Meninges, sinuses, cisterns, ventricles, choroid plexus, CSF (Ch.26)

CSF > Brain parenchyma

1. CSF seeps through ependymal cell lining in ventricles 2. Pia forms wall surrounding blood vessels, Pathway for CSF = paravascular space btwn pia and cell membrane. 3. Glymphatic system pathway to clear waste + enter csf into parenchyma CSF influx through para-arterial spaces of blood vessels. CSF efflux through para-venous space. Carrying compounds back into SAS blood vessels get thinner as you go up until final release.

3 exits of waste products

1. venous systems 2. CSF - AG - Sinuses 3. Lymphatic system lymph= water/like fluid attacks and kills infectious agents open system extra 3 liters that come to brain, clean, and bring back to brain found in lymph vessels in sinuses waste through cervical lymph nodes

CSF volume in humans

150-250 ml 600-700 ml made per day 25% stay in ventricle, the rest is pushed out into SAS

Dura mater Tissue organization

Between layers are loose dural boarder cells. loose cells Adjacent to arachnoid

CSF absorption into blood vessels

CSF absorption into venous blood vessels occurs by way of "arachnoid villi" as they protrude into dural venous sinuses. pressure of CSF>venous blood

unique features of the choroidal epithelium.

Cuboidal cells which are tightly bound to each other laterally by tight junctions so water and solutes cannot follow into the ventricle between them. The basal membrane and the luminal membrane (ventricular side) are specialized to selectively move required ions and molecules into the cell and out to the ventricle respectively because of the presence of specialized transporter and channel molecules. The blood vessels entering the plexus are fenestrated (leaky) and allow serum to leak into the choroid.

3 coverings of the brain

Dura mater - outermost layer. Thick pachymenix, covers entire brain adheres to bone closely Leptomeninges: Pia mater - thin and delicate connective tissue, translucent, innermost Arachnoid mater - in between filled with CSF

Meninges in the spinal cord

Epidural space - no natural epispace in brain, rather a potential space DM doesnt fuse to periostium, filled w/ fatty tissue space to inject anesthetics Pia external layer in spine branches "denticulate ligaments" that attach to arachnoid and DM serve to stabilize spine Fillum terminae - thin strand of pia that anchors end of spinal cord to the coccyx.

Na+/K+ -ATPase pump

Exchanges Na+ for K+ by a process that needs energy (ATP) to function. The ATPase catalyzes a reaction that converts ATP into ADP and a phosphate ion, which is the fuel for driving the pump

3 openings from ventricles

Foreman of magendie - passage from midline of 4th ventricle Foreman of Lushka - paired structure, link 4th ventricle to cisterna magna Foreman of Monro - connect paired lat. ventricles with 3 ventricle. midline of brain

Na+/K+/Cl- co-transporter

Is a molecule that transports Na+ and K+ along with 2 Cl- molecules (co-transports) across a membrane

Carbonic anhydrase

It is an enzyme, which catalyzes the break down of carbonic acid into bicarbonate ions and hydrogen ions. The latter ions are traded for sodium and chloride ions into the cell.

What is the blood-CSF (cerebrospinal fluid) barrier

It is the cuboidal epithelium of the choroid plexus

functions of CSF

Maintains the required ionic composition of the extracellular fluid for proper neuronal activity Mechanical support for the brain reducing its effective weight Drainage pathway for metabolic waste products 4 Import route for essential micronutrients reaching the neurons in extracellular space Route for neuronal communication by carrying hormones and even glutamate (paracrine function)

Pia mater tissue organization

Pia interna - wraps around blood vessels and veins but a space between PIT veins Perivascular space attaches closely to brain Pia externa - epipial layer

Subdural space

Potential space btwn layers of arachnoid + Dura mater

Epidural space

Potential space btwn layers of bone + Dura mater

Subarachnoid cisterns

SAS regions with CSF Cisterna magna - regions btwn cerebellum and medulla, gets CSF through 4th ventricle The space surrounding the openings from the 4th ventricle (foramen Magendie and foramen Lushka.) Lumbar cistern - of the spinal SAS. extends from 2nd lumbar vertebrae to 2nd segment of sacrum contains cauda equina ? Is the subarachnoid space in the lumbar region between L2 and the sacrum. It has mainly nerves before exiting the vertebral canal and filled with CSF, and is a place for safely collecting CSF for clinical investigation.

