Meningeal Coverings

Question 1

What 3 meningeal coverings surround the brain?

Answer 1

dura, arachnoid, pia (pia and arachnoid are called leptomeninges)

Question 2

Describe the dura mater.

Answer 2

its a thick connective tissue membrane and serves as the periosteum of the inside of the skull

Question 3

Describe the two layers of dura mater:
outer periosteal layer
inner meningeal layer

Answer 3

outer periosteal layer- firmly attached to the skull, contains meningeal arteries

inner meningeal layer -in close contact with arachnoid and continuous with spinal dura

Question 4

Describe the cranial epidural space.

Answer 4

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)

Question 5

What are some pathological conditions associated with the cranial epidural space?

Answer 5

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)

Question 6

Describe the dural folds.

Answer 6

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

Question 7

Describe the dural venous sinuses.

Answer 7

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

Question 8

Describe the emissary veins.

Answer 8

they connect extracranial veins to the venous sinuses inside the cranium (to dural venous sinuses)

have an important route for spread of infection

Question 9

Describe the arachnoid:

subarachnoid space
arachnoid trabeculae
arachnoid granulations or villi

Answer 9

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)

Question 10

How does CSF enter the venous system?

Answer 10

through arachnoid villi

Question 11

Describe the arachnoid barrier.

Answer 11

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

Question 12

Describe pia mater.

Answer 12

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.

Question 13

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?

Answer 13

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

Question 14

What does pia covering the spinal cord give?

Answer 14

denticulate ligaments

filum terminale

Question 15

Describe the following hemorrages in meningeal spaces.
epidural bleeding
subarachnoid bleeding
subdural bleeding

Answer 15

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

Question 16

Describe the ventricles of the brain.

Answer 16

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)

Question 17

Describe the ventricles of brain including connections.

Answer 17

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

Question 18

Where is CSF secreted from?
What is the rate of formation?
What is the total volume of CSF/where is it?

Answer 18

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

Question 19

Where is the choroid plexus formed?

Answer 19

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

Question 20

What is choroid epithelium?

Answer 20

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

Question 21

Describe CSF circulation.

Answer 21

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

Question 22

What are subarachnoid cisterns?

Answer 22

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)

Question 23

Describe the functions of CSF.

Answer 23

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

Question 24

Compare CSF to serum.

Answer 24

very little protein present in CSF

less concentrations of glucose, Ca2, K+ ions in CSF

more concentrations of Na+, Cl-, and Mg2+ in CSF

Question 25

Describe hydrocephalus.

Answer 25

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)

Question 26

Describe the circumventricular organs.
What do they consist of?
What do they have a critical role in?

Answer 26

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

Question 27

Describe sensory circumventricular organs.

Answer 27

subfornical organ, vascular organ of the lamina terminalis, area postrema

Question 28

Describe secretory circumventricular organs.

Answer 28

median eminence of the hypothalamus, neurohypophysis, pineal gland

Question 29

Describe the CSF flow in the cerebellomedullary cistern.

Answer 29

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

Question 30

How is CSF absorbed?

Answer 30

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.