Signal from Baroreceptors goes to ?

Ans. is 'b' i.e., Rostral ventrolateral medullaBaroreceptors are mechanoreceptors that are located in the adventia of carotid aery and aoa, at specialized locations called sinuses.1) Carotid sinus is a little bulge at the root of internal carotid aery, located just above the bifurcation of the common carotid aery. It is innervated by the sinus nerve, a branch of glossopharyngeal (IX cranial) nerve.2) Aoic arch (aoic sinus) also contains mechenoreceptors (stretch receptors) which are similar to carotid sinus receptors. However, their afferent nerve fibers travel in the aoic nerve, a branch of Vagus (X cranial) nerve.The sinus nerve (from carotid sinus) and aoic nerve/vagal fibers (from aoic sinus) are together called `Sinoaoic nerves'. They, together, are also refered to as 'Buffer nerves' because they are the afferents of cardiovascular reflexes that buffer abrupt changes in blood pressure.Baroreceptors are highly sensitive to any change in mean blood pressure. Sinoaoic nerves (buffer nerves) normally discharge rhythmically, synchronous with the pressure fluctuation during systole and diastole. They respond to BP changes between 70 mm Hg and 150 mm Hg. When BP rises, baroreceptors are stimulated and their afferents (through sinoaoic nerves) stimulate nucleus of tractus solitarus (NTS) which inturn inhibits the pressor area ofVMC, i.e., Rostral ventrolateral medula (RVLM). This results in decreased sympathetic outflow and therefore decreases in vasomotor tone and vasodilation. Vasodilation brings down the BP, thereby helping hemostasis. Activated NTS also stimulates nucleus ambiguous (cardioinhibitory center) of medulla, which increases parasympathetic (vagal) output, through vagus, that decreases hea rate. Reduction in hea rate reduces the cardiac output, which also reduces BP. Baroreceptor stimulation also weekly inhibits respiration.When BP falls, for instance while changing the posture from lying down to standing, reverse change takes place. When a person stands up, his blood is pooled in the veins of lower limbs by the effect of gravity. Central venous pressure and venous return decrease, which causes a fall in stroke volume. Hence the systolic BP falls. As a result, the discharge rate of baroreceptors decreases leading to a decrease in the inhibitory influence on the pressor area of VMC. Hence vasomotor tone increases, leading to vasoconstriction, and consequently an increase in BP. Simultaneously, the nucleus ambiguous of the vagus is also inhibited, increasing the hea rate and consequently stroke volume and eventually BR Thus fall in BP due to change ofposture is very brief (Transient).