Where are the sensors for the arterial baroreceptor reflex located?
a. carotid sinus and aortic arch
b. The sympathetic and parasympathetic nervous systems
c. cardiovascular centers in the medulla oblongata
The Correct Answer and Explanation is:
Correct Answer: a. carotid sinus and aortic arch
Explanation
The arterial baroreceptor reflex is a critical homeostatic mechanism that helps regulate blood pressure on a moment-to-moment basis. The sensors for this reflex—known as baroreceptors—are located in the carotid sinus and the aortic arch.
Baroreceptors are mechanoreceptors, meaning they respond to changes in mechanical pressure or stretch within blood vessels. When blood pressure rises, the walls of the arteries stretch more. This mechanical stretch is detected by the baroreceptors, which then increase their rate of firing. Conversely, if blood pressure falls, the reduced stretch causes a decrease in baroreceptor firing.
These signals are transmitted via two cranial nerves:
- The glossopharyngeal nerve (cranial nerve IX) carries signals from the carotid sinus.
- The vagus nerve (cranial nerve X) carries signals from the aortic arch.
These afferent signals travel to the cardiovascular centers in the medulla oblongata, specifically the nucleus tractus solitarius (NTS). Although the medulla oblongata is involved in processing the baroreceptor signals and generating appropriate autonomic responses, it is not where the sensors are located—hence option (c) is incorrect.
Once the information is processed, the medulla adjusts autonomic output:
- It can decrease sympathetic activity and increase parasympathetic activity if blood pressure is high, leading to vasodilation, slower heart rate, and reduced cardiac output.
- If blood pressure is low, it does the opposite—increasing sympathetic activity to raise heart rate, increase contractility, and constrict blood vessels.
Option (b), referring to the sympathetic and parasympathetic nervous systems, pertains to effectors, not sensors, and is thus also incorrect.
In summary, the carotid sinus and aortic arch are the key locations for the sensors involved in the arterial baroreceptor reflex, making option (a) the correct answer.
