chapter 14 – a synopsis of the cranial nerves of the brainstem
DESCRIPTION
Chapter 14 – A Synopsis of the Cranial Nerves of the Brainstem. Michelle-Lee Jones February 18, 2009. OUTLINE. Introductory Points Cell Columns & Nuclei – Motor & Sensory Cranial Nerves of the Medulla Oblongata Cranial Nerves of the Pons-Medulla Junction Cranial Nerves of the Pons - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 14 – A Synopsis of the Cranial Nerves of the Brainstem
Michelle-Lee JonesFebruary 18, 2009
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OUTLINE
Introductory Points Cell Columns & Nuclei – Motor & Sensory Cranial Nerves of the Medulla Oblongata Cranial Nerves of the Pons-Medulla
Junction Cranial Nerves of the Pons Cranial Nerves of the Midbrain
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Introductory Points Regarding the brainstem:
Transit point for all ascending & descending tracts connecting the spinal cord to the forebrain
Associated with the exit/entry & nuclei of 10/12 cranial nerves
Lesions often involve cranial nerves & have long tract signs great localizing signs
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Motor Cell Columns and Nuclei
Recap: basal plate derivatives CN motor nuclei oriented in discontinuous rostrocaudal cell columns
Nuclei from the same column possess common developmental, structural and functional features
3 motor cell columns:General Somatic Efferent (GSE), General
Visceral Efferent (GVE) & Special Visceral Efferent (SVE)
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Motor Cell Columns and Nuclei
1. GSE column features:• Most medial & anterior to the ventricular space • Nuclei include hypoglossal (XII), abducens
(VI), trochlear (IV) & oculomotor (III)• Motor neurons innervate skeletal muscle from
head mesoderm – tongue (occipital) & extraocular muscles (orbit) [ mesoderm NOT located in pharyngeal arches]
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Motor Cell Columns and Nuclei
2. GVE – preganglionic parasympathetic column features:
• Lateral to GSE• Forms cranial portion of craniosacral division of
visceromotor system (parasympathetic) & preganglionic fibres travel on the CN
• Nuclei include dorsal motor vagal nucleus (X), inferior salivatory nucleus (IX), superior salivatory nucleus (VII–intermediate), Edinger-Westphal nucleus (III)
• Preganglionic axons peripheral ganglion postganglionic fibres visceral structure
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Motor Cell Columns and Nuclei
3. SVE:• Most lateral motor column in medulla & pontine
tegmentum• Nuclei include nucleus ambiguus (efferents on
IX & X), facial motor nucleus & trigeminal motor nucleus
• Muscles innervated originate from mesenchyme located within the pharyngeal arches
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Motor Cell Columns and NucleiPharyngeal
Arch Associated muscle
I Mastication (V)
II Facial expression (VII)
III Stylopharyngeus (IX)
IV Pharynx constrictors, intrinsic laryngeal muscles (including vocalis), palatine muscles (except TVP), skeletal muscle upper half of esophagus (X)
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GSE
GVE
SVE
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Sensory Cell Columns & Nuclei
Recap: alar plate derivatives CN sensory nuclei oriented in continuous cell column
Lateral location for sensory columns 3 sensory cell columns:
Solitary tract and nucleusVestibular/cochlear nucleiTrigeminal sensory nuclei
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Sensory Cell Columns & Nuclei
1. Solitary tract & nucleus (CN VII, IX & X)• Visceral afferent centre of brainstem (solitary tract
receives all the 1°visceral afferent central processes) • Taste or Special Visceral Afferent (SVA) fibres
Gustatory nucleus (rostral area of solitary nucleus)• General Visceral Afferent (GVA) fibres
Cardiorespiratory nucleus (caudal area of the solitary nucleus)
• Solitary tract & nucleus (medulla) do not extend rostrally beyond the pons-medulla junction (most rostral CN = VII)
