Term
*Cerebrospinal Fluid (CSF)* |
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Definition
•Produced by choroid plexus— in lateral, 3rd, & 4th ventricles
•Choroid plexus consists of capillary tufts covered by epithelium called ependyma
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Term
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Definition
•CSF is produced constantly: 21mL/hr, 500 mL/day-thus renewed 3- 4 times/day
•percolates through ventricles and leaves through small openings in dura mater and into the superior sagittal sinus (venous blood blow).
•Compounds entering CSF favor lipophilic ones.
•Blood brain barrier refers to all interfaces between blood, brain, and CSF
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Term
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Definition
•Lateral ventricles converge at midline, called interventricular foramen
•3rd ventricle
•cerebral aqueduct (in midbrain)
•4th ventricle (in pons and medulla)
•foramen of Magenti OR foramen of Luschka
•subarachnoid space (bathing the brain & spinal cord and maintained by arachnoid mater)
•superior sagittal sinus
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Term
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Definition
•Cushions brain and spinal cord by absorbing shocks
•Clear in color-does not normally contain blood, pus, bacteria. Neurochemical composition determined from spinal tap
•150 ml volume (total intracranial volume which includes CSF, brain, and blood is 1700 ml)
•Pressure maintained by arteriolar BP
•A “sink” for waste products of cerebral metabolism: CO2, lactate, H+
•Normal CSF pressure = 6-13 mm Hg
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Term
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Definition
•brain, blood, and CSF volume determine ICP. An increase in volume of any one will be at the expense of the other two, particularly at ICP>25 mm Hg.
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Term
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Definition
•Cerebral or extracerebral mass—tumor, infarction, traumatic contusion, parenchymal, subdural, or extradural hematoma
•Generalized brain swelling-ichemic-anoxic states, acute hepatic failure, encephalopathy
•Increase in venous pressure-thrombosis of cerebral sinuses, heart failure
•Obstruction to CSF flow or absorption
•Processes that increase CSF volume-meningitis, choroid plexus tumor.
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Term
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Definition
•Meningeal-ant. & post. branches of middle meningeal arteries blood supply to dura mater, arachnoid mater, and pia materà laceration leads to epidural hematoma
•Opthalmic—first major branch of internal carotid artery. Blood supply to the retina
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Term
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Definition
•The cerebral arteries:
•Anterior (1)-medial frontal & parietal lobes, motor & sensory areas for lower extremities, some basal ganglia
•Middle (5)-somatic motor area (face, arm, & trunk), Broca’s area, parietal lobes, basal ganglia
•Posterior (8)-occipital lobe, calcarine cortex, subthalamic nucleus, midbrain
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Term
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Definition
•Posterior inferior cerebellar artery—inferior surface of cerebellum, some vestibular nuclei, inf. cerebellar peduncle, spinothalamic tract, fibers of CN IX & X
•Anterior inferior cerebellar artery—facial nucleus, vestibular nuclei, cochlear nuclei, inf. & middle cerebellar peduncles
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Term
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Definition
•Small vessels that are branches of the larger arteries.
•Supply the basal ganglia, brain stem, cerebellum, thalamus, and hypothalamus
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Term
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Definition
•Anterior and posterior choroidal supplies the lateral ventricle
•Posterior choroidal supplies the third ventricle
•Branch of posterior inferior supplies fourth ventricle
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Term
Some Major Sinuses and Veins |
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Definition
•Great vein of Galen: receives blood from internal cerebral veins and drains into straight sinus
•Straight Sinus: drains superior surface of cerbellum
•Superior sagittal sinus: drains CSF from subarachnoid space & superficial cerebral veins
•Inferior sagittal sinus: joins Great Cerebral vein to form straight sinus
•Cavernous Sinus: receives blood from superior & inferior opthalmic veins
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Term
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Definition
•Brain receives 15% of cardiac output, though comprising just 2% of body weight
•Autoregulation-CBF is maintained over a BP range of 50-150 mm Hg by dilation or constriction of pial blood vessels, cerebral arteries, or arterioles.
•This feature protects the brain from changes in perfusion pressure due to increased ICP, decreased cardiac output, or even body posture changes
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Term
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Definition
•CBF is adjusted to metabolic need. High plasma CO2, low tissue pH, & adenosine stimulate CBF.
•Each 1 mm Hg change in arterial pCO2 produces a 2.5% change in CBF.
•Functional activity of brain correlates with CBF.
•This activity imaged by PET scans or fMRI
•Minor effect of pO2 and glucose on CBF—
•pCO2 very important
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Term
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Definition
•Major need due to huge metabolic demand.
•ATP required for maintaining neuronal electrochemical gradient
•Brain accounts for 20% of the body’s total oxygen consumption (50% or more in infants)
•Brain lacks anaerobic metabolism mechanism.
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Term
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Definition
•Glucose is primary source, other monocarboxylic acids (MCA) such as lactate and ketone bodies are also used
•Array of transporters (glucose, MCA) exist for these compounds
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Term
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Definition
•Getting glucose in: facilitated diffusion across the BBB via glucose transporters GLUT1, -2, -3
•GLUT1 located on brain endothelial cells of the BBB and on astrocytic processes called endfeet in association with capillaries.
•Delivery of glucose from blood to brain occurs 1) through these endfeet, 2) directly into neurons, and 3) into the glia.
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Term
GABA-Glutamate-Glutamine Cycle |
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Definition
-Interaction between TCA cycle with neurotransmitter biosynthesis via α-ketoglutarate. Glutamate & GABA are the major excitatory and inhibitory neurotransmitters of the CNS.
•Direct, one-step reaction of α-ketoglutarate (α-KG) in an amino-group transfer reaction or transamintation of α-oxoglutatrate
•the glutamine cycle. Gln released from glia is taken up by neurons and converted into glu by glutaminase (50% of neuronal glutamate derived from this cycle).
•Glutamate is in equilibrium with a-ketoglutarate. The glutamine cycle is critical for offsetting loss of α-KG from the TCA cycle.
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