Cranial Nerves: Central and Peripheral connections Flashcards
What proportion of optic nerve volume comprise macula nerve fibres?
80-90%
Which CN3 subnuclei provides ipsilateral vs contralateral innervations to the EOM’s?
CN III subnuclei supply their respective ipsilateral extraocular muscles
Exceptions are the subnucleus for the superior rectus muscle, which innervates the contralateral superior rectus
Do SO EOM fibres cross over after leaving the cranial nucleus?
Yes. CN IV fascicles completely decussate after leaving the nucleus, thus innervating the contralateral superior oblique muscle
Which is the only cranial nerve to exit dorsally from the brainstem?
CN IV
Which is the longest cranial nerve intracranially?
CN IV
What does CN V provide innervation to?
CN V, the largest of the CNs, provides sensation to the face and eye, as well as other structures of the head.
Which nerve is susceptible to injury from raised ICP
CN VI
Which CN provides efferent limb of tear reflex?
CN VII
Are olfactory nerves myelinated or unmyelinated?
Unmyelinated
How many axons make up the optic nerve?
The optic nerve (CN II) consists of more than 1 million axons that originate in the ganglion cell layer of the retina and extend toward the lateral geniculate nucleus
Where does the optic nerve anatomically begin at?
Optic nerve head
Where does the optic nerve physiologically begin at?
physiologically and functionally within the ganglion cell layer that covers the entire retina and continues to the optic chiasm.
What are the 4 topographic areas of the optic nerve?
- intraocular region (ONH, consisting of the superficial nerve fiber layer [NFL], pre- laminar area, laminar area, and retrolaminar area)
- intraorbital region (located within the muscle cone)
- intracanalicular region (located within the optic canal)
- intracranial region (ending at the optic chiasm)
What are the different lengths of the segments of the optic nerve?
Intraocular- 1mm
Intraorbital- 25-30mm
Intracannalicular- 4-10mm
Intracranial- 3-16mm usually 10mm
What is the blood supply to the intraocular section of the optic disc?
Branches of posterior ciliary arteries
What is the blood supply to the intraocular section of the prelaminar region?
Short posterior ciliary arteries
recurrent choroidal arteries (debated)
Cilioretinal arteries, if present
What is the blood supply to the intraocular section of the laminar region?
Branches of arterial circle of Zinn- haller, which arises from the para- optic branches of the short posterior ciliary arteries
What is the blood supply to the intraocular section of the retrolaminar region?
Primary: Pial vessels and short posterior ciliary vessels
Secondary: CRA and recurrent choroidal arteries
Which part of the encephalon does the optic nerve arise from?
Diencephalon
Which cells myelinate the optic nerve?
Oligodendrocytes
What is the average vertical and horizontal size of the optic nerve head?
1.76 mm horizontally and 1.92 mm vertically.
Where is the central depression/cup located on the optic nerve head
slightly temporal to the geometric center of the nerve head and represents an axon-free region
Where are macula fibres located on the retinal topograph?
Macular fibers, which constitute approximately one-third of the nerve, occupy the immediate temporal aspect of the ONH
What is the papillomacular bundle?
Axons arising from ganglion cells in the nasal macula project directly to the ONH as the papillomacular bundle
What type of collagen in found in the lamina region of the intraocular segment?
Type 1, Type 3
What are the functions of the lamina cribrosa?
- scaffold for the optic nerve axons
- point of fixation for the CRA and CRV
- reinforcement of the posterior segment of the globe
Where in the intraocular segment of the optic nerve does myelination occur?
Retrolaminar portion
Which meningeal sheath of the optic nerve is continuous with the pia and arachnoid mater
The internal sheath, the innermost meningeal sheath of the optic nerve
Which cells of the optic nerve give rise to optic nerve meningioma?
The meningothelial cells can give rise to optic nerve sheath meningioma
Where does the subarachnoid space end in the optic nerve?
Lamina cribrosa
What does SVP indicate?
The presence of SVP indicates normal ICP. However, some individuals have normal ICP and absent SVP. Thus, the loss of previously documented SVP is more indicative of elevated ICP.
What is the outermost meningeal sheath of the optic nerve?
The external, or dural, sheath of the optic nerve
Which sheaths of the optic nerve are continuous with the optic nerve septa?
Elements from both the arachnoid and the internal sheaths are continuous with the optic nerve septa
What is the nerve innervation to the meninges of the optic nerve?
supplied by sensory nerve fibers, which account in part for the pain experienced by patients with retrobulbar neuritis or other inflammatory optic nerve diseases.
Where do the retinal fibres segregate into right and left optic tracts?
