Flashcards in Exam #2: Cranial Nerve II Deck (58):
What are the functional components of CN III?
- GSE= skeletal motor to upper eyelid & extraocular muscles
- GVE= PNS to smooth muscles of the eye
What skeletal muscles are innervated by CN III i.e. what muscles are innervated by the GVE portion of CN III? What is the mnemonic to help remember these?
- Levator palpebrae superioris
- Superior rectus
- Medial rectus
- Inferior rectus
- Inferior oblique
What smooth muscles are innervated by the PNS division of CN III? What are their functions?
- Sphincter pupillae m.= constriction of the pupil
- Ciliary m.= accommodation for near vision
What is the oculomotor complex?
Edinger-Westphal nucleus (EW-N)
What is the difference between the oculomotor nucleus & EW-N?
Oculomotor= GSE to most of the extraocular muscles
EW-N= GVE i.e. PNS
Where is the oculomotor complex located?
Describe the pathway of the axons that arise from the oculomotor nucleus.
Oculomotor nucleus is located inferior to the EW-N & periaqueductal gray in the rostral midbrain. Axons:
- Pass through Red Nucleus into
- Exit in the Interpeduncular fossa
Where is the EW-N relative to the oculomotor nucleus? Describe the pathway of its axons.
Superior--axons follow the same path as the oculomotor nucleus
Where does CN III travel relative to the cerebral vasculature?
- Superior Cerebellar Artery
Where are aneurysms most common in the cerebral arteries? What are the clinical implications?
Bifurcations--this is close to the space that contains CN III
What foramen does CN III pass through to enter the orbit?
Superior orbital fissure
What sinus does CN III pass through? What is the clinical implication?
Cavernous sinus--infection or aneurysm in this sinus can impact the function of CN III
Where do preganglionic PNS fibers of EW-N terminate?
What nerve carries postganglionic fibers from the ciliary ganglion?
Short ciliary nerves of the trigeminal nerve (CN V)
What muscles do the short ciliary fibers of CN V innervate?
Sphincter pupillae m.
What is the function of the ciliary muscle?
Lens accomondation for near vision
What is the function of the sphincter pupillae muscle?
Describe the presentation of a CN III lesion in regards to its GSE function.
The following muscles will be impacted:
LPS = ptosis
- Compensation by raising the eyebrow= wrinkling of forehead
Sup/ Inf. Rectus= no vertical movement
Medial rectus= inability to move medially & no tone= eye pulled laterally
Inferior Oblique paralyzed but Superior oblique intact= down & out
Describe the presentation of a CN III lesion in regards to its GVE function.
Sphincter papillae= pupil is dilated (mydriasis)
Ciliary muscle= no accommodation of the lens for near vision/ focus i.e cannot focus on near objects
What is Horner's Syndrome?
Damage of SNS fibers to the head from cervical ganglia
How do you know the difference between CN III Lesion & Horner Syndrome?
CN III lesion:
- Ptosis (more severe)
- Defective eye movements
- Eye down & out
- Mydriasis (dilated)
- Ptosis (less severe)
- NO defective eye movement
- NO deviation
- Miosis (constricted pupil)
Outline the pupillary light reflex.
Afferent= optic nerve
Is the pupillary dilation reflex associated with the oculomotor nerve? SNS or PNS?
*****Not associated with the oculomotor nerve******
What is Medial Midbrain Syndrome or Weber Syndrome?
Lesion to the rostral midbrain that affects the:
1) Corticospinal tracts
2) Corticonuclear tracts
3) CN III
****Results from occlusion of PCA or Basilar A.
What is the functional component of CN IV?
GSE to the superior oblique
Where is the trochlear nucleus located?
Ventral to the periaqueductal gray in the caudal midbrain
What is special about the trochlear nerve?
1) Only CN to decussate in the brain
2) Emerges dorsally
Where are the cell bodies of the right nerve are located?
In the left trochlear nucleus
What space does the trochelar nerve pass through relative to the cerebral vasculature?
Space between PCA & superior cerebellar artery
****Like CN III
Where does the CN IV enter the orbit?
Superior orbital fissure
What sinus does CN IV pass through?
What are the three main actions of the Superior Oblique muscle?
What is the mnemonic to remember the actions of the Superior Oblique?
"Salvation Army Muscle" i.e. down & out muscle
What muscle assists the Superior Oblique in downward gaze? What are the clinical implications?
Inferior rectus--damage to the trochlear nerve/ nucleus results in WEAKNESS to downward gaze, but NOT total inability
How does damage to the Trochlear nerve differ from damage to the trochlear nucleus?
Nerve= ipsilateral defect
Nucleus= contralateral defect
What is the clinical manifestation of damage to the Trochlear nerve?
- Upward gaze due to unopposed action of antagonist, the inferior oblique--referred to as "hypertropia"
- Extorsion (rotation around axis laterally)
What makes hypertropia worse?
1) Looking down, as in going down stairs
2) Medial gaze, as in reading
3) Tilting the head TOWARD the affected side
How do patients compensate for hypertropia/ superior oblique lesion?
1) Tilt head away from affected side
What is the functional component of the abducens nerve?
GSE to the lateral rectus muscle
Where is the abducens nucleus located?
Where does the abducent nerve emerge?
What foramen does the abducent nerve traverse to enter the orbit?
Superior orbital fissure
What sinus does the abducent nerve pass through?
How does a lesion to the abducent nerve present?
Medial rotation of the eye i.e. "medial strabismus"
How will a patient compenstate for a abducent nerve lesion?
Patient will turn the chin in the direction of the lesion
What are the two groups of cell bodies contained in the abducens nucleus?
1) motor neurons to the abducent nerve
2) internuclear neurons (interneurons) that cross the midline, join the medial longitudinal fasiculus (MFL), & synapse with the oculomotor nucleus --specifically with cell bodies that innervate the medial rectus
How does damage to the abducens nucleus manifest?
Horizontal gaze paralysis to the ipsilateral side i.e.
- Abduction deficit on ipsilateral side
- Adduction deficit on contralateral side
What is the CNS center for conjugate horizontal gaze?
What higher brain center stimulates the abducens nucleus?
If the right abducens nucleus is stimulated, which direction will the eyes move?
What is Internuclear Ophthalmolegia (INO)?
ADduction deficit of one eye during conjugate horizontal gaze away from the side of the lesion i.e. right lesion:
- Gaze to the right is NORMAL
- Gaze to the left is abnormal b/c
1) Imparied adduction of right eye
2) Nystagmus w/ abduction of left eye
Where is the site of the lesion in INO?
MLF (medial longitudinal fasiculus) the tract that connects the abducens nucleus to the oculomotor nucleus of CN III
Can a patient with INO converge their eyes?
YES--this is independent of the MLF
What is "one-and-a-half" syndrome?
Lesion of one AN & ipsilateral MLF
- Ipsilateral eye has NO horizontal movement
- Contralateral eye can ABduct with nystagmus
Where is the oculomotor complex located in the brainstem?
Where is the trochlear nucleus located in the brainstem?
Where is the abducens nucleus located in the brainstem?