Meninges and Blood Supply of the Brain pdf - Neuroanatomy

Lecture

Meninges and Blood

supply of Brain

Coronal section of the upper part of the head showing the layers of the scalp,

sagittal suture of the skull, falx cerebri, venous sinuses, arachnoid

granulations, emissary veins, and relation of the cerebral blood vessels to

the subarachnoid space

The Meninges of the Brain

Dura Mater

as two layers:

the endosteal layer

: is nothing more than the periosteum covering the

inner surface of the skull bones

At the foramen magnum, it does not become continuous with the Dura

mater of the spinal cord.

Around the margins of all the foramina in the skull, it becomes continuous

with the periosteum on the outside of the skull bones.

At the sutures, it is continuous with the sutural ligaments

It is most strongly adherent to the bones over the base of the skull

meningeal layer

a dense, strong fibrous membrane covering the brain and is continuous

through the foramen magnum with the Dura mater of the spinal cord.

It provides tubular sheaths for the cranial nerves as they pass through the

foramina in the skull. Then the sheaths fuse with the epineurium of the

nerves outside the skull

Four septa derived from meningeal layer extended to intracranial are dividing

it into freely communicating spaces that lodge the subdivisions of the brain

falx cerebri is a sickle-shaped fold of Dura mater that lies in the midline
between the two cerebral hemispheres

it has a narrow ant. end attached to the internal frontal crest and the crista

galli and a broad posterior part blends in the midline with the upper
surface of the tentorium cerebelli

superior sagittal sinus runs in its upper fixed margin, the inferior sagittal

sinus runs in its lower concave free margin, and the straight sinus runs
along its attachment to the tentorium cerebelli

tentorium cerebelli is a crescent-shaped fold of Dura mater that roofs over
the posterior cranial fossa

tentorial notch is an ant opening for the passage of the midbrain with an

inner free border and an outer attached or fixed border.

The fixed border is attached to the posterior clinoid processes, the superior

borders of the petrous bones, and the margins of the grooves for the
transverse sinuses on the occipital bone

The falx cerebri and the falx cerebelli are attached to the upper and lower

surfaces of the tentorium, respectively

The falx cerebelli, a small, sickle-shaped fold of Dura mater attached to the

internal occipital crest, projects forward between the two cerebellar
hemispheres. Its posterior fixed margin contains the occipital sinus

diaphragma sellae is a small, circular fold of Dura mater that forms the roof

for the sella turcica

A small opening in its center allows passage of the stalk of the hypophysis

cerebri

Interior of the skull showing the Dura mater and its contained

venous sinuses

Dural Nerve Supply

Branches of the trigeminal, vagus, and the first three cervical spinal

nerves and branches from the sympathetic trunk pass to the Dura

neuron endings sensitive to stretching, which produce the sensation of

headache

Dural Arterial Supply

Branches of internal carotid, maxillary, ascending pharyngeal,

occipital, and vertebral arteries

Clinically middle meningeal artery is the most important it arises

from the maxillary artery in the infratemporal fossa entering the

cranial cavity through the foramen spinosum and then lies between

the meningeal and endosteal layers of Dura, giving the ant and post

branches

Dural Venous Sinuses

The venous sinuses of the cranial cavity are situated between the layers of the

Dura mater

Their main function is to receive blood from the brain through the cerebral

veins and the cerebrospinal fluid from the subarachnoid space through the
arachnoid villi

blood in the Dural sinuses drains into the internal jugular veins in the neck
Emissary veins, which are also valve less, connect the Dural venous sinuses

with the diploic veins of the skull and with the veins of the scalp

Arachnoid Mater

a delicate, impermeable membrane covering the brain and lying between the

pia mater internally and the Dura mater externally.

