B3: Meninges & Ventricular System Flashcards
Features of Dura Mater
Two layers: periosteal (adhered to skull) and meningeal dura layers
Forms the Falx Cerebri (between hemispheres) and Tentorium Cerebelli (between cerebellum & occipital lobe)
Location & Function of Falx Cerebri and Tentorium Cerebelli
Falx Cerebri - attached anteriorly to ethmoid bone. Posteriorly attaches to tentorium cerebelli. Separates the 2 cerebral hemispheres.
TentoriumCerebelli - attached to ocipital bone, posteriorly. Separates occipital lobe and cerebellum. Separates brain into Supratentorial and Infratentorial Compartments*
Function: Stabilization of the brain within the skull
Which blood vessels supply the dura mater?
Middle Meningeal Artery - supplies largest area on lateral side. Its Anterior Branch lies just beneath the Pteryon (junction of fromtal, parietal, sphenoid and temporal bones)
Opthalmic Artery - Anterior regions
Occipital and Vertebral Arteries - Posteriorly
Innervation of Dura Mater
Supratentorial regions: CNV (Trigeminal)
Infratentorial Regions: Vagus (CNX), and cervical nerves C2 and C3
*Dura Mater is sensitive to pain
What are Dural Sinuses?
What are the main 5 ones, and where are they/what are they formed by?
Large veins englosed by dural layers
Recieve CSF via Arachnoid granulations
Superior Sagittal Sinus (superior edge of falx cerebri)
Inferior Sagittal Sinus (inferior free edge of falx cerebri)
Straight Sinus (line of attachment between falx cerebri and tentorium cerebelli) Transverse sinus (along posterior line of attachment of tentorium cerebelli) Occipital Sinus (edge of falx cerebri)
Describe flow through the dural sinuses
General flow is Front - to -back:
The superior and Inferior Sagittal Sinuses, and Straight Sinus, branch posteriorly, to the Confluence of Sinuses.
From the confluence, drainage occurs through the Transverse sinuses (i.e. along tentorium cerebelli), then to the sigmois sinuses which curve inferiorly…
Before draining into the Internal Jugular Veins (L and R)
*(Note the petrosal sinuses that drain the cavernous sinuses. Superior petrosal sinus drains from cav sinus to transverse sinus; inferior petrosal sinus drains from sav sinus to IJV)
Where does the IJV exit the skull, which important structures accompany it?
Exits via jugular foramen -> foramen between the Petrous Temporal (anteriorly) and Occipital (posteriorly) bones.
Accompanied by CNIX, X and XI
Structure and Function of Arachnoid Mater
Barrier Function: comprised of tight jusnctions between arachnoid cells
Arachnoid Trabeculae (collagenous CT) extend through subarachnoid space to the Pia Mater (anchoring function)
Contains arteries and veins on brain’s surface befre they penetrate the pia mater to enter the brain parenchyma
Most frequent cause of serious neurological disorders?
Cerebrovascular Accidents
Causes of CVAs?
hint: 2 major categories, list causes for both
Vascular occlusion: thrombosis, embolism, -> hypoxia
= ischaemic stroke
or Haemorrhage: (harmorrhagic stroke): subarachnoid (i.e. circle of willis), intracerebral, intraparenchymal (i.e. of penetrating vessels), epidural or subdural
Features of Subdural Haemorrhage
Concave surface on CT
-> appears concave because, as blood is contained between the dura and arachnoid -> arachnoid is softer, allowing more spread ot haemorrhagic blood -> thus takes on concave appearance
Usually caused by tear in vein entering Dural Sinus (weak point due to sheering force)
Often consequence of blow to head
Can occur in shaken baby syndrome
Why are Older people particularly susceptible to subdural haemorrhages
Older age -> brain atrophy
Thus, less support for veins entering venous sinuses -> more potential for tearing due to sheering force
Also more prone to falls*
Features or Epidural (extradural) Haemorrhage
Convex Surface on CT Scan
-> because dura very tough, it can contain the blood in one place for a long time, giving rise to a convex shape against the skull
Usually due to ruptured Meningeal Artery
May be consequence of blow to the head
Features of Subarachnoid Haemorrhage
Usually caused by aneurysms (e.g. circel of willis - especially at bifurcations)
Blood mixes with CSF in this space
Post rupture, blood spreads through cisterns and fissures
Describe events of herniation secondary to epidural haemorrhage & hematoma
Hematoma, if large enough, will compress that cerebral hemisphere.
