L2: BRAIN, MENINGES, DURAL VENOUS SINUSES & BLOOD SUPPLY TO THE BRAIN
Parts of the brain- cerebrum, cerebellum, and brainstem
Nervous tissue= neuron + neuroglia
Gray mater= cell body + neuroglia + blood vessels
White mater= axon + neuroglia + blood vessels
MENINGES – connective tissue membranes that surround the brain (cranial m) and spinal cord (spinal m)
Functions- cover and protect CNS, protect BV, contain CSF in subarachnoid space
3 layers of meninges:
I. Dura mater ( outermost layer )
- Tough and thick membrane
- Outer periosteal layer: firmly attached to the skull
- Inner meningeal layer: close contact with arachnoid
mater & continues with spinal dura mater
II. Arachnoid mater ( middle layer )
- Thin, avascular membrane
- Does not enter the grooves/fissures of the brain
III. Pia mater ( innermost layer )
- Thin, closely invest the surface of the brain
- Follows the shape of the brain and enters it grooves &
fissures.
Feature Brain DM Spinal cord DM
Layers Single layer
Double-layer (periosteal and meningeal)
Attachment Attached to the inner skull, forms folds Attached to the vertebral canal, no folds
Function Divides the brain into diff compartments Protects the spinal cord
Epidural space Potential space True space, contains fat and veins
Subdural space Potential space between dura and Potential space between dura and arachnoid
arachnoid
Blood supply Middle meningeal artery Small branches from vertebral arteries
Venous drainage Dural venous sinuses Venous plexuses
Cranial dural septa
the dural partitions project into the cranial cavity
Functions: divide the cranial cavity into comp, forms partition btwn parts of brain, support
, i. Falx ceribri
- Sickle-shaped that dips into longitudinal fissure
- Separates 2 cerebral hemispheres
- Ant: crista galli & frontal crest of frontal bone, post: internal
occipital protruberance
- Content: sup & inf sagittal sinus
ii. Tentorium cerebelli
- A horizontal projection of meningeal DM
- Covers & separates the cerebral hemispheres from
the cerebellum in posterior cranial fossa
- Post: occipital bone, lat: sup border of temporal
bone, ant: ant & post clinoid p.
- Contents: sup petrosal sinuses, straight sinus,
tranverse sinuses
iii. Falx cerebelli
- Small sickle-shaped midline projection of meningeal DM in post
cranial fossa
- Separates the 2 cerebellar hemispheres
- Base: inferior surface of TC, apex: foramen magnum, post:
occipital bone
- Content: occipital sinus
iv. Diaphragma sellae
- Small horizontal shelf of meningeal DM
- Covers the hypophysial fossa in sella turcica of sphenoid bone
- Ant: tuberculum sellae, post: dorsum sellae, lat: continues with DM
Dural blood supply
a.
a. Anterior cranial fossa: ant meningeal branches of ant & post ethmoidal A
b. Middle cranial fossa: middle and accesory meningeal branch of maxillary A,
branches of ICA, recurrent branch of lacrimal A
c. Posterior cranial fossa: post meningeal branches of vertebral & ascending pharyngeal A
Dural venous drainage – accompanies meningeal arteries
Dural nerve supply
a. Trigeminal nerve: supra tentorial part
b. First 3 cervical spinal & vagus nerve: infra tentorial part
, Arteries of the Brain & Spinal cord
Brain receives arterial supply from vertebral & internal carotid arteries
These two arteries form the Circle of Willis
Vertebral artery
- Arises from 1st part of each subclavian A, passes transverse foramina of upper 6CV
- Enters cranial cavity through foramen magnum & gives off a small meningeal branch
- Gives rise to 3 more branches b4 joining with its companion vessel forming basilar A
Internal carotid artery
- 2 ICA arises as a terminal branch of common carotid arteries
- Proceed to the base of the skull and enter the carotid canal to enter cranial cavity
- Gives off branches like ophthalmic A, middle & ant cerebral A, post communicating A
Circle of Willis
- Pentagon-shaped circle
- Located at the inferior surface of the brain
( interpeduncular fossa )
- Imp anastomosis of 4 arteries ( 2VA & 2 ICA )
- Functions: equalize the blood flow to the
different parts of the brain
- Branches: ant communicating & cerebral A, ICA,
post communicating & cerebral A
Blood supply of Brain
a. Anterior cerebral A: medial & superior surface of brain & frontal pole
b. Middle cerebral A: lateral surface of brain & temporal pole
c. Posterior cerebral A: inferior surface of brain & occipital pole
- Special features: cortical & central systems supply the entire cerebrum
- Cortical system: supply the gray matter, derived from ant, post, mid cerebral A
- Central system: supply diencephalon & basal nuclei, derived from the circle of Willis
Venous drainage of Brain
- Small venous channels - larger cerebral veins – cerebellar veins – veins draining
brainstem – empties into dural venous sinuses
Dural venous sinuses – endothelial lined spaces between the outer periosteal and inner meningeal layers
of DM, leading to IJV
Superficial & deep veins – dural venous sinuses – internal jugular veins
Characteristics: lined by epithelium, valveless, devoid of muscular coat, absorb the CSF
Collect blood from the brain, meninges, skull bones, internal ear, and orbit
Veins emptying into DVS:
a. Diploic veins: run between internal & external tables of compact bone
Parts of the brain- cerebrum, cerebellum, and brainstem
Nervous tissue= neuron + neuroglia
Gray mater= cell body + neuroglia + blood vessels
White mater= axon + neuroglia + blood vessels
MENINGES – connective tissue membranes that surround the brain (cranial m) and spinal cord (spinal m)
Functions- cover and protect CNS, protect BV, contain CSF in subarachnoid space
3 layers of meninges:
I. Dura mater ( outermost layer )
- Tough and thick membrane
- Outer periosteal layer: firmly attached to the skull
- Inner meningeal layer: close contact with arachnoid
mater & continues with spinal dura mater
II. Arachnoid mater ( middle layer )
- Thin, avascular membrane
- Does not enter the grooves/fissures of the brain
III. Pia mater ( innermost layer )
- Thin, closely invest the surface of the brain
- Follows the shape of the brain and enters it grooves &
fissures.
