Meningeal coverings, ventricles, and CSF Flashcards
What are the three meningeal coverings of the brain?
Dura, arachnoid, and pia
Describe the dura mater layers
Outer periosteal layer: firmly attached to the skull, contains the meningeal arteries
Inner meningeal layer: in close contact with the arachnoid and continuous with spinal dura
In the spinal area, it is single layered and suspended in the vertabreal canal.
What is important about the cranial epidural space and spinal epidural space?
Cranial is a potential space that only exists and becomes filled with fluid during pathalogical conditions. Spinal is real space between dura and vertebral periosteum
What are the dural folds?
- Falx cerebri
- Falx cerebelli
- Tentorium cerebelli
- Diaphragma sellae
What are the dural venous sinuses?
Endothelial lined spaces between the periosteal and the inner meningeal layers of the dura mater that lead to the jugular veins
- Superior sagittal
- Inferior sagittal
- Straight
- Occipital
- Confluence of sinuses
- Transverse
- Sigmoid (right and left)
- Cavernous (paired)
- Intercavernous
- Sphenoparietal (paired)
- Superior petrosal (paired)
- Inferior petrosal (paired)
- Basilar
Inflammation like meningitis or traction by an expanding mass can cause headache-why?
The dura and some subarachnoid blood vessels are pain sensitive structures
What is the role of emissary veins?
They connect the extracranial veins to the venous sinuses inside the cranium, and are an important route for the spread of infection
What space is the CSF in?
he subarachnoid space
What are two important components of arachnoid mater?
Arachnoid trabeculae (suspends the brain) Arachnoid granulations/villi: outpouchings of the aracnhoid mater which poke through holes in the walls of venous sinouses, allows CSF to pass uni-directionally to the venous sinuses.
What is 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
How is the pia mater attached?
It is attached on one side to arachnoid trabeculae and on the other to astrocyte feet that carpet the surface of the CNS
The pia gives off what two structures?
Denticulate ligaments and filum terminale
At what level do the spinal dura and arachnoid end?
S2
What causes epidural bleeding?
Tearing a meningeal artery, typically as the result of a skull fracture
What causes subdural bleeding?
Tearing a cerebral vein as it penetrates the arachnoid on its way into a venous sinus
What causes subarachnoid bleeding?
Rupture of a cerebral artery (burst aneurysm)
What kind of hematoma does a dural venous sinus injury cause?
epidural or subdural hematoma
What are the ventricles of the brain?
- a pair of lateral ventricles in the telecephalon (one for each cerebral hemisphere)
- A midline third ventricle (cavity of the diencephalon)
- A midline fourth ventricle (cavity of the rhombencephalon)
Describe the ventricle map
Two lateral ventricles –> two interventricular foramina of Monro –> third ventricle –> aqueduct of Silvius –> fourth ventricle –> median aperature (foramen of mramen of magendiea) and two lateral aperatures (foramina of luschka) to the subarachnoid space
What is the rate of formation of CSF? Total volume?
500 mL/day
90 to 150 mL (23 in ventricles and remaining is subarachnoid space)
Describe the nature of the movement of CSF across the arachnoid villi
it is passive, driven by the difference in hydrostatic pressure between the CSF in the subarachnoid space adn the venous blood in the superior sagittal sinus. The villi act like tiny flap valves so that reverse flow is prevented if venous pressure exceeds CSF pressure
What is the choroid plexus?
the joining of the inner lining of the ventricle and the outer covering of the CNS without any intervening neural tissue. Located at lateral ventricle, roof of third ventricle, roof of fourth ventricle
What is the choroid epithelium?
Ependymal cells in the choroid plexus that are specialized as a secretory epithelium. Adjaecnt cells are joined by tight junctions, forming a diffusion barrier.
What are subarachnoid cisterns?
Large parts of subarachnoid space, corresponding to major irregularities in the surface of the CNS. Cisterna magna is an important one
What are the functions of CSF?
Mechanical support, cushioning effects, dampens effects of trauma, vehicle for removal of metabolites, route for spread of neuroactive hormones
Describe CSF composition
Very little protein. Less glucose, ca2+, and K+ ions than serum. More Na+, Cl-, and Mg2+ ions than serum.
What is hydrocephalus?
Dilation of the ventricles with increased intracranial pressure that occurs when circulation of the CSF is blocked or its absorption impeded
What are the two types of hydrocephalus?
Non communicating: obstruction of flow in ventricular system
communicating: impaired CSF absoprtion in arachnoid granulations, obstruct of flow in the subarachnoid space
What is the composition of circumventricular organs?
neurons, glia, ependymal cells, leptomeningeal and vascular elements. Around the 3rd and 4th ventricles and lack a BBB (fenestrated capillaries)
What is the role of circumventricular organs?
sodium/water balance, CV regulation, energy metabolism, and immunomodulation
