- An isolated carotid sinus was prepared so that the pressure may be regulated by a pump and the resulting discharge in single carotid sinus nerve fibre could be recorded. The following are the possible observations.
A. No discharge when carotid sinus perfusion pressure was below 30 mm Hg.
B. Linear increase in discharge frequency when carotid sinus perfusion pressure was gradually increased from 70 to 110 mm Hg.
C. Increase in discharge frequency was more prominent in greater pulsatile changes of carotid sinus pressure keeping the mean pressure identical in all cases.
D. Increase in discharge was more prominent in the falling phase of pulsatile change of carotid sinus pressure than in the rising phase.
Which one of the following is correct?
(1) A, B and C (2) A and C
(3) B and D (4) D onlyCarotid Sinus Baroreceptor Discharge with Changes in MAP
Baroreceptors in the carotid sinus are crucial sensors of arterial blood pressure. Their firing frequency depends on both the magnitude of arterial pressure (mean arterial pressure, MAP) and its pulsatile nature (phasic changes during cardiac cycles).
Statement Analysis
-
A. Baroreceptors are more sensitive to phasic change of aortic pressure at normal MAP
Correct. At normal MAP, baroreceptors respond vigorously to the pulsatile waveform of arterial pressure, showing pronounced phasic firing. -
B. The baroreceptor firing rate is reduced at lower MAP than in normal MAP
Correct. Reduced arterial stretch at lower MAP leads to decreased firing rate. -
C. The phasic change in baroreceptor fiber is less prominent at lower MAP
Correct. Lower pressures mean less pulsatility and hence diminished phasic firing. -
D. A burst of action potentials appear in a single baroreceptor fiber during diastole at normal MAP
Incorrect. Baroreceptor activity is typically higher during systole where pressure peaks, bursts are not prominent in diastole. -
E. The discharge of baroreceptors even extends to systole at higher MAP
True in context, but the question asks for a pair of correct statements; options do not pair E with clear correctness.
Choosing the Correct Pair of Statements
-
Only (1) A and B and (2) B and C are both fully correct combinations.
-
Since A emphasizes phasic sensitivity at normal MAP and B highlights firing reduction at low MAP, which aligns better with the key characteristics of baroreceptors, option:
(1) A and B is the most accurate.
Physiological Explanation
-
Baroreceptors are sensitive to both steady-state pressure and the rate of pressure change during each heartbeat.
-
Their firing increases with higher pressure and pulsatility to inform the central nervous system for blood pressure adjustments.
-
As MAP declines, reflex firing diminishes to trigger compensatory sympathetic activation.
Summary Table
Statement Correct? Explanation A Yes Increased sensitivity to phasic changes at normal MAP B Yes Lower firing rate at reduced MAP due to less stretch C Partial Phasic firing less pronounced at low MAP D No Bursts mainly in systole, not diastole E Partial Discharge extends into systole at high MAP
Conclusion
The correct pair of statements describing carotid sinus baroreceptor firing at various MAP levels is:
(1) A and B
-
2 Comments
Varsha Tatla
September 17, 2025Done
Aakansha sharma Sharma
October 3, 2025A,B&C