Prof. Dr. Bayram YılmazProf. Dr. Bayram Yılmaz

Yeditepe UniversityYeditepe University

Faculty of MedicineFaculty of Medicine

Department of PhysiologyDepartment of Physiology

Meninges Meninges

Cerebro Spinal Fluid (CSF) & Cerebro Spinal Fluid (CSF) &

Blood Brain Barrier (BBB)Blood Brain Barrier (BBB)

Protection of the BrainProtection of the Brain

The brain is protected by The brain is protected by bonebone, ,

meningesmeninges, and , and cerebrospinal fluidcerebrospinal fluid

Harmful substances are shielded from Harmful substances are shielded from

the brain by the the brain by the blood-brain barrierblood-brain barrier

Hair, skin, craniumHair, skin, cranium

Venous sinus bloodVenous sinus blood

MeningesMeninges

– DDurura matera mater

– Arachnoid Arachnoid

membranemembrane

– Pia materPia mater

Cerebrospinal fluidCerebrospinal fluid

Protecting the BrainProtecting the Brain

MeningesMeninges

DDura mater, arachnoid mater and ura mater, arachnoid mater and pia materpia mater

Functions of the meningesFunctions of the meninges– Cover and protect the CNSCover and protect the CNS– Protect blood vessels and enclose Protect blood vessels and enclose

venous sinusesvenous sinuses– Contain cerebrospinal fluid (CSF)Contain cerebrospinal fluid (CSF)– Form partitions within the skullForm partitions within the skull

MeningesMeninges

Dura MaterDura Mater

Leathery, strong meninx composed of two fibrous connective tissue layers

The two layers separate in certain areas and form dural sinuses

Dura MaterDura Mater

Three dural septa extend inward and limit

excessive movement of the brain

– Falx cerebri – fold that dips into the

longitudinal fissure

– Falx cerebelli – runs along the vermis of the

cerebellum

– Tentorium cerebelli – horizontal dural fold

extends into the transverse fissure

Dura MaterDura Mater

Arachnoid Mater

The middle meninx, which forms a loose brain

covering

It is separated from the dura mater by the

subdural space

Beneath the arachnoid is a wide subarachnoid

space filled with CSF and large blood vessels

Arachnoid villi protrude superiorly and permit

CSF to be absorbed into venous blood

Arachnoid Mater

Pia Mater

Deep meninx composed of delicate

connective tissue that clings tightly

to the brain

Spinal Cord and Meninges

1) dura mater (yellow)

2) arachnoid mater

(green)

3) pia mater (red)

4) subarachnoid space

(CSF fills this space)

Ventricles of the BrainVentricles of the Brain

Arise from expansion of the lumen of the Arise from expansion of the lumen of the

neural tubeneural tube The ventricles are:The ventricles are:

– The paired C-shaped The paired C-shaped lateral ventricleslateral ventricles

– The The third ventriclethird ventricle found in the diencephalon found in the diencephalon

– The The fourth ventriclefourth ventricle found in the hindbrain found in the hindbrain

dorsal to the ponsdorsal to the pons

Ventricles of the BrainVentricles of the Brain

Cerebrospinal Fluid (CSF)Cerebrospinal Fluid (CSF)

Watery solution similar in composition to blood plasma Contains less protein and different ion concentrations

than plasma Forms a liquid cushion that gives buoyancy to the CNS

organs Prevents the brain from crushing under its own weight Protects the CNS from blows and other trauma Nourishes the brain and carries chemical signals

throughout it

Plasma and Plasma and CSFCSF Fluid Fluid CompositionComposition

Choroid Plexuses

Clusters of capillaries that form tissue

fluid filters, which hang from the roof

of each ventricle

Have ion pumps that allow them to

alter ion concentrations of the CSF

Help cleanse CSF by removing wastes

Choroid PlexusesChoroid Plexuses

Normal volume is Normal volume is

about 150 mlabout 150 ml

Forms and drains at Forms and drains at

a constant ratea constant rate

Drains into dural Drains into dural

sinuses through the sinuses through the

arachnoid villiarachnoid villi

Cerebro Spinal Fluid Cerebro Spinal Fluid (CSF)(CSF)

Site of production : Choroid plexus

Daily absorption rate : 500-800 ml

Site of absorption : Arachnoid villi

Production per Day : 500-800 ml

Total volume : 120-150 ml

Density : About 1006

Appearance : Colorless, clear

CSF Production and Drainage

Lumbar Puncture for CSF samplingLumbar Puncture for CSF sampling

Lumbar puncture (LP) is Lumbar puncture (LP) is

the insertion of a needle the insertion of a needle

into the subarachnoid into the subarachnoid

spacespace

Although the Although the

subarachnoid space can subarachnoid space can

be accessed from other be accessed from other

levels, the lumbar region levels, the lumbar region

is most often used as it is most often used as it

allows the needle to be allows the needle to be

inserted below the end of inserted below the end of

the spinal cord.the spinal cord.

Lumbar Puncture for CSF samplingLumbar Puncture for CSF sampling

Lumbar Puncture for CSF samplingLumbar Puncture for CSF sampling

Blood-Brain Barrier: Functions

Selective barrier that allows nutrients to pass

freely

Is ineffective against substances that can diffuse

through plasma membranes

Absent in some areas (vomiting center and the

hypothalamus), allowing these areas to monitor

the chemical composition of the blood

Stress increases the ability of chemicals to pass

through the blood-brain barrier

Extensive capillaries & sinusesExtensive capillaries & sinuses

Tight junctions: limit permeabilityTight junctions: limit permeability

Astrocyte foot processes: secrete paracrinesAstrocyte foot processes: secrete paracrines

Protects brain: hormones & circulating chemicalsProtects brain: hormones & circulating chemicals

Many glucose transportersMany glucose transporters

Blood Brain Barrier

Blood Brain BarrierBlood Brain Barrier

Includes the least permeable capillaries of the body

Excludes many potentially harmful substances Useless against some substances

Lipid soluble molecules Respiratory gases Alcohol Nicotine Anesthesia

1) 1) Continuous endothelium of capillary Continuous endothelium of capillary wallswalls2) T2) Thick basal laminahick basal lamina3) Extentions of 3) Extentions of astrocytesastrocytes

Blood-Brain Barrier

Protective mechanism that Protective mechanism that

helps maintain a stable helps maintain a stable

environment for the brainenvironment for the brain

Bloodborne substances are Bloodborne substances are

separated from neurons by:separated from neurons by:

– Continuous endothelium of Continuous endothelium of

capillary wallscapillary walls

– Relatively thick basal laminaRelatively thick basal lamina

– Bulbous feet of astrocytesBulbous feet of astrocytes

HydrocephalusHydrocephalus: excessive fluid accumulation in the brain

Ventriculo-Peritoneal ShuntVentriculo-Peritoneal Shunt

http://www.medicaforum.com/content/csf-shunt-animation