Can push the Cingulate Gyrus beneath the Falx Cerebri, over to the contralateral side.
Herniation due to Mass (haematoma, tumour, etc.) in Supratentorial region
Possible consequences?
Can force the uncus through the Tentorial Notch, into the Infratentorial Compartment
Compression of midbrain -> implications for important cranial nuclei (e.g. nuclei of III and IV) -> thus can present with functional defecits to eye movements
Herniation due to haematoma/tumour mass in infratentorial compartment
Tonsil (of vermis) overlies the foramen magnum. Can be pushed through.
This compresses the medulla (containing cardio-respiratory centres)
Life of death emergency
List the differences between Spinal and Cranial Meninges
Dura Mater:
C: Double layer. Anchored to inner calvarial surface of skull.
SC: Single layer. Suspended in vertebral canal.
Epidural Space:
C: Potential Space
SC: REal space, between Dura and Vertebral Periosteum
Arachnoid:
C & SC: Same. Attached to inner surface of Dura Mater
Pia:
C: Attached to CNS surface
SC: Attached to CNS surface but also modified to give off dentate ligaments (tooth-like projections) that help to anchor the SC to surrounding dura and bones
What gives rise to the ventricles?
Neural Canal of ventricles and central canal of SC
Features of CSF
Simialr to plasma, but low in: Protein, Potassium and Calcium
Cushions brain from physical trauma agiainst skull
Effectively reduces weight of the brain
Blood Supply to the Choroid Plexuses:
Lateral Ventricle Choroid Plexus:
Anterior Choroidal Artery (from Internal Carotid)
Posterior Choroidal Artery (from Posterior Cerebral Artery)
4th Ventricle Choroid Plexus:
Anterior Inferior Cerebral Artery
Posterior Inferior Cerebral Artery
Describe endothelium of choroid plexus
And describe the choroid epithelium
Choroid Endothelium = Fenestrated Ependymal Cells between the ventricle and the CNS. Scattered Pial Cells and Collagen
Choroid Epithelium = Layer of fenestrated ependymal cells, a layer of pial cells, then the choroidal capillary wall.
Tight junctions regulate transport of Glucose and Ions into the ventricle
Describe flow of CSF through ventricles
CSF made in choroid plexuses of ventricles*
Circulates through lateral ventricles -> Interventricular Foramen -> 3rd Ventricle -> Cerebral Aperture -> 4th Ventricle -> (Out through medial and lateral apertures to cranial SAS_->
Further flow from 4th ventricle to Central canal of spinal cord -> lumbar cistern (absorption via arachnoid villi down there)
Location of major subarachnoid cisterns
Superior Cistern (overlies the colliculi; dorsal to midbrain)
Interpeduncular Cistern (cetween the cerebral peduncles, anterior to midbrain)
Pontine Cistern (anterior to basal pons)
Cisterna Magna (inferior to cerebellum)
Lumbar Cistern (distal end of SC)
What is hydrocephalus and common causes of it?
Most common cause?
Too much CSF, eventuating in enlargement of the affected ventricle(s), due to:
Blockage of CSF circulation through ventricles ***
OR
Excess production of CSF
OR
Deficiency in CSF reabsorption
Most common causes and sites of CSF obstruction
Tumour occluding interventricular foramen
Tumour of pineal gland compressing cerebral aqueduct
