Embryology Meninges And Ventricular System Flashcards
Definition of meninges
Series of CT layers that surround the brain and spinal cord to protect them. We find 3 layers:
● Dura mater
● Arachnoid mater
● Pia mater
Origin of the meninges
Mesoderm and neural crest cells
(mesenchymal: NCC will form the mesenchyme that surrounds the spinal cord and brain as they develop, forming the meninges)
Dura mater developes from
Ectomeninx
Pia and arachnoid mater develope from
Endomeninx
Location dura mater
Encasing the brain and continuous with the same dural sac that encloses the spinal cord
What nerve is encased by the dura mater?
Optic nerve (it may become compressed when pressure increases in the brain, as neither dura mater nor the skull are distensible)
Artery that irrigates the meninges and gives branches in the cranium.
Middle meningeal artery
Course of the middle meningeal artery
In between bone and dura mater to supply meninges and bone; its branches make impressions on the calvaria
Difference cranial dura mater and spinal dura mater
Cranial dura has 2 layers and spinal dura has only 1
Layers of cranial dura
Outer periosteal layer: lines the cranium internally and become continuous with the periosteum at the foramen magnum.
Inner meningeal layer: continuous with the dural sac, creates venous sinuses (forms 2 layer reflections) and septa (formed by 2 layers)
Cells in each dural layer
Periosteal layer: a few fibroblasts and is mostly fibers + contains the blood vessels
Meningeal dura: also has abundant collagen and more fibroblasts.
Dural border cell layer / Plane of structural weakness
Additional subyacent layer to meningeal and periosteal ones which is slightly different (slightly different fibroblasts) and is in contact with meningeal layer.
Hemorrhage: blood leakes in this area —> dissects the 2 upper layers from arachnoid —> Subdural space can be formed = new pathological space (dura - arachnoid)
Dural reflections or septa
Falx cerebri
Falx cerebelli
Tentorium cerebeli
Diaphragm sellae
Falx cerebri: plane, attachment, location
Sagittal plane
Attached to Crista galli
Dura extends from anterior to posterior and partially separates both hemispheres
Falx cerebelli: plane, location
Sagittal plane
Separates the lobes of cerebellum
Tentorium cerebeli: plane, location, shape
Horizontal plane
Separates the brain and cerebellum
Triangular shape
Diaphragm sellae: location
Separates the infundibulum from the gland itself, covering the sella turcica
Venous sinuses definition
Space left as the meningeal dura invaginates to form the reflections, through which venous blood flows along, towards the jugular vein.
Dura mater vs brain parenchyma innervation
Dura mater is very innervated by sensory fiber (acute pain)
Brain parenchyma barely has any innervation (doesn’t hurt)
Cranial dura mater innervation
V1 (ophthalmic nerve branches: branches from ant ethmoidal nerves & tentorial nerve)
V2 and V3 meningeal branches
C2 and C3 branches
V1(branches of ophthalmic nerve) innervates…
Falx cerebri anteriorly (ant ethmoidal nerves branches).
Falx cerebri posteriorly (Tentorial nerve)
V2 and V3 meningeal branches innervates…
Middle cranial fossa region (neuronal bodies in trigeminal ganglion)
Branches of C2 and C3 innervates…
Inf post cranial fossa (penetrate via jugular canal, foramen magnum,… but belong to cervical level —> body in dorsal root ganglia)
Dural venous sinuses
Superior longitudinal/sagittal sinus (SSS)
Inferior longitudinal/sagittal sinus (ISS)
Straight venous sinus
Transverse venous sinus
Cavernous sinus
What drains into superior longitudinal/sagital sinus (SSS)?
Veins from falx cerebri
Veins from falx cerebri drain into
Superior longitudinal/sagittal (SSS) sinus
What drains into straight venous sinus?
Deep cerebral veins (Great cerebral vein or vena de galeno)
Where do the deep cerebral veins (Great cerebral vein or vena de galeno) drain into?
Straight venous sinus
Transverse venous sinus is continuos with
Internal jugular vein
Point where the dural venous sinuses join
Confluence of the sinuses
Layers of arachnoid mater
Central layer
Trabecular layer
Components of the central layer of arachnoid mater
Arachnoid barrier cells, lining and in contact with the dura border cells
Components of the trabecular layer of arachnoid mater
Trabeculae: modified fibroblasts w/ cell body at middle + expansions going —> arachnoid barrier cells & pia mater. However there are spaces between them = SUBARACHNOID SPACE
Subarachnoid space is filled with
CSF
What are the subarachnoid spaces?
Spaces between trabeculae from trabeculae layer of the arachnoid mater
Pia mater is found…
Surrounding the blood vessels in the subarachnoid space an accompaning the arteries to a certain distance within the parenchyma of the brain.