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Sensory Cell Columns & Nuclei
2. Vestibular/cochlear nuclei• Just posterior to solitary tract & nucleus• Includes medial & spinal vestibular nuclei,
anterior and posterior cochlear nuclei at pons-medulla junction, superior and lateral vestibular nuclei (caudal pons)
• Sensory input from VIII only• Hearing (SSA, exteroceptive) & balance and
equilibrium (SSA, proprioceptive)
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http://instruct.uwo.ca/anatomy/530/8nucl2.gif
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Sensory Cell Columns & Nuclei
3. Trigeminal sensory nuclei• From spinal cord-medulla junction to rostral
midbrain• 3 subdivisions
Spinal trigeminal nucleus (pars caudalis, pars interpolaris & pars oralis) – lateral medulla to caudal pons
Principal sensory nucleus (mid-pontine level) Mesencephalic nucleus (lateral to periaqueductal
grey)
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Sensory Cell Columns & Nuclei
3. Trigeminal sensory nuclei• Principal sensory nucleus & particularly the
spinal trigeminal nucleus GSA reception centre of brainstem
• Receives all the general somatic afferent (pain & thermal) central processes
• CN V, VII, IX & X
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Cranial Nerves of the Medulla Oblongata (CN XII, XI, X & IX)
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Hypoglossal Nerve (Motor)
Nucleus - internal to the hypoglossal trigone Course: anterior medulla lateral aspects of
medial lemniscus & pyramids pre-olivary fissure (rootlets) hypoglossal canal intrinsic tongue muscles + hypo-, stylo- & genioglossus muscles
Hypoglossal Canal: XII nerve, emissary vein, meningeal branch from ascending pharyngeal artery (dura posterior fossa)
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Hypoglossal nucleus + fibres:
supplied by anterior spinal artery (ASA)
Medial Medullary Syndrome (ASA) Deviation of tongue to side of lesion (GG) Contralateral hemiparesis (CST) Contralateral loss of position sense, vibration & 2-point
discrimination (ML)
Root lesion – tongue deviation to side of lesion
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Hypoglossal nucleus + fibres:
Internal capsule lesion tongue deviation to the contralateral
side (injury to crossed corticobulbar fibres innervating XII nucleus)
Contralateral hemiplegia Drooping of facial muscles
contralateral lower quadrant
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Accessory Nerve (Motor):
SCM and trapezius muscles are innervated by motor neurons in the cervical spinal cord (NOT MEDULLA)
Cranial part of XI misnomer (XI fibres temporarily join vague, then separate to exit skull)
Course: Cervical SC axons exit SC laterally merge to form nerve foramen magnum briefly join caudal part of X in post. fossa jugular foramen
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Accessory Nerve (Motor):
Root lesions: trapezius & SCM paralysis (ipsilateral shoulder droop & difficulty turning head to contralateral side)
C-spine lesion – above deficits are eclipsed by hemiplegia (CST)
Internal capsule lesion – similar deficits as above (uncrossed corticobulbar fibres to XI nucleus injured)
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Vagus Nerve (Motor & Sensory):
Intermediate location (b/w midline & lateral medulla); exits post-olivary sulcus (exits cranial cavity via jugular foramen)
2 ganglia immediately external to the foramen: Superior Ganglion (GSA) Inferior Ganglion (GVA, SVA)
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Vagus Nerve - Motor cells of the medulla:
1. Dorsal motor nucleus of the vagus (GVE-PNS preganglionic) terminal (intramural) ganglia viscera (trachea, bronchi, heart, GI tract – just proximal to splenic flexure
Effects: bronchiole constriction, HR, blood flow, peristalsis, gut secretions
2. Nucleus Ambiguus (SVE) 4th pharyngeal arch muscles (refer to previous table)
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Vagus Nerve – Sensory (GSA, GVA & SVA)
1. GSA (pain & thermal):– Small area of ear, part of external auditory meatus & dura
