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neuro 2019 Exam 3 > Cranial Nerves > Flashcards

Cranial Nerves Flashcards

1
Q

Olfactory Nerve components, fxn, course

A

I. Olfactory Nerve (CN I)
A. Components
1. SVA
2. Olfaction

B. Function – sense of smell

C. Course

  1. The bipolar neurons that compose CN I are located in the superior portion of the nasal cavity epithelium.
  2. The olfactory neurons are the receptors for smell – responding to odor molecules dissolved in mucus.
  3. The axon processes of CN I pass through the cribriform plate of the ethmoid bone to synapse in the olfactory bulb of the brain.
  4. The olfactory bulb is an extension of the forebrain (telencephalon); thus, the pathway of olfaction synapses directly within the telencephalon.
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2
Q

olfactory nerve clinical correlations

A

D. Clinical correlations

  1. Lesions of CN I results in anosmia/hyponosmia; the inability to perceive odor.
    a. Causes
  2. Upper respiratory tract infections, sinus infections
  3. Aging
  4. Trauma to base of skull (fracture to cribriform plate) can result in a shearing of CN I. This will result in anosmia and CSF rhinorrhea.
  5. Tumors of frontal lobe can compress olfactory tracts.
  6. Testing CN I – have patient identify various odors (cinnamon, toothpaste, etc)
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3
Q

Optic nerve components, fxn, course

A

II. Optic Nerve (CN II)
A. Components
1. SSA
2. Vision

B. Function – sense of vision

C. Special features and Course

  1. The optic nerve is formed from an evagination of the diencephalon; thus CN II is completely invested in all layers of meninges.
  2. CN II is composed of axonal projections of ganglion cells (third order neurons)
  3. within the retina; these axons extend from the retina to the diencephalon (primarily the lateral geniculate body).

Here fibers form the optic nerve which passes through the optic canal to enter the middle cranial fossa.

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4
Q

Optic nerve correlations

A
  1. Testing CN II
    a. Visual acuity and visual fields exams
    b. Fundoscopic exam
    c. Pupillary light reflex exam (optic nerve and oculomotor nerve)
  2. Demyelination of optic nerve
    a. CN II forms as an evagination of the brain; it is myelinated by oligodendrocytes.
    b. Thus, CN II is susceptible to CNS demyelination pathologies, ie multiple sclerosis.
  3. Optic Neuritis
    a. Inflammation of the optic nerve
    b. Causes – MS; exposure to toxic substances; infections; diabetes.
  4. Increased intracranial pressure can affect the eye due to the fact that the meninges and CSF continue along the optic nerve. Thus, the optic nerve, central retinal artery, and central retinal vein can be compressed and occluded.
    a. Occlusion of the central retinal vein can cause papilledema (retinal edema).
    b. Compression of the optic nerve can cause blindness.
    c. Retinal artery occlusion can also cause blindness due to loss of blood to retina.
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5
Q

CN III components, fxns, ganglia, course

A

III. Oculomotor Nerve (CN III)
A. Components
1. GSE – motor to eye muscles
2. GVE-P – parasympathetic to ciliary muscle and sphincter pupillae muscle.

B. Functions

  1. Eye movements
    a. Motor innevation to 5/7 extraocular eye muscles
    b. Muscles innervated: levator palpeprae superioris, superior rectus, inferior rectus, medial rectus, inferior oblique
  2. Accomodation
    a. Parasympathetic innervation to ciliary muscle
    b. Edinger-westphal nucleus (preganglionic cell bodies) → oculomotor nerve (preganglionic fibers) → ciliary ganglion (postganglionic cell bodies) → short ciliary nn (postganglionic cell bodies) → ciliary muscle.
    c. Contraction of ciliary muscle causes loosening of tension on lens from lens fibers; allows lens to round-up and focus on near objects.
  3. Constriction of pupil
    a. Parasympathetic innervation to sphincter pupillae muscle
    b. Edinger-westphal nucleus (preganglionic cell bodies) → oculomotor nerve (preganglionic fibers) → ciliary ganglion (postganglionic cell bodies) → short ciliary nn (postganglionic cell bodies) → sphincter pupillae muscle.
    c. Contraction of sphincter pupillae muscle causes constriction of pupil; allowing less light to enter the eye.

