| Question | Answer |
| Where is CSF found? | In sub-arachnoid space & ventricles of brain |
| Functions of CSF | Preserve homeostasis (reservoir, nourishes brain tissue);
Buoyancy for brain;
Drains brain of unwanted stuff;
Cushion;
Path for pineal secretions to get to pituitary |
| Where is CSF formed? | Choroid Plexuses |
| CSF pH | Lower than blood pH |
| CSF Production | Continuously produced, even if resorption rates decrease |
| Main Sites of CSF Absorption | Arachnoid villi;
Dural venous sinuses (esp sup. sagittal sinus) |
| What causes absorption into venous sinuses? | CSF Pressure > Venous Sinus Pressure;
Rate of absorption of CSF thru arachnoid villi controls CSF pressure |
| Sub-Arachnoid Extensions | Around optic n. to back of eyeball;
Arachnoid & pia mater fuse to sclera;
Central a. & v. of retina cross extension to enter optic n. & may be compressed in pts with increased CSF pressure |
| Cisterns | Brain surface separated from skull |
| Where are some major cisterns? | Cistern cerebellomedullaris (cesterna magna);
Medullary cistern;
Cisterna pontis;
Cisterna interpeduncularis;
Quadrigeminal (superior) cistern;
Chiasmatic |
| Where is the limit of sub-arachnoid space? | S2 |
| Permeability of B-B Barrier/Blood-CSF Barrier? | Inversely related to size of molecules, directly related to lipid solubility;
Gases/water pass quickly;
Glucose, electrolytes pass slower;
Not permeable: plasma proteins, large organic molecules |
| Tight Junctions | Hard for things to pass through |
| What population has an increased permeability? | Newborns |
| Where is the blood-CSF barrier? | Choroid plexus; tight junctions b/c choroidal epithelial cells = barrier |
| What 3 structures separate CSF from nervous tissue? | Pia- covered surface of brain & SC;
Perivascular extensions of sub-arachnoid space into nervous tissue;
Ependymal surface of ventricles- lines ventricles |
| What are intercellular channels? | Free communication b/t ventricular cavity & extracellular neuronal space |
| What is the importance of barriers? | 2 important semi-permeable barriers protect brian/SC from potentially harmful substances;
Permit gases & nutrients to enter nervous tissue |
| B-B Barrier readily absorbs what? | Glucose & Oxygen |
| Brain capillaries possess what? | Tight junctions;
Few pinocytotic vessels (fluid pockets);
Foot processes of astrocytes encasing capillaries;
Lots of mitochondria |
| Barrier Permeability | Likes: small molecules, carrier-mediated substances (transported by proteins), highly soluble lipid substances
HATES: substances bound to serum proteins; larger proteins |
| What causes brain edema? | Increased brain volume due to increased water & sodium |
| Vasogenic Edema | Most common;
Due to increased permeability of brain capillary endothelial cells to large molecules |
| Cellular (Cytotoxic) Edema | Swelling of cell elements of the brain with accompanying decrease in volume of extracellular space |
| Interstitial (Hydrocephalic) Edema | Increased water and sodium in peri-ventricular white matter b/c of mvmt of CSF across ventricular walls |
| What can brain edema cause? | Gyri flattening, brain herniation through tentorial notch or foramen magnum, or death |
| Papilledema | Increase in CSF pressure due to tumor: compression of thin walls of retinal vein -> congestion of vein, bulging of optic disc & papilledema;
Persisten papilledema- optic n. atrophy/death, blindness |
| Hydrocephalus | Abnormal increase in CSF volume |
| If hydrocephalus accompanied by increased ICP it's due to? | Abnormal increase in CSF formation;
Blockage of CSF circulation;
Decreased absorption- b/c of inflammatory exudate, venous thrombosis, venous sinus pressure, int. jugular v. obstruction |
| What happens with obstructed IV foramen? | Blocks drainage of lateral ventricle which leads to distended ventricle & atrophy of surrounding neuronal tissue |
| What happens with obstructed cerebral aqueduct (congenital, b/c of tumor pressure)? | Symmetrical dilation of both lateral ventricles & 3rd ventricle;
Obstruciton of foramen of Magendia & foramina of Luschka b/c of inflammatory exudate or tumor growth will produce symmetrical distention of all ventricles |
| What happens with hydrocephalus secondary to meningitis? | Inflammatory exudate blocks sub-arachnoid space with obstructed flow over outer surface or cerebral hemispheres; entire ventricular system would become distended |
| Non-Communicating Hydrocephalus | Increased pressure b/c of blockage |
| Communicating Hydrocephalus | No obstruction within or to outflow
CSF- sub-arachnoid space under normal pressure
Normal- pressure disorder characterized by tried |
| Triad that comes with communicating hydrocephalus | Dementia;
Unsteady gait;
Urinary incontinence |
| Tumor of SC/Meninges | Flow of CSF blocked, normal variation in pressure corresponding to pulse-respiration are decreased/absent during lumbar puncture |
| Compression of Internal Jugular vv in neck | Increased cerebral venous pressure & inhibits CSF absorption in arachnoid villi & granulations- increased CSF pressure during lumbar puncture |
| Tumor completely occupying vertebral canal near cauda equina | No flow of CSF during lumbar puncture |
| What kind of drugs enter the brain faster/better? | Lipid-Bound |
| Any obstruction to normal passage of CSF causes? | Increased fluid in ventricles;
General ICP;
Swelling of optic n. (papilledema) |
| S/sx of Brain Tumor | Persistent HA & vomiting, usually worse in morning
May be improved by sitting/standing (Gravity drains CSF) |
| BS/cblm tumors | Close to ventricles, so can cause increased ICP when relatively small; +/- papilledema |
| 4th Ventricle Tumors | May arise in vermis or pons & invade 4th ventricle or ependymoma
Pt will display s/sx cblr deficiency
Pressure on vital BS centers in floor of 4th ventricle (medulla) |
