Unit 1 Flashcards
The skull, excluding the ossicles, is composed of __ bones.
22
are all the bones of the cranium paires?
nope - some are paired but some are single
are of these bones are firmly attached to each other via sutures and are immovable
all but 1. the only moveable one is the mandible
whats the only movable cranial bone?
the mandible
describe how the cranial vault ossifies?
it ossifies in membrane
The cranial vault ossifies in membrane to form ……
The cranial vault ossifies in membrane to form the frontal, parietal, occipital and squamous temporal bones
how does the scull base ossify?
and what does it ossify around?
in cartilage.
around the cranial nerves to form foramina
the skull vault comprises which bones?
4 unpaired bones (ethmoid, frontal, sphenoid and occipital)
and 2 paired bones (temporal and parietal)
describe the ethmoid bone
cribriform plate with the crista galli, perpendicular plate superior and middle conchae, ethmoidal air cells
describe the frontal bone
contains air sinuses; in two parts at birth but usually fuses early in life superior ciliary ridges and supra-orbital notches
describe the sphenoid bone
greater and lesser wings, medial and lateral pterygoid plates sella turcica for the pituitary gland
optic canals, superior orbital fissures foramen rotundum, foramen ovale, foramen spinosum
what are the pterygoid processes of the sphenoid bone
describe the occipital bone
squamous and basal parts, hypoglossal canals, foramen magnum occipital condyles, occipital protuberance, superior nuchal line
describe the temporal bone
- squamous part:* zygomatic process, mandibular fossa
- petromastoid part:* middle and inner ear, internal auditory meatus, facial canal, air cells in the mastoid process
- tympanic part:* external auditory meatus, attachment of tympanic membrane
- styloid process*: attachment for ligaments and muscles, adjacent to stylomastoid foramen, where CN VII emerges
describe the parietal bone
contains foramina for emissary veins that connect scalp veins with venous dural sinuses inside the skull
Describe what is meant by the tiered floor of the cranial cavity?
3 tiers
lowest posteriorly
each tier forms the floor of a cranial fossa
what bone forms the middle of the anterior crainal fossa?
the cribriform plate of the ethmoid bone
what passes through the foramina of the cribriform plate?
olfactory filaments
whats the crista galli?
a midline projection to which the falx cerebri attaches.
whats the falx cerebri?
just so you know
The falx cerebri, also known as the cerebral falx, is a large, crescent-shaped fold of meningeal layer of dura mater that descends vertically in the longitudinal fissure between the cerebral hemispheres of the human brain. The falx cerebri attaches anteriorly at the crista galli in proximity to the cribriform plate and to the frontal and ethmoid sinuses. Posteriorly, it is connected with the upper surface of the cerebellar tentorium.
what mostly occupies the anterior cranial fossa?
frontal lobes of the brain
describe the central portion of the middle cranial fossa?
central portion is formed by the body of the sphenoid which has a deep depression for the pituitary gland - the pituitary fossa
The pituitary fossa and clinoid processes together form the sella turcica
what is the sella turcica?
saddle-shaped depression in the body of the sphenoid bone
The pituitary gland or hypophysis is located within the most inferior aspect of the sella turcica, the hypophyseal fossa.
what is housed by the lateral middle cranial fossa?
temporal lobes of the brain
the clinoid processes serve as anchor points for what?
tentorium cerebelli, a membranous sheet that divides the brain.
does the middle cranial fossa have a sort of cresent of foramina?
yep
can you name the 8 formaina of the middle cranial fossa?
Optic canal
foramen Lacerum
Hiatus of the greater petrosal nerve
Carotid canal
Superior orbital fissure
foramen rotundum
foramen ovale
foramen spinosum
describe the optic canals
anteriorly in the middle cranial fossa.
They transmit the optic nerves (CN II) and ophthalmic arteries into the orbital cavities.
The optic canals are connected by the chiasmatic sulcus, a depressed groove running transversely between the two.
