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

Answer and Explanation

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.

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Correct Answer is B

Explanation

A. Bronchophony: Bronchophony is an increase in clarity of spoken sounds when auscultating the lungs, typically indicating lung consolidation or pathology. It is not an adventitious sound associated with airflow through narrowed bronchioles.

B. Wheezes: Wheezes are high-pitched, musical sounds that occur when air passes through narrowed or obstructed airways, such as in cases of severe asthma. They are often heard during expiration and indicate bronchoconstriction or inflammation in the airways. This is the correct answer for the scenario presented.

C. Bronchial sounds: Bronchial sounds are normal breath sounds typically heard over the trachea and major bronchi. They are characterized by a higher pitch and a hollow quality. They are not classified as adventitious sounds and are not indicative of asthma.

D. Whispered pectoriloquy: Whispered pectoriloquy is a clinical finding where whispered sounds are heard more clearly over areas of lung consolidation. Like bronchophony, it does not represent an adventitious sound caused by airflow through narrowed bronchioles and is more indicative of lung pathology.

A. Top-to-bottom comparison B. Side-to-side comparison C. Posterior-to-anterior comparison D. Interspace-by-interspace comparison

Correct Answer is B

Explanation

A. Top-to-bottom comparison: Systematic progression from top to bottom is important, but it does not ensure direct comparison between corresponding lung fields. Without a side-to-side comparison, asymmetrical lung sounds may go unnoticed, leading to an incomplete assessment.

B. Side-to-side comparison: The correct method for auscultation is to compare lung sounds bilaterally, moving from one side to the other at each level. This approach helps identify asymmetries, such as unilateral crackles, wheezing, or decreased breath sounds, which may indicate conditions like pneumonia, pleural effusion, or pneumothorax. A zigzag pattern from right to left ensures an accurate evaluation of lung symmetry.

C. Posterior-to-anterior comparison: While both anterior and posterior thoracic assessments are necessary, comparing sounds from posterior to anterior does not ensure side-to-side evaluation. Since lung sounds can vary based on body positioning and structure, direct lateral comparisons are essential for detecting differences.

D. Interspace-by-interspace comparison: Although breath sounds should be assessed at each intercostal space, a method focusing only on progressing downward would miss direct left-to-right comparisons. Identifying localized abnormalities requires listening at the same level on both sides before moving downward.

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Which sequence does the electrical stimulus of the cardiac cycle follow?

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