1. Abduct (LR) 2. Look up (SR) 3. Look down (IR) 4. Adduct (MR) 5. Look up (IO) 6. Look down (SO)

3.4 Cranial Nerves III-VII Flashcards by Will Bradley

Which cranial nerves are responsible for extraocular eye movement?

CN III, IV, VI

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When the superior and inferior oblique muscles contract together, they ___ the eye

Adduct

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When the superior and inferior oblique muscles contract together, they ___ the eye

Abduct

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Does the superior oblique depress or elevate the eye (in addition to intorsion and adduction)? Why?

It runs anterior to posterior
Therefore, it depresses the eye

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Does the inferior oblique depress or elevate the eye (in addition to extorsion and abduction)? Why?

It runs anterior to posterior
So it elevates the orbit

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Which of the superior/inferior rectus intort/extort the eye?

Superior: intorts
Inferior: extorts

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What is the name of the muscle innervated by the occulomotor nerve that controls the eyelid?

Levator palpebrae superioris

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What are the two parasympathetic functions of the oculomotor nerve?

Pupil constriction
Lense accommodation (slackening) for near vision

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What are the two midbrain nuclei of the oculomotor nerve? What are their functions?

Oculomotor nucleus (somatic motor)
Edinger Westphal nucleus (parasympathetic)

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Between which two arteries does the oculomotor nerve emerge from the ventral brain?

Superior cerebellar artery and posterior cerebral artery

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Does the oculomotor nerve control ipsilateral or contralateral eye movements?

Ipsilateral

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Does the trochlear nerve supply ipsilateral or contralateral eye muscles?

Contralateral

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Describe the path of CN IV from the midbrain to its effector

Originates in nucleus of trochlear nerve
Crosses over, and emerges dorsally just beneath the inferior colliculi
Heads up to superior orbital fissure
Innervates superior oblique

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Does the abducens nerve control ipsi/contralateral eye muscles?

Ispilateral

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Describe the passage of the abducens nerve to its destination

Nucleus is in pons
Emerges at pontomedullary junction ventrally
Travels up to superior orbital fissure, passing over a bump in the occipital bone

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Draw the H path gaze

Abduct (LR)
Look up (SR)
Look down (IR)
Adduct (MR)
Look up (IO)
Look down (SO)

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Describe the consensual light reflex

When light is shone in one eye, both pupils constrict
This is due to bilateral connections between pretectal nuclei and edinger westphal nuclei; CN III carries the “constrict” signal to both eyes

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Consensual vs direct light reflex

Consensual: other eye
Direct: same eye

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What are some signs of CN III palsy (outside of the light reflex)

Superior tarsal muscle is gone (drooping eyelid)
No more Para. innervation (pupil is dilated)
Only the SO and the LR remain (eye is depressed and abducted)

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Describe the distribution of individual fibres within CN III; how does this affect the features of various pathologies?

Para. are on the outside, motor on the inside
In vascular diseases, blood can more easily get to Para, so this is less impaired
In compression (e.g. uncal herniation, PCA aneurysm), motor is more spared

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Explain the presentation of a CN IV palsy

SO depresses, abducts, intorts
In palsy, eye rotates upwards and outward
Double vision (different angles)
May adopt compensatory head tilt

Explain the presentation of a CN VI palsy

LR abducts
Therefore eye is adducted
Patient fails to abduct
Double vision

Describe the sensory function of the trigeminal nerve

Pain, temp, touch, and proprioception
Of the face, mouth, nasal cavity and cranial dura

Describe the motor function of the trigeminal nerve (which muscles?)

Supplies muscles of mastication:
- Temporalis
- Medial/lateral pterygoid
- Masseter

What are the three CN V sensory nuclei of the brainstem?

- Mesencephalic (proprioception of temporomandibular joint) - Main sensory (discriminative touch & roprioception) - Spinal (pain, temp, crude touch)

From which sensory nucleus of the trigeminal nerve does the trigeminal ganglion arise?

Main sensory nucleus

Which sensory division of CN V is joined by the motor root?

Mandibular division.

The neuronal cell bodies for pain/temp and touch/pressure of the face are located in the...

Trigeminal ganglion (everything except proprioception)

What are the names of the three nuclei that the three branches of the sensory trigeminal nerve synapse at in the medulla?

- Mesencephalic nucleus - Main sensory nucleus - Spinal trigeminal nucleus

True or false: after reaching their brainstem nuclei, the secondary nerves in trigeminal pathways decussate to the other side of the brain

True

What is the trigeminal lemniscus?

It's a combination of the decussated fibres from the spinal nucleus and the main sensory nucleus of the trigeminal nerve; they bundle together, and head to the thalamus.

What fibres are in the trigeminothalamic tract?

Those that have decussated from the trigeminal spinal nucleus

Which nucleus in the thalamus do the sensory fibres of the periphery/CN V synapse on?

Periphery: ventral posteriolateral (VPL) CN V: ventral posteriomedial (VPM)

Which CN controls the sensory vs motor aspect of the jaw jerk?

- Trick question - Both are CN V

Are the trigeminal motor neurons ipsilateral or contralateral?

Ipsilateral

What are the clinical signs of trigeminal nerve palsy?

- Sensory loss - Jaw deviates towards side of lesion when mouth opened

What are the classic clinical features of trigeminal neuralgia? What causes is it associated with?

- Sudden, brief, excrutiating facial pain attacks in one/more branches - Thought to be caused by neurovascular compression -> demyelination & ion channel disregulation

Which kinds of functions does the facial nerve have?

- Motor - Special sense - Parasympathetic

Which muscles does the facial nerve innervate?

Muscles of facial expression

What is the special sensory function of CN VII?

Taste from anterior 2/3 of tongue

What is the parasympathetic function of CN VII?

Tear glands and saliva glands (except parotid)

At what level of the pons are the facial nerve nuclei?

Caudal

Where does the facial nerve exit the brainstem?

Pontomedullary junction (remember: alongside 8)

Where does the facial nerve exit the skull?

Internal acoustic meatus (facial canal)

Where do the sensory/motor/para. components of the facial nerve exit the skull?

Motor: stylomastoid foramen Para/sensory: facial canal

Why doesn't the facial nerve innervate the parotid gland?

Because by the time it exits the stylomastoid foramen, it has lost its parasympathetic and sensory components

What are the five branches of the motor component of CN VII? What structures do they innervate?

- Temporal (forehead) - Zygomatic (forceful eye closure) - Buccal (nostril, upper lip, blinking, raising mouth corner) - Mandibular (depressing lower lip) - Cervical (lower corner of mouth)

Describe innervation of upper vs lower face (i.e., lateral vs bilateral)

Upper: bilateral Lower: only contralateral

LMN vs UMN facial lesion

UMN: Innervation of upper face is still intact due to other side (contralateral lower paralysis) LMN: Innvervation of whole face is lost, since lesion is distal to mixing of fibres (ipsilateral, whole paralysis) Remember the story of the nurse who thought she had Bell's palsy

Which nerves form the afferent/efferent arms of the corneal reflex?

Afferent: CN V Efferent: CN VII

What are some causes of lower facial nerve palsy?

- Idiopathic (Bell's) - Acute otitis media - Neoplasm

CN VII lesion in facial canal vs in/outside stylomastoid foramen

Stylomastoid: muscle paralysis of lower face Facial Canal: Also reduced lacrimation (para) and loss of taste (sensory)