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Neurosurgery > Crainial Nerves > Flashcards

Crainial Nerves Flashcards

1
Q

Somatic Motor Nuclei

A
  • Oculomotor (III): all extraocular eye movements except superior oblique and lateral rectus
  • Trochlear (IV): superior oblique
  • Abducens (VI): lateral rectus
  • Hypoglossal (XII): all intrinsic and extrinsic muscles of tongue except palatoglossus
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2
Q

Branchial motor nuclei

A
  • Masticator (V): muscles of mastication
  • Facial (VII): muscles of facial expression
  • Ambiguus (IX, X): muscles of pharynx and larynx
  • Accessory (XI): trap and SCM
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3
Q

Visceral motor nuclei

A
  • Edinger-Westphal (III): ciliary muscle and constrictor pupillae
  • Superior salivatory (VII): all glands of the head except integumentary and parotid
  • Inferior salivatory (IX): parotid gland
  • Dorsal vagus (X): all thoracic viscera and abdominal viscera to the splenic flexure
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4
Q

Visceral sensory nuclei

A

-Solitarius AKA nucleus of the tractus solitarius (IX, X): visceral afferent info necessary for visceral reflexes, nausea, but not pain

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5
Q

General sensory nuclei

A

-Trigeminal (V, VII, IX, X): pain, temp, touch, proprioception from the head and neck, sinuses, and meninges

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6
Q

Special sensory nuclei

A
  • Mitral cells of olfactory bulb (I): smell
  • Ganglion cells of the retina (II): vision
  • Gustatory which is the rostral portion of hte nucleus of the tractus solitarius (VII, IX): taste
  • Vestibular (VIII): balance
  • Cochlear (VIII): hearing
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7
Q

Projections of olfaction

A
  • Olfactory epithelium - cribriform plate - olfactory bulb (secondary neuronal cells of mitral and tufted) - lateral, intermediate, and medial olfactory areas
  • Lateral olfactory area (primary olfactory area): pyriform (pear shaped) area made up of uncus and entorhinal area (anterior part of hippocampal gyrus), limen insula (point of junction between cortex of insula and cortex of frontal lobe), and amygdaloid body (nuclear complex located aboce tip of inferior horn of lateral ventricle)
  • Intermediate olfactory area: enter anterior perforated substance, thought to be insignificant in man
  • Medial olfactory area: subcallosal region of medial surface of frontal lobe, thought to mediate emotional response to odors through connections with limbic system
  • Diagonal band of Broca: connects all three olfactory areas
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8
Q

Projections of vision

A
  • Rods/Cones - bipolar cells - ganglion cells (secondary neurons) which make up optic nerves - chiasm - optic tracts - lateral geniculate body of thalamus or bilateral pretectal area
  • Lateral geniculate body - geniculocalcarine axons (optic radiations) which are either Myer’s loop through temporal lobe or other loop through parietal - calcarine fissure (primary visual cortex) with lower retina projecting to lower calcarine fissure and upper retinal projecting to upper calcarine fissure
  • Pretectal area projects to Edinger-Westfal nuclei then via CN III to mediate pupilary constriction reflex
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9
Q

Components of oculomotor nerve

A
  • Somatic motor: supplies levator palpebrae superiorus, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles
  • Visceral motor: supplies parasympathetic to constrictor pupillae and ciliary muscles via the ciliary ganglion
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10
Q

Visceral motor component of CN III

A

-Edinger-Westphal nucleus located in midbrain dorsal to anterior part of oculomotor complex - preganglionic (lower motor neuron) leave nucleus and course ventrally through midbrain with somatic motor neurons - run through middle cranial fossa - cavernous sinus - superior orbital fissure - enter orbit and leave the nerve to inferior oblique muscle - terminate in ciliary ganglion near apex of cone of extraocular muscles - postganglionic axons travel as 6-10 short ciliary nerves along with sympathetic fibers - enter eyeball near exit of optic nerve - travel between choroid and sclera - terminate in ciliary body and iris

