84 terms

Meninges, ventricular system and cerebral spinal fluid

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Meninges
-the connective tissue membranes that envelop the brain and spinal cord
3 layers of meninges
- Dura mater (outermost and thickest layer)

-Arachnoid mater/arachnoid (delicate middle layer)

-Pia mater (very thin inner layer, adherent to CNS)
Leptomeninges
arachnoid + pia mater
Pachymenix
dura mater

(only when the arachnoid and pia mater are referred to as leptomeninges)
Space between the arachnoid and pia mater is called
-subarachnoid space

-filled with cerebrospinal fluid
General functions of menginges
-Protection of CNS (dura mater and CSF help a lot)

-CSF helps keep brain from collapsing under its own weight

- help w blood supply of CNS
Dura mater: what is it composed of
-dense irregular collagenous connective tissue
- with two layers that are firmly fused (except at the dural venous sinuses)
Dura mater: 2 layers
1) Periosteal/endosteal layer

2) Meningeal
Dura mater: 2 layers: Periosteal/endosteal layer
-outer layer

-forms periosteum on inner side of inner table of skull bones

-fused to inside of compact bone of parts of skull that form the cranial cavity
Dura mater: 2 layers: Meningeal layer
-inner layer

-thinner and lined with simple squamous epithelium on inner surface

-forms tubular sheaths for cranial nerves as they exit skull--> dural root sleeves transition into epineurium
Dura mater: NOTE dura sheath of optic nerve is continuous with
-the sclera
Dura mater: epidural space
-abnormal space created if attachment of periosteal layer is torn from bone and fluid forces its way in (skull fracture and arterial blood)

epidural hematoma blood from damage to the meningeal blood vessels forms this (dura pealed off from skin) BAD KILL PPL, 20 mins

-there is a true epidural space filled with fat and the internal vertebral venous plexus located in the vertebral canal where dura mater does NOT attach to surrounding bone
Dura mater: subdural space
-potential space between inner surface of meningeal layer of dura mater and arachnoid

-subdural hematoma -fluid gathers in this space and usually results from damage to external cerebral veins or dural venous sinuses (dura still attached to skull venous blood) (hours to days)
-Damage to cerebral arteries and/or deep cerebral veins usually causes bleeding in brain tissue itself (intracranial hemorrhages)
its true
Dural folds
-partially divide the cranial cavity into compartments
Dural folds: falx cerebri
-lies on longitudinal fissue between right and left cerebral hemispheres

-single midline structure
Dural folds: Falx cerebelli
-vertical fold in the midline lying between cerebellar hemispheres

-single structure
Dural folds: tentorium cerebelli
-horizontal orientation located between occipital lobes of cerebrum and cerebellum

-has large curved hiatus (tentorial notch/tentorial incisures) between free margin and dorsum sellae (MIDBRAIN IS FOUND IN HERE)
Potential injury site of oculomotor nerve
-Runs between the attachment sites of the tentorium cerebelli with the anterior and posterior clinoid processes
Dural folds: Tentorium cerebelli: expanding lesions of cerebrum
causes medial portion of temporal lobes to herniate through this tentorial notch and midbrain displaced laterally and injured by tentorium cerebelli--> ipsilateral motor paresis
Dural folds: tentorium cerebelli: divides cavity into two regions
1) supratentorial compartment (contains forebrain)
2) Infratentroial compartment (contains hindbrain)

-these regions are connected by narrow gap between midbrain and border of tentorial incisures--> region cannot get obstructed, leading to ventricular dilation
Dural folds: diaphragma sellae
-round, horizontal sheet that forms roof over sella turica (pituitary fossa)
Dura mater blood supply: What arteries supply the dura mater? What veins drain the dura mater?
Anterior, middle, posterior meningeal arteries and veins
Dura mater blood supply: anterior meningeal artery
arises from ophthalmic artery
Dura mater blood supply: middle meningeal artery
-largest, arises from maxillary artery

-enters cranial vault through foramen spinosum
Dura mater blood supply: posterior meningeal artery
-arises from occipital and/or vertebral arteries

-since these arteries run in the periosteal layer of the dura mater--> injuries to these arteries usually cause epidural hematomas
Dura mater blood supply: irriation of dura mater can lead to severe headaches (migraines, cluster headaches) when there is a problem in these areas
-anterior cranial fossa ( refers pain to forehead, temples, and eyes Opthalmic division of CN 5)

