BIOLOGY 03048, ANATOMY WEEK 11: CRANIAL BLOOD AND CSF SUPPLY 11/11/99
W. Crone (303 FTZ, 629-7439, cronewil@hvcc.edu, http://www.hvcc.edu/academ/faculty/crone/index.html)
Texts: Moore and Dalley, Ch. 7, pp. 875-898; Young and Young, Chs. 1, 19, 20
possible HVCC library a/v resource for the brain and associated structures:
VT 1820,"Human Nervous System" (overview of CNS structures, cadaver-based)
Meninges were discussed with the spinal cord: remember dura, arachnoid, and pia mater? In the brain, there are two layers of cranial dura mater, the bone-adhering endosteal layer, and the more conventional meningeal layer. These two separate out into the dural sinuses, where blood pools before drainage into the internal jugular veins. Overall flow of blood: superior sagittal sinus to transverse sinus to sigmoid sinus. Additional path: inferior sagittal sinus to straight sinus; superior petrosal sinus from cavernous sinus to sigmoid sinus; and inferior petrosal sinus to internal jugular vein.
Cavernous sinus thrombosis, e.g., from infected (and squeezed) facial boil , can affect the cranial nerves that control eye movement, and thus present with a patient with a tender, swollen face, and loss of eye movement in the affected eye. To complicate matters, the cavernous sinus contains many trabeculae that make thrombosis more likely.
The internal carotid artery reaches the base of the skull and once in the inferior surface of the brain has the following branches:
1) ophthalmic artery, supplying the eye and associated structures
2) anterior cerebral artery that supplies the medial aspects of the cerebral hemispheres
3) middle cerebral artery that supplies the lateral aspects of the cerebral hemispheres
An anterior communicating artery, two posterior communicating arteries, and two posterior cerebral arteries (occipital lobe region) off of the basilar artery are also part of the cerebral arterial circle (circle of Willis).
Additional blood supply to be seen (I hope) in lab, in the order"SAP":
superior cerebellar arteries off of basilar artery just posterior to posterior cerebral artery
anterior inferior cerebellar arteries off of basilar arteries at vertebral artery junction
posterior inferior cerebellar arteries off of vertebral arteries
We will defer on particular stroke patterns until we've gone over brain parts on Tuesday. Until then…head injuries can be associated with intracranial bleeding. Three major types:1
1) epidural hemorrhage leading to an epidural hematoma, is extradural and is usually caused by a tear in the middle meningeal artery. Pressure can build up and herniate the brain through the foramen magnum. Classically, the patient loses consciousness after the head injury, reawakens, but several hours later slips into coma.
2) subdural hemorrhage leading to a subdural hematoma, is more common in elderly/drunk patients, and is often the result of tearing in a superior cerebral vein as it feeds into the superior sagittal sinus. These tend to be more chronic than the epidural hematoma, and typically present with drowsiness that may be fluctuating.
3) subarachnoid hemorrhage is usually the result of the rupture of an intracranial artery, leading to signs of meningeal irritation (severe headache, stiff neck).
Cerebrospinal fluid (CSF) forms a protective cushion, nourishes, and feeds the brain. It is produced by specialized ependymal cells forming choroid plexuses. Major sites for CSF are the ventricles and subarachnoid space. The lateral ventricles are connected to the third ventricle by narrow interventricular foramina (of Monro).
The cerebral aqueduct (aqueduct of Sylvius) connects the third and fourth ventricle. CSF exits the fourth ventricle into subarachnoid space via median and lateral aperatures. The CSF returns to venous blood via arachnoid villi (granulations as they hypertrophy with age).
Internal (obstructive) hydrocephalus: CSF building up in the ventricles, most commonly from congenital aqueductal stenosis, so more common in preossified infants. Usually causes cerebral cortex to atrophy and cranial bones to thin if not treated by ventricular shunting.
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Please send comments and questions to: cronewil@hvcc.edu
Copyright 1999 by Wilson Crone
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This page updated on November 15, 1999