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11
Q

Weber’s syndrome

A

-Infarction of basal midbrain damaging efferent axons of CN III causes ipsilateral ophthalmoplegia and contralateral hemiplegia due to interruption of nearby corticospinal fibers

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12
Q

Benedikt’s syndrome

A

-Infarction of basal midbrain damaging efferent axons of CN III which extends more dorsal in midbrain and involves red nucleus too, causes ipsilateral ophthalmoplegia plus contralateral intention tremor

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13
Q

Pathologies affecting CN III

A
  • Vascular: aneurysm of posterior cerebral or superior cerebellar arteries (CN III emerges between these two arteries), infarction of basal midbrain (Weber’s and Benedikt’s syndromes)
  • Inflammation: syphilitic and TB meningitis tend to localize between chiasma, pons, and temporal lobes where CN III emerges from brainstem
  • Herniation of enlarged temporal lobe: tumor, abscess, trauma
  • Pathology of cavernous sinus
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14
Q

Strabismus

A

-Inability to direct both eyes toward same object and consequent diplopia

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15
Q

Ptosis

A
  • Lid droop due to inactivation of levator palpebrae superioris and subsequent unopposed action of orbicularis oculi
  • Pt will compensate by contracting frontalis to raise eyebrow and attached lid
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16
Q

Unopposed action of superior oblique and lateral rectus causes:

A

-Down and out (downward abducted eye)

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17
Q

Combination of findings in oculomotor ophthalmoplegia

A
  1. Strabismus
  2. Ptosis
  3. Dilation of pupil
  4. Downward abducted eye
  5. Paralysis of accommodation
18
Q

Trochlear nucleus and nerve

A
  • Located in tegmentum of midbrain at level of inferior colluculus
  • Located near midline (like other somatic motor nuclei), it’s just ventral to the cerebral aqueduct
  • Axons leave nucleus and course dorsally around the aqueduct - decussate within the superior medullary velum - exit midbrain from DORSAL surface
  • Due to crossing, each superior oblique is innervated by the contralateral trochlear nucleus
  • Axons curve forward around cerebral peduncle and emerge between posterior cerebral and superior cerebellar arteries with CN III
  • Pierce dura at angle between free and attached borders of tentorium cerebelli
  • Runs through cavernous sinus anteriorly along the lateral wall of the sinus
  • Enters orbit through superior orbital fissure above the tendinous ring
  • Crosses medially lying close to roof of orbit, runs diagonally across levator palpebrae and superior rectus, then reaches superior oblique and breaks into 3 or more branches to enter the muscle along its proximal 1/3
19
Q

Four unique aspects of trochlear nerve

A
  1. Smallest (2400 axons compared with ~1,000,000 in optic nerve)
  2. Only nerve to exit dorsally from brain stem
  3. Only nerve in which all the lower motor neuron axons decussate
  4. Has the longest intracranial course (7.5 cm)
20
Q

Conditions that can injure trochlear nerve

A
  • Inflammatory disease
  • Compression by aneurism of posterior cerebral and superior cerebellar arteries
  • Pathology of cavernous sinus or superior orbital fissure
  • At risk during surgical approaches to midbrain (due to long intracranial course and position just inferior to free edge of the tentorium cerebelli)
21
Q

Result of superior oblique paralysis

A
  • Extortion (due to unopposed action of inferior oblique) - causes diplopia
  • Weakness of downward gaze which is most prominent during attempted medial gaze (will complain of visual difficulty when going downstairs)
  • Consider in DDx of torticolis because of tendency to tilt head to compensate for paralyzed superior oblique
22
Q

Components of trigeminal nerve

A
  • Branchial motor (associated with first branchial arch): to muscles of mastication, tensor tympani, tensor veli palatini, mylohyoid, and anterior belly of digastric
  • General sensory: from face and scalp as far as top of head, conjunctiva, bulb of eye, mucous membranes of paranasal sinuses, nasal and oral cavities including tongue and teeth, part of external aspect of tympanic membrane, from meninges of anterior and middle cranial fossae
23
Q

