3.4 Cranial Nerves III-VII Flashcards
Which cranial nerves are responsible for extraocular eye movement?
CN III, IV, VI
When the superior and inferior oblique muscles contract together, they ___ the eye
Adduct
When the superior and inferior oblique muscles contract together, they ___ the eye
Abduct
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
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
Which of the superior/inferior rectus intort/extort the eye?
Superior: intorts
Inferior: extorts
What is the name of the muscle innervated by the occulomotor nerve that controls the eyelid?
Levator palpebrae superioris
What are the two parasympathetic functions of the oculomotor nerve?
- Pupil constriction
- Lense accommodation (slackening) for near vision
What are the two midbrain nuclei of the oculomotor nerve? What are their functions?
- Oculomotor nucleus (somatic motor)
- Edinger Westphal nucleus (parasympathetic)
Between which two arteries does the oculomotor nerve emerge from the ventral brain?
Superior cerebellar artery and posterior cerebral artery
Does the oculomotor nerve control ipsilateral or contralateral eye movements?
Ipsilateral
Does the trochlear nerve supply ipsilateral or contralateral eye muscles?
Contralateral
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
Does the abducens nerve control ipsi/contralateral eye muscles?
Ispilateral
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
Draw the H path gaze
- Abduct (LR)
- Look up (SR)
- Look down (IR)
- Adduct (MR)
- Look up (IO)
- Look down (SO)
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
Consensual vs direct light reflex
Consensual: other eye
Direct: same eye
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)
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
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)
