Flashcards in Sievert: Cranial Cavity Deck (96):
What are the two components of skull development?
(blank) surrounds the brain, while (blank) makes up the bones of the face.
The bones of the skull and larynx come from how many different embryological origins? What are they?
neural crest (ectoderm)
paraxial mesoderm (somites)
lateral plate mesoderm
Most flat bones are formed by (blank) ossification
Where does the division between neural crest and paraxial derived components of the skull occur? What is found "in front" of this landmark? What is found posterior to it?
The division between neural crest and somites occurs at the rostral end of the notochord at the prechordal plate. Anything in front of this division is from neural crest. Anything posterior to this division is from paraxial mesoderm (somites).
The accumulation of mesenchyme at the front of the notochord is the same block of mesenchyme that gives rise to the heart fold in the heart tube. Why is this relevant?
If there is a genetic facial deformity, there are typically associated heart defects, because they are derived from the same block of neural crest cells.
The neurocranium can be divided into two parts. What are they? Which part consists of most of the flat bones that surround the brain (frontal, parietal, parts of temporal, occipital)?
membranous **name comes from their method of ossification, which is intramembranous
The neurocranium forms primarily as intramembranous bone. What are the exceptions?
part of the occipital bone
part of the temporal bone
**formed by endochondral ossification
Includes most of the sphenoid bone, ethmoid bone, part of the temporal bone, and part of the occipital bone. Develops by endochondral bone ossification.
Bones of the floor of the cranial cavity form in CARTILAGE. What are they?
sphenoid, ethmoid, and part of the temporal
Viscerocranium develops primarily from (blank) and comes from (blank).
membrane; neural crest
Some parts of the viscerocranium develop from (blank) models: middle ear ossicles, laryngeal cartilages, and hyoid bone.
Which parts of the viscerocranium develop from cartilagenous models (instead of from membrane)?
middle ear ossicles
Because considerable portions of the skull arise from neural crest, (blank) are quite common.
Defects are often associated with the (blank).
craniofacial defects; maxilla **cleft palate
List some features of the newborn skull.
small face form **No teeth = small jaw
no paranasal sinuses
facial bones generally underdeveloped
How many fontanelles are there in the skull? What are fontanelles? What is their purpose?
six; areas where flat bones and the skull meet; allow for overlap during the birthing process
Fontanelles are places where the skull plate comes together. What do these allow for? List the fontanelles.
allow for a lot of movement of the skull plates;
anterolateral (sphenoidal) **one on each side
posterolateral (mastoid) **one on each side
What is premature closure of the sutures?
Failure of the neurocranium to close due to a failure
of the neural tube to close. Brain tissue exposed to amniotic fluid degenerates and results in some type of anencephaly and the fetus is usually not viable.
What are two variants of cranioschisis?
meningocele **meninges bulge out
meningoencephalocele **both meninges and brain vesicles bulge out
Is there an epidural space?
The dura mater forms this component of the interior cranial cavity?
What travels within the potential epidural space (between the two layers of the dura and the skull)?
NO; periosteum; meningeal arteris
What are the two layers of the dura mater? Which is adjacent to bone? Which is adjacent to the arachnoid? Can these layers be separated?
periosteal **adjacent to bone
meningeal **adjacent to arachnoid
These layers can not usually be separated, because they are fused together. However, there are places where they separate by themselves called dural sinuses.
The dura mater is fused tightly to the cranial bones all the way down to this landmark
What blood vessels travel between the layers of the dura and the skull, and make depressions in the skull bones?
meningeal arteries **middle, anterior, posterior
Which meningeal artery is the most important to consider? Why? What can damage to this artery result in?
The middle meningeal artery is the most important, because the bones in the anterior/posterior skull are much thicker than the area of thin bone that the middle meningeal artery runs through. Thus, this artery is more susceptible to damage in a fracture of the skull. **can result in epidural hematoma
Epidural hematoma is usually from what artery? Where does it occur?
middle meningeal artery; forms between the dura and the bone (there is usually no epidural space, but this type of high pressure bleed creates a space, and dissects the dura away from the bone)
What is a hallmark feature of epidural hematoma?
**patients have transient unconsciousness
Patients may regain consciousness, only to relapse suddenly intounconsciousness (“Talk and Die Syndrome”).
What % of pts with epidural hematomas die of the injury? Why do they die?
Pts do not die from bleeding, but die because this is a space-occupying lesion of the cranial cavity. There is no place for the blood to go except down the foramen magnum (only available opening). This will first compress the respiratory and cardiovascular centers. High pressure bleeds occupy a lot of space, so they must be treated quickly.
The arachnoid is normally pushed up tight against the dura due to the CSF below it. What does this do to the "subdural space?" What does this do to the "sub What happens to the arachnoid if the CSF is gone?
makes it a "potential" space; it will collapse against the brain
What lies in the subarachnoid space?
the cerebral arteries and veins **they are not bathed in CSF
What happens to the cerebral veins in the subarachnoid space? Where are they headed? How do they get there?
cerebral veins reach the point where they must penetrate the arachnoid and empty into one of the dural sinuses
Can you remove the arachnoid from the dura? Are they fused? Can you remove the dura from the bone?
yes, the subdural space is not fused;
maybe, but you will really have to PULL the dura from bone, because the epidural space is not a space and these two layers are tightly adhered.
