Chapter 9 Cardiac Muscle Flashcards
What are intercalated discs role in cardiac muscle?
Membrane between muscle fibers, that allow communication and ultimately form gap junctions for diffusion of ions.
How does an electrical current pass from the atrial syncytium to the ventricle syncytium?
Potentials are conducted only by way of a specialized conductive system called the AV bundle.
Which of the following highlights a difference between cardiac action potential (AP) and skeletal muscle APs?
A) Skeletal muscle has a plateau
B) Cardiac APs start out solely by a tremendous opening of fast sodium channels that close abruptly
C) The permeability of cardiac muscle after the start of APs to potassium decreases significantly
D) Calcium channels are a big component of the rapid depolarization and repolarization of the skeletal muscle
C) The skeletal muscle action potential (AP) is made of opening of fast sodium channels and then rapidly closing of the same channels.
In cardiac muscle, the AP is initiated by opening of fast sodium channels and slow calcium channels. Calcium is responsible for activating the muscle contractile process.
In cardiac muscle, after the onset of an AP, the permeability to potassium decreases 5fold, decreasing the outflux of potassium and preventing early return of the AP to resting levels.
Which of the following best describes the function of calcium ions and the transverse tubules in skeletal and cardiac muscle fibrils?
A) Both skeletal and cardiac muscle rely on the passing of the action potential along the sarcoplasmic reticulum.
B) The calcium ions released from the sarcoplasmic reticulum are responsible for the movement of the myofibrils, leading to muscle contraction.
C) Skeletal muscle also relies on the release of calcium from the T-tubules to open ryanodine receptor channels in the sarcoplasmic reticulum for more release of calcium.
D) The cardiac muscle T-tubules have a large amount of mucopolysaccharides that are electropositive and bind to an abundant store of calcium ions.
B) The calcium ions released from the sarcoplasmic reticulum are responsible for the movement of the myofibrils, leading to muscle contraction.
Both skeletal and cardiac muscle rely on the passing of the action potential offer the membrane of a T-tubule. This then acts on the membrane of the sarcoplasmic reticulum and allows for lease of calcium ions into the muscle sarcoplasm. The influx of calcium promotes the sliding of the actin and myosin filaments, producing the muscle contraction. Cardiac muscle also relies on the release of calcium from the membrane of the T-tubule, to stimulate ryanodine receptor channels in the sarcoplasmic reticulum. The sarcoplasmic reticulum is less developed than that of skeletal muscle and relies on calcium from T-tubules. The T-tubules also contain large stores of mucopolysaccharides, that are electronegative, which also bind large stores of calcium. This calcium is available fo diffusion into the muscle fiber when an action potential occurs.
The cardiac cycle…
A) … starts by a spontaneous generation of action potential in the AV bundle.
B) … is carried out by primer pumps located in the ventricles.
C) … has a period of relaxation called diastole and a period of contraction called systole.
D) … has a major source of power located in the atria.
C) The cardiac cycle has a period of relaxation called diastole, in which the heart fills with blood. The period of contraction is called systole.
The cardiac cycle is initiated by a spontaneous generation of an action potential in the sinus node, located in the superior lateral wall of the right atrium. This AP then travels to the AV bundle into the ventricles. The atria are known as primer pumps and the ventricles are known as the major source of power for pumping blood through the body. The cardiac cycle has a period of relaxation called diastole and a period of contraction called systole.
Which of the following is correct when describing the electrocardiogram?
A) P wave is caused by the spread of depolarization through the atria.
B) The QRS segment is caused by atrial depolarization.
C) At the point of the T wave, the volume in the ventricles is at its highest.
D) The AV valves open at the beginning of the the QRS segment.
A) P wave is caused by the spread of depolarization through the atria.
The QRS segment is caused by ventricular depolarization. The T wave represents the state of repolarization of the ventricles. At this time, the volume in the ventricles is almost at its lowest, as ejection is occurring. Once the T wave is done, the AV valves open, allowing for isovolumic relaxation.
How much additional filling of the ventricles occurs with atrial contraction?
