control of cardiac muscle

Question 1

what is the heart also knowns as

Answer 1

myogenic

Question 2

what are the two different action potentials controlled heart rate

Answer 2

pacemaker potential (SAN)
atrial/ventricular potential

Question 3

whats modulation of both these action potentials by

Answer 3

the ANS

Question 4

where are the SAN located

Answer 4

wall of the right atrium

Question 5

what are the firing rate of APs

Answer 5

usually 1/s

Question 6

what does the firing rate of APs equal

Answer 6

the resting heart rate (60-80bp)

Question 7

what happens to electrical activity when it reaches the AVN

Answer 7

it slows down

Question 8

what type of resting membrane potentials do SA node cells have

Answer 8

unstable/non-equilibrium resting membrane potentials

Question 9

what is the RNP of SA node cells

Answer 9

-60mv (slightly higher than normal)

Question 10

what is the If channel and what is it activated by

Answer 10

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

Question 11

what are the three phases in the generation of pacemaker potentials

Answer 11

phase 4
phase 0
phase 3

Question 12

what occurs in phase 4

Answer 12

RMP

If channels are activated

Question 13

what occurs in phase 0

Answer 13

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

Question 14

what occurs in phase 3

Answer 14

voltage gated potassium channels open
efflux of potassium channels
repolarisation

Question 15

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

Answer 15

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

Question 16

why does the AVN slow down the rate of conduction

Answer 16

to allow ventricles to fill adequately

Question 17

where does the AVN conduct this electricity

Answer 17

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

Question 18

what do atrial/ventricular cells have

Answer 18

a stable resting membrane potential

Question 19

what are the five phases of AV node APs

Answer 19

phase 4 
phase 0 
phase 1 
phase 2 
phase 3

Question 20

what occurs in phase 4

Answer 20

resting potential (around -90mv)

Question 21

what occurs in phase 0

Answer 21

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

Question 22

what occurs in phase 1

Answer 22

repolarising phase and is the peak of the AP

Question 23

what occurs in phase 2

Answer 23

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

Question 24

what is the importance of the plateau phase

Answer 24

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.

Question 25

what is ventricular fibrillation

Answer 25

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

Question 26

what occurs in phase 3

Answer 26

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

Question 27

what is contraction caused by

Answer 27

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

Question 28

what two things that the rise in calcium cause

Answer 28

1) bind directly with troponin | 2) bind to ryanodine receptors

Question 29

how does calcium binding to troponin cause contraction

Answer 29

causes a conformational change and displaces tropomyosin allowing contraction

Question 30

how does calcium binding with ryanodine receptors cause contractions

Answer 30

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...

Question 31

how does calcium induced calcium release occur in smooth muscles

Answer 31

IP3R

Question 32

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

Answer 32

heart rate | force of contraction

Question 33

what heart rate also known as

Answer 33

chronotropic effect

Question 34

what is the force of contraction also known as

Answer 34

inotropic effect

Question 35

what sympathetic nerves innervate the SAN and ventricles

Answer 35

T1-T5

Question 36

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

Answer 36

NA which acts on beta 1 adrenoceptors

Question 37

what does activation of the beta 1 adrenoceptors causes

Answer 37

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

Question 38

what else does activation of these receptors cause

Answer 38

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

Question 39

what does stimulation of parasympathetic nerves have an effect on

Answer 39

heart contraction = chronotropic effect only

Question 40

what parasympathetic nerves innervates the heart

Answer 40

vagus nerve from the brain innervates the SAN

Question 41

what does the vagus nerve release

Answer 41

Act which acts on M2 receptors

Question 42

what does stimulation of the M2 receptors do

Answer 42

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)