The three meningeal layers that envelop the central nervous system are the dura mater, arachnoid mater, and pia mater. The dura mater is the thick outer layer that protects the brain and forms partitions within the cranial cavity. Inside is the arachnoid mater, separated from the pia mater by the subarachnoid space which contains cerebrospinal fluid. The pia mater is a delicate vascular layer that closely invests the surface of the brain. These meningeal layers serve to protect, cushion, and nourish the brain and spinal cord.

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