Feature Brain DM Spinal cord DM
Layers Single layer
Double-layer (periosteal and meningeal)
Attachment Attached to the inner skull, forms folds Attached to the vertebral canal, no folds
Function Divides the brain into diff compartments Protects the spinal cord
Epidural space Potential space True space, contains fat and veins
Subdural space Potential space between dura and Potential space between dura and arachnoid
arachnoid
Blood supply Middle meningeal artery Small branches from vertebral arteries
Venous drainage Dural venous sinuses Venous plexuses
Cranial dural septa
the dural partitions project into the cranial cavity
Functions: divide the cranial cavity into comp, forms partition btwn parts of brain, support
, i. Falx ceribri
- Sickle-shaped that dips into longitudinal fissure
- Separates 2 cerebral hemispheres
- Ant: crista galli & frontal crest of frontal bone, post: internal
occipital protruberance
- Content: sup & inf sagittal sinus
ii. Tentorium cerebelli
- A horizontal projection of meningeal DM
- Covers & separates the cerebral hemispheres from
the cerebellum in posterior cranial fossa
- Post: occipital bone, lat: sup border of temporal
bone, ant: ant & post clinoid p.
- Contents: sup petrosal sinuses, straight sinus,
tranverse sinuses
iii. Falx cerebelli
- Small sickle-shaped midline projection of meningeal DM in post
cranial fossa
- Separates the 2 cerebellar hemispheres
- Base: inferior surface of TC, apex: foramen magnum, post:
occipital bone
- Content: occipital sinus
iv. Diaphragma sellae
- Small horizontal shelf of meningeal DM
- Covers the hypophysial fossa in sella turcica of sphenoid bone
- Ant: tuberculum sellae, post: dorsum sellae, lat: continues with DM
Dural blood supply
a.
a. Anterior cranial fossa: ant meningeal branches of ant & post ethmoidal A
b. Middle cranial fossa: middle and accesory meningeal branch of maxillary A,
branches of ICA, recurrent branch of lacrimal A
c. Posterior cranial fossa: post meningeal branches of vertebral & ascending pharyngeal A
Dural venous drainage – accompanies meningeal arteries
Dural nerve supply
a. Trigeminal nerve: supra tentorial part
b. First 3 cervical spinal & vagus nerve: infra tentorial part
, Arteries of the Brain & Spinal cord
Brain receives arterial supply from vertebral & internal carotid arteries
These two arteries form the Circle of Willis
Vertebral artery
- Arises from 1st part of each subclavian A, passes transverse foramina of upper 6CV
- Enters cranial cavity through foramen magnum & gives off a small meningeal branch
- Gives rise to 3 more branches b4 joining with its companion vessel forming basilar A
Internal carotid artery
- 2 ICA arises as a terminal branch of common carotid arteries
- Proceed to the base of the skull and enter the carotid canal to enter cranial cavity
- Gives off branches like ophthalmic A, middle & ant cerebral A, post communicating A
Circle of Willis
- Pentagon-shaped circle
- Located at the inferior surface of the brain
( interpeduncular fossa )
- Imp anastomosis of 4 arteries ( 2VA & 2 ICA )
- Functions: equalize the blood flow to the
different parts of the brain
- Branches: ant communicating & cerebral A, ICA,
post communicating & cerebral A
Blood supply of Brain
a. Anterior cerebral A: medial & superior surface of brain & frontal pole
b. Middle cerebral A: lateral surface of brain & temporal pole
c. Posterior cerebral A: inferior surface of brain & occipital pole
- Special features: cortical & central systems supply the entire cerebrum
- Cortical system: supply the gray matter, derived from ant, post, mid cerebral A
- Central system: supply diencephalon & basal nuclei, derived from the circle of Willis
Venous drainage of Brain
- Small venous channels - larger cerebral veins – cerebellar veins – veins draining
brainstem – empties into dural venous sinuses
Dural venous sinuses – endothelial lined spaces between the outer periosteal and inner meningeal layers
of DM, leading to IJV
Superficial & deep veins – dural venous sinuses – internal jugular veins
Characteristics: lined by epithelium, valveless, devoid of muscular coat, absorb the CSF
Collect blood from the brain, meninges, skull bones, internal ear, and orbit
Veins emptying into DVS:
a. Diploic veins: run between internal & external tables of compact bone