A) 10%
B) 30%
C) 7%
D) 20%
D) 20% more filling of the ventricles occurs, which increases the ventricular pumping effect as much as 20%. The heart can continue without this extra 20% effectiveness, which is why atrial problems can often go undetected for a while or until a exercise intolerance is noted.
List some changes in the cardiac cycle that occur once systole is over.
( 5 )
Isovolemic relaxation T wave is finished Aortic valve closes AV valves open Ventricular pressure and volume are at their lowest
Which of the following DOES NOT occur during isovolumic contraction?
A) Contraction occurring in the ventricles
B) Emptying of the ventricles
C) Cardiac muscle tension is increasing of the ventricles
D) Little or no shortening of the muscle fibers
B) Emptying of the ventricles is NOT occurring during isovolumic contraction.
This occurs at the end of the QRS segment, immediately after ventricular contraction begins. As the pressure rises abruptly, the AV valves close and it takes approximately 0.02-0.03 seconds before the semilunar valves are opened. Contraction is occurring in the ventricles but no emptying occurs. Cardiac muscle tension is occurring, but little or no shortening of the muscle fibers is occurring.
During the period of ventricular ejection, which of the following is occurring?
A) Semilunar valves are opened
B) Approximately 90% of the blood at the end of diastole is ejected during systole
C) Ventricular pressure is at its lowest
D) This is occurring during diastole
A) Semilunar valves are opened when the L ventricular pressure increases over 80 mm Hg. Blood pours out of the ventricles at this time of systole. 60% of the blood in the ventricle at the end of diastole are ejected during systole.
Which of the following is occurring during isovolumic relaxation?
A) Both right and left intraventricular pressures are increased briefly
B) The distended large artery pressures are at a minimum
C) The aortic and pulmonary valves slam shut
D) The ventricular muscle relaxes and volume decreases
C) The aortic and pulmonary valves snap shut due to the increased pressures in the distended large arteries. This is occurring at the end of systole, while ventricular relaxation begins. Howeve, the volume of the ventricles is not changing during this time period, as short as it is. The intraventricular pressures are decreasing rapidly, back to their low diastolic levels.
Define the following:
End diastolic volume
Stroke volume output
End systolic volume
Ejection fraction
End diastolic volume - the volume of the ventricles filled during diastole; approx 110-120 mLs
Stroke volume output - the volume that the ventricles decrease by during systole; about 70 mLs
End systolic volume - the volume remaining in the ventricles after systole, or after the stroke volume output has been removed; approx 40-50 mLs
Ejection fraction - the fraction of the ventricular diastolic fill that is ejected
Which of the following is true about the AV valves
A) These valves consist of the tricuspid and pulmonary valves.
B) These valves close and open passively.
C) These valves require rapid back flow to cause closure.
D) These valves are thick
B) The AV valves close and open passively.
The AV valves consist of the tricuspid and mitral valve, which prevent back flow of the ventricles into the atria during systole. The tricuspid valve is located between the right atria and right ventricle. The mitral valve is located between the left atria and left ventricle. These valves are thin and flimsy; they close when a backward pressure gradient pushes blood backwards and open when a forward pressure gradient forces blood in the forward direction.
Which of the following properly describes the semilunar valves?
A) These valves are supported by the chordae tendinae.
B) These valves have larger openings than the AV valves and thus the velocity of the blood traveling through is far less.
C) These valves undergo great mechanical abrasion along their edges.
D) These valves are flimsy and thin.
C) These valves undergo great mechanical abrasion along their edges.
The semilunar valves, or the aortic and pulmonary valve, close rapidly due to the high pressures in the arteries. These valves are strong, yet pliable, supporting the high velocity of blood traveling through smaller openings than the AV valves. The chordae tendinae only support the AV valves and are not found in relation to the semilunar valves.
How does the pressure inside the aorta change through diastole and systole?
During systole, the entry of the blood into the aorta causes the walls to stretch and the pressure to increase about 120 mm Hg. At the end of systole, once the aortic valve closes, the pressure system in the aorta is still high but is slowly lessening as the blood is distributed throughout the body. At this time, the pressure is approx 80 mm Hg.
