Lecture 6: Cardiac Muscle Flashcards
What are the AV valves?
Tricuspid & Mitral (bicuspid)
What are the Semi-lunar valves?
Pulmonary & Aortic
What are the main differences of cardiac muscle compared to skeletal muscle
Mononucleated Central nuclei Syncytium Intercalated discs Branching of cells
What are Purkinje Fibers
Cardiac muscle fibers that do not contract, but exhibit an action potential (act as nerves in the heart)
What are the characteristics of “Fast” cardiac action potentials
Found in atria, ventricles, and purkinje fibers (conduction system)
Very rapid, but non-contractile in purkinje fibers
Rapid and contractile in atria and ventricles
High amplitude (100mV)
What are the characteristics of “slow” cardiac action potentials?
Found in SA and AV nodal tissue
Conduce slowly
Automatically depolarize during resting phase
Low amplitude (60mV)
What are the phases of fast cardiac action potentials?
Phase 4- Resting phase Phase 0- Depolarization phase Phase 1- Initial repolarization phase Phase 2- Plateau Phase 3- Final repolarization
Which ions cause the fast cardiac action potentials?
Ca++
Na+
K+
How is the action potential reached in slow cardiac muscle potentials?
Slow Ca++ leak into the cell causes the cell to slowly reach its threshold and spontaneously depolarize
What type of muscle cells are fast type, contractile myocytes?
Atrial/Ventricle
What type of muscle cells are fast type, non-contractile myocytes?
Purkinje Fibers
What type of muscle cells are slow type, non-contractile myocytes?
SA/AV nodal tissue
What is the action potential in a ventricular fiber cause by?
Opening of fast Na+ channels and slow Ca++/Na+ channels
What causes the release of Ca++ from RyRs channels of SR in the cell?
Influx of Ca++ from the extracellular area through the DHP (L-type) receptor
Absolute Refractory
Period in which it is impossible to generate another action potential
Relative Refractory
Period in which a stronger than normal stimulus can generate an action potential
What is considered the pacemaker of the heart, and why?
SA node b/c it depolarizes quicker than other spontaneous fibers in the heart
What causes the plateau in cardiac muscle cells?
The large concentration of K+ and Ca++ due to the Ca++ channels staying open longer than the Na+ channels and the K+ having a delayed opening upon depolarization
At what point of the heart beat does SERCA act?
During Diastole
What does the Na+/Ca++ exchanger in the sarcolemma do?
Transports Ca++ out of the cell
How much blood goes from atria—>ventricle prior to contraction? How much during contraction?
~80% prior to contraction
~20% during contraction
Are the AV valves closed during systole or diastole?
Systole
What is isometric/isovolumic contraction?
When the ventricles contract but the semilunar valves do not open for 0.02-0.03 seconds
What is the period of rapid ejection?
When left ventricular pressure reaches just above 80mmHg and right ventricular pressure is just above 8mmHg…this causes the Semilunar valves to open and about 70% of blood to be ejected
What is the period of slow ejection?
Occurs during the last 2/3 of systole…when the remaining 30% of blood is ejected from the ventricles
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 are EDV, ESV, & SV and how do you calculate ejection fraction?
EDV- End Diastolic Volume
ESV- End Systolic Volume
SV- Stroke Volume
Ejection Fraction- SV/EDV
How can you increase SV?
Increasing EDV or decreasing ESV
How does blood flow in the proximal aorta?
It is phasic (moves up and down) and ranges from 120cm/s (during systole) to negative value before aortic valves close in diastole
How does blood flow in the distal aorta and arteries?
Velocity is greater in systole than diastole
Forward flow is continuous b/c of elasticity of vessel walls
What does the Vagus nerve control on the heart?
Parasympathetic activity of the SA/AV nodes
As sympathetic stimulation is increased…
Right atrial pressure also increases
What are the main characteristics of Cardiac muscle compared to skeletal?
T-tubules along Z-disc, form diads Less extensive SR, fewer RyRs channels Form syncytium (no motor unit arrangement)