Epidural space: definition, location, components
Virtual space in the brain that appears only in pathological situations
Superficial to dura mater, continuos with periosteum, only in vertebral canal
Adipose tissue and venous plexuses
Subdural space: definition, characteristic
Virtual space, only present in pathological situations.
There is a plane of weakness where dura mater can detach from arachnoid = abnormal subdural space
Subarachnoid space: definition, location, characteristics
Functional space in the brain and spinal cord, surrounding it.
Between pia and arachnoid mater.
It forms expansions (cisterns) where the CSF accumulates
Epidural hematoma
Expands from suture to suture, has the image of a convex lens, presses against brain
Subdural hemorrhages
Borders much more regular
Subarachnoid hematoma
Extend within the brain parenchyma
Cerebral cisterns definition
Areas where there is more subarachnoid space, filled with CSF
Cerebral cisterns
Cisterna magna
Prepontine cistern
Cisterna magna location
Dorsal to the medulla oblongata, between it and cerebellum
Prepontine cistern location
Inferior to the pons
How is the brain accommodated in the cranium?
Suspended by the trabeculae of the arachnoid mater and floating within a chamber of fluid (CSF)
Ventricles formation
Neural tube has a central canal. As the brain expands, it forms vesicles, which still contain canals within them. As they expand, the spaces also expand with them, forming ventricles.
Initially brain vesicles
Prosencephalon
Mesencephalon
Rhombencephalon
Further divisions of prosencephalon, mesencephalon and rhombencephalon
Prosencephalon —> telencephalon (rostral most) + diencephalon
Mesencephalon —> =
Rhombencephalon —> Cerebellum and Pons + Myelencephalon (medulla oblongata)
Ventricles within each structure
- Telencephalon —> lateral ventricles
-Diencephalon —> 3rd ventricle - Mesencephalon —>Cerebral aqueduct (the space narrows so we don’t call it ventricle but canal)
- Pons —> 4th ventricle
- Medulla —> spinal canal (space narrows once again)
Telencephalic (lateral) ventricles development
They extend rostrally, sup & post, and then back inf to form a C shape. The lat ventricle will subdivide = 1st and 2nd ventricles.
Lateral ventricles are connected to the 3rd ventricle through…
Interventricular foramen
Interventricular foramen connects … to …
Lateral ventricles to the 3rd ventricle
3rd vesicle: location and description
Between the 2 diencephalic vesicles
Single, much flatter ventricle
Cerebral aqueduct (Silvian aqueduct) definition
Connection between 3rd and 4th ventricles
4th ventricle: development, location, dorsal view
It narrows again as it goes to form the spinal canal.
It’s continuous with the canal of the spinal cord.
(by removing the cerebellum) we can see 3 formaina (Magendie and Luschka) from which fluid passes from the ventricular system to the subarachnoid space
Foramina of Magendie and Luschka development
A medial elevation forms, called the medial diverticulum→ site for the foramen of Magendie (1, Medial)
2 lateral diverticulums form and rupture → site for foramen of Luschka (2, Lateral)
When do foramina of Magendie and Luschka form?
By the end of the 1st trimester of gestation
Foramina of Magendie and Luschka location
They perforate laterally the 4th ventricle
Foramina of Magendie and Luschka function
Through them, the CSF can pass to the subarachnoid space, brain and spinal cord. From the subarachnoid, the fluid will drain mostly into the superior longitudinal sinuses and from there, into general circulation.
(Subarachnoid→ Sinuses → int Jugular vein (gª circulation))
CSF composition vs blood plasma
CSF contains + Na+, Cl-, Mag2+
CSF contains - K+, Ca2+, glucose and proteins
Where is CSF produced?
CSF is produced by epithelial specializations, choroid epithelial cells of the choroid plexuses, which are located in the ventricles.
Location choroid plexus
Ant, inf and post area of the lateral ventricles
We also see them in the 4th ventricle
Formation of the choroid plexus
An artery penetrates into the the ependyma in the ventricles (ependymal cells line the ventricles). Specializations form as very thin threads, with a core that contains the vessels and lined by cells which are initially ependymal but undergo specialization, transforming into choroid cells.
Choroid cells function
Control the flow of ions and metabolites into the CSF by selective transport
Glomus choroideum definition
Enlarged area, posteriorly in lateral ventricles, where there will also be a larger cluster of choroid plexuses.
Drainage of the CSF
Through Arachnoid villi which pierce the meningeal dura and enter the venous sinuses. In this way, the CSF will be drained as it contacts venous blood.
The CSF is being constantly renewed.
Clinical implications of CSF drainage
If the flow is interrupted at any point of the system, there’ll be accumulation of fluid in the brain and an abnormal dilation of the ventricles.
Ex: obstructive hydrocephalus
