003 Meninges, Ventricular System, and Cerebrospinal Fluid

Question 1

dura mater

Answer 1

 Outermost layer
 Thickest layer
 Composed of dense irregular connective tissue (collagenous)

Question 2

o Arachnoid mater

Answer 2

 Delicate middle layer
 Loose connective tissue
 Avascular
 Contacts inner surface of dura mater
 Arachnoid villi (AKA granulations or pacchionian villi) are specialization of the arachnoid that recycle CSF into the blood
 Attached to the pia mater by trabeculae that span the true subarachnoid space which is filled with CSF
 Has subarachnoid cisterns which are extended regions of the subarachnoid space that serves as reservoirs of CSF

Question 3

Pia mater

Answer 3

 Very thin layer
 Inner layer that is adherent to the CNS
 Highly vascular
 Denticulate ligaments
• Folds of extra thick pia mater located on the lateral aspects of the spinal cord
• Span the subarachnoid space and attach to the arachnoid
• Help anchor the spinal cord
 Filum terminale (AKA filum terminale internum)
• Single midline continuation of the pia mater that attaches the conus medullaris to the inferior aspect of the dural sac
• Anchors end of spinal cord to the vertebral column
 Tela choroidea
• Found in specific regions in each of the ventricles of the brain
• Folds of pia mater that support the choroid plexus, which is modified ependymal cells that produce CSF
o Subarachnoid space
 Between the arachnoid and the pia mater
 Filled with CSF

Question 4

Denticulate ligaments

Answer 4

• Folds of extra thick pia mater located on the lateral aspects of the spinal cord
• Span the subarachnoid space and attach to the arachnoid
• Help anchor the spinal cord

Question 5

Filum terminale

Answer 5

(AKA filum terminale internum)
• Single midline continuation of the pia mater that attaches the conus medullaris to the inferior aspect of the dural sac
• Anchors end of spinal cord to the vertebral column

Question 6

Tela choroidea

Answer 6

• Found in specific regions in each of the ventricles of the brain
• Folds of pia mater that support the choroid plexus, which is modified ependymal cells that produce CSF

Question 7

Subarachnoid space

Answer 7

 Between the arachnoid and the pia mater

 Filled with CSF

Question 8

• define the leptomeninges and pachymeninx

Answer 8

o Leptomeninges
 Arachnoid and pia mater
o Pachymeninx
 Dura mater

Question 9

• list the general functions of the meninges

Answer 9

o Protection of CNS
o Keeps the brain and the spinal cord from collapsing under its own weight because CSF keeps them floating
o Involved in the blood supply of the CNS

Question 10

• compare and contrast the cranial and spinal dura mater

Answer 10

o dura mater is made of two layers that are fused together except at the dural venous sinuses
o Cranial
 Periosteal (AKA endosteal)
• Outer layer that forms the periosteum on the inner side of the inner table of the skull bones that form the cranial vault
• Fused to the inside of compact bone of the parts of the skullthat form the cranial cavity
 Meningeal
• Inner layer surrounding the brain
• Thinner than periosteal layer
• Inner surface is lined with simple squamous epithelium
• Forms tubular sheaths for cranial nerves as the exit the skull
o Sheaths transition into the epineurium of these nerves once they exit the skull
o The dural sheath of the optic nerve is continuous with the sclera
o Spinal Column
 Dura mater only has one layer that corresponds to the meningeal layer in the skull
 Ends inferiorly at the level of the 2nd sacral segment
 Anchored to the coccyx by the coccygeal ligament
 Does NOT attach to the surrounding bone so there is a true epidural space in this region
• Filled with fat and internal vertebral venous plexus
 Still forms tubular sheaths like in the cranium
 Dural Root sleeves transition into the epineurium of spinal nerves

Question 11

• explain the epidural and subdural spaces and their clinical significance

Answer 11

o Epidural space
 Only exists abnormally when the periosteal layer of the dura mater is torn and fluid is forced between the dura mater and the surrounding bone
o Subdural space
 Potential space that exists between the inner surface of the meningeal layer of the dura mater and the arachnoid
 Fluid can gather in this space (i.e. hematoma)
• Usually result from damage to external cerebral veins or dural venous sinuses

