3. Physiology
        3.2. Cardiovascular
            3.2.4. Regulatory mechanisms
       Regulation of peripheral blood flow
           Systemic control by nervous system Vasomotor centre

Vasomotor centre

[Ref: WG21:chp31]

See figure 31-7 [WG21:p607]


Cell bodies

... of neurons mediating sympathetic discharge to CVS

Located near the pial surface of the medulla in the rostral ventrolateral medulla (RVLM).


Axons travel dorsally and medially, then descend in the lateral column of the spinal cord


Project to the sympathetic preganglionic neurons in the intermediolateral gray column (IML) of the spinal cord

Preganglionic neurons

Preganglionic neurons then innervate

Postganglionic sympathetic neurons then innervate the heart and blood vessels
* Neurotransmitter: NE



Factors affecting vasomotor centre activity


A. Directly stimulated by

(Presumably directly on RVLM)

B. Excitatory inputs

C. Inhibitory inputs

D. Other factors

Inflation of lungs

(via vagal afferent)

--> Vasodilation and decreased BP


--> Increase BP via reticular formation[WG21:p606]

But prolonged pain

--> Vasodilation and fainting

Somatosympathetic reflex

... refers to stimulation of somatic afferent nerve causing pressor response

Probably via C1 neurons in the RVLM



Stimulation of peripheral chemoreceptor (e.g. in stagnant hypoxia due to hemorrhage) leads to

Stimulation of central chemoreceptor (e.g. by increased PaCO2, decrease pH)
--> Vasoconstriction



Direct stimulation of vasomotor area


Direct effect of hypoxia is small (compared with effects of hypercapnia)


Increase in PaCO2 stimulates vasomotor area
--> Vasoconstriction


Increase in PaCO2 directly causes peripheral vasodilation
* Especially in skin and brain


--> Slow rise in BP

ICP and bradycardia

When ICP is increased
--> Impaired blood perfusion
--> Hypoxia and hypercapnia in vasomotor area
--> Increase in BP (Cushing reflex)
--> Reflex decrease in HR (via baroreceptors)

Thus, increased ICP is characterised by bradycardia

Respiration also slowed [WG21:p621]

Sympathetic vasodilator system

[WG21: p613]

Originates in cerebral cortex

--> Relays in hypothalamus and mesencephalon

--> Passes through (without synapsing) IML gray column of spinal cord

--> Synapse with postganglionic cholinergic neurons to blood vessels

Other notes



Table of contents  | Bibliography  | Index