashcards

control of cardiac muscle Flashcards

1
Q

what is the heart also knowns as

A

myogenic

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2
Q

what are the two different action potentials controlled heart rate

A 
pacemaker potential (SAN)
atrial/ventricular potential
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3
Q

whats modulation of both these action potentials by

A

the ANS

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4
Q

where are the SAN located

A

wall of the right atrium

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5
Q

what are the firing rate of APs

A

usually 1/s

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6
Q

what does the firing rate of APs equal

A

the resting heart rate (60-80bp)

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7
Q

what happens to electrical activity when it reaches the AVN

A

it slows down

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8
Q

what type of resting membrane potentials do SA node cells have

A

unstable/non-equilibrium resting membrane potentials

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9
Q

what is the RNP of SA node cells

A

-60mv (slightly higher than normal)

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10
Q

what is the If channel and what is it activated by

A

a Na+ ion channel activated by hyperpolarisation (unlike normal vgc’s which are activated by depolarisation)

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11
Q

what are the three phases in the generation of pacemaker potentials

A

phase 4
phase 0
phase 3

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12
Q

what occurs in phase 4

A

RMP

If channels are activated

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13
Q

what occurs in phase 0

A

threshold value is exceeded
voltage gated calcium channels open
influx of calcium ions
depolarisation

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14
Q

what occurs in phase 3

A

voltage gated potassium channels open
efflux of potassium channels
repolarisation

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15
Q

what are the low resistance pathways between myocytes called that facilitate the conduction of electricity

A

intercalated discs - allows everything to contract at the same time because its very quick

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16
Q

why does the AVN slow down the rate of conduction

A

to allow ventricles to fill adequately

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17
Q

where does the AVN conduct this electricity

A

bundle of His and then to the purkinje fibres which allows both ventricles to be contracted together

18
Q

what do atrial/ventricular cells have

A

a stable resting membrane potential

19
Q

what are the five phases of AV node APs

A 
phase 4 
phase 0 
phase 1 
phase 2 
phase 3
20
Q

what occurs in phase 4

A

resting potential (around -90mv)

21
Q

what occurs in phase 0

A

upon stimulation by electrical activity from the SAN the voltage gated sodium channels open allowing an influx of sodium into the cells causing depolarisation once threshold value is exceeded

22
Q

what occurs in phase 1

A

repolarising phase and is the peak of the AP

23
Q

what occurs in phase 2

A

plateau phase (lasts for about 200-400ms)
caused by opening of voltage gated calcium channels
causes calcium to influx in
but this is much slower and the channels stay open for longer
this causes a sustained depolarisation

24
Q

what is the importance of the plateau phase

A

the myocytes are unexcitable (refractive) which means no twitching as only one AP produces a contraction. this is essential for proper ejection from the heart.

25
Q

what is ventricular fibrillation

A

when there are loads of APs firing so the ventricles don’t get a chance to fill properly so theres no CO and on perfusion and death occurs

26
Q

what occurs in phase 3

A

vgcc’s will close
vgkc’s will open
allows k+ to efflux
repolarisation occurs

27
Q

what is contraction caused by

A

an increase in cytosolic Calcium levels during the plateau phase (calcium rises from 0.1 micro moles to 2 micro moles)

28
Q

what two things that the rise in calcium cause

A

1) bind directly with troponin

2) bind to ryanodine receptors

29
Q

how does calcium binding to troponin cause contraction

A

causes a conformational change and displaces tropomyosin allowing contraction

30
Q

how does calcium binding with ryanodine receptors cause contractions

A

calcium binds to RyR receptors
RyR is an LGIC on the SR
this causes calcium induced calcium release
these calcium then also bind to troponin…

31
Q

how does calcium induced calcium release occur in smooth muscles

A

IP3R

32
Q

what does stimulation of sympathetic nerves in the heart have an effect on

A

heart rate

force of contraction

33
Q

what heart rate also known as

A

chronotropic effect

34
Q

what is the force of contraction also known as

A

inotropic effect

35
Q

what sympathetic nerves innervate the SAN and ventricles

A

T1-T5

36
Q

What do sympathetic nerves release and what receptors do they act on

A

NA which acts on beta 1 adrenoceptors

37
Q

what does activation of the beta 1 adrenoceptors causes

A

an increase in pacemaker frequency causing an increase in heart rate (tachycardia)

38
Q

what else does activation of these receptors cause

A

causes calcium channels to be open for longer
(beta 1 adrenoceptors are Gs coupled and so positively coupled with adenylate cyclase, so cAMP is increased and more PKA is activated which phosphorylates calcium channels and also phosphorylates potassium channels leading to hyperpolarisation. this leads it to hyper polarise quicker so that contraction is briefer which causes a greater influx of calcium) = increases force of contraction

39
Q

what does stimulation of parasympathetic nerves have an effect on

A

heart contraction = chronotropic effect only

40
Q

what parasympathetic nerves innervates the heart

A

vagus nerve from the brain innervates the SAN

41
Q

what does the vagus nerve release

A

Act which acts on M2 receptors

42
Q

what does stimulation of the M2 receptors do

A

M2 receptors are Gi and so are negatively coupled with adenylate cyclase and so cause a decrease in cAMP and theres less activated PKA and therefore calcium channels will be less open.
this causes a decrease in pacemaker frequency resulting in a decrease in heart rate (bradycardia)

cardiovascular (5 decks)

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