Chapter 3: Cranial Nerves Flashcards Preview

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Flashcards in Chapter 3: Cranial Nerves Deck (117):

Where does cranial nerve 1 originate? what is its path of travel? Are the fibers myelinated or unmyelinated?

The olfactory nerve originates from the small olfactory receptors located in the mucous membrane of the nose. The fibers are unmyelinated, and travel through the cribiform plate to the olfactory bulb, and then travel posteriorly on the inferior surface of the cerebrum as olfactory tracts


How many axons of the gcl originate in the retina?

1x10^6, or 1 million axons


What are the 4 regions of the optic nerve?

1- intraocular region
2- intraorbital region (located within muscle cone)
3- intracanalicular region (located within optic canal)
4- intracranial region (ends in the optic chiasm)


T/F: is the optic nerve surrounded by schwann cells?

False. As the optic nerve is considered part of the brain for developmental purposes, they have oligodendrocytes, not schwann cells, surround it.


How long is the intraorbital portion of the optic nerve? How does this effect it course of travel?

The optic nerve is 25-30 mm within the orbit, making it long than the distance b/w the back of the globe and the orbit). Therefore, it has a sinuous path to compensate for the increased distance


What is the average size of the optic disc?

1.76 mm wide x 1.92 mm tall


What is the physiologic cup? Where is it located?

represents and "axon free" zone, where the branches of the central retinal artery and vein pass through its center.

It is located slightly temporally from the geometric center


What are the 4 parts of the optic nerve?

-the superficial nerve fiber layer
- prelaminar area
- laminar area
- retrolaminar area


How are the fibers arranged in the superficial nerve fiber layer?

the fibers from the upper retina are located above, the lower retina below, the nasal retina medially and the temporal retina laterally.

Macular fibers, which constitute 1/3 of ON, are laterally placed (foveal fibers located peripherally, peripapillary fibers centrally)


What is the Prelaminar Area?

area where mullers cells are replaced by astrocytes in the ILM and ganglion cells are separated into "fascicles" by the astrocytes.

New astrocytic ILM is continuous with the previous Muller cell ILM


What is pathologic cupping of the disc?

when the ON is damaged, axons and glial cells may be lost, resulting in pathologic enlargement of the cup.


What is the laminar area?

the area where the nerve is trasmitted through pores in the lamina cribosa, which consists of approximately 10 CT sheets


What is the lamina cribosa made up of?

Collagen types I and III, elastin, fibronectin, and laminin


What are the functions of the lamina cribosa?

1- scaffold for ON axons
2- Point of fixation for the CRA/CRV
3- Reinforcement of the posterior segment of the globe


What is the retrolaminar area?

The area where the diameter of the ON increases to 3 mm due to myelination of the nerve fibers and presence of oligodendroglia/surrounding meningeal sheaths


What is the intraorbital region?

In this region, the ON passess through the muscular cone, where the superior and medial rectus muscles share a CT sheath with the ON.

At the optic canal, the dural sheath of the nerve fuses wtih periosteum, completely immobilizing it (however, makes it susceptible to traumatic shearing forces)


What is the Pia Mater?

the innermost portion of the ON sheath

sends numerous septa into the ON, dividing its axons into bundles (this provides mechanical support as well as nutrition for the axons and glial cells)


What is the arachnoid mater?

Middle layer of the meningeal sheath, is connect to the Pia across the subarachnoid space via vascular trabeculae


Where does the subarachnoid space end anteriorly? Posteriorly?

Anteriorly, the SAS ends at the level of the lamina cribosa. Posteriorly, it is continuous with the SAS of the brain


What is the Dura mater? What is it made of?

the outer layer of the meningeal sheath, measuring 0.3-0.5 mm thick
The dura is made of dense bundles of collagen and elastic tissue that fuse anterioly with the outer layer of the sclera


What is the blood supply of the ON in the intracanalicular region?

blood supply is derived from pial vessels that are branches from the ophthalmic artery


In the intracanalicular region, what structure are the ON and sheath tethered to?

the periosteum of the optic canal


What is indirect traumatic optic neuropathy?

blunt trauma that causes shearing of the blood supply of the ON in the intracanalicular region


What is the pathway of the optic nerve to the brain after leaving the optic canal?

