Flashcards in Interval 12: Skull, Cranial cavity, nerves, Deck (86):
The skull consists of the cranium and the facial skeleton. The cranium consists of _____ bones, which form the ________ and the ________. The facial skeleton is formed by _____ bones which enclose the orbits, nasal cavity, oral cavity, and paranasal sinuses.
-calvaria and cranial base
Bones of the calvaria consist of 2 layers of ______ bones separated by the ______, which is a ______.
-layer of bone marrow
What 3 things do the bones of the cranial base articulate with?
-bones of the facial skeleton
The bones of the cranium are joined by _______. How many are there? Name them and what bones they connect.
-coronal: frontal bones and 2 parietal
-sagittal: 2 parietal bones
-lambdoidal: 2 parietal bones and the occipital
Where is the pterion? Is it in close proximity to anything? Why is this problematic?
-on the lateral aspect of the skull superior to the zygomatic arch and posterior to the lateral wall of the orbit
-it is superficial to the anterior branch of the middle meningeal artery, which supplies the dura and the skull
-if you fracture your pterion you may lacerate the middle meningeal artery and cause an epidural or extradural hematoma
What is the thinnest part of the calvaria?
What will the epidural hematoma of the middle meningeal artery form?
-a biconvex lens-shaped hematoma between the skull and the periosteal dura, which does not pass the sutures
What symptoms may someone with a pterion fracture demonstrate and why?
-may have initial lucid asymptomatic internal, followed by weakness of limb muscles, a dilated pupil resulting from compression of the oculomotor nerve (CN III), and deterioration of cardiovascular and respiratory functions
-an epidural hematoma may compress the lateral part of the cerebral hemisphere and result in herniation of the medial part of the temporal bone through the tentorial notch of the dura. The herniated temporal bone may compress the brain stem
Bregma vs. Lamda
-Bregma: on the superior aspect of the skull just anterior to the vertex; junctions of coronal and parietal suture
-lambda: posterior aspect of skull superior to the inion, part of the external occipital protuberance; junction of sagittal and lamdoidal suture
What arteries supply the brain? and what special structure do they form via their anastomoses?
-internal carotid and vertebral arteries
-circle of Willis
Describe how the internal carotid and vertebral arteries enter and course through the skull and what they give rise to.
-internal carotid: enters skull through carotid canal, crosses the width of the foramen lacerum, and passes through the cavernous sinus. At the base of the brain, each internal carotid divides into a small anterior cerebral artery and large middle cerebral artery
-vertebral: enter skull through foramen magnum and unit to form the basilar artery; the basilar artery divides into a pair of posterior cerebral arteries
Describe the structure of the Circle of Willis
-anterior communicating artery connects the anterior cerebral arteries
-pair of posterior communicating arteries connect the internal carotid arteries with the posterior cerebral arteries
What are Berry Aneurysms and where do they occur?
-saccular dilatations of the walls of arteries
-most commonly occur in the anterior part of the circle of willis at branch points of the anterior communicating artery, posterior communicating artery, or middle cerebral artery
What can happen as a result of a Berry Aneurysm and what will the patient present with?
-blood may accumulate in the subarachnoid space and cause a subarachnoid hematoma
-patients may experience an acute explosive "worst headache of my life" due to blood leaking from aneurysm, which irritates the meninges
-patients may also have stiff neck due to irritation of spinal dura
-Oculomotor n (CN III) may be compressed by aneurysm at junction of posterior communicating artery and internal carotid or posterior cerebral artery. Patients will initially have a dilated or blown pupil
Where would an aneurysm likely have to occur to compress CN III? Symptoms in patient?
-Junction of posterior communicating artery and posterior cerebral artery or internal carotid artery
Describe the meninges of the cranial cavity
-consist of 2 layers of dura mater, arachnoid mater, and pia mater
The dura of the cranial cavity consists of what layers?
-outer periosteal layer: closely applied to inner surface of bones of the skull and is firmly attached to sutures
-inner meningeal layer: continuous with dura of the vertebral canal
What 3 things does the meningeal dura form?
-septa that extend between the 2 cerebral hemispheres (falx cerebri), between the hemispheres and the cerebellum (tentorium cerebelli) and cover the pituitary gland in the sella turcica (diaphragma sellae)
Is the meningeal dura innervated? If so, by what?
-mostly by meningeal branches of the opthalmic, maxillary, and mandibular divisions of the trigeminal nerve
-posterior cranial fossa is innervated by first 3 cervical spinal nerves, and by meningeal branches of the vagus (CN X)
What is responsible for headaches?
-meningeal dura is sensitive to pain
-irritation or stretching is a common cause of headache
-pain is commonly referred to regions supplies by branches of the trigeminal nerve
What is closely applied to the dura? What is found beneath this layer?
-subarachnoid space contains CSF is found between the arachnoid and pia mater
The pia mater intimately covers what?
-brain and the roots of cranial nerves
What are dural venous sinuses? What do they lack?
-endothelium-lined channels that receive cerebral veins
-lack smooth muscle and valves
Cerebral veins are known as ______ veins, why?
