learning objectives answers to cranial nerves and cranial contents
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| How is a dural venous sinus formed? | By the splitting of the meningeal layer of dura from the endosteal layer of dura. The triangular space formed is a dural venous sinus.
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| What is the function of a dural venous sinus? | It collects blood from the scalp (emmissary vv.); from the thin bone of the calvarium (diploic vv.) as well as from the superficial cerebral vv. and deep cerebral vv. that drain the brain and brain stem.
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| What is the function of an arachnoid villous? | It allows cerebrospinal fluid (CSF) from the subarachnoid space to escape into the dural venous sinus - thus regulating the amount of CSF present since it is continually produced.
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| How is an arachnoid villous formed? | A small finger-like projection of arachnoid protrudes through a small hole in the meningeal layer of dura - gaining access to the dural venous sinus.
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| What is an arachnoid granulation ? | An old arachnoid villus that has grown across lumen of the venous sinus and begins to invaginate it’s way into the bone of the calvarium.
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| Into what bony structure do these granulations embed themselves? | The inner bony diploe (plate) of the calvarium (temporal and/or occipital bone primarily).
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| Be able to trace the pathway of the flow of venous blood within the dural venous sinuses? | superior sagittal sinus→ confluence of sinuses
occipital sinus --> confluence
inferior sagittal sinus and deep cerebral --> confluence via the straight sinus→ From the confluence→right and left transverse sinuses→sigmoid sinus→ jugular foramen
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| Where does the venous blood leave the cranial cavity? | Via the jugular foramen.
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| What vessel forms at the point of exit? | The internal jugular vein.
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| What two sinuses drain from the cavernous sinus? to where specifically? | The superior petrosal sinus drains posteriorly to the upper region of the sigmoid sinus; the inferior petrosal sinus drainly inferiorly to the lower region of the sigmoid sinus.
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| What two venous pathways flow to the cavernous sinus? | The sphenoparietal sinus and the ophthalmic vein.
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| Why is the venous pathway from the face clinically important? | Infection from the face (pimples, boils, etc.) can flow posteriorly through the valveless veins back into the cavernous sinus.
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| How is a dural fold formed? | By the fusion of two layers of meningeal dura.
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| Be able to list the 4 dural folds within the cranial cavity and what components of the CNS they effectively separate. | Falx cerebrum: rt/lt cerebral hemispheres; falx cerebelli: rt/lt cerebellar hemipsheres; tentorium cerebelli: overlying cerebral hemispheres from underlying cerebellar hemispheres; diaphragma sellae: nothing.
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| What sinus is formed in the attached margin of each dural fold? | Falx cerebrum: superior sagittal sinus; falx cerebelli: occipital sinus; tentorium cerebelli: rt/lt transverse sinuses; diaphragma sellae: none.
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| What is formed by the free edge of the tentorium cerebelli? | The tentorial notch.
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| What is found within this opening? | The brain stem.
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| Which cranial nerve is found just under the free edge of the tentorium cerebelli? | CN IV (trochlear).
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| What sinus is found within the junction of the falx cerebri with the tentorium? | The straight sinus.
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| What is the function of the straight sinus? | It drains venous blood from the inferior sagittal sinus (in the free edge of the falx cerebri) as well as from the deep brain regions via the deep cerebral vein (of Galen).
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| Where does the falx cerebri attach anteriorly? | The crista galli (of the ethmoid bone).
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| To what 4 structures does the diaphragma sellae attach? | The two anterior clinoid processes and the two posterior clinoid processes.
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| Which four major vessels arise in the neck and eventually supply blood to the brain? | The left and right common carotid arteries as well as the left and right vertebral arteries.
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| What are the terminal branches of the internal carotid a.? | The middle and anterior cerebral aa.
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| What are the terminal branches of the basilar a.? | The right and left posterior cerebral aa
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| What are the various anatomical relationships superior to the diaphragma sellae? | The optic chiasm and the ophthalmic artery.
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| Why are these relationships clinically important? | Compression of either by an enlarging hypophysis from below will result in blindness.
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| Through what opening does the internal carotid artery enter the bone of the skull? | The opening of the cartoid canal.
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| In which direction does the artery pass once in this bony canal? | Medially in a horizontal fashion.
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| Through what opening does the internal carotid exit this canal? | The foramen lacerum.
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| Into what structure does the internal carotid immediately enter? | The cavernous sinus.
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| What is the anatomical shape of the internal carotid within this structure? | “S”-shaped - a siphon.
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| How does the internal carotid gain access to the cranial cavity? | It passes through the dural roof of the cavernous sinus.
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| What is the first branch of the internal carotid? | The ophthalmic artery.
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| What are the terminal branches of the internal carotid? | The middle and anterior cerebral aa.
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| Be able to list all 12 cranial nerves and their various modalities (motor, sensory, parasympathetic - or any combination of these). | Sensory only: CN I, II, VIII (+ CN V1 and V2); motor only: CN IV, VI, XI, and XIII; motor and sensory: CN V - specifically V3; motor and parasympathetic: CN III; motor, sensory and parasympathetic: CN VII, IX, and X.
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| Which is the only cranial nerve to exit the dorsal aspect of the brainstem? | The trochlear (CN IV).
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| What are the four autonomic ganglia of the head? | Ciliary, pterygopalatine (sphenopalatine), submandibular & otic (COPS).
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| Which division of the ANS synapse in these ganglia? | The preganglionic parasympathetic fibers.
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| Which cranial nerve(s) supply preganglionic fibers to each one? | Ciliary: CN III; pterygopalatine: VII; submandibular: VII; otic: IX.
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| Which branch of CN V takes postganglionic fibers to specific target organs? | Ciliary: V1; pterygopalatine: V2; submandibular: V3; otic: V3.
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| CN I exits face/skull via | accesses cranial cavity via the cribriform plate of the ethmoid
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| CN II exits face/skull via | optic canal
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| CN III, IV and V1 exits face/skull via | superior orbital fissure
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| V2 exits face/skull via | foramen rotundum
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| V3 exits face/skull via | foramen ovale
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| VII and VIII exits face/skull via | internal acoustic meatus
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| IX, X & XI exits face/skull via | jugular foramen
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| XII exits face/skull via | hypopglossal canal.
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| Which cranial nerves are associated with the cavernous sinus and why is this clinically important? | CN V1, IV, VI, III and perhaps V2. They become involved in cavernous sinus syndrome.
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| What is cavernous sinus syndrome? | Infectious thrombi pass to the cavernous sinus, lodge there and cause eventual paralysis of the eye by affecting nerves of extraocular mm. CN VI is affected first as it passes through cavernous sinus, others are embedded in the lateral dural wall
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| What are the symptoms of Horner's syndrome. | Pupillary constriction; ptosis (drooping of upper eyelid); vasodilation and dry face.
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| What is the anatomical basis for Horner’s syndrome? | PC = paralysis of dilator pupillae m.; ptosis= paralysis of superior tarsal m.; vasodilation and dry face= lack of sympathetic innervation
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| What specific structures compose the pharyngeal plexus? | The cranial accessory fibers of CN XI) distributed by the vagus n (XI via X); the fibers of the glossopharyngeal n. (CN IX); and postganglionic sympathetic fibers.
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| What is/are the modalities of the pharyngeal plexus? | Motor, sensory and sympathetic.
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| What are the primary functions of the pharyngeal plexus? | Motor to the pharyngeal constrictors and sensory to the mucosa of the pharynx.
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