Within the chiasm
Where do the cell bodies of the optic tracts lie?
in the ganglion cell layer of the retina
Where do the optic tracts synapse?
LGN
Where is the primary visual cortex?
V1, striate cortex, or Brodmann area 17
What floor of the third ventricle does the optic chiasm make up?
Anterior inferior floor
What is the Willbrand knee?
The extramacular fibers from the inferonasal retina cross anteriorly in the chiasm at the “Wilbrand knee” before passing into the optic tract.
Extramacular superonasal fibers cross directly to the opposite tract.
Where do nasal macula fibres cross over in the chiasm?
Posterior part
What percentage of optic nerves fibres cross and how many are uncrossed?
Approximately 53% of the optic nerve fibers are crossed, and 47% are uncrossed.
Where in the brain is the LGN located?
a mushroom-shaped structure in the posterior thalamus
What percentage of fibres reach the LGN and how many go to the pupillary nucleus?
70% of the optic tract fibers within its 6 alternating layers of gray and white matter (the other 30% of the fibers go to the pupillary nucleus)
Which layers of the LGN contain axons from the contralateral optic nerve?
Layers 1, 4, and 6
Which layers of the LGN contain axons from the ipsilateral optic nerve?
Layers 2, 3, and 5
How are the 6 layers numbered in the LGN
Consecutively Inferior to superior
What do the optic radiations connect?
connect the LGN with the visual cortex of the occipital lobe.
Where do inferior fibres (from the superior visual field) travel to from the LGN?
travel anteriorly, then laterally and posteriorly, looping around the temporal horn of the lateral ventricles in the temporal lobe (Meyer loop)
Where do superior fibres (from the inferior visual field) travel to from the LGN?
course dorsally (posteriorly) in the parietal lobe to terminate in the occipital lobe above the calcarine fissure
Which layers of the LGN form the Magnocellular pathway
Layers 1 and 2
Which layers of the LGN form the Parvocellular pathway
Layers 3,4,5,6
What is the function of the Magnocellular pathway?
concerned with detection of movement
What is the function of the Parvocellular pathway?
responsible for color vision and visual acuity.
What is the blood suply of the LGN
The hilum represents central (macular) vision and is perfused by the posterior choroidal artery, the medial horn represents inferior vision, and the lateral horn represents superior vision. These areas are perfused by the anterior choroidal artery.
How many cellular layers are present in the primary visual cortex?
6 layers
Where is macular function located in the occipital lobe?
occupies the most posterior position at the tip of the occipital lobe. The most anterior portion of the calcarine fissure is occupied by contralateral nasal retinal fibers only
Where does the ophthalmic artery lie in relation to the optic nerve
Inferiorly
Where do the 2 long posterior ciliary arteries and CRA branch off the ophthalmic nerve?
after it enters the muscle cone at the annulus of Zinn.
What are the differences between CRA and retinal arterioles?
contains a fenestrated internal elastic lamina and an outer layer of smooth muscle cells surrounded by a thin basement membrane. The retinal arterioles have no internal elastic lamina, and they lose their smooth muscle cells shortly after entering the retina.
Where is the location of altitudinal (superior or inferior hemifield) visual field defects following an episode of nonarteritic anterior ischemic optic neuropathy
Involvement of the inferior half of the arteries of Zinn Haller at the lamina Cribrosa
What is the blood supply to the Optic Chiasm?
Branches of anterior cerebral a., superior hypophysial a., internal carotid a., posterior communicating a., and posterior cerebral a.
What is the blood supply to the optic tract?
Branches of posterior communicating a. and anterior choroidal a.
What is the blood supply to the LGN
Branches of anterior and posterior choroidal a.
What is the blood supply to the Optic radiations
anterior: anterior choroidal a.
Posterior: Lateral striate a. (middle cerebral a.) and branches of posterior cerebral a.
What is the blood supply to the primary visual cortex?
Calcarine a. (primarily derived from the posterior cerebral a.) and sometimes branches of the middle cerebral a.
What encephalon layer does the CN 3 arise from?
Mesencephalon
Where is the CN 3 nucleus located?
at the level of the superior colliculus.
This nuclear complex lies ventral to the periaqueductal gray matter, is immediately rostral to the CN IV nuclear complex, and is bounded inferolaterally by the medial longitudinal fasciculus.
Which nucleus provides the parasympathetic preganglionic innervation to the ciliary body?
