Exam 1: Coverings of CNS and CSF

Dr. Ghosh - Fall 2023

meninges

membraneous tissue that covered the brain and spinal cord; 3 components and all are continuous

meningeal layers

dura mater, arachnoid, and pia mater

dura mater location

outer, thick layer of the meninge

arachnoid location

the thin, middle layer of the meninge

pia mater location

the thinnest, and innermost layer of the meninge

components of the dura mater

periosteal and meningeal layers

periosteum

consists of collagenous connective tissue and arteries that cover the inner side of the skull

what are the periosteum and cranial bones supplied by?

meningeal arteries

middle meningeal artery

largest vessel supplying the cranium

what does the middle meningeal artery split into? when?

anterior and posterior branches

after entering the cranial cavity

what does the anterior and posterior branches of the middle meningeal artery supply?

lateral surface of the cranium

how many fossae does the cranial fault (floor) have? names?

3 fossae: anterior, middle, and posterior

what is the anterior fossa formed by?

frontal + ethmoid and sphenoid bones

what is the middle fossa formed by?

temporal and sphenoid bones

what is the posterior fossa formed by?

occipital and petrous part of the temporal bone

calvarium

roof of the cranial cavity

structures in the anterior cranial fossa

frontal lobes of the brain, crista galli, and cribriform plates

crista galli

sharp ridge in the midline of the anterior fossa and is the attachment site for the falx cerebri (a portion of the dura)

cribriform plates

depression on both sides of the crista galli and is the location for the olfactory bulb

structures in the middle cranial fossa

temporal lobe, hypophyseal fossa, optic foramen, superior orbital fissure, foramen rotundum, foramen ovale, foramen spinosum, and foramen lacerum

hypophyseal fossa

pituitary gland sits on top of this fossa

optic foramen

optic nerve (CN II) and the ophthalmic artery pass through

superior orbital fissure

oculomotor, trochlear, ophthalmic division of the trigeminal nerve, and abducens nerve pass through

(CN III, IV, V, and VI)

foramen rotundem

maxillary division of CN V (Vagus) pass through

foramen ovale

mandibular division of CN V (Vagus) passes through

foramen spinosum

middle meningeal artery passes through

foramen lacerum

internal carotid artery passes through

structures in the posterior cranial fossa

occipital lobe, cerebellum, brain stem, foramen magnum, hypoglossal canal, and jugular foramen

what part of the brain stem is included in the posterior cranial fossa?

mainly the pons and medulla

foramen magnum

vertebral arteries pass through here

hypoglossal canal

hypoglossal nerve (CN XII) passes through here

jugular foramen

internal jugular vein, glossopharyngeal nerve, vagus nerve, and accessory nerve pass through (CN IX, X, and XI)

what protects the brain?

the skull, cranial meninges, cerebrospinal fluid, and blood-brain barrier

purpose of the cranial meninges

protects the brain from cranial trauma

dura mater composition

opaque and is a single layer around the spinal cord and a double layer inside the skull

what is located between the two dura mater layers?

venous sinuses

what is occupied in the dura mater epidural space?

simple squamous epithelium and some fluid

arachnoid mater composition

spider web-like, transparent appearance and contacts the epithelial layer of dura mater

pia mater composition

follows all the tissues of the brain and spinal cord and cannot be distinguished from nervous tissue

how is the pia mater attached?

to the brain surface by astrocytes

epidural space

potential space superior to the dura

subdural space

potential space between dura and arachnoid mater

subarachnoid space

consists of connective tissue strands from pia to arachnoid

filled with CSF and contains the blood vessels supplying the brain

arachnoid granulations

projections of the arachnoid membrane into the dural sinuses to allow CSF to pass through to the venous system

dural folds

folded inner layer of the dura mater that extends into the cranial cavity to stabilize and support the brain

what do the dural folds contain?

collecting veins for dural sinuses

dural fold names

falx cerebri, tentorium cerebelli, and falx cerebelli

falx cerebri

where: attached to the front of the crista galli and goes back to tentorium cerebelli and hangs above corpus callosum

what: vertical divide in the longitudinal fissure between the cerebral hemispheres

tentorium cerebelli

lies between the occipital lobes of the cerebral hemispheres and the cerebellum

runs transversely

falx cerebelli

located in the posterior cranial fossa and extends vertically for a short distance between the cerebellar hemispheres

what ventricles are located in the brain

lateral, third, and fourth

location of lateral ventricle

deep within the cerebrum

location of the third ventricle

connected by interventricular foramen

location of the fourth ventricle

connected by cerebral aqueduct and connects to the subarachnoid space so it can return to the bloodstream

venous draining in dural sinuses

veins draining the brain empty into the sinuses of the dura mater then goes into the internal jugular veins

superior sagital sinus

space between the layers of the meninges and communicates with nasal vein in the front

what drains into the superior sagital sinus

the superior cerebral vein and it is continuous with the right transverse sinus

inferior sagital sinus

lies alone the free border of falx cerebri and drains into the straight sinus

straight sinus (rectus)

located where the falx cerebri and tentorium cerebelli meet

transverse sinus

lies in a groove on the occipital bone alone the margin of the tentorium cerebelli

when does the transverse sinus become the sigmoid sinus?

when it reaches the petrous part of the temporal bone and is continuous with the internal jugular vein

cavernous sinuses

located on the side of the sphenoid bone and drains into the transverse sinus via the superior petrosal sinus

internal jugular vein

direct continuation of sigmoid sinus and receives all blood from inside the skull

what is the 3rd major fluid of the body? what is the adult and newborn volume?

CSF

adult: 90-150 mL

neonate: 10-60 mL

where is CSF produced? what is the rate?

choroid plexus of the 4 ventricles by modified ependymal cells

20mL/hour

where does CSF flow through? what is the volume here?

through the subarachnoid space at a volume of 90-150 mL for adults

where is CSF reabsorbed?

arachnoid granulation to eventually be reabsorbed into the blood

CSF circulation

lateral ventricles → third ventricle → interventricular foramen → third ventricle → cerebral aqueduct → fourth ventricle → medial OR lateral aperture → cerebello medullary cistern (medial) OR pontine cistern (lateral) →subarachnoid space and central canal → arachnoid villi → superior sagittal sinus → sinuses → internal jugular vein

how is the movement of CSF assisted?

pulsation of arteries in the subarachnoid space

roles of CSF

1: cushions and insulates delicate nervous tissue

2: gives buoyancy to the brain

3: exchange of gases, nutrients, and wastes

4: transports nutrients, chemical messengers, and waste products

properties of CSF

volume: 80-150 mL

pressure: 80-180 cm H2O

glucose: 40-60 mg / dL

protein: very low

hydrocephalus

enlarged ventricles with excess CSF

blood brain barrier

restrictive barrier around blood vessels in the brain and is created by astrocytes

blood brain barrier purpose

prevents most blood-borne toxins from entering the brain but not ABSOLUTE

what can pass through the BBB?

O2, glucose, CO2, alcohol, nicotine, and anesthetics