SCHEMATIC
OF THE MENINGES AND THEIR RELATIONSHIPS TO THE BRAIN
AND SKULL
The meninges provide
protection and support for neural tissue in the central nervous system. The
innermost membrane, the pia mater, adheres to every contour of neural tissue,
including sulci, folia, and other infoldings. It adheres tightly to glial end foot processes
of astrocytes; this association is called the pialglial membrane.
The arachnoid
mater, a fine, lacy membrane external to the pia, extends across the neural
sulci and foldings. The space between these two membranes is the subarachnoid
space, a space into which the cerebrospinal fluid flows, providing buoyancy and
protection for the brain. Arteries and veins run through the subarachnoid space
to and from the central nervous system. The rupture of an arterial aneurysm in
a cerebral artery results in a subarachnoid hemorrhage. The dura mater, usually
adherent to the inner arachnoid, is a tough protective outer membrane. It
splits into two layers in some locations to provide channels, the venous
sinuses, for return flow of the venous blood. The arachnoid granulations,
one-way valves, extend from the subarachnoid space into the venous sinuses,
especially the superior sagittal sinus, allowing cerebrospinal fluid to drain
into the venous blood and return to the heart. Blockage of these arachnoid granulations
(e.g., in acute purulent meningitis) can result in increased intracranial
pressure. Cerebral arteries and veins traverse the subarachnoid space. The
veins, called bridging veins, drain into the dural sinuses. As they enter the
sinus, these bridging veins are subject to tearing in cases of head trauma. If
there is atrophy in the brain, as occurs with age, these veins may tear with
relatively minor head trauma; in younger adults, more severe head trauma is
needed to tear these bridging veins. Such tearing permits venous blood to
accumulate in the subdural space as it dissects the inner dura from the
arachnoid. This process may be gradual (chronic subdural hematoma) in older
individuals or may be abrupt (acute subdural hematoma) with severe head trauma.
A subdural hematoma, especially when it occurs acutely, may be life-threatening
as the result of increased intracranial pressure caused by accompanying edema
and by the accumulation of the blood in the hematoma itself. The dura is
closely adherent to the inner table of the skull. A skull fracture may tear a
branch of the middle meningeal artery, permitting arterial blood to dissect the
dura from the skull, resulting in an epidural hematoma.
Inferior sagittal sinus,
Venous lacuna, Arachnoid granulation indenting skull (foveola), Superior sagittal sinus Epidural space (potential), Dura mater (outer layer), Dura mater (inner layer), Inner layer of dura mater,
Falx cerebri, Arachnoid, Subarachnoid space, Pia mater, Middle meningeal, artery and vein, Skin, Arachnoid granulation Venous lacuna, Subarachnoid space, Pia mater, Galea aponeurotica, Epicranium, Calvaria, Dura mater (outer and inner layers), Subdural space (potential),
Arachnoid, Cerebral hemisphere
