Meningeal Coverings Flashcards
What 3 meningeal coverings surround the brain?
dura, arachnoid, pia (pia and arachnoid are called leptomeninges)
Describe the dura mater.
its a thick connective tissue membrane and serves as the periosteum of the inside of the skull
Describe the two layers of dura mater:
outer periosteal layer
inner meningeal layer
outer periosteal layer- firmly attached to the skull, contains meningeal arteries
inner meningeal layer -in close contact with arachnoid and continuous with spinal dura
Describe the cranial epidural space.
There is no space between dura and cranium so cranial epidural space is a potential space that becomes filled with a fluid only in pathological conditions
pain sensitive (innervated by branches of trigeminal and cervical nerves) (dura and some subarachnoid blood vessels are the only pain-sensitive intracranial structures. so inflammation such as meningitis or traction by an expanding mass causes headache)
What are some pathological conditions associated with the cranial epidural space?
epidural hematoma
(dura and some subarachnoid blood vessels are the only pain-sensitive intracranial structures. so inflammation such as meningitis or traction by an expanding mass causes headache)
Describe the dural folds.
falx cerbri - sep the two cerebral hemispheres
falx cerebelli - partially sep. cerebllar hemispheres located in posterior fossa
tentorium cerebelli - tent-like roof over posterior cranial fossa and it separates cerebrum from cerebellum
diaphragma sellae - covers hypophysial fossa in sella turcica
Describe the dural venous sinuses.
Superior sagittal inferior sagittal straight occipital confluence of sinuses transverse (right and left) sigmoid (rt and left) cavernous (paired) intercavernous sphenoparietal (paired) superior petrosal (paired) inferior petrosal (paired) basilar
Describe the emissary veins.
they connect extracranial veins to the venous sinuses inside the cranium (to dural venous sinuses)
have an important route for spread of infection
Describe the arachnoid:
subarachnoid space
arachnoid trabeculae
arachnoid granulations or villi
thin, delicate membrane
subarachnoid space (between arachnoid and pia) is filled with CSF
arachnoid trabeculae (suspends the brain)
arachnoid granulations or villi (impouching in absorbing CSF)
How does CSF enter the venous system?
through arachnoid villi
Describe the arachnoid barrier.
A layer of cells that are connected to each other by bands of tight junctions. This forms a barrier to the diffusion of extracellular substances from the dura into CSF, or in the reverse direction
Describe pia mater.
it is attached on one side to arachnoid trabeculae and on the other to astrocyte end-feet that carpet the surface of the CNS. This completes the mechanical suspension system.
Describe the differences between cranial and spinal meninges.
What is the spinal epidural space between?
What is it filled with?
Where do spinal dura and arachnoid end?
spinal epidural space is between periosteum and dura
spinal epidural space is filled with connective tissue and vertebral venous plexus
spinal dura and arachnoid end at S2
large subarachnoid cistern- lumbar cistern
What does pia covering the spinal cord give?
denticulate ligaments
filum terminale
Describe the following hemorrages in meningeal spaces.
epidural bleeding
subarachnoid bleeding
subdural bleeding
epidural bleeding- tearing a meningeal artery, typically as the result of a skull fracture
subarachnoid bleeding- rupture of a cerebral artery, as in a burst aneurysm
subdural bleeding- tearing a cerebral vein as it penetrates the arachnoid on its way into a venous sinus casuses subdural bleeding which actually separates the innermost layers of the dura
Describe the ventricles of the brain.
pair of lateral ventricles in the telencephalon (one for each cerebral hemisphere)
midline third ventricle (cavity of the diencephalon)
midline fourth ventricle (cavity of the rhombencephalon)
Describe the ventricles of brain including connections.
two lateral ventricles two interventricular foramen of Monro third ventricle aqueduct of Silvius Fourth ventricle
Median aperture- Foramen of Magendie
Lateral aperture-Forament of Luschaka
Where is CSF secreted from?
What is the rate of formation?
What is the total volume of CSF/where is it?
choroid plexuses
rate of formation is 500mL/day
total volume of CSF is 90 to 150mL, of which about 23 mL is in the ventricles, remaining is in subarachnoid space
Where is the choroid plexus formed?
choroid plecus is formed at certain areas where the inner lining of the ventricle (i.e. ependyma) and the outer covering (pia) of the CNS are directly applied to each other, with no intervening neural tissue
What is choroid epithelium?
ependymal cells are specialized as a secretory epithelium called choroid epithelium; adjacent cells are joined by tight junctions, forming a diffusion barrier. Vascular connective tissue invaginates this pia/ependyma membrane, forming multiple folded choroid plexus
Describe CSF circulation.
Secreted within the ventricles, fills them, flows out of fourth ventricle through three apertures to fill subarachnoid space
lateral ventricles
interventricular foramen of Monro
third ventricle to aqueduct of Sylvius
fourth ventricle
through the two lateral (Luschka) and the median (Magendie) foramen
enters the cerbellomedullary cistern (cisterna magna)
moves through subarachnoid space through the brain and spinal cord
What are subarachnoid cisterns?
Large pockets of subarachnoid spcae, corresponding to major irregularities in the surface of the CNS, are called subarachnoid cisterns.
Prominent intracranial cisterns include cisterna magna (between medulla and inf. surface of the cerebellum)
Describe the functions of CSF.
physical/mechanical support, cushioning effect on CNS and dampens effects of trauma
serves and vehicle for removal of metabolites form the NS
route for spread of “neuroactive” hormones
Compare CSF to serum.
very little protein present in CSF
less concentrations of glucose, Ca2, K+ ions in CSF
more concentrations of Na+, Cl-, and Mg2+ in CSF
Describe hydrocephalus.
dilation of ventricles occurs when the circulation of the CSF is blocked or its absorption is impeded
noncommunicating- obstruction in duct or ventricles
communicating- all ventricles can communicate, and obstruction is OUTSIDE ventricles (in villi or subarachnoid space)
Describe the circumventricular organs.
What do they consist of?
What do they have a critical role in?
consist of neurons, glia, ependymal cells, leptomeningeal and vascular elements; around the 3rd and 4th ventricles and lack a BBB (fenestrated capillaries)
have a critical role in sodium/water balance, CV regulation, energy metabolism and immunomodulation
Describe sensory circumventricular organs.
subfornical organ, vascular organ of the lamina terminalis, area postrema
Describe secretory circumventricular organs.
median eminence of the hypothalamus, neurohypophysis, pineal gland
Describe the CSF flow in the cerebellomedullary cistern.
flows downward into the spinal subarachnoid space and then ascends along the ventral surface of the spinal cord into the basal part of the brain where it courses dorsally to empty into the dural sinuses
How is CSF absorbed?
CSF travels rostrally over the cerebral hemisphere where it enters the arachnoid villi
it is absorbed into the venous system through the arachnoid villi (most of which protrude into superior sagittal sinus)
movement across the arachnoid villi is passive and driven by the difference in hydrostatic pressure between CSF in subarachnoid space and the venous blood in the superior sagittal sinus.