It is separated from the Dura by the subdural space, filled by a film of fluid.
separated from the pia by the subarachnoid space, which is filled with

cerebrospinal fluid

in certain situations, the arachnoid and pia are widely separated to form the

subarachnoid cisternae (cisterna cerebellomedullaris and The cisterna
interpeduncularis)

Pia Mater

a vascular membrane covered by flattened mesothelial cells. It closely invests

the brain, covering the gyri and descending into the deepest sulci

The pia mater forms the tela choroidea of the roof of the third and fourth

ventricles of the brain, and it fuses with the ependyma to form the choroid
plexuses in the lateral, third, and fourth ventricles of the brain

Falx cerebri and the tentorium cerebelli. Note the continuity between the

meningeal layer of Dura mater within the skull and the Dura mater of the spinal

cord at the foramen magnum

Right side of the head

showing the relation of
the middle meningeal
vessels to the layers of
the Dura mater and the
skull

Sagittal section of the eyeball showing the attachment of the

meninges to the sclera. Note the extension of the subarachnoid

space around the optic nerve to the eyeball

Diagrammatic representation of an epidural hemorrhage and a subdural

hemorrhage

Blood Supply of the Brain

Arteries of the Brain

The brain is supplied by the two internal carotid and the two vertebral

arteries.

The four arteries lie within the subarachnoid space, and their branches

anastomose on the inferior surface of the brain to form the circle of Willis

Internal Carotid Artery

Originate by the bifurcation of the common carotid artery, possesses a localized

dilatation, called the carotid sinus, enter the skull through the carotid canal
of the temporal bone

then runs forward through the cavernous sinus
by perforating the Dura mater and the arachnoid mater it reach the region of

the medial end of the lateral cerebral sulcus. Here, it divides into the
anterior and middle cerebral arteries

Origin and courses of the internal carotid and vertebral

arteries as they ascend the neck to enter the skull

Branches of the Cerebral Portion

The ophthalmic artery:
It enters the orbit through the optic canal
supply the frontal area of the scalp, the ethmoid and frontal sinuses, and the

dorsum of the nose

The posterior communicating artery:
forming part of the circle of Willis
The choroidal artery

The anterior cerebral artery:
it is joined to the anterior cerebral artery of the opposite side by the anterior

communicating artery

The middle cerebral artery:
Largest branch, Cortical branches supply the entire lateral surface of the

hemisphere, except for the narrow strip supplied by the anterior cerebral

artery, the occipital pole, and the inferolateral surface of the hemisphere,

which are supplied by the posterior cerebral artery

Vertebral Artery

a branch of the first part of the subclavian artery
passing through the foramina in the transverse processes of the upper six

cervical vertebrae

It enters the skull through the foramen magnum and pierces the Dura mater

and arachnoid to enter the subarachnoid space

At the lower border of the pons, it joins the vessel of the opposite side to form

the basilar artery

Branches of the Cranial Portion of Vertebral Artery

The meningeal branches

The posterior spinal artery

The anterior spinal artery

The posterior inferior cerebellar artery

The medullary arteries

Basilar Artery

formed by the union of the two vertebral arteries
ascends in a groove on the anterior surface of the pons
At the upper border of the pons, it divides into the two posterior cerebral

arteries

Branches

The pontine arteries supply the pons

The labyrinthine accompanies the facial and the vestibulocochlear nerves
into the internal acoustic meatus and supplies the internal ear

The anterior inferior cerebellar artery.

The superior cerebellar artery

The posterior cerebral artery form the cortical branches, central branches
and choroidal branch

Circle of Willis

It is formed by the anastomosis between the two internal carotid arteries and

the two vertebral arteries

lies in the interpeduncular fossa at the base of the brain

The anterior communicating, anterior cerebral, internal carotid, posterior

communicating, posterior cerebral, and basilar arteries all contribute to the
circle

The circle of Willis allows blood that enters by either internal carotid or

vertebral arteries to be distributed to any part of both cerebral hemispheres

Arteries of the inferior surface of the brain. Note the formation of the
circle of Willis

Veins of the Brain

have no muscular tissue in their very thin walls, and they possess no valves
They drain into the cranial venous sinuses

External Cerebral Veins:

superior cerebral veins

superficial middle cerebral vein

deep middle cerebral vein joined by the anterior cerebral and striate veins
to form the basal vein which in turn joins the great cerebral vein

Internal Cerebral Veins

two internal cerebral veins formed by the union of the thalamostriate vein and

the choroid vein they unite beneath the splenium of the corpus callosum to
form the great cerebral vein, which empties into the straight sinus