Mastering Ch 18B
Which of the following is NOT a difference between cardiac and skeletal muscle? a) Cardiac muscle cells quickly die in the absence of oxygen; skeletal muscle cells are better able to adapt to oxygen deficiency. b) Cardiac muscle cells contain more mitochondria than do skeletal muscle cells. c) The plasma membranes of cardiac muscle cells interlock, but skeletal muscle fibers are independent. d) Cardiac muscle does not use the sliding filament mechanism for contraction; skeletal muscle does.
d) Cardiac muscle does not use the sliding filament mechanism for contraction; skeletal muscle does. Both skeletal muscle and cardiac muscle are striated, and both utilize the sliding filament mechanism for contraction.
Which of the following structures collects the depolarization wave from the atria to pass it onto the ventricles? a) bundle branches b) AV node c) atrioventricular bundle d) SA node
b) AV node The AV node receives the depolarizing wave from the atria and delays and coordinates that distribution to the ventricles.
Which part of the intrinsic conduction system delays the impulse briefly before it moves on to the ventricles? a) bundle branches b) AV node c) SA node d) AV bundle (bundle of His) e) Purkinje fibers
b) AV node Yes, the AV node slows down the impulse giving the atria time to contract before the ventricles contract.
One of the changes that occurs in the pacemaker potential (unstable resting membrane potential) in the SA node (an autorhythmic cell) is a decreased efflux of what ion? a) calcium b) sodium c) potassium
c) potassium Yes, if there is a decreased efflux of potassium while there is a normal influx of sodium, the inside of the cell would become less negative. Thus, threshold would be reached. The ability of these autorhythmic cells to spontaneously depolarize is what results in the pacemaker potential.
During which portion of the electrocardiogram do the atrioventricular valves close, correlating with the first heart sound ("lub")? a) R-S waves b) T wave c) P wave d) P-R interval
a) R-S waves When the ventricles enter systole, the atrioventricular valves close. This valve closure is associated with the first heart sound, the "lub."
Suppose a patient develops a myocardial infarction that disables the sinoatrial node. Would the heart still pump blood to the aorta and the pulmonary trunk? a) Yes, because the atrioventricular node will still stimulate ventricular systole. b) No, because there will be no contraction of the atria. c) No, because there would be no more connection between the atrioventricular node and the bundle branches. d) Yes, because the ventricles will depolarize on their own at a rate of 50 times per minute.
a) Yes, because the atrioventricular node will still stimulate ventricular systole. The atrioventricular node spontaneously depolarizes similarly to the sinoatrial node, but more slowly. It can lead to the ventricles pumping blood to the aorta and pulmonary trunk around 50 times per minute.
Consider the following characteristics of the cells found in muscle tissue. Which feature is shared by both cardiac muscle and skeletal muscle? a) striations b) branched cells c) intercalated discs d) triads
a) striations Since both cardiac and skeletal muscles possess arrangements of motor proteins in regularly arrayed sarcomeres, they both display the banding known as striations.
In order to cause cardiac muscle contraction, the contractile cells must also depolarize. What causes the depolarization of the contractile cells? a) the flow of positive ions from adjacent cells b) the flow of negative ions from adjacent cells c) an unstable resting membrane potential in the contractile cells
a) the flow of positive ions from adjacent cells Yes, the flow of positive ions from the autorhythmic cells (or adjacent cells) brings the membrane to threshold initiating depolarization of the contractile cell.
Contraction of the atria results from which wave of depolarization on the ECG tracing? a) T wave b) P wave c) QRS complex
b) P wave Yes, the P wave represents atrial depolarization, which leads to atrial contraction.
Which part of the conduction system initiates the depolarizing impulse, which spreads throughout the heart? a) AV bundle (bundle of His) b) SA node c) Purkinje fibers d) AV node
b) SA node Yes, the SA Node spontaneously depolarizes, causing the wave of depolarization that spreads through the rest of the conduction system and heart.
The order of impulse conduction in the heart, from beginning to end, is __________. a) SA node, bundle branches, AV node, bundle of His, and Purkinje fibers b) SA node, AV node, bundle of His, bundle branches, and Purkinje fibers c) SA node, bundle of His, AV node, bundle branches, and Purkinje fibers d) SA node, bundle branches, bundle of His, AV node, and Purkinje fibers
b) SA node, AV node, bundle of His, bundle branches, and Purkinje fibers The impulses of the heart originate at the SA node (pacemaker). The impulse is then transmitted to the AV node (atrioventricular node), where the impulse slows down to allow the atria to completely contract and thereby fill the adjacent ventricles. The AV node then transmits the impulse to the bundle of His, which branches into left and right bundle branches. The bundle branches give rise to the Purkinje fibers, which transmit the impulse to the ventricle walls and stimulate ventricular contraction.
