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The Brain and the Meninges
Meninges: the layers of membranes surrounding the brain and spinal cord
- Cranial Dura Mater: tough outer layer
o
o
Periosteal layer: firmly attached to the skull, serves as the
periosteum of the cranial cavity, contains the meningeal
arteries
Meningeal layer: in close contact with the arachnoid mater
and is continuous with the spinal dura through the foramen
magnum
 These layers separate to form special structures:
o Dural Partitions: falx cerebri, tentorium
cerebri, falx cerebelli, and the diaphragma
sellae
o Intracranial Venous Structures
-Arterial Supply to the Dura Mater: travels in the outer periosteal layer of the dura
-Anterior Meningeal (branches of ethmoid artery), Middle Meningeal (branch of maxillary
artery), Accessory Meningeal (branch of maxillary artery), and Posterior Meningeal Arteries
(branch of ascending pharyngeal artery), meningeal branches from occipital and vertebral
arteries
-Innervation to the Dura Mater: all 3 branches of Trigeminal Nerve [V] ([V1] does floor, posterior
and anterior falx cerebri and also tentorium cerebelli; [V2] does medial middle cranial fossa; and
[V3] does lateral middle cranial fossa), Vagus Nerve [X], and the 1st, 2nd, and sometimes 3rd cervical
nerves (posterior cranial fossa)
-Arachnoid Mater: thin, avascular membrane that lines (not adherent to) the inner surface of dura.
The arachnoid does not enter the grooves or fissures of the brain except for the longitudinal fissure
between the two cerebral hemispheres.
-Pia Mater: thin, delicate layer that closely invests the surface of the brain and enters the grooves and
fissure on its surface.
-Meningeal Spaces:
-Extradural Space: the potential space between the dura mater and the cranial bones. Can
become a real space following trauma to the brain, causing blood/fluid to collect in this space
(causing either extradural or subdural hematomas)
-Subarachnoid Space: the real space between the arachnoid mater and the pia mater which
contains CSF. The CSF returns to the venous system through arachnoid villi (arachnoid
granulations that project into the superior sagittal sinus and the lateral lacunae). In certain
areas the subarachnoid space expands into larger areas called cisterns.
The Brain: the brain can be divided into 5 parts during development
1) Telencephalon: becomes the cerebral hemispheres (made up of frontal, parietal, temporal, and
occipital lobes)
2) Diencephalon: consists of the thalamus, hypothalamus, and related structures
3) Mesencephalon: the “midbrain”, the first part of the adult brainstem
4) Metencephalon: gives rise to the cerebellum and the pons
5) Myelencephalon: the medulla oblongata
Blood Supply to the Brain:

Arterial Supply:
 Vertebral Arteries: give off meningeal, anterior
spinal, posterior spinal, and posterior inferior
cerebellar branches before uniting with its twin to
form the basilar artery
 Internal Carotid Arteries: give off ophthalmic,
posterior communicating, middle cerebral, and
anterior cerebral branches
 Cerebral Arterial Circle: circle of Willis is formed at
the base of the brain by the interconnecting
vertebrobasilar and internal carotid system of
arteries (anterior communicating artery connects
the right and left anterior cerebral arteries, and 2
posterior communicating arteries connecting the
internal carotid artery with the posterior cerebral
artery)
 Basilar Artery: created by union of vertebral
arteries, gives off anterior inferior cerebellar,
pontine, superior cerebellar, and posterior cerebral
arteries (terminal) branches
-Venous Drainage: networks of small venous channels lead to larger cerebral, cerebellar, and brainstem
veins and diploic and emissary veins which empty into dural sinuses.
-Dural Sinuses: superior sagittal, inferior sagittal,
straight, occipital, confluence of sinuses, right and left
transverse, right and left sigmoid, cavernous (paired),
intercavernous, sphenoparietal (paired), superior and
inferior petrosals (paired), basilar
-Cavernous Sinuses: the internal carotid artery and
Abducent nerve [VI] pass through each cavernous sinus,
and the Oculomotor nerve [III], Trochlear nerve [IV],
Ophthalmic nerve [V1], and Maxillary nerve [V2] are
located in the lateral wall of each cavernous sinus
-The intercavernous sinuses connect the 2 cavernous sinuses on the anterior and posterior sides of the
pituitary stalk