After leaving the canal, the ON lies above the ophthalmic arteries, above and medial to the ICA's. Then passes posteriorly over the cavernous sinuses and forms the optic chiasm, which then divides into the left and right optic tracts, which then travel to their respective lateral geniculate bodies. From here, they leave as geniculocalcarine pathways (optic radiations), and pass to the primary visual cortex.


When do the CRA and long posterior ciliary arteries branch off from the ophthalmic artery?

When the OA enters the muscular cone


What is the blood supply of the retrolaminar optic nerve?

supplied by pial vessels and short posterior ciliary vessels, with some help from the CRA and recurrent choroidal arteries.


What is the blood supply of the laminar optic nerve?

supplied by short posterior ciliary arteries or branches of the arterial circle of hall and zinn (arises from branches of short posterior ciliary arteries, and is usually embedded in the sclera around the ON head)


What is the blood supply of the prelaminar optic nerve?

supplied by short posterior ciliary arteries and recurrent choroidal arteries (NFL is supplied by CRA)


WHat is the blood supply of the intraorbital region of the ON?

Proximally supplied by pial vessels and neighboring branches of the ophthalmic artery
Distally by intraneural branches of the CRA
Anteriorly, supplied by short posterior ciliary arteries and occasionally peripapillary choroidal arteries


What is the blood supply of the intracanalicular region?

supplied almost exclusivelu by ophthalmic artery


What is the blood supply in the intracranial region?

supplied primarily by branches of the ICA and ophthamic artery


What is the difference between the CRA and retinal arterioles?

The CRA contains fenestrated internal elastic lamina and an outer layer of muscle cells surround by a thin basement membrane


What is the optic chiasm? What are its dimensions?

the decusation of the two optic nerves. 12 mm wide x 8 mm long x 4 mm thick


Where do extramacular fibers from the inferonasal retina cross in the chiasm?

They cross anteriorly in the chiasm, at "Wilbrands knee"


Where do the extramacular superonasal fibers cross in the chiasm?

They cross directly opposite to their tracts


Where do the temporal fibers cross?

Trick question--the temporal fibers remain uncrossed


What is the course that the temporal macular fibers run?

They pursue a direct course through the chiasm, as a bundle of uncrossed fibers


What is the course that the nasal macular fibers run?

The nasal fibers cross in the posterior aspect of the chiasm


What percentage of of the fibers are crossed? Uncrossed?

53% crossed, 47% uncrossed


What kind of fibers does the optic tract contain?

ipsilateral temporal and contralateral nasal fibers

upper retinal projections travel medially in the tract; lower projections travel laterally


What kind of orientation do the macular fibers adopt in the optic tracts?

The macular fibers adopt a dorsolateral orientation


What is the lateral geniculate body?

a synaptic zone for higher visual projections, receives 70% of the optic tract fibers within 6 alternating layers of white and gray matter


What layers of the LGN synapse with fibers from the ipsilateral nerve? Contralateral nerve?

Layers 1, 4, & 6 synapse with contralateral fibers

Layers 2,3, & 5 synapse with ipsilateral fibers


What are the optic radiations? By what name are they also known?

aka geniculocalcarine pathways, they connect the LGN to the primary visual cortex


What is the pathway from the LGN to the visual cortex?

radiations leave the LGN and wind around the temporal horn of the lateral ventricles (called "meyers loops), swee backward toward the visual area of the occipital love


Facts about visual cortex?

Thinnest area of the human cerebral cortex
Has 6 layers
occupies the superior and inferior lips of the calcarine fissues


What is the blood supply of the visual cortex?

The visual cortex is supplied by the posterior cerebral artery, which is a branch of the basilar artery.

Note: In some people, the MCA also contributes


What does CN III supply?

Innervates all of the EOM except the SO and LR

Carries cholinergic fibers to the pupillary sphincter and ciliary muscles


How many nerve fibers does CN III have?

24,000 nerve fibers


Where does CN III originate?

