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MENINGES OF BRAIN


INTRODUCTION



There are three meninges.

A tough outer layer - THE DURA MATER.

A delicate, middle layer - THE ARACHNOID MATER.

An inner layer firmly attached to the surface of brain - THE PIA MATER.


The cranial meninges are continuous with, and similar to the spinal meninges, through the foramen magnum, with one important distinction - The cranial dura mater consists of two layers and only one of these is continuous through the foramen magnum.

CRANIAL DURA MATER

The cranial dura mater is a thick, tough outer covering of the brain.

It consists of two layers :

1. OUTER PERIOSTEAL LAYER - It is firmly attached to the skull, contains meningeal arteries.

2. INNER MENINGEAL LAYER - It is in close contact with the arachnoid mater.

The two layers of dura separate from each other at numerous locations to form two unique type of structures DURAL PARTITIONS and INTRACRANIAL VENOUS SINUSES.


DURAL PARTITIONS



The dural partitions project into the cranial cavity and partially subdivide the cranial cavity. They include the FALX CEREBRI, TENTORIUM CEREBELLI, FALX CEREBELLI, and DIAPHRAGMA SELLAE.


FALX CEREBRI

It is a crescent shaped downward projection of dura mater that passes between the two cerebral hemispheres and separate them.


#BOUNDARIES:

ANTERIOR - Attached with the CRYSTA GALLI of ethmoid bone and FRONTAL PROCESS.

POSTERIOR - Attached on the superior surface of TENTORIUM CEREBELLI.

SUPERIOR - Attached with the grooves lodging SUPERIOR SAGGITAL SINUS.

INFERIOR - This margin is concave and free.


#SINUS ENCLOSED:

SUPERIOR and INFERIOR SAGGITAL SINUS, STRAIGHT SINUS


TENTORIUM CEREBELLI

It is a tent shaped horizontal projection of the meningeal dura mater that covers and separates the cerebellum from cerebrum.


#BOUNDARIES:

ANTERIOR - Attached with the clinoid processes from its edges, rest margin is concave and free and forms TENTORIAL NOTCH from where MIDBRAIN makes its passage.

POSTERIOR - Attached with the occipital bone.

LATERAL - On both sides attached with the dura mater of middle cranial fossa.


#SINUS ENCLOSED:

TRANSVERSE and SUPERIOR PETROSAL SINUS.


FALX CEREBELLI

It is a small midline projection of meningeal dura mater inside posterior cranial fossa and it separates two cerebellar hemispheres incompletely.


#BOUNDARIES:

ANTERIOR - This margin is free and present between cerebellar hemispheres.

POSTERIOR - Attached with the occipital crest.

BASE - Attached with the inferior surface of tentorium cerebelli.

APEX - It reaches till FORAMEN MAGNUM.


#SINUS ENCLOSED:

OCCIPITAL SINUS


DIAPHRAGMA SELLAE

This is a small horizontal shelf of meningeal dura mater covers the hypophysial fossa in the sella turcica of sphenoid bone. there is an opening in the center of the diaphragma sellae through which passes the infundibulum, connecting the pituitary gland with the hypothalamus.


#BOUNDARIES:

ANTERIOR - Attached with the TUBERCULUM SELLAE

POSTERIOR - Attached with the DORSUM SELLAE


#SINUS ENCLOSED:

ANTERIOR and POSTERIOR INTERCAVERNOUS SINUS


BLOOD SUPPLY TO DURA MATER


Dura mater ( outer periosteal layer) mainly supplied by three meningeal arteries:


1. ANTERIOR MENINGEAL ARTERY - branch of ethymoidal artery

2. MIDDLE MENINGEAL ARTERY - main supply of dura, branch of maxillary artery which in turn is the branch of external carotid artery.

3.POSTERIOR MENINGEAL ARTERY - branch of ascending pharyngeal artery which in turn is the branch of external carotid artery.


NERVE SUPPLY TO DURA MATER


Dura mater is sensitive to pain and it is innervated by branches from all three divisions of trigeminal system (V1, V2 and V3) vagus (X) and roots of C1 to C3.


1. OPHTHALMIC DIVISION (V1) - Supplies the part of dura present in anterior cranial fossa, falx cerebri and tentorium cerebelli.

2.MAXILLARY (V2) and MANDIBULAR (V3) DIVISION - Supplies the part of dura present inside middle cranial fossa.

3.VAGUS(X) and ROOTS OF C1 to C3 - Supplies the part of dura present inside posterior cranial fossa.


ARACHNOID MATER


It is a thin , avascular membrane present between dura and pia mater.

It has prolongations known as TRABAECULI which dips into pia matter by crossing subarachnoid space.

It bridges all irregularities of brain because it does not dips inside sulci and gyrii of brain.

It is separated from dura mater by subdural space and from pia mater by subarachnoid space.


PIA MATER


It is a thin, delicate membrane intimately covering the brain substance.

It is highly vascular.

It is the first covering of brain.

It dips into all sulci and gyrii of brain.


To be continued.....................





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