The dura mater or pachymeninx is made up of two layers of whitish membrane. The outer layer endosteal is called the periosteum. An inner layer meningeal , lines the inside of the entire skull and creates little folds or compartments in which parts of the brain are protected and secured.
Because the two layers are indistinguishable except in a few areas, it's simpler to consider the dura as one layer, which serves as both endocranium and meninx.
Instead of being considered as separating two layers, the venous sinuses are usually described as being situated within a single dura. The two special folds of the dura in the brain are called the falx and the tentorium. The falx separates the right and left half of the brain and the tentorium separates the upper and lower parts of the brain. The dura, like the scalp, is supplied by both cranial chiefly the trigeminal and cervical nerves. The brain itself is normally insensitive, and headaches are commonly either of vascular intracranial or extracranial or dural origin.
The leptomeninges include the arachnoid and pia mater. These layers bound the subarachnoid space, which is limited externally by a water-tight layer of connective tissue, the arachnoid, and internally by a thinner layer, the pia mater. The pia mater adheres intimately to the surface of the brain and spinal cord.
There is a trabecular structure of connections between the arachnoid and the pia that bridges the subarachnoid space which is otherwise full of circulating CSF. The arachnoid is a thin and delicate membrane that surrounds the brain loosely and is separable from the dura by a potential space into which subdural hemorrhage may occur. There is a space between the dura and the arachnoid membranes that is called the subdural space.
The arachnoid is made up of delicate, elastic tissue and blood vessels of varying sizes. The arachnoid dips into the longitudinal interhemispheric fissure but not into the sulci. Near the dural venous sinuses, the arachnoid has microscopic projections, called arachnoid villi, which are believed to be concerned with the absorption of CSF.
Enlargements of the villi, known as arachnoid granulations, enter some of the sinuses and their associated lateral lacunae and are visible to the naked eye. Both the granulations and the lacunae lie in granular pits on the internal aspect of the calvaria. The pia mater is the layer of meninges closest to the surface of the brain.
It covers the entire surface of the brain intimately and follows the brain into the gyri of the cerebral hemispheres and the folia of the cerebellum. The pia mater has many blood vessels that reach deep into the surface of the brain. The major arteries supplying the brain provide the pia with its blood vessels. The space that separates the arachnoid and the pia is called the subarachnoid space. It's within this area that the CSF flows. Protecting The Brain. The brain is the best protected organ in the body.
The Ventricular System The ventricular system is divided into four cavities called ventricles, which are connected by a series of holes called foramen, and tubes. Two ventricles enclosed in the cerebral hemispheres are called the lateral ventricles first and second. They each communicate with the third ventricle through a separate opening called the Foramen of Munro. The third ventricle is in the center of the brain, and its walls are made up of the thalamus and hypothalamus. The third ventricle connects with the fourth ventricle through a long tube called the Aqueduct of Sylvius.
CSF flowing through the fourth ventricle flows around the brain and spinal cord by passing through another series of openings. Error Email field is required. Error Include a valid email address. To provide you with the most relevant and helpful information and to understand which information is beneficial, we may combine your e-mail and website usage information with other information we have about you.
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