From a complex group of cells located in the rostral midbrain (mesencephalon) at the level of the superior colliculus


Where is the CN III nucleus located in relation to the CN IV nucleus?

CN III nucleus is located immediately rostral to the CN IV nucleus


What does the CN III nucleus consist of?

It consist of several distinct pairs of large nuclei, each subserving the muscle they innervate

However, LPS only has one nucleus that subserves the muscles bilaterally


Where do the fibers of the dorsal nucleus decussate?

the caudal aspect of the nucleus, and supply the SR muscles


Where is the Edinger-Westphal nucleus located? What is its function?

Located cephalic and dorsomedially

Provides parasympathetics to the ciliary muscle and iris sphincter


What is the most ventral group of nuclei in the CN III nucleus?

MR nuclei


Where do aneurysms that affect CN III commonly occur?

At the junction of the posterior communicating arteries and the ICA


What is the pathway of CN III to the globe?

It pierces the dura on the lateral side of the posterior clinoid, runs along the lateral wall of the cavernous sinus (and above CN IV), enters the orbit via the superior orbital tissue and then separates into the superior and inferior divisions after passing through the annulus of Zinn


Which division of CN III is larger?

The inferior division, as it supplies three muscles compared to two.


What path does the parasympathetic aspect of CN III take to the orbit?

It winds around the periphery of the nerve, enters the inferior division, travels through to the IO branch, joins the ciliary ganglion, emerges as short ciliary nerves, pierces the sclera, travels through the choroid, and innervates the ciliary muscle and pupillary sphincter


What is the Light Reflex?

consists of simultaneous and equal constriction of pupils in response to illumination of one eye


What is the afferent pathway of the light reflex?

Coincides with that of the afferent visual pathway, including decussation of nasal fibers at optic chasm


What is the efferent pathway of the light reflex?

At the posterior optic tract, pupillary fibers leave the visual tract and pass to the pretectal nuclei (located at level of superior colliculus of lateral midbrain), and then pass to the Edinger-Westphal nuclei (where they partially decussate). They then exit the EW nucleus and travel with CN III as it leaves the brainstem, and then travel with the inferior division after entering the orbit. Fibers synapse on ciliary ganglion, exit as postganglionic short ciliary nerves (3-5% of total nerve are pupillomotor fibers)


What is the Near Reflex?

the synkinesis that occurs when visual focus is changed from distance to near, including accommodation, convergence, and pupillary constriction


What is the pathway of the near reflex?

Originates in the occipital association cortex, impulses descent down the corticofugal pathway to the pretectal nuclei +/- tegmentum, after which the fibers pass to the EW nucleus and motor nuclei of MR and nuclei of CN VI

Efferent Fibers for accommodation follow the same pathway as the light reflex (however, final destination via the short ciliary nerves is the ciliary muscle)


What is Cranial Nerve IV?

The trochlear nerve, which supplies the SO muscle.

Contains the fewest nerve fibers of all the cranial nerves (3400)

Travels the longest course of any cranial nerves (75 mm)


Where is the nucleus located for CN IV?

the caudal mesencephalon at the level of the inferior colliculus

is continuous with the caudal end of CN III nucleus (only difference is that its cells are smaller in size)


T/F: CN IV is the only nerve to completely decussate?

True. After leaving its nucleus, the nerve fascicles curve dorso-caudally around the peri-aqueductal gray matter and completely decussate in the superior medullary velum.


What affect does retrobulbar anesthesia have on CN IV?

It usually does not affect CN IV (b/c of its location outside the muscle cone inside the orbit)


Where does CN IV exit the nervous system? What is unique about its pathway?

It exits the nucleus/nervous system dorsally, and is the only cranial nerve to do so.


What does CN V (Trigeminal Nerve) supply?

Provides motor innervation to the muscles of mastication (pterygoid, masseter, and temporal is)

Sensory innervation to scalp, forehead, face, eyelids, eyes, lacrimal glands, EOM, ears, dura mater, and tongue


How many nuclei does CN V have? Where is its nucleus located?

CN V has 4 nuclei

The CN V nuclear complex extends from the midbrain to the upper cervical segments (C4)


What are the nuclei of CN V?

