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Meninges
CSF
The Nervous System
Introduction
• Protection of the brain
– Bone (skull)
– Membranes (meninges)
– Watery cushion (cerebrospinal fluid)
– Blood-brain barrier (astrocytes)
The Meninges
• Series of membranes
• Cover and protect the CNS
• Anchor and cushion the brain
• Contain cerebrospinal fluid (CSF)
The Meninges
• Three layers
– Dura mater
– Arachnoid mater
– Pia mater
Figure 12.24
Skin of scalp
Periosteum
Falx cerebri(in longitudinalfissure only)
Blood vesselArachnoid villusPia materArachnoid mater
Duramater Meningeal
Periosteal
Bone of skull
Superiorsagittal sinus
Subduralspace
Subarachnoidspace
The Meninges
• Dura mater – “Tough mother”
– Strongest meninx
– Fibrous connective tissue
– Limit excessive movement of the brain
– Forms partitions in the skull
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Figure 12.25a
Falx cerebri
Superior
sagittal sinus
Straight
sinus
Crista galliof theethmoid bone
Pituitary
gland
Falx
cerebelli
(a) Dural septa
Tentorium
cerebelli
The Meninges
• 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
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
Figure 12.30Figure 12.30Figure 12.30Figure 12.30
LigamentumLigamentumLigamentumLigamentumflavumflavumflavumflavum
SupraSupraSupraSupra----spinousspinousspinousspinousligamentligamentligamentligament
Lumbar punctureLumbar punctureLumbar punctureLumbar punctureneedle enteringneedle enteringneedle enteringneedle enteringsubarachnoidsubarachnoidsubarachnoidsubarachnoidspacespacespacespace
FilumFilumFilumFilumterminaleterminaleterminaleterminale
InterInterInterInter----vertebralvertebralvertebralvertebraldiscdiscdiscdisc
TTTT12121212
LLLL5555
Cauda equinaCauda equinaCauda equinaCauda equinain subarachnoidin subarachnoidin subarachnoidin subarachnoidspacespacespacespace
DuraDuraDuraDuramatermatermatermater
LLLL5555
LLLL4444
SSSS1111
ArachnoidArachnoidArachnoidArachnoidmattermattermattermatter
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Cerebrospinal Fluid (CSF)
• Solution that bathes the CNS
• Composition
– Watery solution
• Modified plasma (less protein, different ion
concentrations)
– 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
• Reduces brain’s effective weight by 97%!
– Protects the CNS from blows & other trauma
– Nourishes the brain & carries chemical signals
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
Figure 12.26b
Ependymal
cells
Capillary
Connectivetissue ofpia mater
Wastes andunnecessarysolutes absorbed
Section
of choroid
plexus
(b) CSF formation by choroid plexuses
Cavity of
ventricle
CSF forms as a filtratecontaining glucose, oxygen, vitamins, and ions(Na+, Cl–, Mg2+, etc.)
Figure 12.26aFigure 12.26aFigure 12.26aFigure 12.26a
SuperiorSuperiorSuperiorSuperiorsagittal sinussagittal sinussagittal sinussagittal sinus
Arachnoid villusArachnoid villusArachnoid villusArachnoid villus
Subarachnoid spaceSubarachnoid spaceSubarachnoid spaceSubarachnoid space
Arachnoid materArachnoid materArachnoid materArachnoid mater
Meningeal dura materMeningeal dura materMeningeal dura materMeningeal dura mater
Periosteal dura materPeriosteal dura materPeriosteal dura materPeriosteal dura mater
Right lateral ventricleRight lateral ventricleRight lateral ventricleRight lateral ventricle(deep to cut)(deep to cut)(deep to cut)(deep to cut)
Choroid plexusChoroid plexusChoroid plexusChoroid plexusof fourth ventricle of fourth ventricle of fourth ventricle of fourth ventricle
Central canalCentral canalCentral canalCentral canalof spinal cordof spinal cordof spinal cordof spinal cord
ChoroidChoroidChoroidChoroidplexus plexus plexus plexus
InterventricularInterventricularInterventricularInterventricularforamenforamenforamenforamen
Third ventricleThird ventricleThird ventricleThird ventricle
Cerebral aqueductCerebral aqueductCerebral aqueductCerebral aqueduct
Lateral apertureLateral apertureLateral apertureLateral aperture
Fourth ventricleFourth ventricleFourth ventricleFourth ventricle
Median apertureMedian apertureMedian apertureMedian aperture
(a) CSF circulation
CSF is produced by theCSF is produced by theCSF is produced by theCSF is produced by thechoroid plexus of eachchoroid plexus of eachchoroid plexus of eachchoroid plexus of eachventricle. ventricle. ventricle. ventricle.
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CSF flows through theCSF flows through theCSF flows through theCSF flows through theventricles and into the ventricles and into the ventricles and into the ventricles and into the subarachnoid space via the subarachnoid space via the subarachnoid space via the subarachnoid space via the median and lateral apertures. median and lateral apertures. median and lateral apertures. median and lateral apertures. Some CSF flows through the Some CSF flows through the Some CSF flows through the Some CSF flows through the central canal of the spinal cord.central canal of the spinal cord.central canal of the spinal cord.central canal of the spinal cord.
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CSF flows through theCSF flows through theCSF flows through theCSF flows through thesubarachnoid space. subarachnoid space. subarachnoid space. subarachnoid space.
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CSF is absorbed into the dural venousCSF is absorbed into the dural venousCSF is absorbed into the dural venousCSF is absorbed into the dural venoussinuses via the arachnoid villi. sinuses via the arachnoid villi. sinuses via the arachnoid villi. sinuses via the arachnoid villi.
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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