-they traverse the subdural space (potential space) between the arachnoid and meningeal dura to drain into dural venous sinuses
What can cause a subdural hematoma?
-skull trauma may cause a searing of bridging veins at points where they enter dural venous sinuses; venous blood may accumulate in the subdural space and result in a subdural hematoma
What will a subdural hematoma look like and what will patients present with?
-crescent-shaped hematoma not bound by sutures of the skull
-chronic subdural hematoma can cause headache, impairment of cognitive skills, and gait instability
Compare what an epidural hematoma will look like to what a subdural hematoma will look like? What may cause either of these?
-Epidural: middle meningeal artery laceration; a biconvex lens-shaped hematoma between the skull and the periosteal dura, which does not pass the sutures
-Subdural: laceration of bridging veins (cerebral veins); crescent-shaped hematoma not bound by sutures of the skull
Dural venous sinuses not only receive cerebral veins, but also do what else? Which sinus is particularly important in this?
-sites of resorption of CSF from subarachnoid space by way of arachnoid granulations that protrude into the sinuses
-superior sagittal sinus
What are emissary veins?
-valveless veins that pass through openings in the skull and allow dural sinuses to communicate with extracranial veins
What 3 sinuses carry cerebral venous blood toward the confluence of the sinuses? Where is the confluence of the sinuses located?
-superior sagittal sinus
-near the posterior midline deep to the occipital bone
What forms the straight sinus?
-union of the inferior sagittal sinus and the great cerebral vein of Galen
Once blood is in the confluence of the sinuses, where does it go?
-taken by the transverse sinuses into the sigmoid sinuses
-most blood from superior sagittal sinus passes through right transverse sinus and most from straight sinus enters left transverse
-then each sigmoid sinus passes through a jugular foramen, oins with an inferior petrosal sinus, and drains into an internal jugular vein
What are the cavernous sinuses? What do they receive and continue in to? Are they connected?
-dural venous sinuses situated lateral to the body of the sphenoid and the pituitary gland
-receive venous blood from cerebral veins and from sphenoparietal venous sinuses
-each drains into a superior and inferior petrosal sinus
-connected to eachother by intercavernous sinuses
What can be found coursing through each cavernous sinus?
-internal carotid artery and its periarterial plexus of postganglionic sympathetic axons and the abducens nerve (CN VI) course through the middle of each
-Opthalmic and maxillary divisions of CN V, the oculomotor n (CNIII), and the trochlear nerve (CN IV) course in the lateral wall of each
What type of veins are the superior and inferior ophthalmic veins and what do they do?
-emissary veins that link the cavernous sinus with tributaries of the facial vein near the orbit and with the pterygoid plexus of veins in the infratemporal fossa
What type of veins are the basilar plexus of veins and what do they do?
-emissary veins which link the inferior petrosal sinuses with the internal vertebral plexus of veins in the epidural space of the vertebral canal
The floor of the cranial cavity can be divided into 3 fossae. Name them.
-anterior, middle, and posterior cranial fossae
4 foramina found in the anterior cranial fossa
1. foramen cecum
2. cribiform plate
3. anterior and posterior ethmoidal foramina
4. optic foramen
What does foramen cecum transmit?
-transmits a small emissary vein from the nasal cavity to the superior sagittal sinus
What does the cribiform plate transmit?
-transmits olfactory nerve filaments running from the nasal cavity to the olfactory bulbs
What do the anterior and posterior ethmoidal foramina transmit?
-anterior: transmits the anterior ethmoidal vessels and nasociliary nerve (V1)
-posterior: transmits the posterior ethmoidal vesselss and nerve
What does the optic foramen transmit?
-optic nerve (II) and ophthalmic artery
List the names of the 7 fissures/foramina in the middle cranial cavity.
1. superior orbital fissure
2. inferior orbital fissure
3. foramen rotundum
4. foramen ovale
5. foramen spinosum
6. foramen lacerum
7. hiatus for the greater petrosal nerve
What does the superior orbital fissure transmit?
-oculomotor nerve (CN III)
-trochlear (IV) n
-abducens nerve (VI)
-ophthalmic division of trigemical (V1)
-sympathetic nerve fibers from the internal carotid plexus
-meningeal ophthalmic veins
What does the inferior orbital fissure?
-maxillary nerve (VII) and infraorbital artery and vein
What does the foramen rotundum transmit?
-maxillary divsion of the trigeminal nerve (V2)
What does the foramen ovale transmit?
-mandibular division of trigeminal (V3)
-accessory meningeal artery
-lesser petrosal nerve (IX)
What travels through the foramen spinosum?
-middle meningeal artery
What travels through the foramen lacerum?
-covered with fibrocartilage in the living
-transmits a meningeal branch of the ascending pharyngeal artery
-crossed by internal carotid artery but not traversed by it
What does the internal carotid artery cross yet not go through?
What does the hiatus for the greater petrosal nerve transmit?
-greater petrosal nerve (V2)
Name the 4 foramen in posterior cranial fossa
1. internal acoustic meatus
2. jugular foramen
3. foramen magnum
4. hypoglossal canal
What does the internal acoustic meatus transmit?
