Memory Check 3:  Blood Supply to the Brain

I’ll try to summarize the blood supply to the brain – 

*  The brain receives approximately 20% of the cardiac output, or 800 to 1000 mL of blood flow per minute. Carbon dioxide is a potent vasodilator in the CNS and ensures an adequate cerebral blood supply. The brain derives its arterial supply from two systems: the internal carotid arteries and the vertebral arteries.

 •  The internal carotid arteries originate from the common carotid arteries, enter the cranium through the base of the skull, and pass through the cavernous sinus. After giving off some small branches, they divide into the anterior and middle cerebral arteries. The vertebral arteries originate at the subclavian arteries, pass through the transverse foramina of the cervical vertebrae, and enter the cranium through the foramen magnum. They join to form the basilar artery. The basilar artery divides at the level of the midbrain to form paired posterior cerebral arteries. Superficial arteries supply small branches that project into the brain. The circle of Willis is a structure having the ability to provide collateral blood flow. Many communicating arteries that extend to various brain structures form it. 

•  The venous drainage of the brain stem and cerebellum parallels the arterial supply; the venous drainage of the cerebrum does not. The cerebral veins are classified as superficial and deep. The veins drain into venous plexuses and dural sinuses and eventually drain into the internal jugular veins at the base of the skull. The blood-brain barrier selectively inhibits certain substances in the blood from entering the interstitial spaces of the brain or CSF. It is believed that the supporting cells and tight junctions between endothelial cells are involved in the formation of the blood-brain barrier and are responsible for its impermeability.

MemChk.Neuro.3.MdP