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Cerebral blood flow (CBF) is the blood supply to the brain in a given period of time. [8] In an adult, CBF is typically 750 millilitres per minute or 15.8 ± 5.7% of the cardiac output. [9] This equates to an average perfusion of 50 to 54 millilitres of blood per 100 grams of brain tissue per minute. [10] [11] [12]
The midbrain is the shortest segment of the brainstem, measuring less than 2cm in length. It is situated mostly in the posterior cranial fossa, with its superior part extending above the tentorial notch. [2] The principal regions of the midbrain are the tectum, the cerebral aqueduct, tegmentum, and the cerebral peduncles.
This continuous flow into the venous system dilutes the concentration of larger, lipid-insoluble molecules penetrating the brain and CSF. [9] CSF is normally free of red blood cells and at most contains fewer than 5 white blood cells per mm 3 (if the white cell count is higher than this it constitutes pleocytosis and can indicate inflammation ...
The adaptive flow that the circle of Willis introduces can also lead to reduced cerebral perfusion. [ 8 ] [ 9 ] In subclavian steal syndrome , blood is "stolen" from the vertebral artery on the affected side to preserve blood flow to the upper limb .
When significant, arteries can become narrowed enough to reduce blood flow. It contributes to the development of dementia, and has protein similarities to those found in Alzheimer's disease. [176] The brain, although protected by the blood–brain barrier, can be affected by infections including viruses, bacteria and fungi.
The cerebral aqueduct (aqueduct of the midbrain, aqueduct of Sylvius, Sylvian aqueduct, mesencephalic duct) is a small, narrow tube connecting the third and fourth ventricles of the brain. [ 1 ] [ 2 ] The cerebral aqueduct is a midline structure that passes through the midbrain .
The temporal pole of the cerebrum and a portion of the cerebellar hemisphere have been removed on the right side (left half of diagram). Inferior aspect (viewed from below). The superior cerebellar artery supplies deep parts and superior parts of the cerebellum. [1] [2] It supplies parts of the midbrain (tectum, including the cerebral crus). [1]
Diagram showing the position of the colliculi. Superior shown in green and inferior in orange. View of the midbrain showing covering tectum and tegmental floor. The midbrain is further subdivided into three parts: tectum, tegmentum, and the ventral tegmental area. The tectum forms the ceiling.