Meninges of the Brain

Meninges of the Brain

A. Pia mater

• Is a delicate investment that is closely applied to the brain and dips into fissures and sulci.
• Enmeshes blood vessels on the surfaces of the brain.

B. Arachnoid layer

• Is a filmy, transparent, spidery layer that is connected to the pia mater by web-like trabeculations.
• Is separated from the pia mater by the subarachnoid space , which is filled with CSF.
• May contain blood after hemorrhage of a cerebral artery.
• Projects into the venous sinuses to form arachnoid villi , which serve as sites where CSF diffuses into the venous blood.

1. Cerebrospinal fluid (CSF)

• Is formed by vascular choroid plexuses in the ventricles of the brain and is contained in the
• subarachnoid space.
• Circulates through the ventricles, enters the subarachnoid space, and eventually filters into the
• venous system.

2. Arachnoid granulations

• Are tuft-like collections of highly folded arachnoid (aggregations of arachnoid villi) that project into the superior sagittal sinus and the lateral lacunae, which are lateral extensions of the superior sagittal sinus.
• Absorb the CSF into the dural sinuses and often produce erosion or pitting of the inner surface of the calvaria, forming the granular pit.

C. Dura mater

• Is the tough, fibrous, outermost layer of the meninges external to the subdural space , the space between the arachnoid and the dura.
• Lies internal to the epidural space , a potential space that contains the middle meningeal arteries in the cranial cavity.
• Forms the dural venous sinuses , spaces between the periosteal and meningeal layers or between duplications of the meningeal layers.

1. Innervation of the dura mater

• Anterior and posterior ethmoidal branches of the ophthalmic division of the trigeminal nerve in the anterior cranial fossa.
• Meningeal branches of the maxillary and mandibular divisions of the trigeminal nerve in the middle cranial fossa.
• Meningeal branches of the vagus and hypoglossal (originate from C1) nerves in the posterior cranial fossa.
  
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2. Projections of the dura mater

Falx cerebri

• Is the sickle–shaped double layer of the dura mater, lying between the cerebral
• hemispheres.
• Is attached anteriorly to the crista galli and posteriorly to the tentorium cerebelli.
• Has a free inferior concave border that contains the inferior sagittal sinus , and its upper convex margin encloses the superior sagittal sinus.
  

Falx cerebelli

• Is a small sickle shaped projection between the cerebellar hemispheres.
• Is attached to the posterior and inferior parts of the tentorium.
• Contains the occipital sinus in its posterior border.

Tentorium cerebelli

• Is a crescentic fold of dura mater that supports the occipital lobes of the cerebral hemispheres and covers the cerebellum.
• Has a free internal concave border, that bounds the tentorial notch , whereas its external convex border encloses the transverse sinus posteriorly and the superior petrosal sinus anteriorly. The free border is anchored to the anterior coronoid process, whereas the attached border is attached to the posterior clinoid process.

Diaphragma sellae

• Is a circular, horizontal fold of dura that forms the roof of the sella turcica, covering the pituitary gland or the hypophysis.
• Has a central aperture for the hypophyseal stalk or infundibulum.

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