Dural and Venous sinuses

Superior sagittal sinus * - from widows peak to back of head and divides horizontally to fork - transverse sinus veins running to SSS re curvy waste > SSS > sigmoid sinus > jugular veins Inferior sagittal sinus - runs along bottom of faux cerebri. gets veins from med cerebral hemispheres connects to straight sinus Straight sinus - lies at attachment btwn faux tentorium and faux cerebelli. Recieves great cerebral vein. Runs continuously with transverse sinuses. lie in a groove on occipital bone akong part of tentorium cerebelli Transverse sinus Sigmoid sinus * * = curved - moe susceptible to injury / tearing All drein to jugular vein

Faux cerebri and tentorium cerebeli

These are deep extensions of the meningeal layer of the dura dividing the cranial cavity into sub chambers. The falx cerebri separates the two cerebral hemispheres, while the tentorium cerebelli separates the cerebellum from the cerebral hemispheres.

Dura mater: Periosteal vs. meningeal layer

Thick, dense layer of "collagenous connective tissue" Periosteal: blood vessels, nerve, pain receptors. Outer layer Meningeal: looser cell organization. Inner layer divide and outline brain into subchambers

Dural membranes (Septa)

This is a space created by the separation of the periosteal and meningeal dura in certain places They are channels into which CSF (via arachnoid granulations) and venous blood empty (by the opening of veins into them) and eventually drains out the venous blood by emptying into the jugular veins. Faux ceribri - divides cranial cavity into three compartments. Vertical along the longitudinal fissure dividing the cerebral hemispheres Tentorium cerebelli - btwn occipital lobes and cerebellum. Attachment with faux draws it upward into a "tent-like" shape Tentorial notch - opening in tentoriam cerebelli through which brain stem extends, providing a space btwn supra/infra tentorial spaces Faux cerebelli - vertical, runs at posterier cranial fossa, short distance btwn cerebellar hemispheres

Aquaporins

Water gets moved in when the ionic concentration in ventricles is higher than in the choroid epithelial cells, by the operation of water transporter molecules (Aquaporin 1)

Dural Sinuses

Where two layers separate Venous blood is collected and drained back to the heart and other waste products

subdural hematoma

a blood hemorrhage (ruptured blood vessel) under the Dura

arachnoid granulations

arachnoid extends into dural sinuses acts as one-way valve for CSF to flow to the venous system CSF is pushed by pressure up to sinus system by AG + jugular veins These are extensions of the arachnoid membrane (covered by ependymal cells) into the supra-sagittal sinus, which function as one-way valves for the flow of CSF from subarachnoid space into the sinus.

3 major blood vessels

arteries capillaries veins

subdural space

between DM and arachnoid. A little bit of fluid. Arachnoid is closely applied to DM

properties of Choroid epithelial cells

bigger mitochondria, large nucleus, cytoplasm, tight junction between adjacent cells, blocking fluid from freely entering the cell membrane. fenestrated openings plasma moves through fenestrations - fluid seeps into basal sides. Components diffuse through the cells which leads to CSF.

Sub-arachnoid hemorrhage

blood is SAS

CSF

cerebrospinal fluid

Confluence of sinuses

configuring of various channels that connect two transverse sinuses Transverse > sigmoid > cont. with internal jugular vein

Cerebral aqueduct

fluid from 3rd to 4th ventricle

3rd and 4th

invagination of of PM attached to roof of ventricles lined by ependymal cells, arteries modified by pushing through > Choroidal epithelium cells make CP.

Circulation of CSF

lateral U through intraventricular foramina to the third and by the cerebral aqueduct. to 4th ventricle.

The what part of the brain are the following ventricles located?

lateral ventricles, Cerebral hemispheres third ventricle, Diencephalon (or between the two thalami) cerebral aqueduct Midbrain 1 4th ventricle Pons and medulla 1 foramen of Monroe, opening between lateral ventricle and third ventricle foramina of Luschka and Magendie. At the caudal end of the medulla

Cisterns

openings constituted by SAS btwn Pia mater These are enlarged regions of the subarachnoid space

CSF formation: Choroid plexus

plexus of cells within the lateral ventricles makes/releases CSF in ventricular space CP made by invagination of PM of medial cerebral hemisphere

Plasma vs. CSF

proteins abundant in plasma (6500 vs. 25) proteins in the blood whereas hardly any in the CSF. Lower K+ and slightly higher Mg++ and CL- in CSF than blood.

Normal Epithelial cells

proteins: (APSase, pumps, K+, aquaporins) found in membrane -same proteins in apical membrane + carbonic anhydrase, enzyme breaks down carbonic acid into H+ and HCO3-, you can use the components by trading them for wanted components. Cl- and Na+ from the plasma H2o comes into membrane because of increased NA+ CSF becomes combo of Na+ and H2O + others also formed in ventricles. K+ leaky channels because too much K+ swells.

Lateral ventricles

set of hollow spaces within the two cerebral spaces

Ventricles

spaces in the brain where fluid is formed

Pia-arachnoid

start as one layer Trabiculae - strands of connective tissue with epithelial cells extending cells and fibers create the SAS

Dural and venous veins

veins draining the brain to the venous sinuses of dura, where blood flows into jugular veins