Blood Supply And CSF Flashcards
T/F neurons have no significant ability to store O2 or glucose
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Blood flow to the brain
. 750-1000 ml/min
. Blood volume turns over 5-7 times/minute
. Unconsciousness results if blood flow ceases for more than 10 sec
. W/in 4-5 min of hypoxia, irreversible tissue damage begins
Vascular supply of brain
. Internal carotid a. And branches: ant. Circulation and supply 80% of blood to the brain
. Vertebral a. And branches: post. Circulation, supply 20% of blood supply to the brain
Internal carotid artery
. Arises from bifurcation of common carotid
. Courses through petrous portion of temporal bone and through cavernous sinus
. C-shaped configuration of vessel through cavernous sinus is apparent on cerebral angiography (carotid siphon)
. Intracranial (cerebral) segment emerges from cavernous sinus to give off ophthalmic, ant. Choroidal a., post. Communicating a., ant. Cerebral a., and middle cerebral a.
Ophthalmic artery
. Given off as soon as internal carotid a. Enters subarachnoid space
. Supplies the eyeball and other contents of the orbit
Anterior choroidal artery
. Passes caudally and laterally . Supplies: . Optic tract . Choroid plexus of inf. Horn of lat. ventricle . Ventromedial portion of temporal lobe . Globus pallidus . Thalamus . Ventral (ant.) portion of internal capsule
Posterior communicating artery
. Passes post. And inf. To optic tract to anastomose w/ post. Cerebral a.
. Branching point of the post. Communicating a. Is common site for aneurysms
Anterior cerebral artery
. Smaller of the 2 terminal branches of internal carotid a.
. Travels med. from point of origin to course sup. To the optic n.
. Primary branch enters longitudinal (interhemispheric) fissure
. Supplies sup. Surface of the corpus callosum and ant. 3/4 of the med. surface of the cerebral hemisphere (med. and orbital surface of frontal lobe, med. surface of parietal lobe, dorsomed. Portions of primary motor and somatosensory cortices)
Anterior communicating artery
. Joints left and right ant. Cerebral aa. At the midline
Medial striate artery
. Recurrent a. Of Heubner
. Given off by the proximal part of ant. Cerebral a.
. Supplies anteromedial region of basal ganglia and the internal capsule
Middle cerebral artery
. Larger of the 2 terminal branches, most of hte time it is direct continuation of ICA
. It travels laterally to enter the lat. fissure of Sylvius
. Distal branches of MCA emerge from lateral fissure in fan-like fashion
. Supplies most of the lat. surface of cerebral hemisphere (frontal, parietal, temporal, occipital lobes)
. Functional areas supplied: primary motor areas, somatosensory areas, premotor cortex, frontal eye field, primary auditory cortex, Broca’s and Wernicke’s areas, parietal association area, optic radiations
Lateral striate (lenticulostriate) artery
. Supplies deep structures of diencephalon and telencephalon, parts of striatum, and ant. And post. Limbs of internal capsule
. Damage to these vessels can cause neurological deficits disproportionate to their size
Vertebral artery
. Part of vertebral basilar system
. Provides post. Circulation and supplies 20% of blood to the brain
. Arises from subclavian a. And courses through transverse foramina of vertebral column
. Enters post. Cranial fossa through foramen magnum
. Runs on ventrolat. Surface of medulla then unites w/ counterpart of opposite side at caudal border of pons to form basilar a.
. Branches: post. Inf. Cerebellar a., post. Spinal a., ant. Spinal a.
Posterior inferior cerebellar artery (PICA)
. Largest branch of vertebral a.
. Supplies post. And inf. Aspects of cerebellum and choroid plexus of 4th ventricle and dorsolateral medulla
Posterior spinal artery
. Runs on dorsolateral surface of spinal cord as plexiform network of small aa.
. Supplies dorsal horns and dorsal funiculi (dorsal columns)
Anterior spinal artery
. Formed by joining of small contributions from each vertebral a. Just before the vertebral aa. Fuse to form the basilar a.
. Runs in the ventral median fissure
. Supplies ant. 2/3 of spinal cord
. Blood flow reinforced by radicular aa.
Branches of basilar artery
. Anterior inf. Cerebellar a. . Labyrinthine (internal acoustic) a. . Pontine aa. . Sup. Cerebellar a. . Post. Cerebral a.
Anterior inferior cerebellar artery (AICA)
. Arises just rostral to formation of basilar a.
. Supplies lat. caudal pons ant. And inf. Aspects of cerebellum (flocculus and middle cerebellar peduncle)
Labyrinthine artery
. May branch off AICA
. Runs through internal acoustic meatus
. Middle ear: occlusion causes vertigo and ipsilateral deafness
Pontine aa.
Collective term for small branches of basilar a.
. Some penetrate pons as paramedics branches
. Some short circumferential branches and long circumferential branches
Superior cerebellar artery (SCA)
. Arises just prior to the bifurcation of the basilar a. Into post. Cerebral aa.
. Supplies lat. rostral pons and caudal midbrain, sup. Aspect of cerebellum (vermis, deep cerebellar nuclei, most cerebellar white matter)
Posterior cerebral artery (PCA)
. Forms terminal branches of basilar a., runs laterally around midbrain
. Supplies rostral midbrain, caudal diencephalon, med. and inf. Surface surface of temporal and occipital lobes
Calcarine artery
. Branch of PCA
. Supplies primary visual cortex and occlusion of this vessel causes visual field deficits
Circle of Willis
. Arterial polygon located on base of brain
. Formed by ant. An dpost. Communicating aa., and prox. Portions of the internal carotid, ant. And post. Cerebral aa.