Question 12

Falx Cerebri

Answer 12

o Falx Cerebri
 Vertical partition that lies in the longitudinal fissure, so it is a single midline structure
 Attachments
• Anteriorly – crista galli of the ethmoid
• Superiorly – midline of cranial vault
• Posteriorly – internal occipital protruberance
• Inferiorly
o Posterior ¼ the midline portion of the tentorium cerebelli
o Anterior ¾ - free edge that does not attach to anything but lies along the corpus callosum

Question 13

Sinuses associated with falx cerebri

Answer 13

	Sinuses
•	Superior sagittal sinus
•	Inferior sagittal sinus
•	Straight sinus
•	Confluence of sinuses

Question 14

Falx Cerebelli

Answer 14

 Lies between the cerebellar hemispheres
 Attachments
• Anterior – free edge
• Posterior – midline of the skull in the region of the cerebellum
• Superior – falx cerebri and tentorium cerebelli

Question 15

Tentorium Cerebelli

Answer 15

 Horizontal
 Between the occipital lobes and cerebellum
 Tent shaped, with highest portion in the midline, which attaches to the posterior inferior portion of the falx cerebri
 Tentorial Notch
• Between the free margin and the dorsum sellae
• Midbrain is in this notch
 Peripheral attachments (anterior to posterior)
• Posterior clinoid processes
• Petrous portions of the temporal bones
• Grooves for the transverse sinus
• Internal occipital protruberance
 Sinuses
• Transverse sinuses
• Superior petrosal sinus
• Straight sinus
• Confluence of sinuses
 Divides the cranial cavity into two
• Supratentorial compartment – contains the forebrain
• Infratentorial compartment – contains the hindbrain

Question 16

Diaphragm Sellae

Answer 16

 Round horizontal sheet that forms a roof over the sella turcica/pituitary fossa
 Has a hole in the middle for the infundibulum (pituitary stalk)

Question 17

• describe blood and nerve supply of the dura mater

Answer 17

o	Blood Supply – meningeal arteries
	Anterior meningeal arteries
•	Arises from the ophthalmic artery
	Middle meningeal arteries
•	Largest
•	Arises from the maxillary arteries
•	Enters cranium through foramen spinosum
	Posterior meningeal arteries
•	Arise from occipital and/or vertebral arteries
o	Nerve supply
	Trigeminal Nerve – ophthalmic division
•	Anterior cranial fossa
•	Tentorium cerebelli
•	Lining of superior aspect of cranial cavity
•	Falx cerebri
	Trigeminal nerve – maxillary division
•	Middle cranial fossa
	Trigeminal nerve – mandibular division
•	Middle cranial fossa
	Vagus nerve
•	Posterior cranial fossa
	C1-3 spinal nerves
•	Posterior cranial fossa
	Spinal nerves (segmentally)
•	Spinal dura
	***irritation of the dura mater leads to headaches and migraines

Question 18

• describe the subarachnoid space, including the subarachnoid cisterns

Answer 18

o	Cisterna magna 
o	Superior cistern 
o	Mesencephalic cisterns 
o	Interpeduncular cisterns 
o	Chiasmatic cistern
o	Pontine cistern
o	Cisterns of the lateral cerebral fissure
o	Lumbar cistern

Question 19

Cisterna magna

Answer 19

(AKA cerebellomedullary cistern
 Largest cistern
 Located posterior to the medulla and inferior to the cerebellum
 Just above the foramen magnum
 Single midline structure
 CSF can be sampled from here but this is rarely done

Question 20

Superior cistern

Answer 20

(AKA cisterna vena magna cerebri)
 Deep in the space between the cerebral hemispheres and the cerebellum
 Posterior to the midbrain and superior to the cerebellum
 Single midline structure
 Contains the great cerebral brain

Question 21

Mesencephalic cistern

Answer 21

(AKA cisternae ambiens)
 NOT midline structures
 Located on the lateral sides of the midbrain, so have right and left
 Connect superior cisterns and the interpeduncular cisterns