-facial (VII) and vestibulocochlear (VIII) nerves
What does the jugular foramen transmit?
-sigmoid dural sinus becomes the internal jugular vein at this point
-also transmits the glossopharyngeal (IX), the vagus (X), and the accessory (XI) nerves
What does the foramen magnum transmit?
-transmits spinal cord
-vertebral venous plexus
-spinal roots of the accessory nerve (XI)
What does the hypoglossal canal transmit?
-hypoglossal nerve (XII)
5 canals/foramen present in in the cranial base?
1. carotid canal
2. auditory (Eustachian) tube
3. petrotympanic fissure
4. stylomastoid foramen
5. pterygoid canal
what does the carotid canal transmit?
-internal carotid artery and a plexus of the postganglionic sympathetic axons
What is the auditory (eustachian) tube?
-bony portion of the auditory tube
What does the petrotympanic fissure transmit?
-chorda tympani (VII)
What does the stylomastoid foramen transmit?
-trunk of the facial nerve (VII) which supplies the posterior belly of the digastric and the muscles of facial expression
What does the pterygoid canal transmit?
-transmit the N. of pterygoid canal (vidian n)
What is found in the cranial vault?
-external auditory (acoustic) meatus which does NOT transmit any structures
What are the 8 foramen found on the face (including the palate and mandible)?
1. supraorbital foramen
2. external auditory (acoustic) meatus
3. infraorbital foramen
4. mandibular foramen
5. mental foramen
6. Greater palatine foramen
7. lesser palatine foramen
8. incisive foramen
What does the supraorbital foramen transmit?
-transmits the supraorbital N (V1) and vessels
What does the external auditory meatus transmit?
What does the infraorbital foramen transmit?
-infraorbital nerve (V2) and vessels
What does the mandibular foramen transmit?
-inferior alveolar n (V3), artery, and vein
-forms the proximal opening of the inferior alveolar canal
What does the mental foramen transmit?
-transmits mental n. of (V3) and vessels
-constitutes the termination of inferior alveolar canal
What does the greater palatine foramen transmit?
-inferior opening of the pterygopalantine canal
-transmits the greater palantine nerves (CN V2) and vessels to the hard palate
What does the lesser palatine foramen transmit?
-inferior opening the******
What does the incisive foramen transmit?
-nasopalatine nerves to the anterior portion of the hard palate
The optic canal and superior orbital fissure transmit structures into and out of the orbit. Name these structures.
-optic canal: optic nerve and ophthalmic artery
-SOF: CN III, IV, V1, VI and superior opthalmic vein
Where do the 6 EOM attach?
-4 rectus muscles have an attachment to a common tendinous ring of Zinn at back of orbit
-SO attaches to sphenoid bone above tendinous ring
-IO: attaches to the orbital plate of the maxilla in anterior part of the orbit
Which EOM traverse the length of the orbit?
-all of them but the IO
Name the 4 smooth muscles of the orbit
1. superior tarsal: SM part of levator palpebrae superioris which elevates upper lid
2. dilator pupillae
3. constrictor pupillae
4. ciliary muscle: in ciliary body and acts when ciliary muscle contracts, suspensory ligaments relax resulting in changes allowing lens to round up for near vision curvature
Describe the accommodation reflex and what nerves and muscles are involved
-aka near response
-ciliary muscle contracts and the lens becomes thicker and there is constriction of the pupils and convergence
-convergence is due to both medial rectus muscles
-all muscles in this response receive parasympathetic or skeletal motor fibers in CN III
What nerves are involved in the pupillary light reflex? What should happen in this reflex under normal conditions?
-sensory fibers of optic CN II
-parasympathetics of CN III
-presentation of light to 1 eye should result in constriction of both pupils
Where is the lacrimal gland located? What is its innervation?
-upper lateral corner of orbit
-innervated by preganglionic parasymp. from CN VII and postganglionics from pterygopalatine ganglion
What gives rise to the optic nerve? Why is this nerve affected by MS?
-retinal ganglion cells give rise to axons that form the optic nerve
-all the myelin of CN II is formed by oligodendrocytes, so that consequently, ON is susceptible to CNS demyelinating diseases such as multiple sclerosis which typically do not affect other cranial nerves
In addition to myelin, what else surrounds the axons of the optic nerve?
-ensheathed by 3 layers of meninges that surround the rest of the CNS
-Subarachnoid space containing CSF extends along the optic nerve to the optic disk at the back of the eyeball
What is papilledema? What causes it?
-increase in intracranial CSF pressure may result in papilledema, a swelling of the nerve at the optic disk caused by reduced venous return from the retina
Where do the optic nerve fibers converge?
-in the midline anterior and superior to the pituitary gland to form the optic chiasm
There are no synapses in the optic nerves, chiasm or tracts. Therefore, axons of the ganglion cells of the retina extend uninterrupted to synapse mainly in the ________.
-lateral geniculate nucleus of the thalamus for primary visual processing
-these cell bodies then project to primary visual cortex
What can a pituitary tumor cause?
-compression of the optic chiasm in the midline will affect the decussating fibers from the nasal half of both eyes, which are responsible for perception of light from the lateral or temporal fields of vision