Meninges and Ventricular System Flashcards
meninges
connective tissue, envelop the brain and spinal cord, function to protect the brain and keep it from collapsing under its own weight (CSF)
meningeal layers
1) dura mater - outer layer, thick
2) arachnoid mater - delicate, subarachnoid space filled with CSF
3) pia mater - very thin layer adherent to CNS
dura mater
dense, collagenous CT
two layers:
1) periosteal layer - outer layer
2) meningeal layer - inner layer
usually no space between layers except at venous sinuses
dural septa
inner dura folds onto itself, partially separates compartments of the brain
1) falx cerebri
2) tentorium cerebelli
3) falx cerebelli
4) diaphragma sellae
falx cerebri
separate cerebral hemispheres
- occupies longitudinal fissure
- runs from ethmoid bone to internal occipital protuberance
- fuses with tentorium cerebelli
tentorium cerebelli
separates cerebral hemispheres from cerebellum
- attached to falx cerebri, occipital bone, petrous temporal bone
blood supply of dura
meningeal arteries: run in the periosteal layer, supply the bones of the skull
- injury leads to epidural hematoma
meningeal veins: generally parallel arteries
- injury leads to subdural hematoma
blood supply to lateral surface of dura mater
middle meningeal artery
blood supply to anterior surface of dura mater
ophthalmic artery
blood supply to posterior surface of dura mater
branches of occipital and vertebral
dura mater nerves
trigeminal nerve - most of dura (except posterior fossa)
- near meningeal arteries pain is localized
- near venous sinus pain is referred to eyes, temple, forehead
vagus nerve - posterior fossa
- pain is referred behind the ear or back of neck
arachnoid mater
loose CT, avascular
1) outer layer that attaches to dura
2) arachnoid trabeculae
arachnoid trabeculae
attach to and merge with pia mater, keep brain suspended within meninges
arachnoid functions
1) connect pia to dura
2) act as a barrier between dura and CSF
3) bring CSF to venous system
4) bridge over irregular surfaces forming cisterns in the subarachnoid space
arachnoid villi
act as valve for CSF entering venous system - transport CSF to dural sinuses
subarachnoid cisterns
1) cisterna magna
2) superior cistern
3) chiasmatic cistern
4) pontine cistern
5) interpeduncular cistern
6) ambient cistern
cisterna magna
aka cerebellomedullary cistern, largest cistern
superior cistern
deep in transverse cerebral fissure
chiasmatic cistern
below optic chiasm
pontine cistern
ant. to pons and medulla
interpeduncular cistern
between cerebral peduncles, ant. to midbrain
ambient cistern
on lateral sides of midbrain, connects superior cistern to interpeduncular cistern
pia mater
very delicate, loose CT, follows contours of brain, blood vessels within subarachnoid space are held tighly to pia by CT
blood brain barrier (BBB)
keeps substances injected into the bloodstream from reaching/affecting the brain
true BBB
tight junctions between endothelial cells of cerebral capillaries (blood vessel walls)
other BBBs
tight junctions of other cells generalized as BBBs
choroid epithelium (blood CSF barrier; BCSFB)
arachnoid barrier
function of true BBB
selective barrier
- lipid-soluble substances can diffuse across
- glucose can cross via facilitated diffusion
- active transport of other substances
keeps out microbes but also keeps out treatments for brain infections
circumventricular organs (CVOs)
- cerebral capillaries are fenestrated, free mixing of brain ECF and blood
- found in walls of third and fourth ventricles
tanycytes
specialized ependymal cells that cover the CVOs, in contact with CSF
functions of CVOs
1) secrete hormones
2) sense blood-borne signals
hormone secretion by CVOs
- neuroendocrine (median eminence, post. pituitary)
- circadian rhythm (pineal gland)
sensing blood-borne signals - CVOs
- fluid balance (subfornical organ, vascular organ of lateral terminalis)
- toxins in blood (area postrema)
lateral ventricle derived from?
telencephalon
third ventricle derived from?
diencephalon
cerebral aqueduct derived from?
mesencephalon
fourth ventricle derived from?
metencephalon and myelencephalon
central canal derived from?
myelencephalon
CSF pathway
1) lateral ventricles
2) formaen of Monroe
3) third ventricle
4) cerebral aqueduct
5) fourth ventricle
6) foramen of Magendie/foramena of Luschka
7) central canal or around brain
8) joins venous system (through arachnoid villi)
lateral ventricles
largest, in cerebral hemispheres, C-shaped, ends at interventricular foramen
horns of lateral ventricles
1) body (parietal)
2) inferior horn (temporal)
3) posterior horn (occipital)
4) anterior horn (frontal)
third ventricle
midline, slit between thalami, thalamus and hypothalamus form most of walls
recesses of third ventricle
1) optic recess - next to optic chiasm
2) infundibular recess - next to infundibular stalk
3) pineal recess - next to pineal gland
4) suprapineal recess - above pineal gland
fourth ventricle
part of pons and medulla form floor, superior and inferior medullary velum form peaked roof
- superior: cerebellum
- inferior: choroid plexus membrane
apertures of fourth ventricle
apertures communicate with subarachnoid cisterns
- 2 lateral apertures (foramena of Luschka)
- median aperture (foramen of Magendie)
choroid plexus
site of CSF production, consists of choiroid epithelium + pia + capillary complex
choroid epithelium
- filters ions, proteins from the blood and secretes CSF into ventricle
- tight junctions
- continuous with ependymal cells
ependymal cells
no tight junctions, thought to direct CSF flow - cilia are aligned rostral to caudal in lateral, 3rd and 4th ventricles
choroid plexus locations
- in the C of lateral ventricle (none in ant. or post. horns)
- interventricular foramen
- in roof of third ventricle
- IMV of fourth ventricle
plexus
interface between ventricles and subarachnoid space
- subarachnoid spaces are invaginated by choroid plexi
choroid fissure
invagination in lateral ventricle
transverse cerebral fissure
finger of subarachnoid space
hydrocephalus
too much CSF, increase in CSF pressure causing ventricles to expand
remedy by using shunts
three types of hydrocephalus
1) blockage of CSF circulation - tumour growth obstucts foramen/aqueduct
2) too much CSF production - tumour of choroid plexus (papillomas)
3) too little CSF reabsorption - subarachnoid bleeding clogs arachnoid villi