C. Associated ganglia
1. Ciliary ganglion – contains cell bodies of postganglionic parasympathetic neurons.

D. Course

  1. Exits ventral surface of midbrain, courses along lateral edge of cavernous sinus.
  2. Enters orbit via superior orbital fissure.
  3. Divides into superior and inferior divisions.
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6
Q

CN III divisions

A

E. Divisions

  1. Superior division
    a. Levator palpebrae superioris
    b. Superior rectus
  2. Inferior division
    a. Medial rectus
    b. Inferior rectus
    c. Inferior oblique
    d. Carries GVE-P fibers
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7
Q

CN III clinical correlations

A
  1. Testing CN III
    a. Extraocular movements tested with “H” shape.
    b. Pupillary light reflex exam (optic nerve and oculomotor nerve)
    c. Test for accommodation reflex
    d. Check for ptosis (levator palpebrae superioris)
  2. Oculomotor nerve palsy
    a. Paralysis of most extraocular eye muslces – eye held down and out
    b. Paralysis of levator palpebrae superioris – ptosis or inability to elevate eyelid
    c. Paralysis of sphinter pupillae muscle – pupil will be dilated; will not constrict with pupillary light reflex.
    d. Paralysis of ciliary muscle – loss of accommodation reflex
  3. Causes of lesion
    a. Uncal herniation
    b. Cavernous sinus pathologies
    c. Aneurysms of posterior cerebral or superior cerebellar aa causing compression of CN III.
    d. Increased intracranial pressure causing compression against temporal bone.
  4. With compression of CN III, the peripherally-located parasympathetic fibers will be affected earliest.
  5. Thus, the first symptom of CN III compression is a dilated pupil on the ipsilateral side and loss or slowness of pupillary light response. Diplopia will often occur later (depending on the severity and timing of compression).
    e. Diabetic neuropathy
  6. Diabetes can result in microvascular injury to small blood vessels of nerves (vasa nervorum).
  7. Usually presents with pupillary sparing; because parasympathetic fibers are located peripherally in the nerve and are initially spared with ischemic events.
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8
Q

Trochlear Nerve (CN IV)

A

A. Components

  1. GSE
  2. One function – motor to superior oblique (moves eye down and out; rotates eye nasal-ward).

B. Course

  1. Exits dorsal midbrain, courses along lateral edge of cavernous sinus.
  2. Enters orbit via superior orbital fissure.

C. Clinical correlations

  1. Testing CN IV – Extraocular movements tested with “H” shape.
  2. Trochlear nerve palsy – eye held slightly up and in; cannot depress adducted eye.
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9
Q

V. Trigeminal Nerve (CN V) components and functions

A

A. Components

  1. SVE – muscles of first pharyngeal arch
  2. GSA – general sensation to face, teeth, oral cavity, external ear, paranasal sinuses, conjunctiva, eye, nasal cavities, dura mater

B. Functions

  1. Motor to first pharyngeal arch musculature
    a. Muscles of mastication
    b. Mylohyoid
    c. Anterior belly of digastric
    d. Tensor tympani
    e. Tensor veli palatini
  2. General sensation to all of ectodermally-derived epithelia of head
    a. Face, teeth, oral cavity, external ear, paranasal sinuses, conjunctiva, eye, nasal cavities, dura mater.
    b. There is very little overlap in the dermatomes innervated by each division
  3. Distributes postganglionic parasympathetic fibers to effector organs
    a. V1 distributes postganglionic fibers from the ciliary ganglion to the eye.
    b. V1 also participates in distributing postganglionic fibers to the lacrimal gland via a communicating branch from the zygomatic branches of V2.
    c. V2 distributes postganglionic fibers from the pterygopalatine ganglion to the nasal cavities, paranasal sinuses, palate, and lacrimal gland.
    d. V3 distributes postganglionic fibers from the submandibular ganglion to the submandibular and sublingual glands.
    e. V3 distributes postganglionic fibers from the otic ganglion to parotid gland.
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10
Q

