conduction system Flashcards by mohamed nascer

what are the properties of cardiac muscle?

1- Automaticity and Rhythmicity –> ability of heart to beat and contracts on its own

2- conductivity : the ability of the heart to transmit exciitation wave, IF one cell is deporalized all will be deporalized

3- excitability : THE ABILITY OF THE HEART TO RESPOND TO STIMULUS ( PARA AND SYMP )

4- Contractility : The ability of the heart to contract and pump blood

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whats the normal K status?

mainly intracelluar

Has the highest permeability so its responsible the normal equilbrium membrane potential –> dominant one –> High in resting membrane

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whats the normal Na status?

mainly extracellualr

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whats the normal ca+ status?

mainly extracelluar

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what determines the membrane potential?

1- Ion concentration gradient —> maintained by transport system

2- Ion conduction

3- Electrogenic pump –> NA/K pump for example

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whats a change in conduction?

depolarization and repo?

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IN myocytes whats PHASE 0 IN AP?

Phase 0 :

Opening of fast sodium channels and sodium rushing in

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IN myocytes whats PHASE 1 IN AP?

Closing of sodium channels ( close they are fast, open and close fast)

Opening of voltage gated channels potassium channels

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IN myocytes whats PHASE 2 IN AP?

phasae 2 platue :

Opening of L type calcium channels and calcium rushes in
closing of Voltage gated potassium channels but the others are open

Calcium comes in and potassium goes out = balance

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IN myocytes whats PHASE 3 IN AP?

calcium channels close
all potassium channels open = AP drops du to potassium leaving

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IN myocytes whats PHASE 4 IN AP?

stable memberane is stablished and its maintained by k+ permeability

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whats Absolute refractory period ?

a period of the AP in myocyte and during it the muscle will not respond or accept any stimulus or another APs ,

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why do myocytes have Absolute refractory period?

because cardiac muscles shouldnt go through tetanus period of continous contraction cuz its a pump it needs to contract and relax

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whats the relation between AP and ARP

its the same and they have the same duration

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what are the phases of AP in sa node and other pacemakers ?

they have 3 phases only instead of 5,

Phase 4

Phase 0

phase 1

no phase 2 and 3

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whats phase 4 in pacemakers?

funny sodium hyperporalized cyclic neuclotide HCN will leak sodium until threshold and form a slope

IF the slope is increased = faster firing

If the slope is decreased = less firing rate

This is also what causes the automacity

whats phase 0 in pacemaker?

both L and T type calcium channels open and calcium influx in

whats phase 3 in pacemakers?

voltage gated potassium gates open and potassium efflux out

why is there a delay between AV node and bundle ?

because the AV node holds the signal for second to give the heart time to fil

where is the fastest conduction?

Purkinje fibers

wheres the slowest conduction?

AV node

whats the physiological reason behind the delay? and its mechanism?

allows ventricular filling and it caused by
its due to small number of gap junctions

why is AV node is the only pathway to the ventricles?

because the fibrous tissue of the heart acts as an insulator to stop the signal

what is the pacemaker of the heart? and whats the normal rate firing rate of it

Sa node
100-110 per minute

Other pacemakers :

AV - 40-60

HIS - 40

P fibers - 15-20

whats an ectopic pacemaker?

when other cell take control that is not SA node and starts firing

we said that the normal firing for SA node is 100-110 why is normal heart rate is 60-100

SA node is always affected by either sympathetic or parasym and under normal conditions and rest the PARASYM is stronger and is more dominant so it reduced them from 100-110 to 60-100

whats hyperpolarization current?

Na K atpase pump which is responsible for bringing back the normal state K in and Na out, it will pump 3 na out and 2 k in this will send sodium out making it harder to depolarize and reaching threshold . Pacemaker must overcome this to fire

why is SA node the pacemaker?

1- because its the fastest firer of AP 2- Overdrive suppression, since its the fastest to overcome the hyperpolarization current it forces the other cells to depolarize b4 reaching THEIR OWN THRESHOLD to depolarize on their own, When NA influx happen in SA node and it fires AP it will make NA influx in the other cells too, increasing the NA/K atpase Pump --> increasing the hyperpolarization current and since its higher now the other pacemakers wouldnt be able to overcome it and wont depolarize and js follow SA node

whats the normal sinus rhythm

1- AP is from SA node 2- Regular SA node pulse at 60-100 3-- Correct sequence and timing of the heart activation ( SA-AV-HIS-BRANCHES- P FIBERS)

what is stokes adam syndrome ?

condition where CO is low due to arrhythmia and abnormal heart beat and this decreased CO will cause brain ischemia and fainting and SYNCOPE

what are the 4 types of refractory periods and whats special ?

1- Absolute refractory period ---> CAN NEVER RESPOND TO AP 2- Effective refractory period --> can fire but it wont conduct 3- relative refractory period --> it can respond but it needs to be strong 4- Supranormal period --> can respond and its ready

what receptor does the parasympathetic work on? and which nerve

M2 ( muscrinic ) , Vagus nerve

what are the parasympathetic effects on heart?

1- Negative chronotropic --> decreased firing rate of SA node 2- Negative dromotropic --> decrease the AV conduction

how will the parasympathetic cause it effects?

1- Decrease Na channels via If current via Gi pathway 2- Increased membrane permeability K which lead to K+ efflux and hyperpolarization which making it harder to depolarize ( if NA comes and MORE K leaves its pointless )

what receptor does the sympathetic work on ? and what it releases?

B1 receptor norepinephrine

what are the effects of sympathetic on heart?

1- Positive chronotropic --> increase firing rate of SA node 2- positive dromotropic --> increase AV conduction 3- positive inotropic ---> increase contractility

how does sympathetic causes it effects?

1- Increase NA channels via If current via Gs protein pathway 2- Increases Ca influx making the resting membrane more positive --> easier to fire AP ( THE INCREASED CA INFLUX IS RESPONSIBLE FOR THE INCREASED CONTRACTILITY )