cardiac excitation (midterm 2) Flashcards
what are other functions than contraction the heart does
- generation of rhythmical electrical impulses to cause rhythmical contraction of heart muscle
- conduction of ^ impulses rapidly through cardiac muscle
what are results of the rhythmical excitation of the heart
atria contraction before ventricular
spatial homogeneity of ventricular contraction
what does the sinus node do
it’s a strip of cardiac muscle that generates the normal rhythmical impulse
what do the internodal pathways do
conduct the impulse from the sinus node to the AV node
what does the AV bundle do
conducts impulses from the atria into the ventricles
what do the left and right branches of purkinje fibers do
conduct the cardiac impulse to all parts of the ventricles
where is the sinus node located and how big is it
located in the superior posterolateral wall of the right atrium
3 mm wide, 15 mm long, 1 mm thick
what happens because fibers connect directly with the atrial muscle fibers
any AP that begins in the sinus node spreads immediately into the atrial muscle wall
how is tissue self-excitatory
it doesn’t contract, but hits a threshold where AP fires on its own
how is the sinus node the pacemaker of the heart
the sinus node controls the heart rate of the entire heart - sinus fibers are self-excitatory
what is the resting membrane potential of the sinus nodal fiber between discharges
-55 to -60 mV
what causes the sinus nodal fiber to be less negative
cell membranes of the sinus fibers are naturally to Na+ and Ca++ channels,, which allows Na+ and Ca++ into the cell to eventually generate an AP via threshold value
when are channels active/inactive in sinus nodal fiber and what is the result of this
- fast Na+ are inactivated
- slow Na+-Ca++ channels can open and initiate an action potential
atrial nodal AP is slower to develop than ventricular muscle AP
when does an AP of sinus nodal fibers occur
Na+ influx into cardiac muscle fiber that activates Na+-Ca++ channels
what are internodal pathways
where the ends of the sinus nodal fibers connect directly with surrounding atrial muscle fibers
what is the velocity of AP conduction in atrial muscle
0.3 m/sec or 1 m/sec for small bands of fibers
how long does it take for an impulse to reach the AV node after traveling through the internodal pathways and what is the next delay
0.03 sec followed by a delay of 0.09 sec before impulse enters the penetrating portion of AV bundle, where it passes into ventricles
what is the final delay of impulses in AV node
0.04 seconds occurring mainly in this penetrating AV bundle
what is the total delay before the excitatory signal reaches the contracting muscle of the ventricles
0.16 seconds
what is speed a function of
of gap junctions - less gap junctions = greater resistance to conduction of excitatory ions from one fibers to the next
what does special purkinje fibers do
lead from the AV node through the AV bundle into the ventricles
what is the velocity and size of special purkinje fibers
large - 6x of ventricular muscle, 150x of Av nodal fibers
velocity of 1.5-4 m/s
why is there no retrograde transmission of AP in AV bundle
prevents passage of cardiac impulse between atrial and ventricular muscle
what is the fastest rate of rhythmical dischage in sinus node
70-80/min = pacemaker
impulse is conducted into AV node and purkinje fibers, also discharging their excitable membranes
what is the rate of rhythmical discharge in unstimulated AV nodal fibers
40-60/min
what is the rate of rhythmical discharge in unstimulated purkinje fibers
15-40/min
what is parasympathetic (vagal) stimulation
causes acetylcholine release, decreasing rate of rhythm of the sinus node
what is sympathetic stimulation
increases rate of sinus nodal discharge and rate of conduction + force of contraction - increases overall activity of the heart