trigem associated ganglia

A

C. Associated ganglia

  1. Trigeminal (semilunar) ganglion
    a. Contains cell bodies of origin for sensory component of nerve
    b. Located in dural recess called trigeminal cave; lateral to cavernous sinus.
  2. Parasympathetic ganglia suspended from CN V.
    a. Ciliary ganglion – V1
    b. Pterygopalatine ganglion – V2
    c. Submandibular ganglion – V3
    d. Otic ganglion – V3
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11
Q

trigem course

A

D. Course

  1. Exits brainstem at pons
  2. Exits skull through:
    a. V1 – superior orbital fissure to orbit
    b. V2 – foramen rotundum to pterygopalatine fossa
    c. V3 – foramen ovale to infratemporal fossa
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12
Q

trigem divisions: V1

A
  1. Ophthalmic division (V1)
    a. GSA to orbit and eye, nasal cavities, frontal and ethmoidal air sinuses, dura of anterior cranial fossa, and upper portion of face.
    b. Distributes autonomic fibers to intraocular eye and superior tarsal muscles
    c. Distributes autonomic fibers to lacrimal gland (via communicating branch from zygomatic n (V2) to the lacrimal nerve (V1).
    d. Branches
  2. Nasociliary
    a. Sensory root to ciliary ganglion
    b. Short ciliary nerves
    c. Long ciliary nerves
    d. Posterior ethmoidal n
    e. Anterior ethmoidal n.
    f. Infratrochlear n
  3. Frontonasal
    a. Supratrochlear n.
    b. Supraorbital n.
  4. Lacrimal
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13
Q

trigem divisions: V2

A
  1. Maxillary division (V2)
    a. GSA to dura of middle cranial fossa, sphenoidal and maxillary air sinuses, nasal cavities, palate, maxillary teeth and gingivae, nasopharynx, and middle portion of face.
    b. Distributes autonomic fibers to mucous glands of the deep head (via various branches from the pterygopalatine ganglion).
    c. Distributes autonomic fibers to lacrimal gland (via zygomatic nerves from pterygopalatine ganglion).
    d. Branches
  2. Meningeal branch
  3. Zygomatic n.
  4. Posterior superior alveolar n
  5. Infraorbital n.
    a. Middle superior alveolar n.
    b. Anterior superior alveolar n.
    c. Inferior palpebral nn.
    d. External nasal n.
  6. Pterygopalatine nn.
  7. Greater palatine n.
    a. Posterior inferior lateral nasal n.
  8. Lesser palatine n.
  9. Posterior superior lateral nasal n.
  10. Pharyngeal n.
  11. N. of pterygoid canal
  12. Nasopalatine n.
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14
Q

trigem divisions: V3

A

a. GSA to dura, mandibular teeth and gingivae, anterior 2/3rds of tongue, floor and walls of oral cavity, nasopharynx, TMJ, external ear and lower portion of face.
b. SVE to muscles of first arch derivation.
c. Distributes autonomic fibers to submandibular and sublingual glands (via lingual nerve from the submandibular ganglion).
d. Distributes autonomic fibers to parotid gland (via auriculotemporal nerve from otic ganglion).
e. Branches
1. Meningeal branch
2. Buccal n.
3. Auriculotemporal n. (GSA)
4. Lingual n. (GSA)
5. Inferior alveolar n. (GSA and SVE)
a. Mental n. –exits the mental foramen to supply the chin
b. Mylohyoid n. (SVE) – supplies mylohyoid, anterior belly of digastric
6. Medial pterygoid n
7. Nerve to tensor tympani
8. Nerve to tensor veli palatine
9. Lateral pterygoid nn
10. Masseteric nn
11. Anterior and posterior deep temporal nn.

