Meninges and CSF

MENINGES AND LIQUOR

The CNS tissue is very delicate. For this reason, it has an elaborate protection system consisting of four structures: skull, meninges, cerebrospinal fluid (cerebrospinal fluid) and blood-brain barrier. In this page, we will address the meninges and cerebrospinal fluid, structures that involve the CNS and are of utmost importance for the defense of our body.

Skullcap and Meninges

MENINGES:

The nervous system is surrounded by connective membranes called meninges which are classified as three: dura mater, arachnoid and pia mater. Arachnoid and pia mater, which in the embryo constitute a single leaflet, are sometimes considered to be a single formation known as the leptomeninge; and the thicker dura is known as pachymening.

Skullcap and MeningesSkullcap and Meninges

Dura mater:

It is the most superficial, thick and resistant meninges, formed by connective tissue very rich in collagen fibers, containing nerves and vessels.

Hard Material - Periosteal and Meningeal LaminaIt consists of two leaflets: one external and one internal. The external leaflet closely adheres to the skull bones and behaves like a periosteum of these bones, but without osteogenic capacity (in cranial fractures, it is difficult to form a bony callus).

Due to the adhesion of the dura to the bones of the skull, there is no epidural space in the skull as in the medulla. In the brain, the main artery that irrigates the dura mater is the middle meningeal artery, a branch of the maxillary artery.

HARD MATERIAL BROCHURES
HARD MATERIAL BROCHURES

 

Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

 

The dura mater, unlike other meninges, is richly innervated. Because the brain has no sensitive nerve endings, any or all intracranial tenderness is located in the dura, which is responsible for most headaches.

Dura Folds: In some areas the inner leaflet of the dura detaches from the outer to form folds that divide the cranial cavity into widely communicating compartments. The main folds are:

 Brain scytheIt is a median vertical sickle-shaped septum that occupies the longitudinal fissure of the brain, separating the two hemispheres.

 Cerebellum TentIt projects forward as a transverse septum between the occipital lobes and the cerebellum. The cerebellum tent separates the posterior fossa from the middle cranial fossa, dividing the cranial cavity into an upper or supratentorial compartment and a lower or infratentorial compartment. The free anterior edge of the cerebellum tent, called the tent notch, fits the midbrain.

 Cerebellum Scythe: Small median vertical septum, located below the cerebellum tent between the two cerebellar hemispheres.

 Saddle Diaphragm: Small horizontal blade that closes the turgical saddle superiorly, leaving only one passageway for the pituitary stem.

Dura Folds

Dura cavities: In a given area, the two dural leaflets of the brain separate, delimiting cavities. One is the trigeminal cavus, which contains the trigeminal ganglion. Other cavities are lined with endothelium and contain blood, made up of the dura mater sinuses, which are mainly disposed along the insertion of the dural folds. The dural sinuses were studied in the cardiovascular system along with the venous system.

Arachnoid:

It is a very thin membrane, juxtaposed to the dura mater, from which it is separated by a virtual space, the subdural space, containing a small amount of liquid necessary for lubrication of the membrane contact surfaces. The arachnoid is separated from the pia by the cerebrospinal subarachnoid space, with great communication between the subarachnoid spaces of the brain and spinal cord. It is also considered to belong to the arachnoid, the delicate trabeculae that cross the space to connect to the pia mater, and which are called arachnoid trabeculae. These trabeculae resemble an aspect of cobwebs from where comes the name arachnoid.

HARD MATERIAL AND ARACHNOID
 
HARD MATERIAL AND ARACNOID
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

 Subarachnoid Cisterns: the arachnoid juxtaposes the dura and both only roughly follow the brain and its surface. The pia mater closely adheres to this surface that accompanies the turns, grooves and depressions. Thus, the distance between the two membranes, that is, the depth of the subarachnoid space is very variable, being very small in gyrus and large in areas where part of the brain moves away from the cranial wall. In these areas subarachnoid space dilatations are formed, the subarachnoid cisterns, which contain a large amount of liquor. The most important tanks are as follows:

 Magna Cistern: occupies the space between the inferior surface of the cerebellum and the dorsal surface of the bulb and roof of the III ventricle. It proceeds caudally with the subarachnoid space of the medulla and connects to the IV ventricle through the median opening. The magna cistern is the largest and most important and is sometimes used to obtain liquor through punctures.

