Ventricular System, Ventricular System, Meninges, and CSFMeninges, and CSF

Study suggestion: Read the selected pages Study suggestion: Read the selected pages from Chapter 2 first, then read Chapter 8from Chapter 2 first, then read Chapter 8

Thinking questionsThinking questions

• How to pack something How to pack something very fragile that has to very fragile that has to be shipped cross-be shipped cross-country country

• How to make a person How to make a person who is heavy into a who is heavy into a person who can be person who can be lifted with one handlifted with one hand

Overview of this lecture, so Overview of this lecture, so you see the big pictureyou see the big picture

• CNS is very fragile and vulnerable, and it is CNS is very fragile and vulnerable, and it is constantly being transported aroundconstantly being transported around– Cushion from ___________ and ___________Cushion from ___________ and ___________– Encase the whole thing in _______________ Encase the whole thing in _______________

• CNS would collapse under its own weight if CNS would collapse under its own weight if placed on a table. Brain’s weight is placed on a table. Brain’s weight is reduced from 1500g (3.3 lbs) reduced from 1500g (3.3 lbs) 75 g (1/10 75 g (1/10 of a lb.) because it is ___________ in of a lb.) because it is ___________ in ____________________

Introduction to CSFIntroduction to CSF• Cerebrospinal Fluid (CSF)Cerebrospinal Fluid (CSF)

– ColorlessColorless– Continuously produced deep within Continuously produced deep within

internal brain spaces called ___________, internal brain spaces called ___________, and cushions around whole CNS and cushions around whole CNS ____________________________

– FunctionsFunctions•Mechanical cushion around CNSMechanical cushion around CNS

•Removal of harmful substances & wasteRemoval of harmful substances & waste

Produced in ventricles*, and Produced in ventricles*, and flows caudally through flows caudally through ventricular systemventricular system–Two lateral ventriclesTwo lateral ventricles

•Interventricular foramenInterventricular foramen–One third ventricleOne third ventricle

•Cerebral aqueductCerebral aqueduct–One fourth ventricleOne fourth ventricle

•Two foramina of Luschka Two foramina of Luschka •One foramen of One foramen of

MagendieMagendie

CSF CIRCULATION: Where does it CSF CIRCULATION: Where does it start?start?

* CSF produced by choroid plexus in the ventricular cavities

Can you find the structures mentioned in the previous slide

on these figures?

So, CSF exits the So, CSF exits the ventricular systemventricular system

• Exits from 4Exits from 4thth ventricle ventricle throughthrough– Two foramina on lateral sides Two foramina on lateral sides

of fourth ventricleof fourth ventricle= __________________= __________________

– One foramen in posterior part One foramen in posterior part of fourth ventricle = foramen of fourth ventricle = foramen of ___________________of ___________________

• Enters into a space called Enters into a space called _____________ that _____________ that encircles/covers whole encircles/covers whole CNS!CNS!

More about subarachnoid More about subarachnoid spacespace– Net-line structure within Net-line structure within

the SAS is called the SAS is called arachnoid trabeculaearachnoid trabeculae

– Large Large pockets/enlargements of pockets/enlargements of SAS are called SAS are called ______________________________________________

– Do you see the arachnoid Do you see the arachnoid trabeculae? Do you see trabeculae? Do you see any cisterns?any cisterns?

– Lumbar puncture (spinal Lumbar puncture (spinal tap) from lumbar cisterntap) from lumbar cistern

Subarachnoid space is sandwiched Subarachnoid space is sandwiched between two of the three covering between two of the three covering layers over the CNSlayers over the CNS

• These three layers are called the These three layers are called the MENINGES.MENINGES.

• ??? How is this related to meningitis???? How is this related to meningitis?

Outer covering of brain:Outer covering of brain:Where are the meninges?Where are the meninges?

• (Scalp)(Scalp)

• (Muscles and surface arteries)(Muscles and surface arteries)

• (Bone: Skull)(Bone: Skull)

• Meninges Meninges – Cover brain and spinal cordCover brain and spinal cord– 3 layers3 layers– Between two of the layers is a cushioning Between two of the layers is a cushioning

layer of fluid called cerebrospinal fluidlayer of fluid called cerebrospinal fluid

MeningesMeninges• Three-layer covering of CNS, from Three-layer covering of CNS, from

outermost to innermostoutermost to innermost– Dura mater Dura mater (outermost, tough, (outermost, tough,

DURable)DURable)•has 2 fused, closely united sub-layers has 2 fused, closely united sub-layers

– One next to boneOne next to bone– One next to arachnoid materOne next to arachnoid mater

•2 layers separate in spots to form 2 layers separate in spots to form venous sinusesvenous sinuses

– Arachnoid mater + subarachnoid Arachnoid mater + subarachnoid space (below it):space (below it):

– Pia mater Pia mater (innermost, “tender” fragile)(innermost, “tender” fragile)