Question 22

Interpeduncular cisterns

Answer 22

(AKA cisterna basalis)
	Located between cerebral peduncles 
	Anterior to the midbrain
	Single midline structure
	Oculomotor nerve runs through here

Question 23

Chiasmic cistern

Answer 23

 Small dilation of the subarachnoid space located just above the optic chiasm
 Single midline structure

Question 24

Pontine cistern

Answer 24

 Anterior to the pons
 Contains basilar artery
 Single midline structure

Question 25

Cisterns of the lateral cerebral fissure

Answer 25

 NOT midline structures, have right and left  Located in the anterior aspects of the Sylvian fissures  Between the frontal and temporal lobes of the cerebral hemispheres

Question 26

Lumbar cistern

Answer 26

 Only subarachnoid cistern NOT located in the head  In the lower lumbar region of the spine  Contains the cauda equine  Usual place where CSF samples are taken via a lumbar puncture  Single midline structure

Question 27

• describe the ventricular system of the brain

Answer 27

``` o The remnants of the neural tube cavity in the region of the brain expand to form the ventricles of the brain  lined with ependymal  filled with CSF o 4 ventricles in the brain  2 lateral ventricles  3rd ventricle  4th ventricle ```

Question 28

Lateral ventricles

Answer 28

(right and left)  Largest of the ventricles  Horseshoe shaped (C-shaped)  Remnants of the neural tube cavity in the region of the telencephalon  Located in the cerebral hemispheres  Parts • Body (AKA pars centralis) – located in the parietal lobe o Floor is formed by the thalamus • Anterior horn (AKA anterior cornu) – located in the frontal lobe o Left and right separated by septum pellucidum  Double glial membrane  Located in the midline • Posterior horn (AKA posterior cornu) – located in the occipital lobe • Inferior horn (AKA inferior cornu) – located in the temporal lobe  Other C-shaped structures in relation to lateral ventricles • Corpus Callosum • Caudate nucleus • Hippocampus

Question 29

Third ventricles

Answer 29

 Single structure in the midline  Narrow cleft between the right and left halves of the thalamus  Remnants of the neural tube cavity in the diencephalon  In about 50% of people, the right and left halves of the thalamus form a solid bridge across the 3rd ventricle and meet in the midline • Called interthalamic adhesion  CSF leaves through the cerebral aqueduct • Located on the posteroinferior aspect of the 3rd ventricle • Represents the remnants of the neural tube cavity in the region of the mesencephalon

Question 30

4th ventricles

Answer 30

 Rhombus shaped  Located in the region of the pons and medulla  Represents the remnants of the neural tube in the rhombencephalon (both metencephalon and myelencephalon)  The floor is considered the ventral side (anterior) • AKA rhomboid fossa • Consists of the posterior aspect of the pons and upper medulla  The roof is its dorsal side (posterior) • Made of 2 parts o Superior medullary vellum (upper ½)  Thin layer of neural tissue that separates the CSF of the 4th ventricle from the cerebellum o Inferior medullary velum (lower ½ of the roof)  Glial membrane that separates the CSF of the 4th ventricle from the cerebellum  Openings • Cerebral aqueduct – drains the 3rd ventricle into the 4th • Central canal (of the spinal cord) o Inferior opening o represents the continuation of the neural tube cavity into the region of the spinal cord o The ependyma here produces some serous fluid (that is not true CSF) that mixes with the 4th ventricle at the superior end of the central canal • Foramen of Magendie (AKA median aperture) o Single midline opening o In the posterior aspect of the roof of the 4th ventricle  In the region of the inferior medullary velum o CSF can leave through this foramen to enter the cisterna magna • Foramina of (von) Luschka o Pair of openings (right and left) o In lateral aspects of 4th ventricle o CSF can leave through these to enter the pontine cistern of the subarachnoid space

Question 31

• describe the cerebrospinal fluid

Answer 31

