Which sequence does the electrical stimulus of the cardiac cycle follow?
SA node AV node → bundle branches → purkinje fibers
AV node SA node → purkinje fibers → bundle branches
Bundle branches → AV node → SA node → purkinje fibers
AV node → SA node → bundle branches→ purkinje fibers
The Correct Answer is A
A. SA node → AV node → bundle branches → Purkinje fibers: The sinoatrial (SA) node, located in the right atrium, is the heart's natural pacemaker, initiating electrical impulses. These impulses travel to the atrioventricular (AV) node, where conduction slows to allow ventricular filling. The signal then moves through the bundle of His, dividing into the right and left bundle branches, and finally reaches the Purkinje fibers, which stimulate ventricular contraction. This is the correct sequence.
B. AV node → SA node → Purkinje fibers → bundle branches: The AV node does not initiate the electrical impulse under normal conditions; it receives the impulse from the SA node. The Purkinje fibers are the final part of the conduction pathway, not an intermediate step before the bundle branches.
C. Bundle branches → AV node → SA node → Purkinje fibers: Electrical conduction does not begin at the bundle branches. The SA node initiates the impulse, and the AV node delays transmission before passing the impulse to the ventricles via the bundle branches and Purkinje fibers.
D. AV node → SA node → bundle branches → Purkinje fibers: The SA node, not the AV node, initiates the cardiac cycle. The AV node functions as a relay station that briefly delays the impulse before it proceeds to the bundle branches and Purkinje fibers.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
A. Whisper a set of random numbers and letters, and then ask the patient to repeat them: The whispered voice test is a simple and reliable screening method for hearing loss. The nurse stands about 2 feet behind the patient, whispers a series of random numbers or letters, and asks the patient to repeat them. This helps assess high-frequency hearing loss.
B. Shield the lips so that the sound is muffled: While the test is performed without the patient seeing the nurse’s lips to prevent lip reading, deliberately muffling the sound is unnecessary and may alter the accuracy of the assessment.
C. Stand approximately 6 feet away to ensure that the patient can really hear at this distance: The whispered voice test is conducted at a standard distance of about 2 feet, not 6 feet. Increasing the distance may make the test unreliable.
D. Ask the patient to place his or her finger in their ears to occlude outside noise: The test should be performed in a quiet environment, but instructing the patient to occlude their ears is unnecessary. Instead, the nurse tests one ear at a time by covering the opposite ear.
Correct Answer is B
Explanation
A. Mitral and pulmonic: The mitral valve closure is best heard at the apex of the heart (the left fifth intercostal space) rather than at the base. The pulmonic valve is indeed located near the base but, combined with the mitral valve, does not represent the sounds best heard at the base of the heart.
B. Aortic and pulmonic: The aortic and pulmonic valves are located at the base of the heart. The aortic valve is located in the right second intercostal space at the sternal border, while the pulmonic valve is located in the left second intercostal space. The closure of these valves (S2) is typically loudest at this area, making this option correct.
C. Mitral and tricuspid: The mitral valve is best heard at the apex, and the tricuspid valve is best heard along the left lower sternal border. Both valves are not located at the base of the heart.
D. Tricuspid and aortic: The tricuspid valve is not located at the base of the heart; it is situated along the left lower sternal border, while the aortic valve is at the base. Therefore, this combination does not represent the best valves to listen for at the base.
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