• Three layers continuous: brain & spinal cordThree layers continuous: brain & spinal cord

Meninges cover all of the Meninges cover all of the CNS, including spinal cordCNS, including spinal cord

Dura mater: More detailsDura mater: More details• In certain places, the two layers In certain places, the two layers

separate to form dural venous separate to form dural venous sinuses (system of cavities and sinuses (system of cavities and channels to drain venous blood)channels to drain venous blood)

• Rigid sheets of dura mater extend Rigid sheets of dura mater extend into cranial vault (Fig. 3-11 in into cranial vault (Fig. 3-11 in W&A)W&A)– Falx cerebri Falx cerebri

• flat, crescent-shapedflat, crescent-shaped

• separates two cerebral hemispheresseparates two cerebral hemispheres

– Tentorium cerebelli Tentorium cerebelli • dome-shapeddome-shaped

• separates cerebral hemispheres from separates cerebral hemispheres from cerebellumcerebellum

– Diagphragma sella (not pictured)Diagphragma sella (not pictured)• Roof of structure that encloses pituitary glandRoof of structure that encloses pituitary gland

Do you see where the dural venous sinuses are?

Coronal section: Coronal section: More details on More details on dura materdura mater• Look at falx cerebri and Look at falx cerebri and

tentorium cerebellitentorium cerebelli

• Folds of dura materFolds of dura mater– Brace brain from Brace brain from

displacementdisplacement– Receive blood from brain’s Receive blood from brain’s

cerebral veinscerebral veins– Receive cerebrospinal fluid Receive cerebrospinal fluid

from subarachnoid spacefrom subarachnoid space

Subarachnoid space (SAS): Subarachnoid space (SAS): More detailsMore details

• Sub-arachnoid space filled with cerebrospinal fluid (CSF)

• Extends into sulci (p. 63 of W)

• Larger portions of this space called cisterns (Figure 3-9)

• Arachnoid protrudes into dural venous sinuses – Protrusions = arachnoid villi– CSF absorbed into blood +

removed from SAS

Pia mater: More detailsPia mater: More details• Adheres tightly to Adheres tightly to

surface of brainsurface of brain

• Outer surface has Outer surface has many blood vesselsmany blood vessels– Many blood vessels Many blood vessels

cross the space cross the space between the pia and between the pia and the arachnoid matersthe arachnoid maters

Circulation of CSF:Lateral view

Clinical applications related to Clinical applications related to CSFCSF• Blockage of CSF movement or failure of Blockage of CSF movement or failure of

resorbtion mechanism resorbtion mechanism accumulation of fluid in accumulation of fluid in ventricles or around brain tissue ventricles or around brain tissue hydrocephalushydrocephalus – Treated by Treated by shuntingshunting CSF from CSF from

ventricle to body peritonealventricle to body peritoneal

or pleural cavitiesor pleural cavities

• Medical diagnostics on CSFMedical diagnostics on CSF– CSF pressure CSF pressure (high pressure associated with tumor, (high pressure associated with tumor,

hemorrhage, hydrocephalus, meningitis or hemorrhage, hydrocephalus, meningitis or encephalitis) encephalitis)

– CSF chemical and cell studiesCSF chemical and cell studies

Clinical application related to Clinical application related to meninges meninges Extracerebral hemorrhagesExtracerebral hemorrhages• Hemorrhages from the blood Hemorrhages from the blood

vessels in the meninges or on vessels in the meninges or on the surface of the brain, from: the surface of the brain, from:– Weakness of vessel wallWeakness of vessel wall– Traumatic injuryTraumatic injury– (rarely)-extreme fluctuations in blood pressure(rarely)-extreme fluctuations in blood pressure

• Types, based on where blood accumulatesTypes, based on where blood accumulates– Subarachnoid: b/w arachnoid and pia (most Subarachnoid: b/w arachnoid and pia (most

common, from common, from

•aneurysm aneurysm

•arteriovenous malformation (AVM)arteriovenous malformation (AVM)– Subdural: under dura (esp. from TBI)Subdural: under dura (esp. from TBI)– Epidural: b/w dura and skull (esp. from TBI)Epidural: b/w dura and skull (esp. from TBI)

• After bleeding stops, left with hematomaAfter bleeding stops, left with hematoma

Clinical application: Clinical application: Extracerebral Extracerebral hemorrhages (cont.)hemorrhages (cont.)• Types, based on where blood Types, based on where blood

accumulatesaccumulates– Subarachnoid: b/w Subarachnoid: b/w

arachnoid and pia (most arachnoid and pia (most common, from common, from

•aneurysm aneurysm

•arteriovenous arteriovenous malformation (AVM)malformation (AVM)

– Subdural: under dura (esp. Subdural: under dura (esp. from TBI)from TBI)

– Epidural: b/w dura and skull Epidural: b/w dura and skull (esp. from TBI)(esp. from TBI)

• After bleeding stops, left with After bleeding stops, left with hematomahematoma