posterior fossa superior ganglion (central processes to spinal trigeminal tract, thence to spinal trigeminal nucleus)
2. GVA & SVA:– Heart, aortic arch, pharynx & larynx, lungs, gut to level of
splenic flexure (GVA) + taste buds on epiglottis & tongue base (SVA) inferior ganglion (central processes to solitary tract, thence to solitary nucleus - cardiorespiratory & gustatory portions
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SVE
SVA
GSA
GVE
GVA
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Vagus Nerve – Sensory (GSA, GVA & SVA) Root lesion (vagus): dyphagia & dysarthria, no apparent
lasting visceromotor dysfunction, taste NA & external auditory meatus GSA loss not key
Unilateral medulla injury nucleus ambiguus (Tumours, vascular lesions, syringobulbia)
Deficits as noted above Bilateral medulla lesions aphonia, aphagia, dyspnea,
or inspiratory stridor Critical, especially if dorsal motor nucleus
Thyroid surgery recurrent laryngeal n. injury dysarthria
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Glossopharyngeal Nerve (Motor & Sensory) Leaves medulla @ postolivary sulcus,
just rostral to vagus, leaves skull via jugular foramen
As with vagus, 2 ganglia: inferior ganglion (GVA, SVA) & superior ganglion (GSA)
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Glossopharyngeal Nerve - Motor
Inferior salivatory nucleus (GVE PNS): axons join with tympanic nerve, then lesser petrosal nerve otic ganglion parotid gland
Nucleus ambiguus (SVE): innervation of stylopharyngeus that muscle that helps with swallowing & efferent part of gag reflex
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Glossopharyngeal Nerve - Sensory GSA: Pinna, external auditory canal
superior ganglion
GVA: Parotid gland, oropharynx & carotid body inferior ganglion
SVA: Taste from posterior 1/3 inferior ganglion
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Glossopharyngeal Nerve - Lesions Rare, usually with X & XI roots @ jugular
foramen Nerve lesion: taste posterior 1/3, loss of ipsi.
gag reflex (s-m X) Glossopharyngeal neuralgia:
attacks of intense idiopathic pain in pharynx, caudal tongue, tonsil,? middle ear
Precipitated by spontaneous or artificial stimulation posterior oral cavity, swallowing or talking
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GSA
SVA
GVE
SVE
GVA
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Jugular Foramen & associated syndromes
Right Jugular Foramen – medial, middle & caudal parts
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Jugular Foramen & associated syndromes Vernet syndrome
@ or just internal to the foramen Loss of sensation post 1/3 tongue (IX); loss of sensation in
larynx & pharynx, dysarthria & dysphagia (X); weakness of ipsil. SCM & trapezius (XI)
Collet-Sicard syndrome Immediately external to the jugular foramen Damage to IX, X, & XI + ipsil tongue weakness (hypoglossal
canal is near foramen) Villaret syndrome includes above + sympathetic fibres (SCG)
ipsil Horner’s
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Cranial Nerves of the Pons-Medulla Junction (CN VIII, VII & VI)
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Vestibulocochlear Nerve (Almost exclusively sensory) Most lateral, centrally related to cochlear &
vestibular nuclei; 2 parts originate from specialized receptors within petrous temporal bone combined root in brainstem
Internal acoustic meatus (IAM) contains VIII, VII & labyrinthine artery
Cochlear part: Cochlear Spiral ganglion (bipolar cells) IAM
Cochlear nuclei (ant. & post.) brainstem relay nuclei MGN auditory cortex
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Vestibulocochlear Nerve (Almost exclusively sensory) Note cholinergic cells near the olivary nuclei
olivocochlear tract (efferent cochlear bundle) inner & outer hair cells (dampen responses)
Vestibular part: Ampullae of semicircular canals, utricle & saccule
vestibular ganglion (bipolar cells) IAM PMJ vestibular nuclei (sup, inf, lat, med) in medulla & caudal pons cerebellum + oculomotor nuclei, etc.
