Unit 4 - CSF, BBB, Cerebral Circulation

support systems for the nervous system

cerebrospinal fluid, blood brain barrier and blood supply

ventricular system includes

lateral ventricles, 3rd ventricle, 4th ventricle and central canal

lateral ventricles sends CSF to

3rd ventricle via the interventricular foramen

the 3rd ventricle sends CSF to

4th ventricle via cerebral aqueduct

the 4th ventricle sends CSF to

either through the foramen of luschka or magendie to the subarachnoid space then to the spinal cord, or continues with the central canal of the spinal cord

foramen of luschka

lateral aperature

foramen of magendie

median aperture

Cerebrospinal Fluid (CSF)

plasma-like clear fluid circulating in and around the brain and spinal cord, cushions and bathes the brain and spinal cord

CSF is produced by

choroid plexus in all ventricles, but primarily in the lateral ventricle

choroid plexus

network of capillaries, connective tissue and epithelial cells

CSF after it flows through the ventricles, is absorbed through

arachnoid granulations into venous sinuses to be circulated back into venous blood

CSF flow is

unidirections

what sinuses form the confluence of sinuses

superior sagittal sinus, straight sinus and transverse sinus

the transverse sinus turns and forms the

sigmoid sinus which dumps into the internal jugular vein

venous sinuses sit between

2 layers of dura - arachnoid granulations project through dura into venous sinuses

venous sinuses are not the same as

veins, they dont have valves and are not elastic

two entry points from blood into brain

via CSF or direct from blood into CNS

blood CSF barrier

barrier between blood and CSF by tight junctions of choroidal epithelium

blood brain barrier

barrier between brain and blood supply by tight junctions between capillary endothelial cells

BBB acts to

protect brain tissue and keeps waste away from neurons

BBB damage yields

leaks - brain tumors, meningitis, SCI, stroke

many CNS lesions are due to

damage to arterial blood supply

arterial

blood to tissues, O2 delivery , high pressure

venous

blood to heart, CO2 removal, low pressure

the circle of willis surrounds

optic chiasm and pituitary gland

branches of circle of willis supply

hemispheres, cortex, internal capsule and deeper brain structure

anterior entry to circle of willis is via

internal carotid artery

posterior entry to circle of willis is via

vertebral artery

anterior cerebral artery supplies (ACA)

medial surface of hemispheres

what would be impacted by an ACA clot

leg

middle cerebral artery supplies (MCA)

lateral surface of hemispheres

what would be impacted by a MCA clot

face and hand, majority of strokes occur here

posterior cerebral artery supplies (PCA)

occipital lobe and inferior temporal lobe

what would be impacted by a PCA clot

vision

internal carotid artery feeds

anterior circle and anterior/middle brain

internal carotid artery turns into

middle cerebral artery

vertebral artery feeds

posterior circle/brainstem, cerebellum/posteiror brain

vertebral artery turns into

basilar artery through vertebral foramen

dissection of a vessel

tear in inner wall of a vessel causing impedance and a false lumen

circle of willis is comprised of

posterior cerebral artery, posterior communicating artery, middle cerebral artery, anterior cerebral artery, anterior communicating artery

under normal conditions, flow in communicating arteries is

negligible - there for redundancy of flow to increase the number of routes available to supply flow (more than 50% of healthy brains have abnormalities)