conduction system Flashcards
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
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
whats the normal Na status?
mainly extracellualr
whats the normal ca+ status?
mainly extracelluar
what determines the membrane potential?
1- Ion concentration gradient —> maintained by transport system
2- Ion conduction
3- Electrogenic pump –> NA/K pump for example
whats a change in conduction?
depolarization and repo?
IN myocytes whats PHASE 0 IN AP?
Phase 0 :
Opening of fast sodium channels and sodium rushing in
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
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
IN myocytes whats PHASE 3 IN AP?
- calcium channels close
- all potassium channels open = AP drops du to potassium leaving
IN myocytes whats PHASE 4 IN AP?
stable memberane is stablished and its maintained by k+ permeability
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 ,
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
whats the relation between AP and ARP
its the same and they have the same duration
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
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 )
