Meninges

Meninges

The meninges(singular: meninx) – Protective membranes surrounding the spinal cord and brain. of the brain are continuous with the meninges of the spinal cordThe central nervous system structure that relays signals between the brain and body..  The only difference is that the dura materThe thick, outermost layer of the meninges that protects the spinal cord., the most superficialNear the surface of the body. meninix, is somewhat fused to the periosteum. This fusion occurs at the skull bone overlying it.  There is no epidural spaceThe space between the dura mater and vertebrae, filled with fat and blood vessels. in the brain meninges.  However, the same sequence of structures exists from superficial to deepAway from the surface of the body.. It includes bone, dura mater, subdural space, and arachnoid space. Then, there is the subarachnoid space, pia materThe thin, innermost layer of the meninges that closely adheres to the spinal cord., and finally brain matter.

Dura Mater

The dura mater is fused with the periosteum of the skull bone. This fusion eliminates any epidural space between the dura mater and bone.  In this picture, the dura mater is the brown layer fused to the bone.  The yellow space is the subdural space which, as the name suggests, is deep to the dura mater.  This subdural space houses large veinsBlood vessels that return deoxygenated blood to the heart (except pulmonary veins, which carry oxyge, or sinusesAir-filled spaces in the skull that lighten it and help humidify air., that collect blood leaving the brain.  A subdural hematomaA blood clot that forms at the site of a fracture. is a blood clot in this subdural space.  As with any intrusion in the cranium, the pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. reaches inward, compressing brain tissue.  There can be no outward extension because of the skull bones.

Arachnoid Mater

The arachnoid materThe middle layer of the meninges, located between the dura and pia mater. is the pink structure on the picture above.  This is the meninix that has fibrous extensions into the area deep to the mater.  These fibrous extension form a cobweb-like structure that forms the subarachnoid space.  This space is filled with CSF and is continuous with the subarachnoid space of the spinal cord. 

Strokes

There are two kinds of strokes.  In an ischemic stroke, part of the brain is denied blood delivery.  This can be temporary from a moving blood clot or it can be permanent from arteriosclerosis.  Either way, there’s a part of your brain not receiving blood and the cellsThe basic structural and functional units of life., well, they die.  As you can see from the statistics here, this type of stroke is much more common. It occurs more frequently than a hemorrhagic stroke.

A hemorrhagic stroke is kinda the opposite of an ischemic stroke.  Instead of being denied blood delivery, an artery in the subarachnoid space ruptures. This rupture fills the subarachnoid space with blood.  Again, there can be no outward extension because of skull bones.  So, the pressure of the excess blood pushes in on brain matter.  Notice how, on the picture on the right, you can see blood in the subarachnoid space. You can also see it leaking into these folds. 

Pia Mater

The pia mater is like the brain stocking.  It is a purple line in this picture.  The pia mater actually dips into these folds.  Astrocytes line the deep face of the pia mater. They support it like a framework. This framework creates the shape of hills called gyri. It also forms valleys called sulci.  It also makes sense that the astrocytesStar-shaped glial cells in the CNS that support neurons and maintain the blood-brain barrier. are here because of the blood capillariesThe smallest blood vessels where gas, nutrient, and waste exchange occurs between blood and tissues. that are in the subarachnoid space.  Astrocytes are the neuroglia tasked with regulating the interstitial environment of the brain.  Their location allows them to interact with blood capillaries and the CSF filled spaces.