Course of trigemnial nerve

A
  • Emerges from midlateral surface of pons as large sensory root and smaller motor root
  • Trigeminal AKA semilunar ganglion (sensory ganglion) sits in Meckle’s cave (trigeminal cave) in floor of middle cranial fossa
  • Three divisions ophthalmic (V1), maxillary (V2), and mandibular (V3) exit through superior orbital fissure, foramen rotundum, and foramen ovale respectively
  • V1 and occasionally V2 course through cavernous sinus before leaving cranial cavity
24
Q

Branches of V1

A 
Lacrimal
Frontal
-Supratrochlear
-Supraorbital
-Nerve to frontal sinus
Nasociliary
-Long and short ciliary nerves
-Infratrochlear
-Ethmoidal
--Anterior: internal nasal and external nasal
--Posterior
Meningeal branch: to tentorium cerebelli
25
Q

Branches of V2

A 
Zygomatic
-Zygomaticotemporal
-Zygomaticofacial
Infraorbital
-External nasal branch
-Superior labial
-Superior alveolar nerves
--Posterior
--Middle
--Anterior
Pteygopalatine
-Orbital branches
-Greater and lesser palatine nerves
-Posterior and superior nasal branches
-Pharyngeal
Meningeal branch to middle and anterior cranial fossae
26
Q

Branches of V3

A 
Buccal
Auriculotemporal
-Facial (not to be confused with CN VII)
-Anterior auricular
-External acoustic meatus
-Articular nerve (to TMJ)
Lingual
Inferior alveolar
-Dental
-Incisive
-Mental
Meningeal branch to middle and anterior cranial fossae
Medial pterygoid
-Nerve to tensor veli palatini
-Nerve to tensor tympani
Masseteric
Deep temporal
Lateral pterygoid
Nerve to mylohyoid
Nerve to anterior belly of digastric
27
Q

Tuberculum cinereum

A

-Lateral elevation in the medulla caused by the sensory nucleus of the trigeminal nerve

28
Q

Sensory nucleus of trigeminal nerve

A
  • Largest cranial nerve nucleus; extends from midbrain to spinal cord as far as second cervical segment
  • Three subnuclei: mesencephalic, pontine trigeminal, and nucleus of the spinal tract
29
Q

Mesencephalic nucleus of trigeminal nerve

A
  • Consists of thin column of primary sensory neurons (these are the only known primary sensory neurons within the CNS; usually primary sensory neurons reside in ganglia outside the CNS)
  • Peripheral processes of these neurons run with motor nerves and carry proprioceptive info from muscles of mastication
  • Central processes mainly project to motor nucleus of trigeminal nerve (masticator nucleus) to provide for reflex control of bite
30
Q

Pontine trigeminal nucleus

A
  • Large group of secondary sensory neurons located in pons near point of entry of the nerve
  • Primarily concerned with touch sensation to face
31
Q

Nucleus of the spinal tract of trigeminal nerve

A
  • Long column of cells extending from pons to spinal cord where it merges with dorsal gray matter of spinal cord
  • Concerned primarily with perception of pain/temp, although tactile info pojected here as well as pontine trigeminal nucleus
32
Q

Inputs to motor nucleus of trigeminal (masticator nucleus)

A

Inputs:

  • Acoustic nerve: activates part of the nucleus that innervates tenson tympani so tension on the TM can be adjusted for sound velocity
  • Mesencephalic nucleus: monosynaptic stretch reflex similar to simple spinal reflexes
  • Bilateral inputs from cortex: voluntary control of chewing
33
Q

Course of axons from masticator nucleus

A
  • Exit foramen ovale with sensory fibers of V3
  • Unites with sensory branches of V3 just outside cranium to form mandibular nerve
  • Medial pterygoid nerve branches to course close to otic ganglion - gives off two small branches to tensor veli palatini and tensor tympani (which pass through otic ganglion without synapsing), then the medial pterygoid nerve enters the deep surface of the medial pterygoid muscle
  • Masseteric nerve branches from mandibular nerve, passes laterally above lateral pterygoid muscle through mandibular notch to supply masseter
  • 2 to 3 deep temporal nerves branch from mandibular nerve, turn upwards, pass superior to lateral pterygoid muscle to enter deep surface of temporalis muscle
34
Q