What are arachnoid granulations?
What do they do?
modified parts of the arachnoid;
They pierce the dural venous sinus, and act like one-way valves, which allow CSF (continually formed) to drain into the dural sinus.
So, what are the two components that are mixed in the dural venous sinuses? Where does all of this "stuff" ultimately drain to?
blood from cerebral veins
CSF from arachnoid granulations;
internal jugular vein
What does the CSF do for the brain?
gives it bouyancy **without it, the brain would bruise as it eroded against the skull
Vessels of the brain travel in the (blank) space and need to pierce the (blank) to gain the dural sinuses
What are the vessels on top of the brain called? They communicate between the scalp and the dural venous sinus. Why is this important?
emissary veins; it is possible to transmit infections from the scalp into the cranial cavity
Which layer of the scalp is a prime place for infections of the scalp to transfer to the emissary veins, and into the dural venous sinuses?
loose alveolar tissue layer
What is the most intimate meningeal lining of the brain, that follows each sulci and gyri?
What are these:
Extensions of meningeal dura?
Sites where the two layers of the dura split?
T/F: The periosteal layer and the meningeal layer of the dura are fused everywhere except at sinuses and dural reflections. The meningeal layer peels away to allow for formation of sinuses.
What is this:
A reflection of the dura, which separates the two hemispheres of the cerebrum until the corpus callosum.
Blood occurs quickly in subdural space
Occurs mostly in patients with traumatic brain injury (TBI)
Often associated with other injuries
Often associated with cerebral edema
**Poor outcome (50% mortality rate) and sequelae
Surgery is essential
acute subdural hematoma
Blood appears slowly in subdural space
Long time course
Patients often do not remember an injury
Careful observation or slow drainage
Outcome is relatively good **
chronic subdural hematoma
How can dural reflections play a role in neurological disorders?
When there is a space-occupying lesion one one side of the brain, parts of the brain can get forced underneath the dural reflections, like the falx cerebri, and can be pinched off.
Where is the falx cerebri attached?
What does the falx cerebri house underneath?
What does it create?
ethmoid bone and runs all the way back until it attaches to the tentorium cerebelli;
houses the cerebellum underneath;
creates the tentorial notch, which has sharp edges **can cause problems if something is forced against it
Where opening does the brainstem pass through?
the tentorial notch
**created by the free edge of the tentorium cerebelli and the culvis
T/F: The two lobes of the cerebellum don't have as big of a division between them as the two lobes of the cerebrum.
T/F: Some cranial nerves come off of the brainstem and immediately exit through their foramina, while other nerves run inside of the cranial cavity for awhile before exiting
Where does the superior sagittal sinus run?
What veins empty into this sinus? Where does blood flow from this sinus?
along the attached edge of the falx cerebri;
Blood accumulates from the cerebral veins that enter here, and flows backwards to the confluence of sinuses. Meets up with the left and right transverse sinuses from the sides, and the inferior sinus from below.
Why is the occipital sinus significant?
• Occipital sinus is a form of communication of one of the internal vertebral venous plexuses that can carry cancer from the prostate to the CNS **
Where does the inferior sagittal sinus run? What does it meet up with where the falx meets the tentorium?
along the free edge of the falx cerebri; the straight sinus
Sinuses ultimately drain to the confluence. Where does blood/CSF go from there?
confluence --> transverse sinus --> sigmoid sinus --> internal jugular vein
Where does all blood from the cranial cavity ultimately drain to?
internal jugular vein
The cavernous sinus has septa which divide it into small compartments. What artery runs through this sinus as it ascends to contribute to the circle of Willis? Which cranial nerves pass through this sinus?
CN V1 and V2
Where is the cavernous sinus located? A part of what gland hangs down into the sella turcica?
on either side of the sphenoid bone; pituitary gland
Which divisions of the trigeminal nerve pass through the cavernous sinus?
V1 and V2
In the face, blood can flow in all directions. Ophthalmic plexus, pterygoid plexus and facial vein can all drain to
the cavernous sinus. There are no valves! Why is this important?
infections of the face are common, and can spread and cause infections of the cranial cavity if they occur within the "triangle of death"
Describe the flow of CSF starting at the lateral ventricles
The majority of CSF is produced in the lateral ventricles. From here, it passes thru the interventricular foramen of Monro to the 3rd ventricle, then the cerebral aqueduct to the 4th ventricle. From the 4th ventricle, the fluid passes thru the Foramen of Magendie (medial) and Foramen of Luschka (lateral) to enter the subarachnoid space, which covers the brain and spinal cord. Ultimately flows back to the dural venous sinus through the arachnoid granulations.