The Edinger-Westphal nucleus is rostral in location. It provides the parasym- pathetic preganglionic efferent innervation to the ciliary muscle and pupillary sphincter
Which blood vessels travel in close proximity to the CN 3
In the subarachnoid space, CN III passes below the posterior cerebral artery (PCA) and above the superior cerebellar artery, the 2 major branches of the basilar artery.
It also travels forward in the interpeduncular cistern lateral to the posterior communicating artery (PCoA)
Do the parasympathetic fibres of CN3 travel in superior or inferior occulomotor nerve branches?
The parasympathetic fibers wind around the periphery of the nerve, enter the inferior division, and course through the branch that supplies the inferior oblique muscle
How to investigate a patient presenting with partial ptosis and CN3 palsy?
emergency imaging by computed tomography/computed tomography angiography or magnetic resonance imaging/magnetic resonance angiography
Which bone is the cavernous sinus a part of?
Sphenoid bone
Are the short ciliary nerves myelinated or unmyelinated
Myelinated
What is the near reflex triad?
triad of accommodation, pupil constriction, and convergence
What is the pupillary light reflex pathway?
Light from each eye passes via electrical signals through the optic nerve, and nasal fibers decussate in the optic chiasm, providing signals in both optic tracts.
The pupillary fibers exit the optic tract posteriorly, reaching the pretectal nuclei at the level of the superior colliculus in the midbrain.
Efferent fibers project to the ipsilateral and contralateral EdingerWestphal nuclei. Preganglionic parasympathetic fibers leave each Edinger Westphal nucleus and run on the superficial surface of the oculomotor nerve as it leaves the brainstem. The fibers follow the inferior division of CN III as it enters the orbit, synapsing in the ciliary ganglion.
Postganglionic myelinated short ciliary nerves (3%–5% of which are pupillomotor) then innervate the iris and the ciliary muscle.
Near reflex: Fibers for the near reflex follow a similar efferent course, inducing miosis, but they also act at the ciliary muscle to induce accommodation
Where is the trochlear nerve nucleus located in the brain?
The nerve nucleus is located in the caudal midbrain at the level of the inferior colliculus near the periaqueductal gray matter, ventral to the aqueduct of Sylvius
Like the CN III nucleus, it is bounded ventrolaterally by the medial longitudinal fasciculus.
Where do trochlear nerve fibres decussate?
The fascicles of CN IV curve dorsocaudally around the periaqueductal gray matter and completely decussate in the superior medullary velum.
Why is the trochlear nerve unaffected by retrobulbar injection block
Because of its location outside the muscle cone
What does the trigeminal nerve supply?
The sensory portion serves the greater part of the scalp and the forehead, face, eyelids, eyes, lacrimal glands, extraocular muscles, ears, dura mater, and tongue. The motor portion innervates the muscles of mastication through branches of the mandibular division
Where does the CN V nucleus lie?
The CN V nuclear complex extends from the midbrain, through the pons and medulla, to the upper cervical segments, often as caudal as the C4 vertebra. It consists of the follow- ing 4 nuclei, listed from rostral to caudal:
* mesencephalic nucleus
* main sensory nucleus
* spinal nucleus and tract
* motor nucleus
What fibres does the mesencephalic nucleus of CNV carry?
mediates proprioception and deep sensation from the masticatory, facial, and extraocular muscles. The nucleus extends inferiorly into the posterior pons as far as the main sensory nucleus.
What fibres does the main sensory nucleus of CNV carry?
receives its input from ascending branches of the sensory root and serves light touch from the skin and mucous membranes.
What fibres does the spinal nucleus tract of CNV carry?
The nucleus receives pain and temperature afferents from the descending spinal tract, which also carries cutaneous components of CN VII, CN IX, and CN X that serve sensations from the ear and external auditory meatus.
What is the afferent limb of the oculocardiac reflex?
mediated by the trigeminal nerve
What is the efferent limb of the oculocardiac reflex?
mediated by the parasympathetic neurons of the vagus nerve, via short internuncial fibers to the reticular formation.
What fibres does the motor nucleus of CNV carry?
supplies the muscles of mastication (pterygoid, masseter, and temporalis), the tensor tympani muscle, the tensor veli palatini muscle, the mylohyoid muscle, and the anterior belly of the digastric muscle.
Where is the trigeminal ganglion located?
The crescent-shaped ganglion occupies a recess in the dura mater posterolateral to the cavernous sinus. This recess, called the Meckel cave, is near the apex of the petrous part of the temporal bone in the middle cranial fossa. Medially, the trigeminal ganglion is close to the ICA and the posterior cavernous sinus.
