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MED2042 WEEK 3 - Neuroanatomy (The meninges of the brain and spinal cord)


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What is the meninges?
A series of three membranous coverings from which the CNS is suspended.
What do the meninges do?
They stabilize the position and shape of the nervous tissue during head and body movements.

The brain is mechanically suspended within the meninges, which in turn are attached to the skull, so that the brain moves with the head.
What fluid accompanies the meninges?
There is a layer of cerebrospinal fluid (CSF) within the meninges which bathes the entire CNS.

This provides buoyancy to the brain and maintains its shpae under the pull of gravity and other forces.
List the meningeal layers from the outside in.
Dura (or dura mater "hard mother")
Arachnoid membrane
Pia (or pia mater "soft mother")
Describe the dura.
The dura is a tough collagenous membrane. Within the skull, it adheres closely to the inner surface of the bone. It is considered to have two componenets: an outer endosteal layer and an inner meningeal layer. (There is no histological difference between these layers, its just that the inner part of the dura leaves the bone to form the dural sac that encases the spinal cord).
Describe the arachnoid membrane.
The arachnoid membrane adheres closely to the inner surface of the dura, and normally, there is no space between these membreanes. The pia adheres closely to the contours of the surface of the brain and spinal cord.

The inner surface of the arachnoid membrane is connected to the pia via numerous fibrous strands called arachnoid trabeculae. There is a real space between the arachnoid membrane and the pia which is known as the subarachnoid space. This is filled with CSF. The surface blood vessels also run in the subarachnoid space.
Describe pia mater.
The pia mater closely follows the detailed contours of the brain. CSF flows around the surface of the CNS in the subarachnoid space.
Describe where CSF is found.
CSF is drained into the venous system largely via arachnoid villi protruding into the superior saggital sinus.

The dura and arachnoid do not closely follow the precise contours of the CNS.

For example, they span over the surface of the cerebral cortex and do not follow the sulci and gyri. Thus, there is a normally narrow, CSF-filled subarachnoid space between the cortical sulci. In other areas with major surface irregularities, the subarachnoid spaces are normally enlarged, forming CSF-filled spaces known as subarachnoid cisterns.
List some subarachnoid cisterns.
3rd ventricle
4th ventricle
Superior cistern
Interpeduncular cistern
Medullary cistern (cisterna magna)
What are some important anatomical features of the meninges?
Falx cerebri
Middle meningeal artery
Dura attached to skull
Free edge of dura around upper brain stem
Tentorium cerebelli
Arachnoid villi
Superior sagittal sinus
What is an epidural haematoma. Give two examples.
Hemorrhage between the dura and inner surface of the skull can strip the dura from the bone forming an epidural haematoma. This can develop rapidly with arterial bleeding.

Laceration of middle meningeal artery (CT)
Laceration of superior sagittal sinus
What is a subarachnoid haematoma.
Haemorrhage of vessels in the subarachnoid space produces a subarachnoid haematoma.
What are the two layers of the Dura mater?
Outer interosteal layer (encases spinal cord)
Inner menningeal layer.
What are the important anatomical features of the spinal meninges?
Dura mater
Denticulate ligament
Arachnoid trabeculae
Pia mater and spinal blood vessels
What is the filum terminale?
delicate filament extending downwards from the spinal cord.
What does the floor of the superior saggital sinus contain?
Arachnoid granulations
Cerebral veins

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