Immediately lateral to the central part of the middle cranial fossa are four foramina:
what are they
Superior orbital fissure
foramen rotundrum
foramen ovale
foramen spinosum
describe the location of the superior orbital fissure
superior to the foramen rotundrum and lying between the greater and lesser wings of the sphenoid.
opens anteriorly into the orbit
what does the superior orbital fissure transmit?
oculomotor nerve (CN III)
trochlear nerve (CN IV)
ophthalmic branch of the trigeminal nerve (CN V1)
abducens nerve (CN VI)
opthalmic veins and sympathetic branches
describe the foramen rotundrum
and what does it transmit?
On each side where the anteromedial walls meet the floor is the foramen rotundum
opens into the pterygoid fossa and transmits the maxillary branch of the trigeminal nerve (CN V2)
descrbie the foramen ovale
what does it transmit
anteriomedial, opens into the infratemporal fossa
transmits the mandibular branch of the Trigeminal nerve (CN V3) and accessory meningeal artery
describe the foramen spinosum
opens in into the infratemopral fossa
transmits the middle meningeal artery, middle meningeal vein and meningeal branch of CN V3
what are the 3 major foramina of the temporal bone?
hiatus of the greater petrosal nerve
hiatus of the lesser petrosal nerve
Carotid canal
describe the hiatus of the greater petrosal nerve
which bone does it penetrate?
penetrates the temporal bone
trasmits the greater petrosal nerve (a branch of the facial nerve)
and the petrosal branch of the middle meningeal artery
descrbie the hiatus of the lesser petrosal nerve
transmits the lesser petrosal nerve (a branch of the glossopharyngeal nerve)
It is located posterior to the groove for the superior petrosal sinus and posterolateral to the jugular foramen - wiki
describe the carotid canal
located posteriorly and medially to the foramen ovale.
This is traversed by the internal carotid artery, which ascends into the cranium to supply the brain with blood. The deep petrosal nerve also passes through this canal.
the deep petrosal nerve passes through which canal
carotid canal with the internal carotid artery
whats the foramen Lacerum?
Between the tip of the petrous temporal bone and sella turcica is the cartilage-filled foramen lacerum.
its pierced by only small vessels
what does the poterior cranial fossa house?
cerebellum and much of the brainstem
what bones comprise the posterior cranial fossa?
the occipital bone and the 2 temporal bones
boundries of the posterior cranial fossa
what does the brainstem comprise?
(3 main bits)
The brainstem is comprised of the medulla oblogata, pons and midbrain and continues down through the foramen magnum to become the spinal cord.
the floor of the posterior cranial fossa is what?
the foramen magnum
the hypoglossal canals lie anterior to what?
occipital condyles
posterior cranial fossa temporal bone formain?
what does it transmit
The internal acoustic meatus is an oval opening in the posterior aspect of the petrous part of the temporal bone.
It transmits the facial nerve (CN VII), vestibulocochlear nerve (CN VIII) and labyrinthine artery.
describe the foramen magnum
lies centrally in the floor of the posterior cranial fossa. It is the largest foramen in the skull.
It transmits the medulla of the brain, meninges, vertebral arteries, spinal accessory nerve (ascending), dural veins and anterior and posterior spinal arteries.
Anteriorly an incline, known as the clivus, connects the foramen magnum with the dorsum sellae.
the foramen magnum is a foramen in which bone?
Occipital bone - base of back of skull
describe the jugular foramen
posterior part fo skull
situated either side of foramen magnum
trasmit the:
glossopharyngeal nerve,
vagus nerve,
spinal accessory nerve (descending),
internal jugular vein,
inferior petrosal sinus,
sigmoid sinus
and meningeal branches of the ascending pharyngeal and occipital arteries.
what does the hypoglossal canal transmit?
hypoglossal nerve through the occipital bone
describe the cerebellar fossa
Posterolaterally to the foramen magnum lies the cerebellar fossae. These are bilateral depressions that house the cerebellum. They are divided medially by a ridge of bone, the internal occipital crest.
what are the meninges
the membranous coverings of the brain and spinal cord. There are three layers of meninges, known as the dura mater, arachnoid mater and pia mater.
main functions of the meninges
Provide a supportive framework for the cerebral and cranial vasculature.
