Download The Nervous System Introduction The Meninges The Meninges The

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Introduction
• Protection of the brain
– Bone (skull)
– Membranes (meninges)
– Watery cushion (cerebrospinal fluid)
– Blood-brain barrier (astrocytes)
The Nervous System
Meninges
CSF
The Meninges
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The Meninges
Series of membranes
Cover and protect the CNS
Anchor and cushion the brain
Contain cerebrospinal fluid (CSF)
• Three layers
– Dura mater
– Arachnoid mater
– Pia mater
The Meninges
Superior
sagittal sinus
Subdural
space
Subarachnoid
space
Skin of scalp
Periosteum
Bone of skull
Dura
Periosteal
Meningeal mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood vessel
• Dura mater – “Tough mother”
– Strongest meninx
– Fibrous connective tissue
– Limit excessive movement of the brain
– Forms partitions in the skull
Falx cerebri
(in longitudinal
fissure only)
Figure 12.24
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The Meninges
Superior
sagittal sinus
Falx cerebri
Straight
sinus
Crista galli
of the
ethmoid
bone
Tentorium
cerebelli
• Arachnoid mater – “Spider mother”
– Middle layer with weblike extensions
– Separated from the dura mater by the subdural space
– Subarachnoid space contains CSF and blood vessels
Falx
cerebelli
Pituitary
gland
(a) Dural septa
Figure 12.25a
The Meninges
• Pia mater – “Gentle mother”
– Connected to the dura mater by projections from
the arachnoid mater
– Layer of delicate vascularized connective tissue
– Clings tightly to the brain
Meningitis
• Inflammation of meninges
• May be bacterial or viral
• Diagnosed by obtaining CSF sample via lumbar
tap
T12
Ligamentum
flavum
Lumbar puncture
needle entering
subarachnoid
space
L5
L4
SupraSupraspinous
ligament
L5
Filum
terminale
S1
InterIntervertebral
disc
Arachnoid
matter
Dura
mater
Cauda equina
in subarachnoid
space
Figure 12.30
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Cerebrospinal Fluid (CSF)
• Solution that bathes the CNS
• Composition
– Watery solution
• Modified plasma (less protein, different ion
concentrations)
Cerebrospinal Fluid (CSF)
• Functions
– Gives buoyancy to the CNS organs
• Reduces brain’s effective weight by 97%!
– Protects the CNS from blows & other trauma
– Nourishes the brain & carries chemical signals
– Constant volume (about 150 ml)
• About 500 ml formed daily
• Replaced every 8 hours or so
Cerebrospinal Fluid (CSF)
• Choroid plexuses
– Produce CSF at a constant rate
– Hang from the roof of each ventricle
– Clusters of capillaries enclosed by pia mater & a
layer of ependymal cells
Ependymal
cells
Capillary
Section
of choroid
plexus
Connective
tissue of
pia mater
Wastes and
unnecessary
solutes absorbed
CSF forms as a filtrate
containing glucose, oxygen,
vitamins, and ions
(Na+, Cl–, Mg2+, etc.)
(b) CSF formation by choroid plexuses
Cavity of
ventricle
Figure 12.26b
Superior
sagittal sinus
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Choroid
plexus
Arachnoid villus
Interventricular
foramen
Subarachnoid space
Arachnoid mater
Meningeal dura mater
Periosteal dura mater
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Right lateral ventricle
(deep to cut)
Choroid plexus
of fourth ventricle
3
Third ventricle
Cerebral aqueduct
Lateral aperture
Fourth ventricle
Median aperture
Central canal
of spinal cord
(a) CSF circulation
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1 CSF is produced by the
choroid plexus of each
ventricle.
2 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.
3 CSF flows through the
subarachnoid space.
4 CSF is absorbed into the dural venous
sinuses via the arachnoid villi.
Figure 12.26a
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Cerebrospinal Fluid (CSF)
• Hydrocephalus
– Due to blockage or overproduction of CSF
– Internal hydrocephalus
• CSF accumulates in the ventricles, expanding them outward
– External hydrocephalus
• CSF accumulates in the subarachnoid space, compressing the
brain
Cerebrospinal Fluid (CSF)
• Hydrocephalus
– Due to blockage or overproduction of CSF
– Infants
• Head enlarges because skull bones have not yet fused
– Adults
• Accumulating fluid compresses blood vessels and soft
nervous tissue, causing brain damage
Cerebrospinal Fluid (CSF)
• Hydrocephalus
– Treatment
• 6/10 will die without treatment
• Shunts are placed to divert excess fluid to other areas of the
body
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