- mesencephalic nuclei (Most superiorly located)
- main sensory nucleus
- spinal nucleus and tract
- motor nucleus (most inferiorly located)


What is the function of the mesencephalic nucleus?

Mediates proprioception and deep sensation from the masticatory, facial, and EOM

Extends inferiorly into the Pons as far as the Main Sensory Nucleus


What is the function of the Main Sensory Nucleus? Where is it located?

Located in the Pons next to the motor nucleus; is continuous with the mesencephalic nucleus (above) and the spinal nucleus (below)

serves light touch from the skin and mucus membranes


From where does the main sensory nucleus receive input? What happens to the fibers after entering the Pons?

It receives input from the ascending branches of the sensory root

After entering the Pons, the fibers divide into the ascending tract (terminates in the main sensory nucleus) and descending tracts (terminates in the spinal nucleus)


Where is the spinal nucleus located?

Its extends from the medulla to C4


Where does the spinal nucleus receive fibers from?

Receives pain, temperature, and cutaneous component of CN VII/IX/X from ear/external auditory meatus from the descending tracts


Where do the fibers terminate in the spinal nucleus?

- Sensory fibers from V1 end in most ventral portion of nucleus
- Fibers from V2 end in the mid portion
- Fibers from V3 end in the dorsal aspect
- Fibers from the peri-oral region thought to terminate most rostrally; fibers from peripheral face and scalp most caudally


Where do the axons of the mesencephalic, main sensory, and spinal nuclei travel to?

They relay sensory information to the higher sensory ares of the brain


Where do the axons leaving the CN V nuclei decussate on their way to the brain?

The fibers leaving the CN V nuclei decussate in the Pons en route to the thalamus


What pathway do the axons from CN V take en route to the brain?

The fibers cross in Pons, and ascend to the thalamus via the ventral and dorsal trigeminothalmic tracts, and terminate in the ventral posteromedial nucleus of the thalamus.

Thalamic nucleus then sends axons through the internal capsule to the post-central gyrus of the cerebral cortex


What nerve mediates the oculocardiac reflex?

the Trigeminal nerve mediates the afferent pathway of the oculocardiac reflex


Where is the motor nucleus of CN V located?

medial to the main sensory nucleus in the Pons


Where does the motor nucleus of CN V receive fibers from?

It receives fibers from both cerebral hemispheres, the reticular formation, the red nucleus, the tectum, the MLF, and mesencephalic nucleus


Where does the motor nucleus of CN V send fibers to?

Sends efferent fibers to the muscles of mastication (masseter, pterygoid, and temporal is), tensor tympani, tensor veil palatini, mylohyoid muscle, and the anterior belly of the digastric muscle


What is the pathway of CN V?

The intracranial portion emerges from the superior lateral portion of the ventral points, passes over the petrous apex and forms the trigeminal ganglion, where is divides into its 3 branches


What are other names for the trigeminal ganglion? Where is it located?

aka gasserian or semilumar ganglion, is located in the Meckel Cave


Where is the Meckel Cave?

located near the apex of the petrous part of the temporal bone in the middle cranial fossa.


What is the pathway of the Ophthalmic branch of CN V?

Enters the cavernous sinus lateral to the ICA and courses beneath CN III and IV, and passes into the orbit via the superior orbital fissure, where it divides into its three branches


What are the branches of the Ophthalmic branch of CN V?

Within the cavernous sinus, it gives off a tenurial-dural branch.

Within the orbit, it gives off the Frontal nerve, the lacrimal nerve, and the nasociliary nerve


What does the frontal nerve innervate? Does it have any branches?

Divides into the supraorbital and supratrochlear nerves, which provide sensation to the medial portion of the upper eyelid, conjunctiva, forehead, scalp, frontal sinuses, and side of nose


What does the lacrimal nerve innervate? Does it have any branches?

Supplies sensation to the lacrimal gland and neighboring conjunctiva.

Parasympathetic innervation to retro-orbital plexus


What does the nasociliary nerve innervate? Does it have any branches?

