Where does the electrical signal from the sinus node spread after it fires?

Where does the electrical signal from the sinus node spread after it fires?

• A. Purkinje fibers
• B. Atrioventricular node
• C. Aorta
• D. Left ventricle

Answer: (B)

After the SA node fires, the impulse quickly travels through the atrial myocardium, causing atrial contraction. The next relay point in the normal conduction pathway is the atrioventricular (AV) node. The AV node sits between the atria and ventricles and provides a brief delay, giving the atria time to finish contracting and fill the ventricles before ventricular activation begins. From there, the impulse moves down the His-Purkinje system to depolarize the ventricles. This is why the AV node is the best answer: it is the immediate next station after the SA node in the conduction chain. The Purkinje fibers are reached after passing through the AV node, and the aorta and left ventricle are not involved in the initial spread from the SA node.

After the SA node fires, the impulse quickly travels through the atrial myocardium, causing atrial contraction. The next relay point in the normal conduction pathway is the atrioventricular (AV) node. The AV node sits between the atria and ventricles and provides a brief delay, giving the atria time to finish contracting and fill the ventricles before ventricular activation begins. From there, the impulse moves down the His-Purkinje system to depolarize the ventricles.

This is why the AV node is the best answer: it is the immediate next station after the SA node in the conduction chain. The Purkinje fibers are reached after passing through the AV node, and the aorta and left ventricle are not involved in the initial spread from the SA node.