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zak, physiology > Lecture 6: Cardiac Muscle > Flashcards

Lecture 6: Cardiac Muscle Flashcards

0
Q

What are the AV valves?

A

Tricuspid & Mitral (bicuspid)

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1
Q

What are the Semi-lunar valves?

A

Pulmonary & Aortic

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2
Q

What are the main differences of cardiac muscle compared to skeletal muscle

A 
Mononucleated
Central nuclei
Syncytium
Intercalated discs
Branching of cells
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3
Q

What are Purkinje Fibers

A

Cardiac muscle fibers that do not contract, but exhibit an action potential (act as nerves in the heart)

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5
Q

What are the characteristics of “Fast” cardiac action potentials

A

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)

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6
Q

What are the characteristics of “slow” cardiac action potentials?

A

Found in SA and AV nodal tissue
Conduce slowly
Automatically depolarize during resting phase
Low amplitude (60mV)

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7
Q

What are the phases of fast cardiac action potentials?

A 
Phase 4- Resting phase
Phase 0- Depolarization phase
Phase 1- Initial repolarization phase
Phase 2- Plateau
Phase 3- Final repolarization
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8
Q

Which ions cause the fast cardiac action potentials?

A

Ca++
Na+
K+

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9
Q

How is the action potential reached in slow cardiac muscle potentials?

A

Slow Ca++ leak into the cell causes the cell to slowly reach its threshold and spontaneously depolarize

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10
Q

What type of muscle cells are fast type, contractile myocytes?

A

Atrial/Ventricle

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11
Q

What type of muscle cells are fast type, non-contractile myocytes?

A

Purkinje Fibers

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12
Q

What type of muscle cells are slow type, non-contractile myocytes?

A

SA/AV nodal tissue

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13
Q

What is the action potential in a ventricular fiber cause by?

A

Opening of fast Na+ channels and slow Ca++/Na+ channels

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14
Q

What causes the release of Ca++ from RyRs channels of SR in the cell?

A

Influx of Ca++ from the extracellular area through the DHP (L-type) receptor

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15
Q

Absolute Refractory

A

Period in which it is impossible to generate another action potential

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16
Q

Relative Refractory

A

Period in which a stronger than normal stimulus can generate an action potential

17
Q

What is considered the pacemaker of the heart, and why?

A

SA node b/c it depolarizes quicker than other spontaneous fibers in the heart

18
Q

What causes the plateau in cardiac muscle cells?

A

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

19
Q

At what point of the heart beat does SERCA act?

A

During Diastole

20
Q

What does the Na+/Ca++ exchanger in the sarcolemma do?

A

Transports Ca++ out of the cell

21
Q

How much blood goes from atria—>ventricle prior to contraction? How much during contraction?

A

~80% prior to contraction

~20% during contraction

22
Q

Are the AV valves closed during systole or diastole?

A

Systole

23
Q

What is isometric/isovolumic contraction?

A

When the ventricles contract but the semilunar valves do not open for 0.02-0.03 seconds

24
Q

What is the period of rapid ejection?

A

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

25
Q

What is the period of slow ejection?

A

Occurs during the last 2/3 of systole…when the remaining 30% of blood is ejected from the ventricles

26
Q

Frank-Starling Law

A

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

27
Q

What are EDV, ESV, & SV and how do you calculate ejection fraction?

A

EDV- End Diastolic Volume
ESV- End Systolic Volume
SV- Stroke Volume
Ejection Fraction- SV/EDV

28
Q

How can you increase SV?

A

Increasing EDV or decreasing ESV

29
Q

How does blood flow in the proximal aorta?

A

It is phasic (moves up and down) and ranges from 120cm/s (during systole) to negative value before aortic valves close in diastole

30
Q

How does blood flow in the distal aorta and arteries?

A

Velocity is greater in systole than diastole

Forward flow is continuous b/c of elasticity of vessel walls

31
Q

What does the Vagus nerve control on the heart?

A

Parasympathetic activity of the SA/AV nodes

32
Q

As sympathetic stimulation is increased…

A

Right atrial pressure also increases

33
Q

What are the main characteristics of Cardiac muscle compared to skeletal?

A 
T-tubules along Z-disc, form diads
Less extensive SR, fewer RyRs channels
Form syncytium (no motor unit arrangement)

zak, physiology (20 decks)

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