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15
Q

Testing CN V

A

a. Test touch with a cotton swab in each of the three facial dermatomes. Recall: great auricular n (C2,C3) innervates region over the inferior angle of mandible.
b. Testing CN V1 – corneal reflex (V1 and VII)
c. Testing CN V3 – jaw jerk reflex (not usually part of normal neurologic exam)

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16
Q

Lesions of CN V

A
  1. Lesions of CN V
    a. Causes may be traumatic, tumors, aneurysms, or meningeal infection.
    b. Injury to CN V will lead to a loss of sensory innervation to the face (dermatome specific).
    c. Loss of corneal reflex
    d. Weakness of mm of mastication
    e. Hyperacusis – due to loss of tensor tympani
    f. Jaw will deviate toward the side of the lesion when mouth is opened.
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17
Q

Trigem neuralgia

A

a. Sensory disorder of trigeminal nerve which causes sudden, excrutiating facial pain; pain can become so severe that patients can become suicidal and depressed.
b. The cause is believed to be demyelination of axons within the sensory root of CN V; in some cases due to compression of an aberrant artery.
c. Division affected: V2 >V3 >V1

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18
Q

Nerve blocks for facial/ dental surgery

A

a. Infraorbital nerve – anesthetic injected around infraorbital foramen; accessed by inserting needle through superior portion of oral vestibule.
b. Mental nerve – anesthetic injected around the mental foramen on the chin.
c. Buccal nerve – anesthetic injected posterior to the 3rd mandibular molar.

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19
Q

Abducens components and course

A

A. Components

  1. GSE
  2. One function – motor to lateral rectus (abduction of eye)

B. Course

  1. Exits brainstem at pontomedullary junction, courses THROUGH cavernous sinus.
  2. Enters orbit via superior orbital fissure.
20
Q

abducens clinical correlations

A
  1. Testing CN VI
    a. Extraocular movements tested with “H” shape.
    b. Abducens nerve palsy – eye adducted; cannot abduct eye
  2. Because CN VI passes through the cavernous sinus, it is often affected early with pathologies affecting this region (i.e. atherosclerotic hardening of internal carotid artery, infection, or thrombosis).
21
Q

facial nerve components

A

A. Components

  1. SVE – muscles of second pharyngeal arch
  2. GVE-P – parasympathetic innervation to most mucous glands of head, lacrimal gland, submandibular and sublingual glands.
  3. GSA – general sensation to external auricle
  4. GVA – general sensation to nasopharynx region
  5. SVA – taste to anterior 2/3 of tongue
22
Q

facial nerve functions

A
  1. Motor (SVE) to second pharyngeal arch musculature
    a. Muscles of facial expression
    b. Posterior belly of digastric
    c. Stapedius
    d. Stylohyoid
  2. Parasympathetic (GVE-P) motor innervation to:
    a. Mucous-secreting glands of deep face regions.
    Facial nerve → pterygopalatine ganglion → various branches of V2 to mucous-secreting glands of palate, nasal cavities, paranasal sinuses.

b. Lacrimal gland
Facial nerve → pterygopalatine ganglion → zygomatic branch of V2 and lacrimal branch of V1 to lacrimal gland.

c. Submandibular and sublingual glands
Facial nerve → submandibular ganglion → lingual branch of V3 to submandibular and sublingual glands.