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Vestibulocochlear Nerve
VIII nerve lesions: hearing loss, tinnitus, vertigo, dizziness, ataxia
Cochlea, spiral ganglion or cochlear fibres lesions: ipsilateral sensorineural hearing loss
Lesions to brainstem or higher: ability to localise/interpret sound in space, no hearing loss per se
Conductive hearing loss: conduction through middle ear (typically ossicles)
Tinnitus pertains to auditory portion of VIII (peripheral or central damage)
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Vestibulocochlear Nerve
Injury to vestibular fibres: vertigo (subjective – pt moves or objective – environment moves), nystagmus ± n/v
Nystagmus – vestibular influence over brainstem oculomotor control disconnected
Lesions of vestibular nuclei & central connections – vertigo, ataxia, nystagmus, ± n/v
Causes of vestibular dysfunction are myriad: Meds, trauma, DM, cerebellar lesions, vestibular
schwannoma etc. Meniere’s syndrome:
hearing loss, sound distortion, vertigo, unsteadiness standing or walking
endolymphatic pressure size of utricle, saccule & cochlear
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Cerebellopontine Angle LesionsTUMOR TYPE
Vestibular schwannomas Meningiomas Epidermoid tumours
Prevalence @ CPA
85% 5-10% 5%
Origin/Description
Schwann cells of vestibular root
Margins of internal acoustic meatus (anterior, superior)
Entrapped clusters of epidermis anywhere in CNS
Lined with epithelium & contain cellular debris, proteins & cholesterol
Clinicalmanifestations
Tinnitus, unsteady gait, progressive hearing loss, later ipsil. facial weakness, if > 3 cm, impinge on V sensory ± pain
Significant erosion of internal acoustic meatus
Early facial weakness then hearing loss & trigeminal root associated pain
Spillage of cyst contents recurrent aseptic meningitis
In CPA, deficits related to V, VII & VIII
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Facial Nerve (Motor & Sensory)
Intermediate nerve: GVE + SVA + GSA + few GVA
(Petrous temporal bone)
Sortie
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Facial Nerve
At geniculate ganglion (internal genu), greater petrosal nerve formed by GVE-preganglionic PNS nerves from VII joins deep petrosal nerve to form nerve of the pterygoid canal pterygopalatine ganglion
Post-ganglionic parasympathetic fibres join V2 orbit lacrimal gland
Small SVE branch stapedius muscle
Larger SVE branch (chorda tympani) middle ear joins V3 lingual branch preglanglionic PNS fibres to submandibular ganglion, collects SVA taste afferent fibres (ant 2/3 tongue)
SVE muscles of facial expression, post. belly digastric & stylohyoid
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Facial Nerve
Sensory: SVA: anterior 2/3 tongue lingual V3
changeover to chorda tympani to join VII nerve geniculate ganglion
GSA: fewer in number; external ear & external auditory canal central course on VII geniculate ganglion
GVA: few; mucous membrane of palate & nasopharynx geniculate ganglion enter brainstem in intermediate nerve
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Facial Nerve Ipsilateral face motor cortex provides
bilateral innervation to facial motor neurons of the upper face
But, the face motor cortex projects only contralaterally to facial motor neurons of the lower face
Supranuclear lesions (face motor cortex or internal capsule) drooping of corner of mouth contralateral to the lesion (CENTRAL SEVEN LESION)
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Facial Nerve Peripheral lesions of VII (infranuclear):
Bell’s palsy: Injury proximal to geniculate ganglion & origin of
greater petrosal nerve with ipsilateral findings paralysis of upper & lower portions of face mucosal secretion in nasal & oral cavities tear fluid production & salivary gland output cutaneous sensation external ear & external
auditory canal taste sensation on anterior 2/3 tongue hyperacusis
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Facial Nerve Peripheral lesions of VII (infranuclear):
Distal to the geniculate ganglion but proximal to the origin of the chorda tympani & stapedial nerve
Ipsilateral salivation & taste, hyperacusis, facial expression
Intact tear fluid production & mucosal surfaces (nasal & oral cavities) are unaffected b/c greater petrosal nerve is intact
Caveat: Lesions distal to or @ stylomastoid foramen ipsil. function of all facial muscles in the absence of parasympathetic or taste dysfunction
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Facial Nerve Corneal reflex:
Afferent limb travels via V1 (ophthalmic) trigeminal ganglion spinal trigeminal tract spinal trigeminal nucleus trigeminothalamic fibres facial motor nucleus thalamus
Facial diplegia Myotonic muscular dystrophy Mobius syndrome (upper > lower facial
weakness typically, extraocular palsies, skeletal & extremity defects)
Lyme disease, GBS, Botulism poisoning & Corynebacterium diphtheriae
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Mobius syndrome