o Produced by the choroid plexus o A fluid that fills the ventricles of the brain and subarachnoid space o There is a total of about 150 mL of CSF in the body o 500 mL is produced daily o Has a fairly rapid flow rate o Much gets reabsorbed; it gets totally replaced 3x a day o Similar in composition to blood plasma, with a few differences in ion concentrations o Produced by  Active transport of Na from the blood into the ventricles  Water follows Na

Question 32

• describe the choroid plexus and how it works

Answer 32

o Made of  fenestrated with diaphragms capillaries  pia mater  modified ependymal cells o Supported by tela choroidea o Some choroid plexus is in each of the ventricles

Question 33

• describe the pattern of flow of the cerebrospinal fluid

Answer 33

o Lateral ventricle o Through Interventricular foramen of Monroe o Into 3rd ventricle o Through cerebral aqueduct  AKA inter aqueduct; Sylvian aqueduct o Into 4th ventricle o Through foramen of magendie  Into cisterna magna o Through foramina of (von) Luschka  Into pontine cistern (of the subarachnoid space) o Flow in the suparachnoid space (sluggish flow rate)  Mostly flows superiorly in the head to the sites of reabsorption  Some flows into the spinal portion of subarachnoid space • Travels inferiorly to the lumbar cistern • Then travels back superiorly

Question 34

• What are arachnoid villi

Answer 34

o AKA granulations; pacchionian villi o Envaginations of arachnoid that protrude mainly into the superior sagittal sinus o Act as one-way valves that allow CSF to flow into the blood of the dural venous sinuses (recycling CSF back into the blood)

Question 35

o why the brain has to “float”

Answer 35

 Floating provides mechanical support  Prevents the structures of the brain from being damaged under their own weight  Floating caused by the buoyancy of the brain in CSF

Question 36

o epidural and subdural hematomas

Answer 36

 Epidural hematoma • Caused by damage to the meningeal blood vessels • Can causes detachment of the periosteal layer of the dura mater from the bone • Blood is forced into the region between dura mater and the surrounding bone (this will create an epidural space)  Subdural hematoma • Blood gathers in the space between the inner surface of the meningeal layer of the dura mater and the arachnoid • Usually result from damage to the external cerebral veins or dural venous sinuses

Question 37

o supratentorial and infratentorial regions of subarachnoid space

Answer 37

 connected by the narrow gap between the midbrain and the border of the tentorial incisures  this region can get obstructed leading to ventricular dilation

Question 38

o tentorial incisura

Answer 38

 AKA tentorial notch  U shaped hole in the tentorium cerebelli  Expansion of the cerebelli can cause the medial portion of the temporal lobes to herniate through the tentorial notch • The midbrain can get displaced laterally and get injured by the firm edge of the tentorium cerebelli

Question 39

o nerve supply of the dura mater and headaches/referral patterns

Answer 39

 the dura mater has a rich nerve supply and is sensitive to paint  Headaches result from stimulation of the dura mater nerve supply  Referral patterns • Problems in the anterior cranial fossa refers to : o Structures innervated by ophthalmic division of CN V:  Forehead  Temples  Eyes • Problems in the middle cranial fossa refers to: o Structures innervated by the maxillary and mandibular division of CN V:  Cheeks  Jaw  Mouth • Problems in the posterior cranial fossa refer to: o Structures innervated by the vagus and cervical nerves:  Neck  Region behind the ear

Question 40

o Hydrocephalus

Answer 40

 AKA water on the brain  Occurs with the obstruction of CSF pathways  CSF cannot be recycled back into the blood properly so it builds up in the ventricular system  Causes • Ventricular dilation • Results in pressure on and often damage to brain tissues  In children where the skull has not completely developed, the skull can expand  Communicating hydrocephalus • Occurs when the flow of CSF is NOT obstructed • CSF is either o over-produced (papilloma) o cannot reenter the blood (i.e. blockage of arachnoid villi)  Noncommunicating hydrocephalus • Occurs when there is a blockage of CSF flow either o within the ventricular system where the ventricles communicate with the subarachnoid space o within the subarachnoid space (i.e. at the tentorial notch)