Meninges Flashcards
What are the three layers on the meninges?
Dura Mater
Arachnoid Mater
Pia Mater
What do the meninges cover?
the brain and spinal cord
What are the characteristics of the dura mater?
outermost, thickest, protective, impermeable
What are the 2 layers of the dura mater?
periosteal layer
meningeal layer
Where is the periosteal layer of the dura mater?
continuous with periosteum on the outside of the skull and cranial sutures
Where is the meningeal layer of the dura mater?
penetrates spaces in the cerebral hemisphere
The layers of the dura mater are closely united except for where?
at the venous sinuses
What are the venous sinuses?
large, low-pressure blood vessel return path for cerebral venous blood
What 2 partitions arise from the meningeal layer of the dura mater?
falx cerebri
tentorium cerebelli
What is the falx cerebri?
sickle-shaped fold separating cerebral hemispheres
Where is the tentorium cerebelli located?
between cerebellum and occipital lobes, separates the posterior cranial fossa from the cranial vault
How does the falx cerebri form the sagittal sinus?
superior convex border forms the superior sagittal sinus
inferior border houses the inferior sagittal sinus
How is the venous sinus formed?
Tentorium cerebelli arches upward along the median line to become continuous with the falx cerebri to form straight venous sinus
What is the function of the falx cerebri and the tentorium cerebelli?
restrict brain displacement associated with acceleration and deceleration
What is the epidural space?
tight space between the dura and the skull
What is the usual cause of an epidural hematoma/hemorrhage?
rupture of the middle meningeal artery during a head trauma
What are the symptoms of an epidural hematoma/hemorrhagic?
none initially (lucid interval)
within hours compresses the brain, increases ICP, herniation, and death unless surgery
What is the subdural space?
between the dura and loosely adherent arachnoid
What is the usual cause of a subdural hematoma/hemorrhage?
rupture of bridging veins (vulnerable to shear injury)
How can an acute subdural hematoma/hemorrhage occur?
with high-velocity impact
What is a chronic subdural hematoma/hemorrhage?
slow bleeding over weeks/months (brain accommodates)
vague symptoms - headache, cognitive impairment, unsteady gait
What are the 2 types of chronic subdural hematoma/hemorrhage?
isodense - 1-2 weeks
hypodense - 3-4 weeks (typically elderly due to natural atrophy that decreases the stability of the brain - bridging vein)
What are the characteristics of the arachnoid mater?
middle, impermeable
what are the trabeculae?
delicate threads connecting the arachnoid to the pia
What are the arachnoid granulations?
The site where CSF diffuses into venous sinuses
What is the subarachnoid space?
all arteries/veins send branches that penetrate the brain
filled with CSF
What are the characteristics of the pia mater?
innermost, delicate, permeable, resting on the brain surface
vascular membrane
How is the choroid plexus formed?
pia mater fuses with ependyma
What do arteries carry as they enter the parenchyma?
a sheath of pia
Are there pain receptors in the brain?
no
Where does head pain come from?
the trigeminal and first three cervical nerves innervating the meninges and vasculature
What does the trigeminal ganglion innervate?
dura above the tentorium
What do the first 3 cervical nerves innervate?
dura below the tentorium
Are the meninges densely innervated?
yes very
What is a migraine headache?
activation of trigeminal afferents that densely innervate meninges
What is the proposed mechanism for a migraine headache?
cortical spreading depression event - ions released activate pain receptors and vasodilators released (CGRP) further activate pain fibers *cycle
What is meningitis?
inflammation of meninges
What are meningiomas?
tumours in the meninges (usually benign)
How does a space-occupying lesion cause pain?
increased ICP and stretching of dura
What is a cluster headache?
‘lancinating’ or ‘boring’ periorbital pain
maybe the most painful condition known
What is a hangover?
multifactorial
a toxic effect on meninges
How do immune cells act in the meninges?
potentially decreased activation threshold for pain fibres
recruitment of immune cells to the injury site
some benefit, but a potential cost