Verzijl, Harriette T.F.M., van der Zwaag, Bert, Cruysberg, Johannes R.M., Padberg, George W.Mobius syndrome redefined: A syndrome of rhombencephalic maldevelopmentNeurology 2003 61: 327-333
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Facial Nerve
Hemifacial spasms: Irregular painful facial muscle
contractions May be precipitated by voluntary facial
movements or follows Bell’s palsy Can be 2° to compression of facial
nerve root (e.g abnormal AICA branches)
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Abducens Nerve - Motor
Abducens nucleus: Internal to the facial colliculus, in rhomboid fossa
floor just lateral to median sulcus, above stria medullaris (IV ventricle)
Contains motor neurons (GSE) & interneurons
Abducens nerve exits @ pons-medulla junction (pre-olivary sulcus) cavernous sinus in close association with ICA superior orbital fissure ipsil. lateral rectus (LR)
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Abducens Nerve - Motor
Interneurons in VI nucleus contralateral MLF oculomotor nucleus (ipsi to MLF) medial rectus (MR)
Abducens fibres injury e.g. medial pontine syndrome flaccid paralysis of ipsilateral lateral rectus muscle (introverted eye, impaired ipsil. abduction)
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Abducens Nerve - Motor Abducens nucleus injury (motor- &
interneurons) e.g. IV ventricle tumour invading facial colliculus paralysis ipsi LR + contra. MR on gaze toward side of lesion (LMN of LR + INO)
Medial longitudinal fasciculus lesions internuclear ophthalmoplegia e.g. MS
Injury only to internuclear axons Ipsil abduction intact ± nystagmus but adduction of
contralateral eye is impaired Preserved adduction with convergence (vs. III )
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MLF - INO
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Abducens Nerve - Motor One and a Half syndrome:
Seen with pontine lesion affecting abducens nucleus & fibres + adjacent MLF
No movement of ipsilateral eye horizontally, contralateral eye horizontal movements restricted to abduction ± nystagmus
Cortical Influence: Frontal eye fields (FEF) bilateral projection to
PPRF (horizontal gaze centre) + ipsil. superior colliculus (SC)
SC contralateral PPRF; PPRF ipsil VI nucleus Cortical damage (e.g. CVA, trauma) to FEF
involuntary conjugate deviation of eyes to the side of the lesion
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Clinical Neurology – 6th ed. Greenberg et. al
One-and-a-half syndrome. This results from a pontine lesion (shaded area) involving the paramedian pontine reticular formation (lateral gaze center) and medial longitudinal fasciculus, and sometimes also the abducens (VI) nucleus, and affecting the neuronal pathways indicated by dotted lines. Attempted gaze away from the lesion (A) activates the uninvolved right lateral gaze center and abducens (VI) nucleus; the right lateral rectus muscle contracts and the right eye abducts normally. Involvement of the medial longitudinal fasciculus interrupts the pathway to the left oculomotor (III) nucleus, and the left eye fails to adduct. On attempted gaze toward the lesion (B), the left lateral gaze center cannot be activated, and the eyes do not move. There is a complete (bilateral) gaze palsy in one direction (toward the lesion) and one-half (unilateral) gaze palsy in the other direction (away from the lesion), accounting for the name of the syndrome.
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Cranial Nerves of the Pons (CN V, IV, III)
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Trigeminal - Motor & Sensory Introduction:
Largest CN, exits from lateral pons
Large sensory root (portio major) & small motor root (portio minor)
Exits border between basilar pons & middle cerebral peduncle
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V1
V2
V3
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Trigeminal - Motor & Sensory Brief review:
Sensory nuclei (caudal rostral): Spinal trigeminal nucleus (pars caudalis,
interpolaris & oralis), principal sensory nucleus & mesencephalic nucleus
GSA exteroception: Pain, thermal & non-discriminative touch fibres from head trigeminal ganglion + geniculate ganglion + superior ganglia for CN IX & X (ext. ear) spinal trigeminal tract/nucleus
GSA exteroception for discriminative touch as above but go to principal sensory nucleus
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Trigeminal - Motor & Sensory GSA proprioceptive input from
masticatory muscles, EOM & periodontal ligament receptors mesencephalic nucleus
Sensory input to spinal trigeminal nucleus & to principal sensory nucleus anterior & posterior trigeminothalamic tracts thalamus somatosensory cortex
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Trigeminal - Motor & Sensory Motor nucleus of V 1st pharyngeal arch
(medial & lateral pterygoid, tensor tympani, tensor veli palatini, mylohyoid, & anterior belly digastric)
The motor root of V exits in the foramen ovale along with V3.