-Middle cranial fossa (refers pain to cheeks, jaw, and mouth (maxillary and mandibular division of CN 5)

-Posterior cranial fossa (refers pain to neck region behind the ear, vagus and cervical nerves)
Arachnoid mater: what is it
-thin layer of loose connective tissue

-translucent

-avascular
Arachnoid mater: arachnoid villi/granulations/pacchonian villi
-are specializations of the arachnoid that recycle cerebrospinal fluid back into the blood
Arachnoid mater: subarachnoid cisterns
-regions of the subarachnoid space that is normally dilated and serves as reservoirs of CSF
Subarachnoid cisterns: cisterna magna/cerebellomedullary cistern) location
-single midline structure

-posterior to medulla
-inferior to cerebellum
-just above foramen magnum
Subarachnoid cisterns: cisterna magna/cerebellomedullary cistern) description
-CSF can be sampled here but infrequently used
Subarachnoid cisterns: Superior cistern/cisterna vena magna cerebri location
- single midline structure

-deep in space between cerebral hemispheres and cerebellum
-posterior to midbrain
-superior to cerebellum
Subarachnoid cisterns: Superior cistern/cisterna vena magna cerebri description
contrains great cerebral vein
Subarachnoid cisterns: mesencephalic cisterns/cisternae ambiens location
-paired

-on lateral sides of midbrain
-on right and left
Subarachnoid cisterns: mesencephalic cisterns/cisternae ambiens description
-connect superior cistern and interpeduncular cistern

-NOT a midline structure
Subarachnoid cisterns: Interpeduncular cistern/cisterna basalis location
-single midline structure

-between cerebral peduncles just anterior to midbrain
Subarachnoid cisterns: Interpeduncular cistern/cisterna basalis description
-oculomotor nerves run through this cistern
Subarachnoid cisterns: Chiasmatic cistern location
-single midline structure

-located just above optic chiasm
Subarachnoid cisterns: Chiasmatic cistern description
-small dilation of subarachnoid space
Subarachnoid cisterns: pontine cistern location
-single midline structure

-anterior to pons
Subarachnoid cisterns: pontine cistern description
-contains basilar artery
Subarachnoid cisterns: cisterns of the lateral cerebral fissure (of sylvius) location
-paired

-in the anterior aspect of sylvian fissures between frontal and temporal lobes of cerebral hemispheres
Subarachnoid cisterns: cisterns of the lateral cerebral fissure (of sylvius) description
-not a midline structure
Subarachnoid cisterns: Lumbar cistern location
-single midline structure

-NOT located in the head

-in the lower lumbar region of the spine
Subarachnoid cisterns: lumbar cistern description
-contains cauda equina

-typical place where CSF samples are taken

(procedure = lumbar puncture)
In the spinal region, subarachnoid space extends to the level of the 2nd sacral segment
its true
Pia mater: what is it?
-single layer of cells that can NOT be seen with the naked eye

-Highly vascular
Pia mater: specializations that can be seen with the naked eye
1) denticulate ligaments

2) Filum terminale/filum terminale internum

3) tela choroidea

DTF
Pia mater: specializations that can be seen with the naked eye: denticulate ligaments
-folds of extra thick pia mater located on the lateral aspects of the spinal cord

-they span the subarachnoid space to attach to the deep surface of the arachnoid

-helps anchor the spinal cord in the vertebral canal
Pia mater: specializations that can be seen with the naked eye: filum terminale/filum terminale internum
-single midline continuation of pia mater that attaches the conus medullaris (end of spinal cord) to the inferior aspect of the dural sac (S2 vertebral level)

-anchors the end of the spinal cord in the vertebral canal
Pia mater: specializations that can be seen with the naked eye: tela choroidea
-folds of pia mater covered with typical ependymal that support the choroid plexus (modified ependymal cells that produce CSF)
Ventricular system: what are ventricles
-remnants of the neural tube cavity in the region of the brain expand to form the ventricles of the brain

-lined with ependymal and filled with CSF
Ventricular system: two lateral ventricles anterior horns (cornu) are separated by
-septum pellucidum (double glial membrane located in the midline)