 Pontina Cistern: located ventrally the bridge.

 Interpeduncular Cistern: Located in the interpeduncular fossa.

 Chiasmatic Cistern: situated before the optic chiasm.

 Superior Cistern: located dorsally to the mesencephalic ceiling, between the cerebellum and splenium of the corpus callosum. The upper cistern corresponds at least in part to the ambiens cistern, a term used by clinicians.

 Brain Fossa Cistern: corresponds to the depression formed by the lateral groove of each hemisphere.

CIRCULATIONS AND CIRCULATION OF LIQUOR
 
CIRCULATIONS AND CIRCULATION OF LIQUOR
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

Arachnoid Granulations: In some points of the arachnoid, small tufts that penetrate inside the breasts of the dura are formed, constituting the arachnoid granulations, more abundant in the superior sagittal sinus. Arachnoid granulations carry small extensions of the subarachnoid space, true diverticula of this space, in which the cerebrospinal fluid is separated from the blood only by the sinus endothelium and a thin layer of arachnoid. They are structures admirably adapted to the absorption of liquor, which at this point goes into the blood.

ARACNOID GRANULATIONS
 
ARACNOID GRANULATIONS
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

Sink:

It is the most internal of the meninges, closely adhering to the surface of the brain and spinal cord, whose reliefs and depressions follow to the bottom of the brain grooves. Its deepest portion receives numerous extensions of the astrocytes of the nervous tissue, thus constituting the pioglial membrane. The pia mater gives resistance to the nervous organs, since the nervous tissue is of very soft consistency. The pia mater follows the vessels that penetrate the nervous tissue from the subarachnoid space, forming the outer wall of the perivascular spaces.

In this space there are extensions of the subarachnoid space, containing liquor, which forms a protective cuff around the vessels, very important to cushion the effect of artery pulsation on the surrounding tissue. The perivascular spaces have been found to accompany the larger vessels within a short distance and end by fusion of the sink with the adventitia of the vessel. The small arterioles are enveloped to the capillary level by pre-vascular astrocytes of the nervous tissue.

Spinal Cord Wrap

Space between Meninges:

The extradural or epidural space is usually not a real space but only a potential space between the skull bones and the outer periosteal layer of the dura. It becomes a real space only pathologically, for example in the extradural hematoma.

LIQUOR:

It is an aqueous colorless fluid that occupies the subarachnoid space and the ventricular cavities. The primary function is mechanical protection of the central nervous system.

VENTRICULAR CAVITIES
 
VENTRICULAR CAVITIES
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

Liquor Formation, Absorption and Circulation:

It is now known that CSF is produced in the chorioid plexuses of the ventricles and also that a small portion is produced from the ventricular wall eppendyme and leptomeningeal vessels. There are chorioid plexuses in the ventricles, as we have seen before, and the lateral ventricles contribute with a greater CSF, which passes to the III ventricle through the interventricular foramen and thence to the IV ventricle through the cerebral aqueduct.

VENTRICULAR CAVITIES

SIDE VENTRICLES AND CORIOID PLEX
 
SIDE VENTRICLES AND CORIOID PLEX
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

Through the median and lateral openings of the IV ventricle, the cerebrospinal fluid passes into the subarachnoid space, being reabsorbed mainly by the arachnoid granulations that protrude into the dura. As these granulations predominate in the superior sagittal axis, the circulation of the cerebrospinal fluid is from the bottom upwards and must cross the space between the tent notch and the midbrain. In the subarachnoid space of the medulla, the cerebrospinal fluid descends caudally, but only a part returns, since cerebrospinal fluid resorption occurs in the small arachnoid granulations in the dura mater extensions that follow the roots of the spinal nerves.

LIQUOR CIRCULATION
 
LIQUOR CIRCULATION
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

CSF circulation is extremely slow and the factors that determine it are still discussed. Undoubtedly, the production of liquor at one end and its absorption at the other is enough to cause its movement. Another factor is the pulsation of intracranial arteries, which, each systole, increases CSF pressure, possibly contributing to pushing CSF through arachnoid granulations.

Scheme & #8211; Circulation of Liquor
Scheme - Liquor Circulation

 

 

Structures of
Nervous system
Nervous tissue

Spinal cord

Brainstem

Cerebellum

Diencephalon

Telencephalon

Brain Vascularization

Peripheral Nervous System

 

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