Acting with cerebrospinal fluid to protect the CNS from mechanical damage.
whihc meninge is the outermost layer
dura mater and dural folds
does the dura mater consist of dense connective tissue?
yep
describe the layers which dura mater is divided into
outer endosteal layer, which is continuous with the pericranium through the cranial sutures and foramina,
and an inner meningeal layer
are he 2 layers of dura mater alwasy united?
mostly - except when they separate to enclose the venous sinuses
only one layer surrounds the spinal cord
what forms the dural folds
The meningeal layer is reflected to form four septa or dural folds.
The two main folds are the falx cerebri between the two cerebral hemispheres, and the tentorium cerebelli, separating the cerebellum from the posterior parts of the cerebral hemisphere
what are the dural venous sinuses responsible for?
They are responsible for the venous vasculature of the cranium, draining into the internal jugular veins.
what does the tentorium cerebelli do?
the tentorium cerebelli divides the cranial cavity into supratentorial and infratentorial compartments.
describe the diaphragma sellae
a small horizontal shelf of dura mater, the diaphragma sellae, covers the pituitary fossa in the sella turcica of the sphenoid bone.
dura matter innervation and blood supply
The dura mater receives its own blood supply – primarily from the middle meningeal artery and vein. It is innervated by the trigeminal nerve (V1, V2 and V3).
describe the pia mater
a delicate, highly vascular layer which closely covers the brain and spinal cord
is the pia mater thin or thick?
very thin
describe how the pia mater is adhered to the brain and spinal cord
tightly adhered to
It is the only covering to follow the contours of the brain (the gyri and fissures).
describes what?
pia mater
Like the dura mater, it is highly vascularised, with blood vessels perforating through the membrane to supply the underlying neural tissue.
describes what?
pia mater
- its highly vascularised
which has the thinner pia - brain or spinal cord
the cranial pia is thinner than that of the spinal cord
is pia mater tightly or loosely attached to the brain?
(text book answer - i know earlier card said otherwise)
supposedly loosely attached
The spinal cord has a ______ ____ ______ into which the pia follows; similarly, the brain has numerous _______ and ______ which is invested by pia.
The spinal cord has a ventral median fissure into which the pia follows; similarly, the brain has numerous grooves and sulci which is invested by pia.
what is arachnoid mater?
thin non-vascular layer between the dura and pia.
how does cranial arachnoid differ from that of the spinal cord
cranial = thicker
cranial arachnoid connected to cranial pia by numerous fibrous strands that cross the fluid-filled subarachnoid space.
describe what subarachnoid cisterns are
As the arachnoid does not line the grooves on the surface of the brain or spinal cord, the sulci of the cerebral hemispheres are filled with cerebrospinal fluid (CSF). There are larger accumulations of CSF at sites where cranial arachnoid bridges across larger grooves in the brain surface, the subarachnoid cisterns.
is the arachnoid layer innervated?
no
is the arachnoid layer avascular?
yep
describe the subarachnoid space
Underneath the arachnoid is a space known as the sub-arachnoid space. It contains cerebrospinal fluid, which acts to cushion the brain.
describe arachnoid granulations and their purpose
Small projections of arachnoid mater into the dura (known as arachnoid granulations) allow CSF to re-enter the circulation via the dural venous sinuses.
describe the spinal epidural space
lies between the dura and vertebral periosteum, containing loose connective tissue, venous plexuses and lymphatics
describe the cranial epidural (extradural) space
The cranial epidural (extradural) space is a potential space between the endosteal layer and skull, and is only realised pathologically
(usually from a bleed separating the layers)
describe the subdural space
potenital space between dura and arachnoid
describe the subarachnoid space
and where does it extend to
The subarachnoid space contains cerebrospinal fluid, bathing the brain and spinal cord. In the adult, it extends to the termination of the lumbar cistern, at the level of the second sacral vertebra.
layers of what enclose the dural venous sinuses
dura obvs
they lie between the periosteal and meningeal layers of the dura mater.
what are the dural venous sinuses lined by?
vascular endothelium, with no valves or muscular tissue in their walls
function of the dural venous sinuses?
drain blood from the brain and cranium
heres a diagram of the dural venous sinuses of the brain
All the dural venous sinuses ultimately drain into … what?
