Describe the three layers of the meninges?
Dura mater: outer, tough, fibrous
Arachnoid mater: More delicate, fibrous
Pia mater: Thin layer
What are each of the three layers of the meninges connected to?
Dura mater: Attached to skull
Arachnoid mater: Lines inner of dura
Pia mater: Lines brain tissue
Describe the spaces created by each of the three meninges?
Epidural space: between dura and skull, potential space
Subdural space: between dura and arachnoid, potential space
Subarachnoid space: between arachnoid and pia, occupied by CSF
What can accumulate in the epidural space and when?
Blood collects here when meningeal artery ruptures
What occupies the subarachnoid space?
What can accumulate in the subdural space and when?
Blood collects here as a result of venous bleeding
List the dural petitions that project into the cranial cavity?
How far into the brain do the dural petitions project into the cranial cavity?
Not all the way; don't cut the brain into component parts
What is the purpose of the dural petitions?
Lodge into the brain partway and restrict rotatory displacement of the brain
Describe the shape of the falx cerebri?
Where does the falx cerebri lie?
In midline between the two hemispheres
Describe the attachments of the falx cerebri?
Attaches to inside of skull, immediately along line of sagittal suture Pegs to crista galli anteriorly Attaches posteriorly to internal aspect of occipital protuberance
Describe the shape of the tentorium cerebelli?
Crescent shaped, tented upwards
Where does the tentorium cerebelli lie?
Roofs over posterior cranial fossa, between cerebral hemispheres above and cerebllum below
Where does the falx cerebelli lie?
Between cerebellar hemispheres, beneatch tentorium cerebelli
Describe the orientation of the falx cerebelli?
Where does the diaphragma sellae lie?
Roofs over the sella turcica (pituitary) Lines internal aspect of sphenoid bone and goes across pit
How are the projections of the meninges formed?
Dura is a double layered structure; layers are usually stuck together Projections are formed when the inner layer separates from the outer layer, and meets with the inner layer from the other side
Where do the veins that drain the brain eventually end up?
Dural venous sinuses
Describe the structure of the dural venous sinuses?
Endothelial lined spaces Between inner and outer layer of dura when they come apart to form projections Walls are dura
Where do the dural venous sinuses lie in relation to the dural layers?
Between inner and outer layer of dura when they come apart to form projections
What do the dural venous sinuses receive?
Veins draining the brain
What do diploic veins drain?
The diploie (spongy bone)
What do emissary veins drain?
Why are scalp wounds treated with caution?
Any infection here can cause meningitis, as it is a very short trip to encephalitis, due to the venous communications
What are the major dural venous sinuses?
Superior sagittal sinus
Inferior sagittal sinus
What is the confluence of sinuses?
Point where the superior and straight sinuses meet
How is the straight sinus formed?
Where the inferior saggital sinus meets the Great cerebral vein
Where does the transverse sinus run?
In the root of the attachment of the tentorium cerebelli
What happens at the point of confluence?
Sometimes venous blood mixes, other times it doesn't
Where does the sigmoid sinus begin?
At the point where the tentorium meets the petrous part of the temporal bone
Transverse sinus becomes sigmoid sinus
Describe the course of the sigmoid sinus?
Snakes down from tentorium cerebelli in an s-shaped fashion towards the jugular foramen
What does the sigmoid sinus exit the jugular foramen as?
Internal jugular vein
Where does the cavernous sinus lie?
Either side of body of sphenoid
What is important about the cavernous sinus?
Important structures run through it to access their foraminae and exit the skull
How is the cavernous sinus different to the other dural venous sinuses?
It is not associated with any dural septa
Which is the most important meningeal artery?
Middle meningeal artery
What do the meningeal arteries supply?
Bone and meninges of skull
What is the middle meningeal artery a branch of?
How does the middle meningeal artery enter the skull?
What happens to the middle meningeal artery after it branches from the maxillary artery?
Divides into anterior and posterior divisions, which groove the bone
Where does the medial meningeal artery liein relation to the meninges?
In the extradural space
What is the outcome of a tear in the middle meningeal artery?
Why is an extradural haemorrhage due to a tear in the MMA so dangerous?
Pulsing blood from the artery
With every pulse, more blood gathers
No give in skull > pressure builds quickly
Where do the superior cerebral veins drain into?
Superior sagittal sinus
What is the most common cause of a subdural haemorrhage?
Tearing of veins at the point where they enter the superior sagittal sinus after a fall or head trauma
Why is a subdural haemorrhage due to a tear in the superior cerebral veins less dangerous than an extradural haemrrhage due to a tear in the MMA?
Much lower pressure blood