Nucleus of the spinal tract of trigeminal nerve

A
  • Long column of cells extending from pons to spinal cord where it merges with dorsal gray matter of spinal cord
  • Concerned primarily with perception of pain/temp, although tactile info pojected here as well as pontine trigeminal nucleus
35
Q

Inputs to motor nucleus of trigeminal (masticator nucleus)

A

Inputs:

  • Acoustic nerve: activates part of the nucleus that innervates tenson tympani so tension on the TM can be adjusted for sound velocity
  • Mesencephalic nucleus: monosynaptic stretch reflex similar to simple spinal reflexes
  • Bilateral inputs from cortex: voluntary control of chewing
36
Q

Course of axons from masticator nucleus

A
  • Exit foramen ovale with sensory fibers of V3
  • Unites with sensory branches of V3 just outside cranium to form mandibular nerve
  • Medial pterygoid nerve branches to course close to otic ganglion - gives off two small branches to tensor veli palatini and tensor tympani (which pass through otic ganglion without synapsing), then the medial pterygoid nerve enters the deep surface of the medial pterygoid muscle
  • Masseteric nerve branches from mandibular nerve, passes laterally above lateral pterygoid muscle through mandibular notch to supply masseter
  • 2 to 3 deep temporal nerves branch from mandibular nerve, turn upwards, pass superior to lateral pterygoid muscle to enter deep surface of temporalis muscle
  • Lateral pterygoid nerve arises from mandibular nerve, runs briefly with buccal nerve, then enters deep surface of lateral pterygoid muscle
  • Mylohyoid nerve travels with inferior alveolar nerve but then branches away just before it enters the mandibular canal, continues anteriorly and inferiorly in groove on deep surface of the ramus of the mandible to reach the inferior surface of mylohyoid muscle where it divides to supply anterior belly of digastric and mylohyoid
37
Q

Nucleus of the spinal tract of trigeminal nerve

A
  • Long column of cells extending from pons to spinal cord where it merges with dorsal gray matter of spinal cord
  • Concerned primarily with perception of pain/temp, although tactile info pojected here as well as pontine trigeminal nucleus
38
Q

Inputs to motor nucleus of trigeminal (masticator nucleus)

A

Inputs:

  • Acoustic nerve: activates part of the nucleus that innervates tenson tympani so tension on the TM can be adjusted for sound velocity
  • Mesencephalic nucleus: monosynaptic stretch reflex similar to simple spinal reflexes
  • Bilateral inputs from cortex: voluntary control of chewing
39
Q

Course of axons from masticator nucleus

A
  • Exit foramen ovale with sensory fibers of V3
  • Unites with sensory branches of V3 just outside cranium to form mandibular nerve
  • Medial pterygoid nerve branches to course close to otic ganglion - gives off two small branches to tensor veli palatini and tensor tympani (which pass through otic ganglion without synapsing), then the medial pterygoid nerve enters the deep surface of the medial pterygoid muscle
  • Masseteric nerve branches from mandibular nerve, passes laterally above lateral pterygoid muscle through mandibular notch to supply masseter
  • 2 to 3 deep temporal nerves branch from mandibular nerve, turn upwards, pass superior to lateral pterygoid muscle to enter deep surface of temporalis muscle
  • Lateral pterygoid nerve arises from mandibular nerve, runs briefly with buccal nerve, then enters deep surface of lateral pterygoid muscle
  • Mylohyoid nerve travels with inferior alveolar nerve but then branches away just before it enters the mandibular canal, continues anteriorly and inferiorly in groove on deep surface of the ramus of the mandible to reach the inferior surface of mylohyoid muscle where it divides to supply anterior belly of digastric and mylohyoid
40
Q

Most common causes of LMN damage to trigeminal

A
  • Vascular damage
  • Tumors affecting pons (add cerebellopontine angle syndrome, functional combinations)
  • Tumors in periphery
  • Trauma
  • Skull fractures can damage the nerve as it exits through foramen ovale

Neurosurgery (9 decks)

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