Transcript Layers and blood supply of the brain

THE BRAIN- meninges, blood
supply and venous drainage.
By Francesca Pickwell
The Brain
• The different parts of the brain are the cerebrum,
diencephalon, brainstem and cerebellum.
• The cerebrum is divided into left and right
cerebral hemispheres by the longitudinal fissure
• Each cerebral hemisphere is divided into 4 lobes:
FRONTAL, PARIETAL, TEMPORAL, OCCIPITAL.
• Functions- intelligence, personality, motor
function, planning, touch sensation,
interpretation of sensory impulses.
The brain
The brain
Parietal lobe
Frontal
lobe
Temporal
lobe
Occipital
lobe
The brain
The brain
Corpus
callosum
Thalamus
Hypothalamus
Cerebellum
MIDBRAIN
PONS
MEDULLA OBLONGATA
Blood supply
• The brain receives its blood supply from the:
• INTERNAL CAROTID arteries - branches of the
common carotid artery. Enter skull through the
carotid canals
• VERTEBRAL- branches of the subclavian arteries.
Pass through transverse foramina of cervical
vertebrae and enter skull through foramen
magnum.
• The arteries give off branches to form the CIRCLE
OF WILLIS
CIRCLE OF WILLIS
Meninges
• The meninges are protective layers that surround
the brain
• There are 3 of them:
-DURA MATA- tough, thick outer layer
-ARACHNOID MATA- thin, delicate intermediate
layer
-PIA MATA- inner layer adhered to brain surface
Area between the pia mata and arachnoid mata is
the subarachnoid space. This contains CSF.
Dura Mata
2 layers:
PERIOSTEAL layer:
outer layer attached to
internal surface of skull
MENINGEAL layer:
closely related to the
arachnoid mata.
In certain places, the
inner meningeal layer
separates from the
outer periosteal layer
to form DURAL
PARTITIONS…
Dural Partitions
The dural partitions formed by the dural reflections
divide the cranial cavity into different parts:
1.FALX CEREBRI- divides
left and right hemispheres
of brain.
Anterior attachments:
frontal crest of frontal
bone and crista galli
Posterior attachments:
internal occipital
protuberance
Dural partitions
2. TENTORIUM CEREBELLI- Covers
the cerebellum separating it from
the occipital lobe of the brain.
Anterior attachments: clinoid
processes of the sphenoid bone
Lateral attachments: pertrous parts
of temporal bones
Posterior attachments: internal
surface of occipital bone
Tentorium cerebelli divides cranial
cavity into infratentorial and
supratentorial parts.
Tentorial notch: gap in the
tentorium cerebelli which the
midbrain passes through.
Dural partitions
3. FALX CEREBELLI-divides cerebellum in half
4. DIAPHRAGMA SELLAE- covers posterior gland
in hypophysial fossa.
Dural venous sinuses
• Dural venous sinuses are
endothelial lined spaces
between the two layers of
dura mata
• Important role in VENOUS
DRAINAGE
• The large veins of the
brain empty into these
sinuses
• The sinuses empty into
the internal jugular vein
Dural venous sinuses
• Superior saggital sinuslies in the superior
border of the falx
cerebri. Terminates
posteriorly at at the
confluence of sinuses.
Receives the superior
cerebral veins.
• Inferior saggital sinuslies in the inferior border
of the falx cerebri. Joins
with the great cerebral
vein to form the straight
sinus.
Dural venous sinuses
• Straight sinus- formed by
union of great cerebral
vein and inferior saggital
sinus. Empties into the
confluence of sinuses.
• Left and right transverse
sinuses- receive venous
blood from confluence of
sinuses on either side.
• Sigmoid sinuses- S shaped
continuations of left and
right sinuses. Drain into
internal jugular vein
Dural venous sinuses
• Cavernous sinuses- lie either
side of the side of sella
turcica. Drain into the
superior and inferior
petrosal sinuses.
Clinically important because of
structures that pass through or
alongside them.
• Structures passing through:
-internal carotid artery
-abducent nerve
Structures in lateral wall:
ophthalmic nerve, maxillary
nerve, oculomotor nerve,
trochlea nerve
Quick overview- sinuses
Quick overview- sinuses
CSF flow
• Ventricular system: two lateral ventricles,
3rd ventricle and 4th ventricle
• CSF produced in the choroid plexus of the
third and forth ventricles
• CSF drains from the forth ventricle into the
subarachnoid space
• CSF is absorbed into the venous system by
arachnoid granulations.
• Main source of venous drainage: superior
saggital sinus
Dura mata- blood supply & nervous
innervation
• BLOOD SUPPLY:
• Anterior meningeal artery – supplies anterior
cranial fossa
• Middle meningeal artery- supplies the middle
cranial fossa.
• Posterior cranial artery- supplies posterior cranial
fossa.
• NERVOUS INNERVATION:
• Trigeminal nerve!!! (Clinical relevance: dural
origin of headaches.)
INTRACRANIAL HAEMORRHAGES
• Extradural haemorrhage- arterial in origin. Blood from
damaged middle meningeal artery accumulates
between skull and dura. Get brief concussion, lucid
interval then go into coma!!!
• Subdural haemorrhage- venous in origin. Blood from
venous sinuses collects between dura and arachnoid
layers.
• Subarachnoid haemorrhage- arterial in origin. Can be
caused by rupture of an aneurysm OR by severe head
trauma. Blood collects in subarachnoid space which
results in meningeal irritation and loss of
consciousness.
Questions
• The vertebral arteries branch off the subclavian arteries
T
• The middle cerebral artery connects the two anterior cerebral arteries
F
• The inner layer of the dura is called periosteal and the outer layer is
called meningeal
F
• The tentorial notch is a gap in the tentorium cerebelli through which the
midbrain passes
T
• The inferior saggital sinus joins with the great cerebral vein to from the
straight sinus
T
• The two structures that pass through the cavernous sinus are the
abducent nerve and opthalmic nerve
F
• Nervous innervation to the dura is via the trigeminal nerve
T
• Subdural haemorrhages are venous in origin
F