The medullary vascular centers work in tandem to regulate generalized peripheral resistance. Peripheral resistance, by impeding flow, increases upstream blood pressure in elastic arteries.
Vasoconstrictor (VC) centers are located in the medulla of the brain stem. They are associated with the sympathetic nervous system. Neural pathways travel through the spinal cord to synapse with vasomotor nerves (VM)-- solid lines are stimulatory nerves--leading to muscular arteries throughout the body.
The vasoconstrictor centers maintain a baseline muscle tone (i.e., VCN) in these vessels. If this neural control ceased the precipitous drop in blood pressure would be life threatening. Likewise, if this stimulation was suddenly increased the rapid rise in blood pressure would also be life threatening. Blood pressure must be monitored to prevent either extreme. Follow the interactions that begin with high arterial blood pressure.
A carotid sinus (CS) is located at the bifurcation of each carotid artery. The carotid sinus is stimulated by increasing blood pressure (BP); this direct relationship is indicated by the solid arrow between BP and CS. Neurons travel to the brain travel in the glossopharyngeal nerve (GP); this nerve stimulates the vasodilator center (VD).
The vasodilator center (VD) sends inhibitory signals to the vasoconstrictor center as represented by the dashed line. The vasoconstrictor center (VC) communicates with muscular arteries throughout the body via stimulatory vasomotor (VM) nerves shown as a solid line. The overall result of increased vasodilator activity, by inhibiting the vasoconstrictor center, is generalized vasodilation throughout the body.
Vasodilation is the same as low vasoconstriction. Low vasoconstriction (VCN)--resulting in large diameter vessels--causes low peripheral resistance (PR)--a direct relationship (solid arrow)--throughout the arterioles. Generalized low peripheral resistance (PR) drops the blood pressure (BP) within the arterioles-- a direct relationship indicated by the solid arrow.
Consider the flow of blood from the arteries into the dilated arterioles as shown at the top of the map. The reduced blood pressure (BP) in the arterioles favors flow into them-- an inverse relationship (dashed arrow). This increased flow will decrease the upstream blood pressure (BP)--another inverse relationship (dashed arrow). The increase in flow from the arteries will reduce arterial blood pressure (BP).
Last update: 7/19/2005