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Protection of the Brain
Bone (skull)
Membranes (meninges)
Watery cushion (cerebrospinal fluid)
Blood-brain barrier
Meninges
Series of membranes
Cover and protect the CNS
Anchor and cushion the brain
Contain cerebrospinal fluid (CSF)
Figure 12.24
Skin of scalp Periosteum
Falx cerebri (in longitudinal fissure only)
Blood vessel Arachnoid villus Pia mater Arachnoid mater
Dura
mater Meningeal Periosteal
Bone of skull
Superior sagittal sinus
Subdural space
Subarachnoid space
Figure 12.25a
Falx cerebri
Superior
sagittal sinus
Straight
sinus
Crista galli of the ethmoid bone
Pituitary
gland
Falx
cerebelli
(a) Dural septa
Tentorium
cerebelli
Arachnoid Mater
Middle layer with weblike extensions
Separated from the dura mater by the subdural space
Subarachnoid space contains CSF and blood vessels
Meningitis
Inflammation of meninges
May be bacterial or viral
Diagnosed by obtaining CSF sample via lumbar tap
Figure 12.30
Ligamentum flavum
Supra- spinous ligament
Lumbar puncture needle entering subarachnoid space
Filum terminale
Inter- vertebral disc
T12
L5
Cauda equina in subarachnoid space
Dura mater
L5
L4
S1
Arachnoid matter
Cerebrospinal Fluid (CSF)
Composition
Watery solution
Modified plasma
Constant volume (about 150 ml)
About 500 ml formed daily
Replaced every 8 hours or so
Cerebrospinal Fluid (CSF)
Functions
Gives buoyancy to the CNS organs
Protects the CNS from blows and other trauma
Nourishes the brain and carries chemical signals
Choroid Plexuses
Produce CSF at a constant rate
Hang from the roof of each ventricle
Clusters of capillaries enclosed by pia mater and a layer of ependymal cells
Figure 12.26b
Ependymal
cells
Capillary
Connective tissue of pia mater
Wastes and unnecessary solutes absorbed
Section
of choroid
plexus
(b) CSF formation by choroid plexuses
Cavity of
ventricle
CSF forms as a filtrate containing glucose, oxygen, vitamins, and ions (Na+, Cl–, Mg2+, etc.)
Figure 12.26a
Superior sagittal sinus
Arachnoid villus
Subarachnoid space
Arachnoid mater
Meningeal dura mater
Periosteal dura mater
Right lateral ventricle (deep to cut)
Choroid plexus of fourth ventricle
Central canal of spinal cord
Choroid plexus
Interventricular foramen
Third ventricle
Cerebral aqueduct
Lateral aperture
Fourth ventricle
Median aperture
(a) CSF circulation
CSF is produced by the choroid plexus of each ventricle.
1
CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord.
2
CSF flows through the subarachnoid space.
3
CSF is absorbed into the dural venous sinuses via the arachnoid villi.
4
1
2
3
4
Hydrocephalus
Due to blockage or overproduction of CSF
Internal versus external hydrocephalus
Infants versus adults
Treatment