Lecture 7: Cardiac muscle tissue Flashcards
Cardiac muscle tissue characteristics (6)
Sarcomeric arrangement (striated) Mononucleated Central nuclei Syncytium Intercalated discs Cells may branch
Amplitude of action potential in ventricular fiber
Average 105mv (-85—+20)
What causes plateau
Sodium channels close rapidly, calcium channels stay open longer. Potassium channels open later and plateau is due to both calcium and potassium channels being open simultaneously
Where are T-tubules found in cardiac muscle, and how many cisternae
Along the Z-line, form diads with sarcoplasmic reticulum (one cisterna, one t-tubule)
Sarcoplasmic reticulum is more or less extensive in cardiac tissue compared to muscle
Less extensive
Special requirements of cardiac action potential (3)
Must be self generated
Must be prolonged
Must propogate from myocyte to myocyte in proper sequence.
Action potential is generated in the ______ in cardiac muscle
SA node
Action potential slows down at the _____
AV node
Action potential speeds up in
Bundle fibers and purkinje system
Fast action potentials are found
In the atria, ventricles and perkinje fibers
Perkinje fibers are contractile or non contractile
non contractile
Amplitude of fast potentials
~100mv
Slow potentials are found where
SA and AV nodal tissues
What happens during resting phase in slow tissues
They automatically begin to depolarize (more rapidly in SA than AV)
Amplitude of slow potential
~60mv
Slow potentials are contractile or non contractile
non contractile
Phase 4
resting phase
Phase 0
rapid depolarization
Phase 1
Initial, incomplete repolarization
Phase 2
Plateau or slow decline of membrane potential
Phase 3
repolarization
Fast action potentials are due to , and the conductance pattern is due to
Changes in conductance of calcium, sodium and potassium ions
Voltage dependent gates
These 3 things result in faster conduction velocity
Greater AP amplitude
Greater rate of rise of phase 0
Larger cell diameter
Upstroke in slow action potentials is due to
Calcium (so it proceeds slowly)
Slow action potentials have Na+ gates: T or F
False
Resting potential of fast and slow potentials
Fast: -85
Slow: -60
Amplitude is lower in ____ potentials
Slow potentials (60 compared to 105 in fast)
Which tissues spontaneously depolarize, which have the fastest intrinsic rate of pulsation
SA, AV nodal tissues and perkinje fibers
SA nodal tissues
What causes the spontaneous depolarization
Special leaky sodium channels that open after phase 3
Characteristics of fast type contractile myocytes (3)
Large diameter
High amplitude
Rapid onset of action potential
Characteristics of fast type non-contractile myoctyes (2)
Very large diameter
Very rapid upstroke
Characteristics of slow type non-contractile myocytes (3)
Small diameter
Low amplitude
Slow rate of depolarization (slow upstroke)
Action potential in ventricular fiber is due to what? What causes the initial spike
Opening of fast sodium channels and also slow calcium-sodium channels.
Initial spike caused by fast sodium channels
What is the source of calcium for electro-mechanical coupling
From the T-tubules via diffusion through voltage dependent calcium channels called DHP receptors.
From cisternae of the SR through channels called Ryanodine receptors
What is the normal pacemaker of the heart
SA node
What happens when there is early premature contraction (contraction during early stage relative refractory period)
Amplitude is lower
Resting potential and threshold of SA node
- 55/-60
- 40
At -40mv, which channels open in SA node
Slow sodium-calcium channels
When do Potassium channels open in SA node
When sodium-calcium channels close
Action potentials that did not originate in the SA nodes are said to be from
An ectopic focus or pacemaker
Action potentials originating in the SA node generate
A “sinus” rhythm
of calcium-induced calcium release channels in cardiac muscle compared to skeletal muscle- what impact does this have
Far fewer in cardiac muscle, allowing fine control over sarcoplasmic calcium concentration and contractility
SERCA returns calcium to the SR during _____, which allows for
Diastole
allows for even greater calcium release on next beat and fast clearance of calcium from sarcoplasm
What pumps calcium out of sarcoplasm besides SERCA
Sodium-calcium antiporter. Gradient is created by Na/K ATPase
What % of blood flows from atria to ventricles before atrial contraction
80%, last 20% after contraction
AV valves are closed during ____, which means:
Ventricular systole
Blood cannot flow into ventricles, but still flows into atria
AV valves open at the ___ of ____ because of what
At the end of systole because of increased pressure in the atria
First third of diastole what happens
Rapid filling of ventricles
Middle third of diastole
Small amount of blood flows into ventricles representing blood that continues to flow into atria during diastole
Last third of diastole
Atria contract to push final 20% of blood into ventricles
Isovolumic contraction
Ventricles contract, but semilunar valves do not open for .02-.03 seconds
Period of rapid ejection occurs at what pressure in L and R ventricles
Left: a little above 80 mm hg
Right: a little above 8 mm hg
What occurs during rapid ejection- which valves open, how much blood is ejected, what portion of the total ejection does this take up
Semilunar valves open
70% of blood is ejected
Occurs during first third of ejection
Slow ejection
Last 30% ejected during final 2/3 of ejection
Frank starling law
The greater the heart muscle is stretched during filling, the greater the force of contraction and the greater the quantity of blood pumped into the aorta.
What causes the greater force created in frank starling law
The stretching of cardiac muscle brings the actin and myosin filaments to a more nearly optimal degree of overlap for force generation
