L6 (L7 by uni) - cardiac electrical activity Flashcards
pathway of the cardiac conduction system
- siniatrial node ; pacemaker , generates APs
- electrical actvity spreads through the atria
- pass onto the AVN- delay
- conduction along the purkinje fibers
- then onto the ventricular endocardium to epicardium
cells ( myocytes) in the hearts
-SAN CELLS
AVN cells
Atrial and ventricular cells
purkinje fibers
order of the AP generation from myocytes
SAN>AVN>purkinje fibers> atrial and ventricular (no AP)
how many AP per min for SAN
80-100APs/min
what is teh pacemaker potential by the SAN
the firing rate of AP
- basically the slight increase in the membrane potential in SAN
ions responsible for pacemaker potenial
inwards move of Na and Ca
outwards move of K+
- Em rises slowly
ions responsible for rapid depol phase of AP
CA influx though VGChannels
ion responsible for repolarisation phase
K efflux
two ANS control of SAN
-PNS- vagus nerve
SNS - - cardiac sym nerves
what NT does the vagus nerve release
ACh at M2 receptors
what Nt does the cardiac sym nerves release
NA at B1 receptors
intrinsic rate of SAN is 80-100AP/min so why is the HR aorund 60-70bpm
the vagal tone predominates so decreases HR
what happens to the HR as PNS activty increase
increases K efflux
- reduces pacemaker potential (longer to reach threshold)
Hr low
what happens to the ions and HR as SNS activity increases
increases Na and Ca influcx
-increases pacemkaer potential
-
effect of circurlating of adr
INCREASE HR
why is there a delay the AVN before it can transmit the electrical activity to the purkinje fibers
so the atria can contract and eject the blood to the ventricles befoer the ventricles depolarisation
what will HR be always driven by
fasted pacemaker which is the SAN
phases of ventriculae myocyte AP
0: rapid depol
1: half rapid redepol
2: plateau
3: terminal redepol
4: stable resting potential
action of ions in the phases of the ventricular myocyte AP
0: NA infux
1: inactivation of Na channels and activ of K channels
2: Ca inlfux and K efflux
3: more K efflux out delayed rectifier
what is refractory peroid
time from ininital depol of frist AP to 2nd ap that can be stimulated
two kinds of refractory peroids
absolute and relative
what is refractory peroid determined by
no of available and recovered Na VGChannels
at what volatges can the Na VGchannels can be recovered quickly
recover more faster at more neg voltage
-shorter AP, shorter peroid, quicker to inactivates channels
what are cardiac myocytes coupled to
gap junction
what are gap junctions
allows passage of + ions between cellls - if there is a charge of gradient
what is conduction velocity
determined by the charge graidient
- the karger the gradient and amplitude of current , the faster the CV
