Neuroscience - Ventricles, Cerebrospinal Fluid, & Meninges

What are cranial meninges?

membranous coverings of brain

What are the functions of cranial meninges?

• protect the brain

• form supporting framework for blood vessels and venous sinuses

• provide a fluid-filed cavity for the brain and spinal cord

What are the 3 layers of the cranial meninges?

• dura mater

• arachnoid mater

• pia mater

What are the 2 layers of the dura mater?

• periosteal (outer) layer

• meningeal (inner) layer

What is the dural septa?

meningeal layer of dura gives rise to infoldings (septa) to divide cranial cavity into compartments and separate brain regions

What are dural venous sinuses?

• endothelium-lined spaces between periosteal and meningeal layers

• drain venous blood from nervous system

What makes up the dura mater septa? (4)

• falx cerebri

• tentorium cerebelli

• falx cerebelli

• diaphragma sellae

What is the falx cerebri?

lies in longitudinal fissure and separates right and left hemispheres

What is the falx cerebri continuous with?

tentorium cerebelli

What is the tentorium cerebelli?

separates occipital lobe from cerebellum

What is the tentorial notch of the tentorium cerebelli?

gap through which brainstem extends from posterior to middle cranial fossa

What is the falx cerebelli?

vertical dural infolding inferior to tentorium cerebelli that partially separates cerebellar hemispheres

What is the diaphragma sellae?

• circular sheet of dura suspended to form a roof over hypophyseal fossa (sella turcica)

• covers pituitary gland

Where do dural venous sinuses ultimately drain?

internal jugular vein

Where does venous outflow from the brain travel?

through superficial and deep cerebral veins and drains into dural venous sinuses which ultimately drain into internal jugular vein

What is the confluence of sinuses?

meeting place of superior sagittal, straight, and transverse sinuses

Where does the superior sagittal sinus usually drain into?

right transverse sinus

Where does the straight sinus usually drain into?

left transverse sinus

What are notable paired dural sinuses? (3)

• transverse

• cavernous

• sigmoid

What are notable unpaired dural sinuses? (3)

• superior sagittal

• inferior sagittal

• straight

What do emissary veins connect?

dural venous sinuses with veins outside cranium

Where do the sigmoid sinuses drain?

internal jugular vein

Where is the confluence of sinuses located?

cruciform eminence of occipital bone

Where do the transverse sinuses usually drain?

sigmoid sinus

What is the blood supply to the dura of the anterior cranial fossa? (3)

• cavernous portion of internal carotid artery

• ethmoidal arteries

• ascending pharyngeal artery

What is the blood supply to the dura of the middle cranial fossa?

middle meningeal artery

What is the blood supply to the dura of the posterior cranial fossa? (2)

• branches of ascending pharyngeal artery

• branches of occipital arteries

What is the blood supply to the spinal dura? (3)

vertebral, intercostal, and lumbosacral arteries

What part of the dura do tentorial and ethmoidal nerves ("meningeal branches" of V1) innervate?

• part of dura mater of anterior and middle cranial fossa

• anterior and posterior part of dura mater of tentorium cerebelli

Generally, what innervates the dura of the anterior and middle cranial fossae?

branches of trigeminal (CN V)

What innervates the dura of the posterior cranial fossa?

dorsal roots of C1-C3 (some fibers distributed via hypoglossal and vagus)

What are the two parts of the arachnoid mater?

• arachnoid barrier cell layer

• arachnoid trabeculae

What does the arachnoid barrier cell layer attach to?

dura mater

What does the arachnoid trabeculae layer attach to?

pia mater

What forms within the arachnoid mater layer?

CSF filled spaces

What holds the arachnoid mater against the dura mater?

pressure of CSF

What is another name for subarachnoid space?

leptomeningeal space

What makes up the leptominenges?

inner 2 meningeal layers (arachnoid and pia):

• parietal part = arachnoid mater

• visceral part = pia mater

What is the subarachnoid space?

space between arachnoid and pia that contains CSF, blood vessels, roots of cranial and spinal nerves as they enter/exit

What suspends the brain?

subarachnoid space

What are components of the subarachnoid space? (3)

• arachnoid trabeculae

• arachnoid villi

• subarachnoid cisterns

What are arachnoid trabeculae?

fibroblasts that bridge subarachnoid space

What are arachnoid villi?

small specialized portions of arachnoid that protrude through meningeal layer into venous sinuses

What is the purpose of arachnoid villi?

assist with transfer of CSF from subarachnoid space into venous system

How does the CSF travel through the arachnoid villi?

down a pressure gradient

What are subarachnoid cisterns?

enlarged regions of subarachnoid spaces (pools of CSF)

What are granular foveolae?

impressions of arachnoid villi on skull

What makes up the pia mater?

