Exam #2: Cranial Nerve II Flashcards
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
*SO4LR6
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?
Oculomotor nucleus
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?
Rostral midbrain
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?
Between the
- PCA
- Basilar
- 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?
Ciliary ganglion
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?
Ciliary muscle
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?
Pupillary constriction
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)
Horner Syndrome:
- Ptosis (less severe)
- NO defective eye movement
- NO deviation
- Miosis (constricted pupil)
Outline the pupillary light reflex.
Afferent= optic nerve Nucleus= EW-N Efferent= oculomotor
Is the pupillary dilation reflex associated with the oculomotor nerve? SNS or PNS?
- Not associated with the oculomotor nerve**
- SNS