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Regulation of Cerebral Blood Flow by The Sympathetic Nervous System
Regulation of Cerebral Blood Flow by The Parasympathetic Nervous System Direct stimulation of the facial nerve leads to an increase in total cranial blood flow, however the phsiological role is not clear. The nerves are not directly involved in the most basic cerebrovascular responses, such as hypoxic or hypercapnic vasodilation, nor do thay appear to play a role in autoregulation
Regulation of Cerebral Blood Flow by The Trigeminovascular System This system is the sole sensory innervation of the cerebral vessels. Its function does not appear to be in the maintenance of resting cerebral flow. In situations of abnormal physiology, this system comes into play by mediating vasodilation.
Consequence of Chronic Hypertension The autoregulatory plateau of the pressure-flow relation is shifted to the right in hypertensive patients and experimental animals so that cerebral blood flow may be normal despite very high levels of blood pressure
Vasoactive Mediators of Cerebral Vessels
Amines + vasoconstriction
Norepinephrine (+) - vasorelaxation
Thromboxane A2 (+)
Prostaglandins (PGD2, PGE2(-), PGF2 (+))
Platelet-Activating Factor (- +)
Vasodilator Peptides (-)
Vasoactive Intestinal Peptide (VIP)
Calcitonin Gene-Related Peptide (CGRP)
Substance P (SP)
Vasoconstrictor Peptides (+)
Purine Nucleotides (-)
ADP and ATP
Nitric Oxide (NO)
Carbon Monoxide (CO)
Biology of Cerebral Vascular Muscle
Cerebral Spinal Fluid
Formed at the choroid plexus and drained into the peripheral blood stream at the arachnoid villi.
CSF volume is completely cleared via this bulk flow process in the human brain every 4-5 hr.