19. The discharge patterns in a single afferent nerve fibre from carotid sinus at various levels of mean arterial pressure (MAP) are plotted against changes in aortic
pressure with time in the following figure:

The following statements were proposed from the above figure:
A. Baroreceptors are more sensitive to phasic change of aortic pressure at normal MAP
B. The baroreceptor firing rate is reduced at lower MAP than in normal MAP
C. The phasic change in baroreceptor fibre is less prominent at lower MAP
D. A burst of action potentials appear in a single baroreceptor fibre during diastole at normal MAP
E. The discharge of baroreceptors even extends to systole at higher MAP
Choose the option with both CORRECT statements:
(1) A and B                                             (2) B and C
(3) C and D                                            (4) D and E

Carotid sinus baroreceptors play a crucial role in maintaining blood pressure homeostasis by detecting arterial pressure changes and sending afferent signals to the brain. Their firing patterns vary dynamically with changes in mean arterial pressure (MAP) and arterial pulse phases.

Evaluating the Statements About Baroreceptor Activity from the Figure and Concepts

• A. Baroreceptors are more sensitive to phasic change of aortic pressure at normal MAP.
  Correct. At normal MAP, baroreceptors show a strong phasic firing response correlating with pulsatile aortic pressure changes, indicating high sensitivity.

• B. The baroreceptor firing rate is reduced at lower MAP than in normal MAP.
  Correct. Lower MAP causes decreased arterial stretch, lowering baroreceptor firing rates.

• C. The phasic change in baroreceptor fiber is less prominent at lower MAP.
  Generally correct, because diminished arterial pulsatility at low MAP reduces pronounced phasic firing.

• D. A burst of action potentials appears in a single baroreceptor fiber during diastole at normal MAP.
  Incorrect. Baroreceptor firing is typically greater during systole when arterial pressure peaks, not diastole.

• E. The discharge of baroreceptors even extends to systole at higher MAP.
  Generally true but less critical for this question’s correct pair.

Choosing the Correct Pair of Statements

From the options given:

• (1) A and B

• (2) B and C

• (3) C and D

• (4) D and E

The statements A and B are the most clearly correct pairs relating to baroreceptor physiology:

• (A) emphasizes baroreceptor sensitivity at normal MAP and

• (B) reflects expected firing reduction at lower MAP.

Physiological Explanation

• Baroreceptors primarily sense both the magnitude and rate of change of arterial pressure during the cardiac cycle.

• Firing rates increase during systole, when pressure peaks, and decrease during diastole and hypotension.

• High MAP enhances the tonic and phasic discharge; low MAP reduces both.

• This neural input helps regulate heart rate and vascular tone through central feedback loops.

Summary

Final Answer

The correct option with both correct statements is:

(1) A and B

Additional Context

Baroreceptor discharge patterns are fundamental to short-term blood pressure regulation, helping the body rapidly adjust heart rate and vessel diameter to maintain stable circulation. Disturbances or resetting of this system contribute to conditions like hypertension and syncope.

Would an in-depth explanation of central processing of baroreceptor signals and clinical implications be useful next?

Slug: carotid-sinus-baroreceptor-discharge-patterns-mapncbi.nlm.nih+3

Title: Carotid Sinus Baroreceptor Discharge Patterns at Different Mean Arterial Pressures Explained

Meta Description: Understand how carotid sinus baroreceptors respond to varying mean arterial pressures, highlighting sensitivity to phasic changes and firing rate variations across the cardiac cycle.

Carotid sinus baroreceptors are sensitive mechanoreceptors that detect changes in arterial pressure and relay this information to the central nervous system to maintain cardiovascular homeostasis. Their firing patterns vary dynamically with the level of mean arterial pressure (MAP).

Analysis of Proposed Statements

• A. Baroreceptors are more sensitive to phasic change of aortic pressure at normal MAP.
  This is true. At normal MAP, baroreceptors show pronounced phasic firing corresponding to the pulsatile changes in pressure.

• B. The baroreceptor firing rate is reduced at lower MAP than in normal MAP.
  This is correct. Reduced arterial pressure results in decreased stretch and thus fewer action potentials fired.

• C. The phasic change in baroreceptor fiber is less prominent at lower MAP.
  Generally true but less definitive than A and B.

• D. A burst of action potentials appear in a single baroreceptor fiber during diastole at normal MAP.
  Incorrect. Baroreceptor firing is typically greater during systole.

• E. The discharge of baroreceptors even extends to systole at higher MAP.
  This is generally true but less critical for pairing.

Best Correct Pair

The statements A and B are both correct and most clearly supported by baroreceptor physiology.

Final Answer

(1) A and B

Understanding these patterns helps appreciate how the baroreflex contributes to short-term blood pressure regulation through neural feedback based on arterial pressure fluctuations.