  1. General sensation (GSA) to portion of external ear
  2. General sensation (GVA) to small portion of nasopharynx
  3. Special sensation (SVA) to anterior 2/3rds of tongue.
23
Q

facial nerve associated ganglia

A
  1. Geniculate ganglion – contains cell bodies of sensory component of nerve
  2. Pterygopalatine ganglion
  3. Submandibular ganglion
24
Q

one nucleus for taste

A

solitary tract nucleus

25
Q

facial nerve course

A
  1. Exits brainstem at pontomedullary junction
  2. Exits skull through internal acoustic meatus.
  3. CN VII courses anteriorly along the roof of the internal ear; bending posterolaterally (geniculum of the facial nerve) near the medial wall of the middle ear.
  4. Near the geniculum of CN VII is the location of the geniculate ganglion.
  5. CN VII then courses through the facial canal along the posterior wall of the middle ear, exiting at the stylomastoid foramen.
26
Q

Branches of the facial nerve

A
  1. Greater petrosal nerve (GVE-P)
    a. Given off near geniculum of CN VII.
    b. Exits ear via hiatus for greater petrosal nerve
    c. Synapses in pterygopalatine ganglion.
    d. Supplies GVEP to lacrimal gland and mucous-secreting glands of head
  2. Chorda tympani (GVE-P and SVA)
    a. Given off while CN VII is coursing through facial canal.
    b. Exits ear via petrotympanic fissure; joins lingual nerve (V3).
    c. Synapses in submandibular ganglion.
    d. Supplies GVEP to submandibular and sublingual glands.
    e. Supplies taste to anterior 2/3rds of tongue.
  3. Nerve to stapedius (SVE)
  4. After exiting the stylomastoid foramen, the main trunk of CN VII (SVE) branches into the temporofacial and cervicofacial divisions.
    a. Posterior auricular branch
    b. Temporal nn
    c. Zygomatic nn.
    d. Buccal nn
    e. Marginal mandibular nn
    f. Cervical nn
27
Q

testing cranial n VII

A

a. Test muscles of facial expression (smile, close eyelids, frown, etc).
b. Taste to body of tongue
c. Corneal reflex (V1 and VII)

28
Q

lesions of VII

A

a. Causes: Acoustic neuromas; trauma; see below for Bell’s Palsy
b. Depending on the portion (or branches) of the nerve that is affected, can result in Bell’s palsy (see below), hyperacusis (due to loss of stapedius), loss of taste to the anterior 2/3rds of the tongue, decreased lacrimation, decreased salivation, decreased production of mucous from glands of head.

29
Q

Facial (Bell’s) Nerve Paralysis

A

a. Paralysis of SVE component of CN VII.
b. Causes: many cases are idiopathic; although linked to herpes virus, trauma or lesion anywhere along course of nerve, otitis media
c. Paralysis of muscles of facial expression
d. Facial asymmetry and drooping
e. Drooping of lower eyelid causes drainage of tears and ulceration of eye.
f. Paralysis of orbicularis oris causes dribbling of saliva from mouth
g. Loss of buccinator muscle leads to accumulation of food within the vestibule.
h. Impaired speech

30
Q

VNIII components, functions, ganglia

A

A. Components

  1. SSA
  2. Hearing
  3. Proprioception (balance)

B. Functions

  1. Hearing – via cochlear portion of CN VIII
  2. Proprioception (balance, equilibrium) – via vestibular portion of CN VIII.

C. Associated ganglia

  1. Cochlear ganglion
    a. Contains cell bodies of origin for auditory portion of nerve.
    b. Receives information about sound from the cochlea.
  2. Vestibular ganglion
    a. Contains cell bodies of origin for proprioceptive portion of nerve.
    b. Receives information about position, movements of head from semicircular canals, utricle, and saccule.
31
Q

