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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.

1

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.

2

CSF flows through theCSF flows through theCSF flows through theCSF flows through thesubarachnoid space. subarachnoid space. subarachnoid space. subarachnoid space.

3

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.

4

1

2

3

4

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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