1. ANATOMY OF THE MENINGES, CNS CAVITIES & CSF CIRCULATION
Prof. Mujahid Khan
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6/27/2019

2. Meninges of Brain
The brain in the skull and spinal cord in the vertebral column are surrounded by three protective membranes called meninges
Dura mater
Arachnoid mater
Pia mater
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3. Dura Mater
Dura mater of the brain is described as two layers , the endosteal layer and meningeal layer
Endosteal layer is a periosteum covering the inner surface of the skull bones
At the foramen magnum it does not become continuous with the dura mater of the spinal cord
Around margins of all the foramina in the skull it becomes continuous with the outside periosteum of skull bones
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4. Dura Mater Meningeal layer is the dura mater proper
It is a dense fibrous membrane covering the brain
It is continuous through the foramen magnum with the dura mater of the spinal cord
It provides tubular sheaths for the cranial nerves as nerves pass through the foramina of the skull
Outside the skull the sheaths fuse with the epineurium of the nerves
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5. Dura Mater
The meningeal layer sends four septa which divides cranial cavity into freely communicating spaces that lodges the subdivisions of the brain
Function of these septa restrict the displacement of the brain when the head is moved
Falx cerebri is a sickle shaped fold of dura mater that lie in the midline between the two cerebral hemispheres
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6. Dura Mater
Its narrow anterior end is attached to the internal frontal crest and crista galli
Its broad posterior part blends in the midline with the upper surface of the tentorium cerebelli
Superior sagittal sinus runs in its upper fixed margin
Inferior sagittal sinus runs in lower concave free margin
Straight sinus runs along its attachment to the tentorium cerebelli
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8. Dura Mater
Tentorium cerebelli is a crescent shaped fold of dura mater that roofs over the posterior cranial fossa
It covers the upper surface of the cerebellum
It supports the occipital lobes of the cerebral hemispheres
In the anterior edge there is a gap called tentorial notch for the passage of the midbrain
Its fixed border is attached to the posterior clinoid processes
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10. Dura Mater
The falx cerebri and falx cerebelli are attached to the upper and lower surfaces of the tentorium respectively
Transverse sinus runs along its attachment to the occipital bone
Falx cerebelli is a small sickle shaped fold of dura mater attached to the internal occipital crest and projects forward between the two cerebellar hemispheres
Its posterior fixed margin contains the occipital sinus
The dura possesses numerous sensory endings that are sensitive to stretching which produce sensation of headache
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12. Dural Arterial Supply
Various arteries supply the dura mater from the internal carotid, maxillary, ascending pharyngeal, occipital and vertebral arteries
Clinically important is middle meningeal artery can be damaged in the head injuries
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13. Dural Venous Sinuses
Venous sinuses of the cranial cavity are situated between the layers of dura mater
Their main function is to receive blood from the brain through the cerebral veins and CSF from the subarachnoid space through the arachnoid villi
The blood from the dural sinuses drains into the internal jugular veins in the neck
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14. Arachnoid Mater
Arachnoid mater is a delicate impermeable membrane covering the brain
It lies between the pia mater internally and dura mater externally
It is separated from the dura by a subdural space
It is separated from pia by the subarachnoid space which is filled with cerebrospinal fluid
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15. Arachnoid Mater
In certain areas the arachnoid projects into the venous sinuses to form arachnoid villi
Arachnoid villi serve as sites where the cerebrospinal fluid diffuses into the bloodstream
Structures passing to and from the brain to the skull or its foramina must pass through the subarachnoid space
All the cerebral arteries, veins and cranial nerves lie in the space
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17. Pia Mater
It is a vascular membrane closely invests the brain, covering the gyri and deepest sulci
Cerebral arteries entering the brain substance carry a sheath of pia with them
Pia mater forms tela choroidea of roof of third ventricle
It fuses with ependymal to form the choroid plexus
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19. Cerebrospinal Fluid
Cerebrospinal fluid is formed by the choroid plexuses within the lateral, third and fourth ventricles
It escapes from the ventricular system of the brain through three foramina (magendie & luschka) in the roof of the fourth ventricle and enters the subarachnoid space
It circulates both upward to the surfaces of cerebral hemispheres and downward around the spinal cord
Spinal subarachnoid space extends down till the second sacral vertebra
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20. Cerebrospinal Fluid
CSF provides a fluid medium in which the brain floats and is protected from trauma
It is found in the ventricles of the brain and subarachnoid space around the brain and spinal cord
It removes waste products associated with neuronal activity
Its volume is about 150 ml
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21. Cerebrospinal Fluid
It possesses inorganic salts similar to those in the blood plasma
CSF is an ideal physiologic substrate and thus plays an active role in brain tissue nourishment
The pressure of CSF is kept constant and may be raised by straining, coughing and by compressing internal jugular vein in the neck
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22. Cerebrospinal Fluid Production
CSF is produced continuously at a rate of about 0.5 ml per minute
The production of CSF is not pressure regulated
It continues to be produced even if the reabsorption mechanisms are obstructed
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23. Cerebrospinal Fluid Circulation
CSF passes from the lateral ventricles into the third ventricle through the interventricular foramina
It then passes into the fourth ventricle through the narrow cerebral aqueduct
From the fourth ventricle the fluid passes slowly through the median aperture foramen (magendie) and lateral foramina (luschka) to enter the subarachnoid space
It moves superiorly over the lateral aspect of each cerebral hemisphere
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25. Cerebrospinal Fluid Circulation
Some CSF is moved inferiorly in the subarachnoid space around the spinal cord and cauda equina
At the dead end the fluid circulation relies on the pulsations of spinal arteries and movements of the vertebral column
CSF not only bathes the ependymal and pial surfaces of the brain and spinal cord but also penetrates the nervous tissue along the blood vessels
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27. Cerebrospinal Fluid Absorption
The main sites for absorption of CSF are the arachnoid villi that project into the dural venous sinuses especially the arachnoid granules of the superior sagittal sinus
The arachnoid granulations increase in number and size with age and tend to become calcified with advanced age
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29. Cerebrospinal Fluid Absorption
The arachnoid villi serve as a valves
If venous pressure rise and exceed the CSF pressure, compression of the tips of the villi closes the tubules and prevents the reflux of blood into the subarachnoid space
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31. THE END