18.5 Pacemaker Cells
pacemaker cells contract
the sponteneously produced action is called
where are pacemaker cells located?
throughout heart along special conduction pathways
what spreads the depolarizing current to cardiac muscle cells
pacemaker cells have an unstable resting membrane potential
the resting membrane potential of pacemaker cells is what?
pacemaker cells close K+ channels and open Na+ slowly to let sodium in
the cell become slowly depolarized by the Na+ voltage channels opening
the threshold of pacemaker cells is what?
at the threshold what voltage gated channel opens?
for pacemakers to repolarize what is opened?
K+ voltage gated channels
conduction pathways run throughout the myocardium
what initiates the heart beat
the SA node
where are the SA nodes?
small mass of pacemaker cells in right atrial wall; inferior to the superior vena cava
how many impulses does the SA node generate a minute
The SA node generates a faster impulse than any other heart cell
the SA node is the true pacemaker of the heart
what does the Bachmann's bundle connect?
the right and left atria
the bachmann's bundle keeps both atria at synch
depolarization of the SA node causes what to happen?
atria to contract at the same time
there are gap junctions between atrial and ventricular myocardium
what does the internodal pathways connect?
SA node to AV node
where is the AV node located
in the interatrial septum, near tricuspid
What does the AV node do?
how many impulses does the AV node generate per minute?
the AV node cannot run the heart if the SA is damages
the atrioventricular bundle connects what
AV node to ventricles
bundle of His
what is the only electrical connection between the atria and the ventricles?
atrioventricular bundle splits into right and left bundle branches
atrioventricular bundle does not continue on to form Purkinje fibers
depolarize the contractile cells of ventricles
subendocardial conducting network
purkinje fibers innervate papillary muscles
depolarization of pacemaker cells cause depolarilzation of cardiac muscles cells
what is the resting membrane potential in contractile cells
in resting membrane potential in contractile cells what channel is always open?
what is the resting membrane potential for skeletal muscle?
during depolarization of contractile cells what is opened?
voltage gates fast Na+ channels, Na rapidly flow into cell
sarcolemma depolarizes to +30mV
at +30mV what opens in contractile cells?
voltaged gates slow Ca2+ channels
during repolarization of contractile cells what is opened?
voltage gated K+ channels and K+ leaves the cell
absolute refractory period
time when cell cannot depolarize again
the absolute refractory period is longer in cardiac muscle than skeletal muscle
the absolute refractory period prevents tetanic contractions such as cramps, spasms, and tremors
too much calcium
what does hypercalcemia cause?
prolonged and spastic heart contractions
low calcium levels
hypocalcemia reduces what?
the force of each heartbeat
high potassium levels
what does hyperkalemia do?
speeds up membrane repolarization disrupting heart rhythm
blood Na+ levels are too high
what does hypernatremia prevent
the entry of calcium into myocardium
arrhythmia is a heart defect
uncoordinated atrial and ventricular contraction
two types of arrhythmia
PAT and V-tac
paroxysmal atrial tachycardia; burst of atrial contractions
ventricular tachycardia; rapid uncoordinated ventricular contractions
rapid and irregular contractions of cardiac muscles
what can treat fibrillation
what can lead to fibrillation
defibrillation does what?
restart entire electrical systems
inappropriate region of heart controls rhythm
where can ectopic focuses appear
atria or ventricles
what are ectopic focuses caused by
- ischemic damage to conduction pathways
what can ectopic focuses lead to
arrhythmia and fibrillation
a heart block is damage to what structure in the heart ?
AV node or AV bundle
first degree heart block
depolarization is delayed for too long
second degree heart block
only some of the impulses are transmitted
third degree heart block
no action potential pass to the ventricles
third degree heart block aka
complete heart block
period when heart fails to contract
asystole is when there are electrical signals from cardiac muscles