Cardiac Myocytes
Striated myofibril bundles that have the intrinsic ability to "beat" or contract on their own without stimulation
Sinus nodal myocytes (bpm)
60-80bpm
Atrial myocytes
50-60bpm
AV nodal myocytes
50-60bpm
Purkinje fiber myocytes
40-50bpm
Ventricular myocytes
30-40bpm
Order of blood flow through heart
superior/inferior vena cavas - to right atrium - through tricuspid (atrioventricular) valve - to right ventricle - through pulmonary valve - to pulmonary arteries - to the lungs.
Then it returns through pulmonary vein - to the L atrium - through the mitra
Phase 0 - Action Potential in Cardiac muscle cells
Depolarization - Na+ flows in and causes inside of the cell to become positive for short period of time
Phase 1
Partial Repolarization - Na+ channel closes and K+ begins to flow out due to the depolarization which stops the obstacle for K diffusion
Phase 2
Ca+ moves in slowly along concentration gradient with K going out
Phase 3
restoring of the potential by Na+ (moving out), K+ (moving in) and Ca+ (moving out). Pumps ATP driven.
Phase 4
at resting potential
Calcium's role in action potential
Ca+ channels open allowing influx into cytoplasm and this triggers the SR to release Ca+ to activate the actin-myosin complex and myofibril contraction. During phase 3 and 4, Ca+ is pumped out of the cell or into the SR
Na+ channel dependent
Atria, Ventricles and Purkinje fibers with a fast conduction and slow automaticity
Ca+ channel dependent
Sinus node (SA) and AV node with a slow conduction and fast automaticity
P wave
depolarization in the atrial tissue - positive deflection
QRS wave
ventricular muscle depolarization - positive deflection
T wave
atrial/ventricular muscle repolarization - positive deflection for ventricles, atrial repolarization is obscured by the QRS complex and it is so small it cannot be seen
Pacemaker Potential
gradual depolarization, SA node resting potential start at -60mV and then drifts spontaneously upwards
Isovolumetric contraction of ventricles
occurs after the ventricles depolarize. The AV valves close as ventricular blood surges back against the cusps. Ventricles do not yet eject blood and there is no change in their volume even though they are contracting
Stroke Volume
Ventricular ejection
Isovolumetric relaxation
ventricular filling, complete one cardiac cycle
Hypercalcemia
reduces heart rate - high Ca+
Hypocalcemia
increases heart rate - low Ca+
When are the AV valves closed?
during ventricular systole
When are the AV valves open?
during atrial systole and ventricular diastole
When are the semilunar valves closed?
diastole of heart as a whole and during atria systole
When are the semilunar valves open?
during ventricular systole
What point in the cardiac cycle is the pressure in the heart highest?
ventricular systole
At what point in the cardiac cycle is the pressure in the heart the lowest?
ventricular diastole
Right atrioventricular valve
Tricuspid
Left atrioventricular valve
Mitral
What event within the heart causes the AV valves to open?
ventricular pressure is less than (<) atrial pressure
What causes them to close?
ventricular pressure > atrial pressure
What event causes the semilunar valves to open?
ventricular pressure > pressure int he great arteries (aorta and pulmonary trunk) leaving their chambers
What event causes the semilunar valves to close?
Ventricular pressure<pressure in the great arteries
Are both sets of valves closed during any part of the cycle?
Yes, momentarily after atrial systole and ventricular systole
Are both sets of valves open during any part of the cycle?
No
What event results in the pressure deflection called the dicrotic notch?
Momentary increase in aortic pressure that occurs when its semilunar valve snaps shut
What is effective refractory period?
During phase 0, 1, 2, and part of 3, the cell is refractory to the initiation of new action potentials (allows time for each action potential to complete and re-fill. Prevents sustained contractions
Pacemaker cells - SA node - depolarizing current is carried by what currents?
slow, inward Ca++ currents. Unlike most other cells, there are no fast Na+ currents operating in SA nodal cells
L type channel
(long) Ca+ channel
Atria depolarize from what side to what side?
Left side to Right side
First degree Heart Block
slowing conduction in AV node, PR interval is longer
2nd degree Heart Block Type 1
long PR, longer PR, then P and no R complex, AV node dx - electrical impulses are delayed more and more until a beat is skipped/dropped
2nd degree Heart Block Type 2
P with no R, much more serious, purkinje dx - electrical impulses cannot reach the ventricles, pacemaker may be needed
3rd degree Heart Block
atrium and ventricles beating independently of each other, dissociation of P waves or no normal relationship b/w P and QRS waves
Bundle Branch Block (BBB)
wide QRS, ventricular depolarization is taking longer
P wave
atrial contraction - atrial depolarization
QRS wave
ventricular contraction - ventricular depolarization
T wave
Ventricular repolarization
QT wave
duration of ventricular depolarization and repolarization
MI
elevated ST segment
What receptor does Ca+ bind to?
RyR - Ryanodine receptors - causes more Ca+ to be released from SR
S1
AV valves close
S2
Similunar valves close
S4
atrial contraction (not normal)
Inotropic
Affecting the force of muscle contraction. An inotropic heart drug is one that affects the force with which the heart muscle contracts.
Chronotropic
affecting the rate or timing of a physiologic process, as the heart rate.
Pacemaker Action Potential phases
Phase 0 - depolarization
skips 1&2
Phase 3 - repolarization
Phase 4 - slow depolarization
Phase 0
depolarization is primarily caused by increased Ca+ through the L-type Ca+ channels that began to open toward the end of Phase 4. The "funny" currents, and Ca+ currents through the T-type Ca++ channels, decline during this phase as their respective channe
Phase 3
Repolarization occurs (Phase 3) as K+ channels open thereby increasing the outward, hyperpolarizing K+ currents. At the same time, the L-type Ca+ channels become inactivated and close, which decreases gCa+ and the inward depolarizing Ca+ currents.
Phase 4
At the end of repolarization, when the membrane potential is very negative (about -60 mV), ion channels open that conduct slow, inward (depolarizing) Na+ currents. These currents are called "funny" currents and abbreviated as "If". These depolarizing curr