What are the branches of CN V ophthalmic division CNV1
divides into 3 branches: frontal, lacrimal, and nasociliary
What are the branches of CN V maxillary division CNV2
CN V2 courses through the pterygopalatine fossa into the inferior orbital fissure and then passes through the infraorbital canal as the infraorbital nerve. .
After exiting the infraorbital foramen, CN V2 divides into an inferior palpebral branch, a nasal branch, and a superior labial branch, supplying the lower eyelid, the side of the nose, and the upper lip, respectively. The teeth, maxillary sinus, roof of the mouth, and soft palate are also innervated by branches of the maxillary division.
What does the frontal nerve (branch of V1) do?
divides into the supraorbital and supra- trochlear nerves, which provide sensation to the medial portion of the upper eyelid and the conjunctiva, forehead, scalp, frontal sinuses, and side of the nose
What does the lacrimal nerve (branch of V1) do?
innervates the lacrimal gland and the neighboring conjunctiva and skin. The lacrimal gland receives its parasympathetic supply from the retro-orbital plexus
What does the nasociliary nerve (branch of V1) do?
supply sensation to the middle and inferior turbinates, septum, lateral nasal wall, and tip of the nose. The infratrochlear branch serves the lacrimal drainage system, the conjunctiva, and the skin of the medial canthal region.
Thus, the short ciliary nerves carry sensory (V1), sympathetic, and parasympathetic fibers
What are the branches of CN V mandibular division CNV3
The mandibular division contains sensory and motor fibers. It is the only division of CN V that contains motor fibers.
provides motor input for the masticatory muscles. Sensation is supplied to the mucosa and skin of the mandible, lower lip, tongue, external ear, and tympanum.
Which foramen does the CNV1 pass through
SOF
Which foramen does the CNV2 pass through
Foramen Rotundum
Which foramen does the CNV3 pass through
Foramen Ovale
Where is the nucleus of the abducens nerve located?
in the floor of the fourth ventricle, beneath the facial colliculus in the caudal pons.
Where does the MLF lie in relation to the nucleus of the abducens nerve
The medial longitudinal fasciculus lies medial to the CN VI nucleus.
What is the path of CNVI
CN VI then takes a vertical course along the ventral face of the pons and is crossed by the anterior inferior cerebellar artery.
It continues through the subarachnoid space along the surface of the clivus to perforate the dura mater below the petrous apex, approximately 2 cm below the posterior clinoid process.
It then passes intradurally through or around the inferior petrosal sinus and beneath the petroclinoid (Gruber) ligament through the Dorello canal, after which it becomes extradural and enters the cavernous sinus.
Which cranial nerve innervates the muscles of facial expression?
The motor root of the facial nerve contains special visceral efferent fibers that innervate the muscles of facial expression.
What does the sensory root of the facial nerve innervate?
conveys the sense of taste from the anterior two-thirds of the tongue and sen- sation from the external auditory meatus and the retroauricular skin
What is the parasympathetic innervation of the facial nerve?
provides pre-ganglionic parasympathetic innervation by way of the sphenopalatine and submandibular ganglia to the lacrimal, submaxillary, and sublingual glands.
Where does the fascicular portion of CNVI leave the brainstem?
The fascicular portion of CN VI runs ventrally through the paramedian pontine reticular formation and the pyramidal tract and leaves the brainstem in the pontomedullary junction
How is reflex lacrimation controlled?
by afferents from the sensory nuclei of CN V
Which foramen does the facial nerve travel through in the skull
Internal acoustic meatus
Parasympathetic and sympathetic nerve supply to the lacrimal gland
Cranial Nerve 7 origin from SSN/ Lacrimatory Nucleus.
Parasympathetic nerve leaves nucleus as greater petrosal nerve and enters the pterygopalatine ganglion alongside deep petrosal nerve (carrying sympathetic fibres which have hitchhiked onto ICA) to form nerve of pterygoid canal (vidian nerve).
In the pterygopalatine ganglion, the nerve synapses and travels along branches of CN V2 via zygomaticotemporal nerve to innervate the lacrimal gland
How is emotional lacrimation mediated?
parasympathetic efferent fibers originating in the superior salivatory nucleus and the lacrimal nucleus in the caudal pons, both of which lie posterolateral to the motor nucleus. The lacrimal nucleus receives input from the hypothalamus, mediating emotional tearing; there is also supranuclear input from the cortex and the limbic system.
What can a thrombus in any of the venous sinuses draining the brain cause?
lead to increased venous pressure and may cause intracranial hypertension with secondary CN VI palsy and papilledema.
Which major blood vessels supply the brainstem?
The basilar artery distributes blood primarily to the brainstem and the posterior portion of the brain.