Jaw Jerk reflex: Masticatory muscle receptors V2
mesencephalic nucleus bilateral projections from afferent collaterals trigeminal motor nucleus
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Trigeminal - Motor & Sensory Corneal (previously discussed) Lesions of V nerve or central nuclei
Sensory sx in nerve distribution & masticatory muscle paralysis
Sensory deficits include: Complete loss of pain, temperature, tactile
sensation ipsilateral face & scalp Loss of above sensations in oral cavity ipsil. Loss of corneal reflex
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Trigeminal - Motor & Sensory Tic douloureux (Trigeminal neuralgia)
Severe paroxysmal attacks of lacinating pain restricted to ≥ 1 subdvisions of V
Trigger zones – lip, nose, cheek Precipitants e.g. shaving, make-up application,
chewing, talking etc. Possible malnourishment!!! Patients usually > 35 years Maxillary > Mandibular > Ophthalmic Associated with MS, degenerative changes in
trigeminal ganglion, vascular abn (e.g. SCA) – contradicting autopsy evidence
Status trigeminus tic like contractions masticatory muscles
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Trigeminal - Motor & Sensory Motor deficits:
V root lesion ipsil masticatory muscle weakness, jaw deviation to weak side (unopposed contralateral pterygoid)
Central lesions (tumour, AVM, mets, vascular obstruction) Lateral Medullary syndrome (Wallenberg
syndrome)
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Cranial Nerves of the Midbrain (CN IV, III)
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Trochlear – Motor Only motor CN to cross midline prior to
exit & has long intracranial course
Course: Trochlear nucleus (post. to MLF) @ level of IC arch around PAG decussates in anterior medullary velum exits brainstem immediately caudal to the contra. IC GSE motor axons superior cistern ambient cistern dura cavernous sinus superior orbital fissure superior oblique (inf-lat)
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Trochlear – Motor Trochlear motor neurons innervate
contralateral superior oblique MLF + trochlear nucleus lesion e.g. MS:
Contralateral S.O. paralysis Ipsil INO
Cotical input: FEF rostral interstitial nucleus of the MLF &
superior colliculus riMLF = vertical gaze centre riMLF larger projection to ipsil IV nucleus & smaller
projection to contra nucleus FEF injury involuntary conjugate gaze deviation to
side of lesion
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Oculomotor – Motor Situated within ventral PAG, posterior to MLF,
in rostral half of midbrain
GSE all EOM except SO & LR
Ipsilateral innervation except for SR neurons (decussate within the nucleus)
Just posterior to III complex is Edinger-Westphal nucleus (GVE – PNS) ciliary ganglion
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Oculomotor – Motor
Course: III nerve fibres travel ventrally through & around the
red nucleus exit @ interpeduncular fossa cavernous sinus superior orbital fissure
Superior & inferior divisions of III in the orbit few branches to ciliary ganglion
Ciliary ganglion (PNS) short ciliary nerves sphincter pupillae & ciliary
muscles
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Oculomotor – Motor Post ganglionic sympathetic fibres from SCG
travel on ICA plexus ophthalmic artery optic canal ciliary ganglion directly, nasociliary branch (V2) or oculomotor on route to ciliary ganglion
In ciliary ganglion: SNS fibres continue directly into short ciliary nerves to dilator pupillae muscle, and others travel further via III nerve superior tarsal muscle
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Oculomotor – Motor Sensory input from the orbit via frontal &
nasociliary nerves V1 trigeminal ganglion The III nucleus does not receive direct
cortical input via the corticobulbar system Cortical control of III neurons via riMLF and
SC; SC also projects to the riMLF; riMLF send significant input to ipsi III, less on contralateral side
Cortical damage to FEF involuntary conjugate deviation towards the side of lesion
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Oculomotor – Motor Lesions of III nucleus, oculomotor nerve in
interpeduncular cistern or III in cavernous sinus: EOM paralysis except for SO & LR ( abducted &
depressed) Diplopia Pupil dilation, non-reactive to light, defective
accommodation & ptosis Note that because of peripheral location of PNS
fibres, subtle initial signs with external compression may be ptosis or mildly diminished pupil reactivity prior to EOM dysfunction
DM: EOM dysfunction sine visceromotor changes Ischemia affects the larger internal GSE motor axons 1st
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