CN VIII course

A
  1. Exits brainstem at pontomedullary junction.
  2. Exits skull through internal acoustic meatus.
  3. Enters internal ear to make contact with sensory receptor located in wall of membranous labyrinth.
32
Q

clinical correlations CN VIII

A
  1. Testing cranial nerve VIII
    a. Auditory exam
    b. Vestibular function exams
  2. Lesions of CN VIII often result in impairment of both the vestibular and cochlear portion of the nerve.
    a. Tinnitus – ringing in ears
    b. Vertigo – dizziness, loss of balance
    c. Impairment of hearing
  3. Acoustic neuromas are benign tumors of Schwann cells origin. They typically result in hearing loss, disequilibrium and tinnitus. They usually form at or near the internal acoustic meatus. Thus, these tumors can also cause compression of CN VII.
33
Q

CN IX components

A
  1. SVE – muscle of third pharyngeal arch
  2. GVE-P – parasympathetic innervation to parotid gland
  3. GSA – to external ear
  4. GVA – to pharynx, middle ear, tongue
  5. SVA – taste to posterior 1/3 of tongue
34
Q

CN IX functions

A
  1. Motor (SVE) to third pharyngeal arch musculature – stylopharyngeus
  2. Parasympathetic (GVE-P) innervation to:
    a. Parotid Gland
    CN IX → otic ganglion → auriculotympanic nerve (V3) to parotid gland.
  3. General sensation (GSA) to portion of external ear
  4. General sensation (GVA) to most of pharynx, middle ear, posterior 1/3 of tongue, carotid body and sinus.
  5. Special sensation (SVA) to posterior 1/3rds of tongue.
35
Q

CN IX ganglia and course

A

C. Associated ganglia

  1. Superior and inferior ganglion
    a. Contains cell bodies of origin for sensory components of nerve
    b. Located along extracranial course; after nerve exits jugular foramen.
  2. Otic ganglion – postganglionic parasympathetic cell bodies

D. Course

  1. Exits brainstem at medulla (in postolivary sulcus).
  2. Exits skull through jugular foramen.
  3. CN IX then descends posterior to the structures of the carotid sheath, then follows the course of the stylopharyngeus muscle.
  4. CN IX enters the pharynx by passing between superior and middle constrictors.
36
Q

Branches of CN IX

A
  1. Tympanic nerve (GVE-P and GVA)
  2. Carotid nerve (GVA)
  3. Branch to stylopharyngeus (SVE)
  4. Pharyngeal branches to pharyngeal plexus (GVA)
  5. Tonsillar and lingual branches (GVA and SVA)
37
Q

Clinical correlations of CN IX

A
  1. Testing cranial nerve IX
    a. Test gag reflex (CN IX and X)
    b. Taste to posterior 1/3 of tongue.
  2. Lesions
    a. Cause: trauma, stroke, tumor
    b. Symptoms: difficulty swallowing, loss of gag reflex, xerostomia, loss of taste to posterior tongue.
  3. Glossopharyngeal Neuralgia – sudden, intense pain experienced during swallowing, talking, or touching the palatine tonsillar region. Cause: likely compression from an artery (AICA); similar to trigeminal neuralgia. Very rare.
38
Q

Vagus n. components

A
  1. SVE – muscle of fourth and sixth pharyngeal arches
  2. GVE-P – parasympathetic innervation to gut from pharynx through transverse colon; heart; respiratory tract from larynx to lungs; kidneys and upper ureters.
  3. GSA – general sensation to external auricle and dura
  4. GVA – general sensation to gut track from larynx through transverse colon; heart; respiratory track from larynx to lungs; kidneys, upper ureters, suprarenal glands.
  5. SVA – taste to epiglottic region of tongue
39
Q

Vagus functions

A
  1. Motor (SVE) to second pharyngeal arch musculature
    a. Most muscles of palate (except tensor veli palatini)
    b. Most muscles of pharynx (except stylopharyngeus)
    c. Muscles of larynx and upper esophagus
  2. Parasympathetic (GVE-P) motor innervation to:
    a. Viscera (smooth mm, blood vessels, glands) of neck, thorax, abdomen.
    Vagus nerve → ganglia in wall of organ
  3. General sensation (GSA) to external acoustic meatus; external tympanic membrane
  4. General sensation (GVA) to respiratory track from larynx to lungs; heart; gut from esophagus through transverse colon; kidneys, upper ureters, suprarenal glands.
  5. Special sensation (SVA); taste to epiglottic portion of tongue.
40
Q

vagus ganglia and course

A

C. Associated ganglia
1. Superior and inferior (nodose) ganglia – contain cell bodies of origin for sensory components of nerve

