Carotid sinus baroreceptor is most sensitiveto: (DNB Dec-2010)
|A||Mean blood pressure|
|B||Diastolic blood pressure|
|C||Systolic blood pressure|
1. Are stretch receptor in the heart and blood vessels.
2. Carotid sinus — the internal carotid artery and; Aortic sinus — the wall of the Arch of Aorta
3. Afferent fibers from carotid sinus and Aortic sinus pass through IX CN and X CN to the medulla, respectively.
4. They are stimulated by distention of the blood vessels when pressure increased.
5. The baroreceptor respondextermely rapidly to change in arterial pressure; in fact, the rate of impulse firing increased during systole and decreased again during diastol.
a. Not stimulated at pressure between 0 to 60 mm Hg.
b. Stimulated at pressure > 60mm Hg and maximum at 180 of mmHg.
Maximal carotid sinus sensitivity occurs near the normal mean arterial pressure; therefore, very small changes in arterial pressure around this "set point" dramatically alters receptor firing so that autonomic control can be reset in such a way that the arterial pressure remains very near to the set point. This set point changes during exercise, hypertension, and heart failure. The changing set point explains how arterial pressure can remain elevated during exercise or chronic hypertension.
6. Effect of Baroreceptor stimulation: -
(i) Inhibits the tonic discharge of the vasoconstrictor nerves and excite the vagal innervation of the heart.
(ii) Produces →vasodilation, venodilation increased BP, increased HR, and increase in COP
7. Samson Wright : - Effect of common carotid artery occulation→ fall in pressure of carotid sinus →baroreceptors lesen their discharge → medullary cardiovascular centre is inhibited →increase their drive to the sympathetic vasoconstriction and to the cardiac sympathetic fibers →BP ↑and ↑HR