. Encircles optic chiasm, tuber cinereum, and interpeduncular region
. Parts of diencephalon, basal ganglia and internal capsule supplied by perforating branches of vessels that make up circle
. Normally there is no blood flow around the circle of Willis bc appropriate pressures differential are not present
. If vessel is occluded near it then there is anastomatic blood flow
Blood supply to medulla
. Depends primarily on vertebral-basilar system for blood supply
. Caudal medulla resembles spinal cod
. Rostral medulla has varying supply
Caudal medulla blood supply
. Ventral and lat. areas supplied by ant. Spinal a. (ASA) and/or vertebral a. (VA)
. Dorsal areas supplied by branches of post. Spinal aa. (PSA) and/or post. Inf. Cerebellar a. (PICA)
Rostral medulla blood supply
Ventra and med. areas supplied by branches of ASA and VA
. Lat. and dorsal areas o supplied by branches of post. Inf. Cerebellar a. (PICA) and less extent by pos. Spinal a. And VA
Blood supply to pons
. Mostly by paramedics and circumferential branches of basilar a. (BA)
. Dorsal and lat. pontine tegmentum, middle and sup. Cerebellar peduncles supplied by branches of ant. Inf. Cerebellar a. (AICA) and sup. Cerebellar a. (SCA)
Blood supply to midbrain
. Mostly post. Cerebral a. (PCA)
. Caudal midbrain also supplied by some branches of sup. Cerebellar a. And branches of basilar a.
. Crus cerebri can also get branches from post. Communicating a. And ant. Choroidal a. From internal carotid system
Watershed zones
. Areas of brain located btw terminal distributions of adjacent aa.
. Under normal conditions these are supplied by end aa. That function under low arterial pressure
. If cerebral perfusion drops (falling bp) blood flow to this zone is diminished
Blood brain barrier functions
. Prevents movement of chemical substances btw blood and CNS tissues
. Maintains optimal micro environment for neurons and glial cells
. Makes intercellular diffusion very difficult
Anatomic basis of BBB
. Adjacent endothelial cells joined by tight junctions that maintain high electrical resistance
. Cells lack fenestrations and pinocytotic vesicles
. Macromolecules can’t be moves from blood to brain by intra- or trans-cellular movement
What can pass through BBB?
. Lipid soluble substances diffuse across
. Glucose via facilitated diffusion
. AA by carrier-mediated transport
Circumventricular organs (CVOs)
. Certain brain regions that lack BBB
. Located in relationship to ventricles
. Are highly vascular and have fenestrated capillaries to allow a CNS response to blood-borne macromolecules (direct secretion of substances into blood)
Major CVOs and what they do
. neurohypophysis releases oxytocin and vasopressin into capillaries
. Area postrema monitors blood toxins and triggers vomiting
. Pineal gland secretes melatonin (sleep induction, antigonadotropic effect)
Choroid plexus
. Rich capillary network
. assoc. w/ ependymal and pial cells
Pial and ependymal cells formation of choroid plexus
. Collection of pial capillaries invaginates into ventricle, pushing thin covering of pial and ependymal cells w/in villi differentiate to become choroid plexus epithelial cells
. Cells form villi
. Ependymal cells w/in villi differentiate to become choroid plexus epithelial cells
. Choroid plexus epithelium produce and secrete CSF, not the other pial and ependymal cells
Blood-CSF barrier
. Apical regions of adjacent choroid epithelial cells connected by continuous tight junctions
. Forms anatomic and physiologic barrier to seal off extracellular space of villi from ventricular lumen
CSF production
. Choroid plexus makes 75%
. 25% derived via diffusion from CNS interstitial fluid or blood vessels in subarachnoid space
. Produces 500-700 ml/day
. Total volume is replaced 3-4x per day
. Average human contains 140 ml CSF
. Ventricles hold 30 ml w/ most in lat. ventricles
. Remaining CSF occupies subarachnoid space
CSF composition
. Clear and colorless, 99% H2O
. Acellular
. Isotonic w/ plasma
. Has minimal protein, lower glucose conc., higher Na, Cl, and Mg conc., and lower K and Ca conc.
CSF circulation
. Energy for CSF to move is from arterial pulsation of choroid plexus and cilia movement from apical surface of choroidal epithelium
. Lat. ventricles -> foramina of Monro -> 3rd ventricle -> cerebral aqueduct -> 4th ventricle -> exits system via foramina of Luschka and Magendie -> goes into subarachnoid space -> fluid moves rostrally and caudally
How is CSF returned to venous system
. Arachnoid granulations (tufted prolongation of arachnoid that project through meningeal layer of dura into lumen of sup. Sagittal sinus or venous lacunae adjacent to sup. Sagittal sinus
. Passive, pressure-dependent, 1-way flow valves
. Hydrostatic pressure of CSF is higher than venous pressure in dural sinuses
. 1-way flow of CSF is bull flow because all constituents of CSF leave w/ the fluid
CSF functions
. Buoyancy to prevent weight of brain compressing nn. Roots against skull surface
. Cushions from trauma: buoyancy reduces momentum to minimize shearing and tearing forces w/ overall reduction in concussive damage
. Intracranial volume adjustment and stabilization of intracranial pressure (CSF volume can change)
. Micronutrient transport
. Buffers sudden interstitial solute conc.
. Contains molecules needed for brain cell growth and development
. Excretion of metabolites and toxins into blood
. Drug delivery
Hydrocephalus
. Dilation of ventricles inc. CSF volume
. Overproduction of CSF, blockage of CSF flow, or deficiency in CSF reabsorption are normally causes
. CSF formation occurs independently of pressure w.in ventricles and subarachnoid space
. Elevation in intracranial pressure can reduce arterial blood supply to brain and lead to irreversible CNS damage
. CT an dMRI are best diagnostic tools