T/F: If you block the flow of CSF at any point (ex: cerebral aqueduct), you will increase pressure inside. If you block reabsorption, you can have elevated pressure both outside the brain and inside the ventricular system. There are different forms of elevated CSF pressure!
The capacity for CSF to flow is small, but the turnover of CSF is quite high (constantly being produced). Why is resorption so important?
If it's not reabsorbed, pressure will quickly build up and will lead to hydrocephalus.
How many ml/day of CSF is produced? What is the capacity for CSF?
**most CSF is reabsorbed by arachnoid granulations
(blank) is medial (midline) foramina and (blank) are lateral foramina. Both let CSF out of the ventricles into the subarachnoid space
What are subarachnoid cisterns?
Cisterns are places where CNS tissue makes abrupt change in direction and arachnoid follows a smooth course like the dura creating an enlarged subarachnoid space.
At which cistern does CSF first leave the ventricles?
At which cistern does the tentorium of the cerebellum meet the calculi of the brainstem?
Which cistern has cranial nerves coming off it and is close to cerebral peduncles?
What is another little cistern that we should know about that is in the ventral aspect of the pons?
Excessive accumulation of CSF due to overproduction or inadequate reabsorption resulting in dilation of the cerebral ventricles and raised intracranial pressure. In infants may result in an enlargement of the cranium and in atrophy of the brain.
2 main arteries that contribute blood supply to the brain
This artery is a branch of the carotid artery, that gives off a branch to the orbit, and ultimately ends at the circle of Willis
These arteries come up through the transverse foramina of T1-T6 and enter the foramen magnum. There is one on each side, and they join to form the basilar artery.
This artery runs up a portion of the occipital bone, gets to the base of the cerebral hemispheres, and gives off posterior cerebral branches to the circle of Willis.
List the contributions to the circle of Willis
two *vertebral arteries come together to form one basilar artery
the *basilar artery gives off two *posterior cerebrals to the occipital lobe
two *internal carotids, which give off two *middle cerebrals (which head underneath the temporal lobes to provide lateral hemisphere) and two *anterior cerebrals (which pass between the two cerebral hemispheres
there is a communicating vessel b/w the anterior cerebrals called the *anterior communicating
there is a communicating vessel between the middle and posterior cerebrals called the *posterior communicating
What is significant about the circle of Willis?
Last place in the brain where there is potential collateral flow. After this circle, anything that comes off is an end-artery and is the only vessel supplying that particular brain tissue. The circle of Willis allows for potential collateral flow in the event of a blockage of an internal carotid or one of the other arteries forming the circle.
What is this?
cerebrovascular accident due to obstruction OR rupture of a cerebral blood vessel?
blood clot blocks flow of blood to brain
fatty plaque of blood clot breaks away and flows to the brain where it blocks an artery
break in blood vessel (aneurysm) in brain
What's the difference between an ischemic vs a hemorrhagic stroke?
An ischemic stroke (thrombotic or embolic) deprives the neural tissue of blood. A hemorrhagic stroke is due to a ruptured blood vessel, and causes bleeding into neural tissue.
What lies in the anterior fossa?
What lies in the middle fossa?
What lies in the posterior fossa?
rostral end of the temporal lobes;
occipital lobes and cerebellum
What houses the brainstem, and is the place where the brainstem meets with the cerebral hemispheres?
What passes through the cribriform plate of the ethmoid bone?
olfactory nerve passes thru here to gain access to the nasal cavity
What passes through the optic canal?
CN 2 - optic nerve
What passes through the superior orbital fissure?
CN 3, 4, 6 on their way to the orbit to take care of extraoccular eye muscles, and V1
What passes through the foramen rotundum?
maxillary division of CN 5 (V2)
What passes through the foramen ovale?
mandibular division of CN 5 (V3)
What is significant about the internal acoustic meatus?
This is where CN 7 and 8 enter the skull.
What's the difference between the path of CN 7 and 8 after they enter the skull via the internal acoustic meatus?
7 passes through the temporal bone in the middle ear cavity and leaves the stylomastoid foramen, but 8 never leaves the skull! Just enters, does its thing, and its done.
What passes through the jugular foramen?
CN 9, 10, 11, and the jugular vein
CN 11 is just a weirdo. Where are its cell bodies located?
cell bodies are in the upper cervical spinal cord; cell bodies send out axons which enter skull through foramen magnum and leave again through jugular foramen. Weird!
Which nerves are the most susceptible to damage?
cranial nerves with the longest intracranial course **CN 6
CN 7-12 exit the brainstem and the skull in the (blank)
CN 3-6 exit the brainstem in the posterior fossa and travel intradurally into the (blank) where they leave the skull
middle fossa **long course, susceptible to damage
Which cranial nerves exit the brainstem AND the skull in posterior cranial fossa. Come off either pons OR medulla, and travel a short distance before they enter the appropriate foramina where they exit?
Which cranial nerves exit the brainstem in the posterior fossa, but must travel intradurally all the way to the middle where they finally leave the skull? They have a longer course **more susceptible to damage!