The following anatomic events occur at the level of the sternal angle (angle of Louis) except which?
A. The right and the left pulmonary arteries enter the lungs. B. The right recurrent laryngeal nerve arises from the right vagus nerve. C. The trachea bifurcates. D. The ascending aorta becomes continuous with the arch of the aorta. E. The second costal cartilages articulate with the sternum
The Correct Answer and Explanation is :
The correct answer is B. The right recurrent laryngeal nerve arises from the right vagus nerve.
Explanation:
The sternal angle, also known as the angle of Louis, is an important anatomical landmark located at the junction of the manubrium and body of the sternum, roughly at the level of the second rib. It serves as a reference point for various structures in the thoracic cavity.
Let’s break down the choices:
- A. The right and the left pulmonary arteries enter the lungs: This event does occur at the level of the sternal angle. The pulmonary arteries, which carry deoxygenated blood from the right side of the heart to the lungs, cross the sternal angle as they travel to their respective lungs.
- B. The right recurrent laryngeal nerve arises from the right vagus nerve: This is incorrect. The right recurrent laryngeal nerve does not arise at the level of the sternal angle. Instead, it loops around the right subclavian artery before ascending back to the larynx. This occurs below the sternal angle and not at this landmark.
- C. The trachea bifurcates: This event occurs at the level of the sternal angle. The trachea bifurcates into the right and left mainstem bronchi at this level, marking the transition from the trachea to the bronchial tree.
- D. The ascending aorta becomes continuous with the arch of the aorta: This is true. At the sternal angle, the ascending aorta becomes the aortic arch, which curves around to give rise to the major branches supplying the upper body.
- E. The second costal cartilages articulate with the sternum: This is also correct. The second rib articulates with the manubrium of the sternum at the level of the sternal angle, which corresponds to the attachment of the second costal cartilage.
Thus, the only event that does not occur at the sternal angle is the right recurrent laryngeal nerve arising from the vagus nerve.