Human Brain
Meninges :-
The meninges form a membranous covering composed of fibroblasts and extracellular connective tissue. That covers brain and spinal cord. There are three layers of meninges, known as the Dura mater, Arachnoid mater and Pia mater .
Covering of Brain
The meninges cover the nervous system and are layered in the following manner: the pia mater is the innermost layer; the arachnoid mater overlies it; and the dura mater is the thick outer-covering of the nervous system. Fluid enters the subarachnoid space and then is reabsorbed into the venous sinuses within the dura mater.
Function Of Meninges :-
The primary function of the meninges is to protect the central nervous system ,from mechanical trauma, to support the blood vessels and to form a continuous cavity through which the cerebrospinal fluid (CSF) passes.
The meninges forms a protective barrier that safeguards the sensitive organs of the CNS against trauma. It also contains an ample supply of blood vessels that deliver blood to CNS tissue.
The brain is soft and mushy, and without structural support it would not be able to maintain its normal shape.
Meninges Layer:-
Dura Mater:
This outer layer connects the meninges to the skull and vertebral column. It is composed of tough,consisting of dense irregular fibrous connective tissue.
Dura mater that surrounds the brain consists of two layers. The outer layer is called the periosteal layer , which lies closest to the skull, and the inner meningeal layer, which lies closer to the brain .
It contains larger blood vessels that split into the capillaries in the pia meter and the inner layer is the meningeal layer.
Meninges Structure
The dural venous sinuses are located between the two layers of dura mater. They are responsible for the venous drainage of the cranium and empty into the internal jugular veins.
The Dura has Four areas of infoldings:-
Falx cerebri:- separates the right and left cerebral hemispheres
Tentorium cerebelli :- separates the occipital lobes from cerebellum. The falx cerebri attaches to it giving a tent-like appearance.
Falx cerebelli:- vertical infolding; separating the left and right cerebellar hemispheres.
Diaphragma sellae :- smallest infolding; covers the pituitary gland and sella turcica.
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Arachnoid Layer:
1- The arachnoid mater This thin, transparent membrane is composed of fibrous tissue and it is the middle layer of the meninges, lying directly underneath the dura mater.
2- A potential space exists between the dura and the underlying arachnoid layer called the subdural space.
3- The subarachnoid space provides a route for the passage of blood vessels and nerves through the brain and collects cerebrospinal fluid that flows from the fourth ventricle.
Membranous projections from the arachnoid layer called Arachnoid granulations (villi) ,extend from the subarachnoid space into the dura mater. Arachnoid granulations remove cerebrospinal fluid from the subarachnoid space and send it to the Cranial venous sinuses, where it is reabsorbed into the venous system.
Pia Mater:
This thin inner layer of the meninges is in direct contact with brain and closely covers the cerebral cortex and spinal cord. The pia mater has a rich supply of blood vessels, which provide nutrients to nervous tissue.
pia mater and the ependymal lining of the ventricular system form choroid plexus ( A network of ependymal cell ) , which produces cerebrospinal fluid
cerebrospinal fluid pass from the lateral ventricles through one inter ventricular foramen into the third ventricle.
CSF Formation
Indicate it descends from the third ventricle through the cerebral aqueduct into the fourth ventricle and down the central canal of the spinal cord.
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+ Clinical :-
Meningitis
Meningitis refers to inflammation of the meninges which is mainly caused by pathogens like Bacteria and fungus which causes the inflammation .
Bacteria are the most common infective cause. The most common organisms are Neisseria meningitidis and Streptococcus pneumoniae.
EpiDural Hematoma
An epidural hematoma occurs between the dura mater and the skull. It is typically caused by damage to an artery or venous sinus as a result of severe trauma to the head.
SubDural Hematoma
subdural hematoma occurs between the dura mater and arachnoid mater. It is usually caused by head trauma that ruptures veins. A subdural hematoma can be acute and develop rapidly or it can develop slowly over a period of time.
Maningiomas
Meningiomas are tumors that develop in the meninges. They originate in the arachnoid mater and put pressure on the brain and spinal cord as they grow larger.
SubArachnoid Hemorrhage
Bleeding into the space between the two innermost protective coverings surrounding the brain, the pia mater and the arachnoid mater. A subarachnoid hemorrhage most commonly result of head trauma but may be non traumatic caused by rupture or aneurysm and inflammation of an artery.
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Tags:
Neuro anatomy