D. Course

  1. Exits brainstem at medulla (in postolivary sulcus).
  2. Exits skull through jugular foramen.
  3. Descends within carotid sheath through neck; continues into thorax and abdomen.
41
Q

Vagus branches

A
  1. Meningeal branch to dura (actually from C2 spinal nerve) (GSA)
  2. Auricular nerve (GSA)
  3. Pharyngeal branches to pharyngeal plexus (SVE; GVE-P)
  4. Superior laryngeal nerve (GVE-P; SVE; SVA; GVA)
  5. Recurrent laryngeal nerves (GVE-P; SVE; GVA)
  6. Thoracic nerves (GVA; GVE-P)
  7. Abdominal visceral branches (GVA; GVE-P)
42
Q

Vagus clinical correlations

A
  1. Testing cranial nerve IX
    a. Test gag reflex (CN IX and X)
    b. Examine palatoglossal and palatopharyngeal folds for sagging.
    c. Examine uvula when asked to say “ah”; does it deviate?
  2. Lesions
    a. Cause: trauma, stroke, tumor
    b. Symptoms: deviation of uvula to unaffected side; sagging of faucial pillars on affected side, loss of gag reflex, hoarseness.
43
Q

Spinal Accessory components and course

A

A. Components

  1. GSE
  2. Motor to trapezius and sternocleidomastoid
  3. Note: the sensory innervation of these two muscles is from C2-C4.

B. Course

  1. Originates from motor nuclei in cervical spinal cord.
  2. Enters skull through foramen magnum; then exits via jugular foramen.
  3. CN XI descends posterior to the carotid sheath; penetrating the substance of sternocleidomastoid (which it innervates), it then exits this muscle posteriorly along its middle portion; the nerve then crosses the upper part of the posterior cervical region to descend along the deep surface of trapezius.
44
Q

spinal accessory clinical correlations

A
  1. Testing cranial nerve XI
    a. Have patient elevate shoulders against resistance
    b. Have patient rotate head from side-to-side against resistance.
  2. Lesions of CN XI
    a. CN XI is most susceptible to injury within the posterior triangle of the neck.
    b. Symptoms – drooping of shoulders
45
Q

CN XII components and course

A

A. Components

  1. GSE
  2. Motor to all intrinsic and extrinsic muscles of tongue (except palatoglossus).

B. Course

  1. Exits medulla in preolivary sulcus.
  2. Exits skull through hypoglossal canal.
  3. CN XII descends posterior to the carotid sheath; then courses lateral to the occipital artery, the hypoglossal nerve then enters the paralingual space of oral cavity.
46
Q

CN XII special feature

A
  1. As the hypoglossal nerve exits the skull, it is joined by branches from C1 and C2 spinal nerves.
  2. These nerves travel retrogradely with CN XII to supply the dura of the posterior cranial fossa (GSA).
  3. They also form the superior root of the ansa cervicalis (descendens hypoglossi) and distribute directly to thyrohyoid and geniohyoid (GSE).
47
Q

Clinical correlations of XII

A
  1. Testing cranial nerve XII
    a. Inspect for generalized tongue atrophy.
    b. Have patient protrude tongue to observe if the tongue deviates.
  2. Lesions of CN XII
    a. CN XII can be lesioned with tumors, stroke, or trauma within the neck.
    b. General atrophy of tongue.
    c. Tongue will deviate towards affected side upon protrusion.

neuro 2019 Exam 3 (17 decks)

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