The P wave on an electrocardiogram represents __________. a) ventricular depolarization b) atrial depolarization c) atrial repolarization d) ventricular repolarization
b) atrial depolarization The P wave reflects the depolarization of the atria.
What does the ECG wave tracing represent? a) contraction of the heart b) electrical activity in the heart
b) electrical activity in the heart Yes, the ECG waves show the depolarization and repolarization in various areas of the heart.
What structures connect the individual heart muscle cells? a) anastomoses b) intercalated discs c) trabaculae carneae d) chordae tendineae
b) intercalated discs Intercalated discs connect the heart muscle cells. They include desmosomes (anchoring junctions) and gap junctions (communicating junctions).
What does the QRS complex represent in the ECG wave tracing? a) ventricular repolarization b) ventricular depolarization c) atrial repolarization d) atrial depolarization
b) ventricular depolarization Yes, the QRS complex represents depolarization in the ventricles, which have greater mass than the atria.
Which portion of the electrocardiogram represents the depolarization wave received by the atria from the sinoatrial (SA) node? a) T wave b) QRS complex c) P wave d) S-T segment
c) P wave The P wave represents the depolarization of the left and right atria and the beginning of atrial systole.
Which portion of the electrocardiogram represents the time during which the ventricles are in systole? a) T wave b) P wave c) Q-T interval d) QRS complex
c) Q-T interval The Q-T interval is the period from the beginning of ventricular depolarization through ventricular repolarization, during which the ventricles are in systole.
Action potentials generated by the autorhythmic cells spread to the contractile cells through what structures in the membrane? a) intercalated discs b) tight junctions c) gap junctions d) desmosomes
c) gap junctions Yes, action potentials generated by the autorhythmic cells spread waves of depolarization to contractile cells through gap junctions. If the depolarization causes the contractile cells to reach threshold, they will in turn generate an action potential.
Repolarization of an autorhythmic cell is due to the opening of which channels? a) voltage-gated sodium channels b) chemically gated calcium channels c) voltage-gated potassium channels d) Chemically gated potassium channels
c) voltage-gated potassium channels Yes, opening of voltage-gated potassium channels causes positive potassium ions to move out of the cell. This efflux of potassium causes the cell to become more negative inside thus, repolarizing the cell.
Why are gap junctions a vital part of the intercellular connection of cardiac muscles? a) Gap junctions contract when stimulated, strengthening the force of cardiac cell contraction. b) Gap junctions form strong intercellular connections. c) Gap junctions allow calcium to enter the cell, triggering calcium release from the SR. d) Gap junctions allow action potentials to spread to connected cells.
d) Gap junctions allow action potentials to spread to connected cells. Gap junctions are a form of electrical synapse that allow action potentials to spread to connected cells. This property allows the signal to spread efficiently through the heart.
Which statement regarding cardiac muscle structure is accurate? a) Cardiac muscle cells are independent of one another both structurally and functionally. b) Cardiac cells possess few mitochondria. c) Cardiac cells are long, cylindrical, and multinucleate. d) Myofibrils of cardiac muscle tissue vary in diameter and branch extensively.
d) Myofibrils of cardiac muscle tissue vary in diameter and branch extensively. The myofibrils of cardiac muscle have various diameters; they also branch in order to maintain connections, via intercalated discs, with other muscle cells.
Adding a chemical that reduces Na+ transport near the sinoatrial (SA) node would have what effect on the heart's intrinsic conducting system? a) The SA node would depolarize more quickly, increasing the heart rate. b) The SA node would depolarize less quickly, increasing the heart rate. c) The SA node would depolarize more quickly, decreasing the heart rate. d) The SA node would depolarize less quickly, reducing the heart rate. e) There will be no change
d) The SA node would depolarize less quickly, reducing the heart rate. Na+ leaking into the pacemaker cell causes a gradual depolarization of the cells. If that depolarization slows down, the heart rate will slow down.
When threshold is reached at the SA node (an autorhythmic cell), what channels open causing further depolarization of the membrane? a) fast sodium b) slow calcium c) potassium d) fast calcium
d) fast calcium Yes, unlike nerve cells or cardiac muscle cells, fast calcium channels are responsible for the depolarization phase of the autorhythmic cell action potential. When the fast calcium channels open, calcium rushes into the cell making it less negative (or more positive).
Specifically, what part of the intrinsic conduction system generates the original stimulus that reaches the atrioventricular (AV) node, allowing it to conduct impulses to the atrioventricular bundle? a) interventricular septum b) bundle branches c) subendocardial conducting network (Purkinje fibers) d) sinoatrial (SA) node
d) sinoatrial (SA) node The sinoatrial node, by spontaneously depolarizing faster than the atrioventricular node, initiates heart contraction.