-lateral ventricle is remnant of telecephalon
Ventricular system: Third ventricle
-right and left half of thalamus meet each other in midline that forms a solid bridge called interthalamic adhesion

-remnant of thalamus
Ventricular system: fourth ventricle
-remnant of rhombencephalon (or both metencephalon and myelencephalon)

-floor is considered ventral/anterior side and roof is considered dorsal/posterior side
Ventricular system: 4th ventricle superior medullary velum
-the upper 1/2 of the roof

-is a thin layer of neural tissue that separates the CSF of the 4th ventricle from the cerebellum
Ventricular system: 4th ventricle: Inferior medullary velum
-the lower 1/2 of the roof

-is merely a glial mebrane that separates the CSF of the IV ventricle from the cerebellum
Ventricular system: 4th ventricle openings: cerebral aqueduct/aquaduct of sylvius/aquaduct of iter
-superior opening where CSF enters 4th ventricle
Ventricular system: 4th ventricle openings: central canal (of spinal cord)
-inferior opening that represents the continuation of the neural tube cavity into the region of the spinal cord
Ventricular system: 4th ventricle openings: foramen magendie/median aperture
-single midline opening in posterior aspect of 4th ventricle where CSF can leave to enter into cisterna magna
Ventricular system: 4th ventricle openings: foramina of (von) luschka/lateral apertures
-pair of openings in lateral aspect of 4th ventricle where CSF can leave to enter into pontine cistern
Lateral ventricle: anterior horn location in the brain
-frontal lobe
Lateral ventricle: anterior horn: boundaries
Roof (dorsal)- corpus callosum

Lateral wall- caudate nucleus

Medial wall- septum pellucidum/fornix
Lateral ventricle: body/pars centralis: location in brain
-frontal and parietal lobe
Lateral ventricle: body/pars centralis: boundaries
Roof (dorsal)- corpus callosum

Floor (ventral)- thalamus

Lateral wall- caudate nucleus

-medial wall- septum pellucidum/fornix
Lateral ventricle: inferior horn: location in brain
-temporal lobe
Lateral ventricle: inferior horn: boundaries
Roof (dorsal)- caudate/amygala

Floor (ventral)- hippocampus
Third ventricle location in brain
-diencephalon
Third ventricle boundaries
Roof (dorsal)- fornix

Floor (ventral)- floor of hypothalamus

Lateral wall- thalamus and hypothalamus
Cerebral aquaduct location in brain
-midbrain
Cerebral aquaduct boundaries
roof (dorsal)- superior and inferior colliculi

floor (ventral)- midbrain tegmentum
Fourth ventricle location in brain
pons and upper medulla
Fourth ventricle boundaries
roof (dorsal) - medullary velums/cerebellum

Floor (ventral)- pontine/upper medullary tegmentum

lateral wall- cerebellar peduncles
CSF: what is it
fills the ventricles of the brain and subarachnoid space
CSF: choroid plexus
-produces CSF

- and made of fenestrated with diaphragms capilaries, pia mater and modified ependymal cells
CSF: tela choroidea
-supports choroid plexus
CSF: note ependyma of central canal of spinal cord produces some serous fluid (NOT TRUE CSF) that mixes with CSF in 4th ventricle at the superior end of the central canal
its true
CSF: arachnoid villi/granulations/paccionian
-are evaginations of arachnoid that protrude mainly into superior sagittal sinus--> one way valves that allow CSF to flow into blood of dural venous sinuses
CSF: Damage: hydrocephalus
-occurs with obstruction of CSF pathways and CSF can't be recycled back into blood so it builds up in ventricular system--> causes ventricular dilation that causes pressure on brain tissue (entire head can expand in kids)
CSF: Damage: communicating hydrocephalus
-occurs when the flow of CSF is NOT obstructed--> CSF overproduced or it can't re enter the blood (from blockage of arachnoid villi)
CSF: Damage: Non communicating hydrocephalus
-occurs when there is blockage to CSF flow either within ventricular system (where ventricles communicate w subarachnoid space) or within subarachnoid space
Functions of CSF
1) Mechanical support of CNS by buoyancy

2) Shock absorber

3)acts as a "sink" for waste material to be dumped into CSF from CNS parenchyma
Go over drainage of CSF
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