All the dural venous sinuses ultimately drain into the internal jugular vein.
do the dural venous sinuses have valves?
nope
The …………. are found in the falx cerebri of the dura mater.
The straight, superior, and inferior sagittal sinuses are found in the falx cerebri of the dura mater.
describe the superior sagittal sinus
begins at the crista galli
and runs in the superior margin of the falx cerebri, forming a median groove in the cranial vault.
It usually drains into the right transverse sinus
describe the inferior sagittal sinus
The inferior sagittal sinus runs in the posteroinferior border of the falx cerebri. It joins the great cerebral vein and the right and left basal veins to form the straight sinus.
descrbie the straight sinus
The straight sinus runs in the junction of the falx cerebri and tentorium cerebelli, continuing as the left transverse sinus
describe the transverse sinus
The transverse sinus runs on each side in the lateral margin of the tentorium cerebelli.
It receives the superior petrosal sinus and continues into the sigmoid sinus.
describe the sigmoid sinus
where do the mastoid air cells lie relative to it?
The sigmoid sinus is an S-shaped sinus that deeply grooves the petrous temporal bone. It curves forward onto the occipital bone and passes through the jugular foramen to join the inferior petrosal sinus and form the internal jugular vein. The mastoid air cells lie lateral to it.
describe the superior petrosal sinus
The superior petrosal sinus runs in the edge of the tentorium cerebelli, where it attaches to the petrous temporal bone and thus connects the cavernous sinus with the transverse sinus.
describe the inferior petrosal sinus
The inferior petrosal sinus lies in the groove between the occipital bone and petrous temporal bone. It connects and drains the cavernous sinus into the internal jugular vein.
deascribe the cavernous sinus
The cavernous sinus lies on either side of the body of the sphenoid.
can be found on either side of the sella turcica
what veins does the cavernous sinus drain/
the superior and inferior opthalmic veins,
thus forming extracranial to intracranial venous connections via the facial vein and the pterygoid plexus
describe the structure of the savernous sinus,
and the strucutres nearby
Numerous delicate, interlacing strands of connective tissue create a cavern-like meshwork in one blood-filled space
The internal carotid artery runs through the sinus with the abducent nerve (VI). The oculomotor (III), trochlear (IV), ophthalmic (Va) and maxillary (Vb) nerves lie in its lateral wall.
where does the spinal cord being and end
foramen magnum
and ends at lower border of L1;
the conus medullaris is attached by something to the whatcha-ma-call-it
what on earth does this mean
the conus medullaris is attached by a stalk of pia mater (the filum terminale) to the end of the dural sac at S2
what does the cauda equina consist of?
the roots of the spinal nerves from L2 to Co which pass caudal to the conus to exit at their respective intervertebral foramina.
how do the spinal nerve roots energe from the spinal cord
ermege from vetnral and dorsal aspects
anterior motor
posterior sensory roots
each spinal root is covered by what?
3 meningeal layers
after the roots have emerged as anterior motor and posterior sensory roots what happens?
At each level the two roots join to form a mixed spinal nerve in the intervertebral foramen.
Where the spinal roots unite, the meninges fuse with the epineurium of the spinal nerve.
what is the denticulate ligament
The denticulate ligaments are triangular shaped ligaments that anchor the spinal cord along its length, at each side, to the dura mater. The bases of the ligaments arise in the pia mater and they are firmly attached to the arachnoid mater and dura mater at the apex.
here is a picture
describe the path of the vertebral artery
travels up the neck, enters cranium through foramen magnum
gives:
- small posterior meningeal branch
- anterior and posterior spinal arteries
- branches to the medulla
- posterior inferior cerebellar artery
On ventral surface of brianstell - the 2 vertebral arteries merge to form the single basilar artery inthe midline groove on the ventral surface of the pons
describe the basilar artery
(remember it originated from the united vertebral arteries)
The basilar artery gives branches to the brainstem, the anterior inferior cerebellar and superior cerebellar arteries.