Supplies sensation to the middle and inferior turbinates (via nasal branches), septum, lateral nasal wall, and tip of nose

Its infratrochlear branch supplies the lacrimal drainage system, conjunctiva, and medial canthal region


What does the Maxillary division of CN V innervate?

Inferior Palpebral branch--lower eyelid
Nasal Branch- side of nose
Superior Labial Branch- upper lip

Also supplies teeth, maxillary sinus, roof of mouth, and soft palat


What is the pathway of the Maxillary Division of CN V?

leaves the trigeminal ganglion to exit through the foramen rotundum, courses through the pterygopalatine fossa and into the orbit via the inferior orbital fissure. Then travels through the infraorbital canal as the infraorbital nerve


What does the mandibular division of CN V innervate?

provides motor input to the muscles of mastication

Provides sensory input to the mucosa and skin of mandible, lower lip, tongue, external ear, and tympanum


Where is CN VI (Abducens Nerve) located?

Its situated on the floor of the fourth ventricle

The MLF lies medially to the CN VI nucleus


What is the pathway of CN VI to the Orbit?

Travels vertically along the ventral face of the Pons, continues through the subarachnoid space, perforates the dura mater 2 cm below the posterior clinoid process, passes intradurally into the cavernous sinus, where it runs below and lateral to the ICA. Then enters the orbit through the superior orbital fissure within the annulus of Zinn and innervates the LR on its ocular surface


What does CN VI innervate>

It provides motor input to the lateral rectus muscle


What makes this nerve susceptible to stretch injury in situations of increased ICP?

The long route that it travels makes it susceptible


What is the function of CN VII? Developmentally, where does it come from?

Provides with motor and sensory input to a variety of structures of the face/head

Developmentally comes from the 2nd branchial arch


What does the motor root of CN VII contain?

It contains special visceral efferent fibers that innervate the muscles of facial expression


What does the sensory root of CN VII contain?

contains the nervus intermedius, which itself contains the special visceral afferents, general somatic afferents, and general visceral efferent fibers.


What are the special visceral afferent fibers of CN VII?

the convey taste from the anterior 2/3 of the tongue

terminate centrally in the nucleus of the tracts solitarius


What are the general somatic afferent fibers of CN VII?

convey sensory information from the external auditory meatus and retro-auricular skin

centrally enters the spinal nucleus of CN V


What are the general visceral efferent fibers of CN V II?

Pre-ganglionic parasympathetic innervation via the sphenopalatine ganglion to the lacrimal, submandibular, and sublingual glands


Where is the motor nucleus of CN VII located?

its located in the caudal 1/3 of the Pons

Note: is cigar-shaped and 4 mm long, and contains 4 distinct groups that innervate specific facial muscles

Note 2: the lower half of the face is influenced by the corticobulbar fibers from the opposite cerebral cortex


Where is the sensory nucleus of CN VII located?

located in the Rostral portion of the tractus solitarius


What is the sensory nucleus of CN VII known as? What does it innervate?

also known as the "Gustatory Nucleus", taste from the anterior 2/3 of the tongue are carried here via special visceral efferent fibers


What does the temporofacial division of CN VII innervate?

It gives rise to temporal, zygomatic, and buccal branches

Temporal--upper half of orbicularis oculi, frontalis, corrugator supercilii, and pyramidal is muscles
Zygomatic- supplies lower 1/2 of orbicularis


Where does parasympathetic outflow of CN VII originate from?

the superior salivary nucleus and lacrimal nucleus


What controls reflex lacrimation?

Sensory nuclei of CN V


What does the Greater superficial petrosal nerve supply?

gives rise to unmyelinated postganglionic fibers that innervate the globe, lacrimal glands, glands of palate, and nose


What is the cavernous sinus?

an interconnected series of venous channels located posteriorly to the orbital apex and lateral to sphenoidal air sinus and pituitary fossa


What structures does the cavernous sinus contain?

the ICA (surrounded by sympathetic carotid plexus), CN III, CN IV, CN V1, CN V2, and Cn VI


Where do the cavernous sinus and other venous sinuses drain into?

they carry blood away from the brain and drain into the internal jugular veins


What can thrombosis in the cavernous/other venous sinuses cause?

increased intracranial pressure and papilledema.