• layer of flat cells that closely follow the surface features of the brain and spinal cord

• continuous with the surface of the brain and cannot be separated

What separates the pia mater from the brain?

glial basement membrane

What are perivascular spaces of pia mater?

regions where small vessels penetrate the surface of the brain and spinal cord

What is another name form perivascular spaces of pia mater?

Virchow-Robin spaces

What structures of pia mater are analagous to arachnoid trabeculae in the spinal cord? (3)

• denticulate ligaments

• filum terminale internum (inside dural sac, still a pial structure)

• filum terminale externum (actually a dural structure)

What is tethered spinal cord syndrome?

if a child has an abnormally thick filum terminale, it becomes stretched and taut as the spinal cord is tugged between the lower back and brain stem

What is meningitis?

infection of cranial meninges from viruses, bacteria, etc.

What is leptomeningitis?

infection of arachnoid and pia

What is pachymeningitis?

infection of dura

What is bacterial meningitis and what are symptoms of it?

• fever, chills, neck stiffness, headache, decreased consciousness

• vaccines are available

What is viral meningitis and what are symptoms of it?

• fever, headaches, confusion, altered consciousness

• no antiviral medications are available

• most common in younger patients

How do you confirm a meningitis diagnosis?

with a lumbar puncture to assess CSF composition

Can meningitis be fatal?

yes

What during development gives rise to ventricles and the central canal of the spinal cord?

neural tube

What are the ventricles that the neural tube gives rise to during development? (4)

• lateral ventricles

• third ventricle

• cerebral aqueduct

• fourth ventricle

What is the choroid plexus?

secretes CSF to fill ventricles and subarachnoid space

What secondary region of the brain are the lateral ventricles associated with?

telencephalon

How many lateral ventricles are there?

2 (one in each cerebral hemisphere)

What are the features of the lateral ventricles? (5)

• anterior horn

• body

• atrium

• posterior horn

• inferior horn

What is in the atrium of the lateral ventricles?

glomus choroideum (glomus)- large clump of choroid plexus

What is the medial wall of the lateral ventricle?

septum pellucidum and fornix

What is the roof of the lateral ventricle?

corpus callosum

What is the floor of the lateral ventricle?

thalamus

What is the lateral wall of the lateral ventricle?

caudate nucleus

What is the interventricular foramina (of Monro)?

connects lateral ventricles with third ventricle (bilateral)

What secondary region of the brain is associated with third ventricle?

diencephalon

What is the anterior wall of the third ventricle?

lamina terminalis and anterior commissure

What is the posterior wall of the third ventricle?

pineal gland and posterior commissure

What are the lateral walls of the third ventricle?

thalamus and hypothalamus

What is the roof of the third ventricle?

tela choroidea

What is the floor of the third ventricle?

optic chiasm, pituitary gland, and mammillary bodies

What are the 5 recesses of the third ventricle?

• infundibular

• supraoptic

• anterior

• suprapineal

• pineal

What secondary brain region is associated with the cerebral aqueduct?

mesencephalon

What ventricle does not have a choroid plexus?

cerebral aqueduct

What is the cerebral aqueduct?

very narrow midline channel between third and fourth channels

What surrounds the cerebral aqueduct?

periaqueductal gray matter

Where is the periaqueductal gray matter (PAG) located?

midbrain

What is the function of periaqueductal gray matter (PAG)?

• receive somatosensory input

• high levels of opiate receptor binding activity

• suppression and modulation of pain

What is periaqueductal gray matter interconnected with?

• hypothalamus and thalamus

• has projections to brainstem nuclei

What secondary brain regions is the fourth ventricle associated with?

metencephalon and myelencephalon

Where is the fourth ventricle found?

• forms cavity of hindbrain

• extends into cerebellum

What are the 3 sites that CSF can leave the fourth ventricle and enter the subarachnoid space?

• Foramen of Magendie (median aperture)

• Foramina of Luschka (paired lateral apertures)

What are the lateral walls of the fourth ventricle?

superior and inferior cerebellar peduncles and cuneate and gracile tubercles

What is the roof of the fourth ventricle?

cerebellum

What is the floor of the fourth ventricle?

rhomboid fossa (pons and medulla)

What is the ependyma?

lining of specialized epithelial cells that helps to form the choroid plexus

What specialized epithelial cells make up the ependyma?

simple cuboidal epithelium

What does the ependyma line?

ventricles and central canal of spinal cord

What helps with movement of CSF?

cilia on ependymal cells

How does the ependyma layer help form components of the blood-CSF barrier?

form an interface between CSF-filled ventricles and the blood

What is the development of the choroid plexus?

• roof of fourth ventricle is lined with an internal layer of the ependyma and the outer layer of the pia

• blood vessels invaginate this membrane to form the choroid plexus

Where is the choroid plexus found?

• floors of the bodies and inferior horns of lateral ventricles

• roofs of third and fourth ventricles

What is the structure of the choroid plexus?

series of folds (villi)