Lecture 6 Cardiac Muscle Tissue Flashcards
Syncytium
Network of cells that are branched
Action potential in a ventricular fiber
Averages about 105mV
Rises from -85 to +20mV
Remains depolarized for about 0.2 second following initial spike
-exhibits plateau
Sudden repolarization at the end of the plateau
Skeletal Muscle Fibers T Tubule System
- T tubules are found at the ends of the thick filaments
- There are two T tubules per sarcomere
- T tubules form triads with the sarcoplasmic reticulum
- The sarcoplasmic reticulum is more extensive in skeletal muscle fibers
Cardiac Muscle Fibers T Tubule System
- T tubules are found along the Z line (ends of sarcomere)
- T tubules form diads with the sarcoplasmic reticulum
- The sarcoplasmic reticulum is less extensive than in cardiac muscle fibers
Phonocardiogram
Lub dub heart beat
Systole
Ventricular contraction, lub proceeds this
Diastole
Ventricular relaxation, dud proceeds this
P
Atrial depolarization
QRS
Ventricular depolarization
T
Ventricular repolarization
Atrial repolarization
Is hidden in QRS, just can’t see it
Isovolumic contraction
Pressure changes but volume stays the same
Atria as primer pumps
Priming the ventricles
About 80% of blood flows from the atria to the ventricles before the atria contract
Atria can add an additional 20% by contraction
Ventricular Systole
AV valves are closed during systole
End of ventricular systole
AV valves open at the end of systole because of increased pressures in the atria
Chordae tendineae
Anchors valves down, tendinous cords
First third of diastole
Rapid filling
Middle third of diastole
Small amount of blood flows into the ventricles representing blood that continues to flow into atria during diastole
Last third of diastole
Atria contract to push last 20% of blood into ventricles
Isometric (isovolumic) contraction
Ventricles contract, but semilunar valves do not open for 0.02 to 0.03 seconds
Period of rapid ejection
Occurs when left ventricular pressure is a little above 80mm Hg and right ventricular pressure is slightly above 8mm Hg
Semilunar valves open
About 70% of the blood is ejected
Occurs during the first third of ejection
Period of slow ejection
Remaining 30% of blood is ejected from the ventricles
Occurs during the last two-thirds of ejection
Blood in proximal aorta
Mean velocity = 40 cm/s
Flow is phasic (ebbs and flows)
Velocity ranges from 129 cm/s (systole) to negative value before aortic valves close in diastole
Negative value is
Dicrotic notch
Blood in distal aorta and arteries
Velocity is greater in systole than diastole
Forward flow is continuous because of elastance of vessel walls during diastole
Forces altering flow
The rate of blood flow to each tissue is usually precisely controlled in relation to tissue need
Active tissues may need 20 to 30 times as much blood flow than at rest
Cardiac output cannot exceed 4-7x greater than at rest
Microvessels of each tissue
Microvessels of each tissue
Monitor tissue needs
Act directly on local blood vessels
Nervous control and hormones
ANS
Fight or flight
Action Potential Plateau
In skeletal muscle, the sodium channels close rapidly
In cardiac muscle the sodium channels also close rapidly, but the calcium channels stay open slowly and stay open for a longer period of time
In cardiac muscle there is also a delay in the opening of the potassium channels
The large concentration of both calcium ions and potassium ions is responsible for the plateau
SERCA
Sarcoplasmic reticulum calcium ATPase
Frank-Starling Law
The more it is stretched, the stronger the contracton
EDV
End diastolic volume
110-120mL
SV
Stroke volume
70mL
ESV
End systolic volume
40-50mL
Can be as little as 10-20Ml
Amount left over after ventricle contraction, always a little bit of blood left over
Ejection Fraction
SV/EDV = 70/110 = 64%
Stroke volume output can be increased to more than double by
Increasing EDV - more blood flowing in
Decreasing ESV - decreasing the end systolic volume