More anteriorly, it divides into the posterior cerebral arteries that supply the occipital lobes of the cerebrum.
describe how the vertebral arteries ascend the neck
They then ascend the posterior aspect of the neck, through holes in the transverse processes of the cervical vertebrae, known as foramen transversarium.
describe the course of the internal carotid artery
The internal carotid arteries (ICA) originate at the bifurcation of the left and right common carotid arteries, at the level of the fourth cervical vertebrae (C4). then pass upwards in the carotid sheath.
enters carotid foramen at base of skull
makes right angled turn to travel anteromedially towards the apex of the petrous temporal bone where it emerges superior to the cartilage filling the foramen lacerum.
then makes another right handed turn into the cavernous sinus and runs anteriorly within it grooving the body of the sphenoid
then turns upwards pierces the dural roof of the cavernous sinus and gives off the ophthalmic artery.
Now lying within the subarachnoid space, it turns backwards lateral to the optic chiasma.
On reaching the lateral edge of the posterior clinoid process, it turns superiorly towards the brain, giving the anterior and middle cerebral arteries.
describe the circle of willis
anastomotic connection between the vertebral and internal carotid arteries at the base of the brain in the region of the optic chiasma and pituitary stalk.
circle of willis
The anterior cerebral arteries are connected by the ……….., and each posterior cerebral artery is joined to the corresponding internal carotid artery by a …….
The anterior cerebral arteries are connected by the anterior communicating arteries, and each posterior cerebral artery is joined to the corresponding internal carotid artery by a posterior communicating artery
what does the circle of willis allow?
blood from the vessels on one side of the body to reach those on the other side, or for blood from the vertebral distribution to reach the carotid distribution when necessary
what happens to the terminal branches of the ICA and the vertebral artery?
The terminal branches of the vertebral and internal carotid arteries all anastomose to form a circular blood vessel, called the Circle of Willis.
main components of the circle of willis?
There are three main (paired) constituents of the Circle of Willis:
Anterior cerebral arteries – terminal branches of the internal carotid arteries.
Internal carotid arteries – located immediately proximal to the origin of the middle cerebral arteries.
Posterior cerebral arteries – terminal branches of the basilar artery
To complete the circle, two ‘connecting vessels’ are also present:
Anterior communicating artery – connects the two anterior cerebral arteries.
Posterior communicating artery – branch of the internal carotid, this artery connects the ICA to the posterior cerebral artery.
do weins run along side the intracranial parts of either the vertebral or internal carotid arteries?
No, Instead, veins from the brain follow independent courses to the dural sinuses.
describe te path of te external carotid artery
This artery extends from the bifurcation of the common carotid artery at the level of the upper border of the thyroid cartilage to the neck of the mandible.
Within the parotid gland, it divides into the superficial temporal and maxillary arteries.
The other main branches of the external carotid artery are the superior thyroid, lingual, facial and occipital arteries.
give 3 things the ICA supplies
The brain
Eyes
Forehead
generally what does the ECA supply?
The external carotid artery supplies the areas of the head and neck external to the cranium
the ECA:
After arising from the common carotid artery, it travels up the neck, passing ________ to the mandibular neck and ________ to the lobule of the ear.
After arising from the common carotid artery, it travels up the neck, passing posteriorly to the mandibular neck and anteriorly to the lobule of the ear.
where does the ECA end?
in the parotid gland where it splits into the superficial temporal and maxillary arteries
what does the maxillary supply
and facial / superficial temporal arteries supply (generally)
The maxillary artery supplies the deep structures of the face, while the facial and superficial temporal arteries generally supply superficial areas of the face.
describe the middle meningeal artery
The middle meningeal artery arises from the maxillary artery and enters the skull through the foramen spinosum.
It runs between dura mater and bone, dividing into two main branches.
The anterior branch passes deep to the pterion, where it is liable to be torn in skull fractures.
what does the pterion refer to?
The pterion refers to the area on the lateral aspect of the skull where the sutures of the parietal, frontal, temporal bones and the greater wing of the sphenoid meet.
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