Chapter 9 Flashcards
The 3 major types of cardiac muscle
- atrial muscle
- ventricular muscle
- specialized excitatory and conductive muscle fibers
T/F: The specialized excitatory and conductive muscle fibers contract
true; but barely because they contain very few contractile fibers
What are intercalated discs?
cell membranes that separate individual muscle cells from one another
T/F: normally action potentials are conducted from the atrial syncytium into the ventricular syncytium directly through the fibrous tissue surrounding the AV valvular openings
False
What causes the long action potential and plateau in cardiac muscle but is not present in skeletal? (2)
- Cardiac muscle has L type calcium channels that are slow to open and slow to close
- after the onset of an AP, the permeability of the cardiac muscle to potassium decreases 5x unlike skeletal muscle
Describe the phases of the cardiac muscle AP
Phase 0
Phase 1
Phase 2
Phase 3
Phase 4
Compare the velocity of signal conduction in cardiac muscle
Atrial and muscle fibers- 0.3-0.5m/sec
Purkinje fibers 4 m/sec
What is a refractory period?
the time interval during which a normal cardiac impulse cannot re-excite an already excited area of cardiac muscle
What is a relative refractory period?
The the time interval where the muscle is more difficult to excite than normal but can be excited by a very strong excitatory signal
Compare the refractory period for atrial muscle vs ventricular
much shorter for atrial muscle
Describe the SR and Ca stores of the cardiac muscle
Less developed than that of skeletal muscle and does not store enough Ca for a full muscle contraction.
The strength of the cardiac muscle contraction depends to a great extent on?
The concentration of Ca ions in the extracellular fluids
Cardiac cycle
The cardiac events that occur fromt he begtinning of one heartbeat to the beginning of the next
What happens during diastole
relaxation; the heart fills with blood
Describe the relationship between the heart rate and cardiac cycle?
The total duration of the cardiac cycle is the reciprocal of the HR
What is a phonocardiogram?
A recording of the sounds of the heart mainly by the heart valves
At a normal heart rate of 72 bpm, what portion of the cardiac cycle is systole? what about at 216 bpm?
0.4
0.65
How is the filling of the chambers affected at a rapid HR?
It does not remain relaxed enough to allow complete filling
What percent of blood flows directly from the great veins into the ventricles before the atria contracts?
80%
Describe the a,c, and v atria pressure elevations
a wave- atria contract
c wave- the ventricles begin to contract; caused by slight backflow of blood into the atria mainly by the bulging of the AV valves backward
v- occurs toward end of ventricular contraction; results from slow flow of blood into the atria from the veins while the AV valves are closed during ventricular contraction
What is the period of rapid filling of the ventricles?
The period after systole where the atria pressures increase and immediately push the AV valves open and allow blood to flow rapidly into the ventricles
What is the period of isovolumic contraction
Immediately after ventricular contraction begins and the AV valves close. the cardiac muscle tension is increasing but little to no shortening of the muscle fibers is occuring because the pressure is still building to open the semilunar valves
Approximately what percent of the blood in the ventricle at the end of diastole is ejected during systole? What is this ejection period called?
60%
The period of rapid ejection
What is the period of isovolumic relaxation?
