Meninges-Three layered membranes that surround the brain tissue. CSF functions as well.

1. MENINGES
M E M B R A N E S T H AT E N V E LO P T H E C N S

2. CRANIAL MENINGES
• Are membranous coverings of the brain that lie immediately internal to the cranium.
• Surrounds the brain & spinal cord.
• Serves to:
1. Protect the brain
2. Form the supporting framework for arteries, veins & venous sinuses.
3. Enclose the subarachnoid space, which is vital to the normal function of brain.
• Composed of 3 membranous connective tissue layers:
1. Dura Mater: tough, thick, external fibrous layer.
2. Arachnoid Mater: thin intermediate layer.
3. Pia Mater: delicate internal vasculated layer.
• Arachnoid & Pia Mater(s) collectively make up the leptomeninges, the Arachnoid is
separated from the Pia by the Subarachnoid (leptomeningeal) space-contains CSF.

3. (CONT’D)
• CSF is a clear liquid similar to blood in constitution; it provides nutrients but it has less
protein & a different ion concentration.
• CSF removes waste products associated with neuronal activity.
• CSF also provides a fluid medium in which the brain floats-mechanism effectively
protects the brain from trauma.
• CSF is formed by the Choroid Plexuses of the 4 ventricles of the brain.
• This fluid leaves the ventricular system & enters the subarachnoid space btw Arachnoid
& Pia mater, where it nourishes & cushions the brain.

4. MENINGES-LAYERS

5. DURA MATER• A thick, dense, bilaminar membrane. Also called the Pachymeninx.
• Adherent to the internal table of the calvaria.
• Has 2 layers:
– External periosteal/endosteal layer-formed by periosteum of internal surface of the calvaria
– Internal meningeal layer-strong fibrous membrane that is continuous at Foramen Magnum
with Spinal dura covering the spinal cord.
• Endosteal layer does not extend through the foramen magnum to become continuous
with dura mater of spinal cord.
– At the sutures, it is continuous with the sutural ligaments.
– It is most strongly adherent to the bones over the base of the skull & internal surface of
cranium.
• The meningeal mater is the dura mater proper.
– Is a strong, dense, fibrous membrane covering the brain & is continuous through the
Foramen Magnum with Dura mater of spinal cord.
– Sends inward 4 septa that divide the cranial cavity into freely communicating spaces.
– The function of these septa is to restrict the rotatory displacement of brain.

6. (CONT’D)
1. Falx cerebri-a sickle-shaped fold of dura mater that lies in the midline
btw the 2 cerebral hemispheres.
– Attached ANTERIORLY to the internal frontal crest & crista galli.
– 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.
– The Straight Sinus runs along its attachment to the Tentorium Cerebelli.
2. Falx cerebelli-is a small, sickle-shaped fold of dura mater that is
attached to the Internal Occipital Crest & projects forward btw the 2
cerebellar hemispheres.
1. Its Posterior fixed margin contains the occipital sinus.
2. Attached posteriorly in the midline to the internal occipital crest of the occipital
bone-its anterior edge exists freely btw the partially separated cerebellar
hemispheres

7. (CONT’D)3. Tentorium Cerebelli-a crescent-shaped fold of dura mater that roofs over the posterior cranial
fossa.
– Covers the upper surface of the cerebellum
– Supports the occipital lobes of the cerebral hemispheres.
– In front is a notch, the TENTORIAL NOTCH, for the passage of the midbrain
– Has as inner free border & an outer fixed border.
– The fixed border is attached to the posterior clinoid processes & superior borders of petrous
bones.
– The free border runs forward at its 2 ends, crosses the fixed border & is affixed to the anterior
clinoid process on each side.
– At the point where the 2 borders cross, the 3rd & 4th cranial nerves pass forward.
– Separates the cerebellum & cerebrum.
– The falx cerebri & falx cerebelli are attached to the upper & lower surfaces of the tentorium,
respectively.
– The straight sinus runs along its attachment to the falx cerebri, the superior petrosal sinus
along its attachment to the petrous bone, & the transverse sinus along its attachment to the
occipital bone.

8. 4. Diaphragma Sellae-is a small circular fold of dura mater that forms the roof of the sella
turcica.
• A small opening in its center allows passage of the stalk of the pituitary gland.
• Attached Anteriorly to the Tuberculum Sellae
• Attached Posteriorly to the Dorsum Sellae.
• Encloses the Intercavemous sinuses.

9. DURAL MATER VASCULATURE
• Via the Trigeminal, Vagus, and first 3 cervical nerves & branches from the Sympathetic
system pass to the dura.
• Numerous sensory endings are in the dura,
• Is sensitive to stretching which produces the sensation of headache.
• Numerous arteries supply the dura mater from the internal carotid, maxillary, ascending
pharyngeal, occipital, & vertebral arteries.
• Most important-is the middle meningeal artery-commonly damaged in head injuries.
• Meningeal veins lie in the endosteal layer of dura.
• The middle meningeal vein follows the branches of the midlle meningeal artery & drains
into the pterygoid venous plexus or the sphenoparietal sinus.
• The veins lie lateral to the arteries.

11. ARACHNOID & PIA MATER
• Both develop from a single layer of mesenchyme surrounding the embryonic brain.
• Arachnoid becomes the parietal part & Pia, the visceral part of the leptomeninx.
• The derivation of the arachnoid-pia from a single embryonic layer is indicated in the
adult by the numerous web-like arachnoid trabeculae passing btw the arachnoid & pia.
• The trabeculae is composed of flattened, irregularly shaped fibroblasts that bridge the
subarachnoid space.
• Arachnoid mater contains fibroblasts, collagen fibers, & some elastic fibers.
• The arachnoid is not attached to the dura, rather is held against the inner surface of the
dura by the pressure of the CSF in the subarachnoid space.
• Pia mater is an even thinner membrane.
– Highly vascularized by a network of fine blood vessels.
– Gives surface of brain a shiny appearance.

12. ARACHNOID (CONT’D)• Is a delicate, impermeable membrane.
• Separated from the dura by the Subdural space & from the Pia by the Subarachnoid
space wich is filled with CSF.
• In certain situations, the arachnoid & pia are widely separated to form the subarachnoid
cisternae.
• In certain areas, the arachnoid projects into the venous sinuses to form Arachnoid villi.
• Arachnoid villi are most numerous along Superior sagittal sinus.
• Aggregations of arachnoid villi are referred to as arachnoid granulations.
• The villi serve as sites where CSF diffuses into bloodstream.
• The arachnoid fuses with the Epinerium of the nerves at their point of exit from the skull.

13. PIA MATER (CONT’D)
• Is a vascular membrane that closely invests the brain, covering the gyri & descending into
the deepest sulci.
• Extends over the cranial nerves & fuses with their epineurium.
• The cerebral arteries entering the brain carry a sheath of pia with them.

14. (CONT’D)

15. THE END
• Source:
– Clinical Anatomy, Richard S. Snell, 7th Ed. pg. 804-806
– Clinically Oriented Anatomy, Keith L. Moore, Seventh Edition, pg. 865-873