CN III, IV, VI Flashcards
What is the CNS origin for CN III?
Autonomic: oculomotor nucleus (upper midbrain)
Somatic: Edinger-Westphal nucleus
What is the CNS origin for CN IV?
Somatic: Trochlear nucleus (lower midbrain)
What is the termination for CN III
pupillary sphincter, ciliary muscle
What might be the cause of a lateral strabismus
Injury to CN III ipsalaterally (innervates medial rectus; lateral rectus would be unopposed and cause the eye to deviate laterally)
Why might ptosis occur as a result of an injury to CN III?
CN III innervates levator palpebrae superioris, which raises the eyelid
What is mydriasis? Why might it occur in a patient with damage to CN III?
dilation of the pupil. CN III caries parasympathetics to pupillary sphincter. Pupillary dilator would remain unopposed, causing the pupil to be dilated
Damage to which CN may cause you to have double vision when reading a book or going down stairs?
CN IV
Injury to which nerve will cause a medial strabismus?
CN VI
What is the signficance of the MLF (median longitudinal fasciculus)?
It allows for head and eye movement coordination; connects nuclei from III, IV & VI
What would happen if the MLF were damaged?
- internuclear opthalmoplegia (paralysis of the eye due to damage between the nuclei)
- remove excitatory input to ipsalateral III nucleus
- eye ipsalateral to damage can’t move past midposition
- lateral movements of both eyes - unaffected
Describe what happens in the pupillary light reflex.
- afferent limb: retinal ganglion cells to pretectal nuclei (remember, they cross the midline)
- pretectal nucleus is linked to both EWN
- pregang. parasymp fiber enters CN III, synapse in ciliary ganglion
- post gang. fibers in short ciliary nerves enters iris and supply sphinctor
What happens in the accomodation reflex?
- Ciliary bodies contract, relieving tension on the suspensory ligaments, which causes the lens to bulge (for near vision)
- sphincter pupillae contracts
increased tone in the medial rectus muscles (eyes converge slightly)
What term describes the smooth pursuit of the eyes, following an area of interest across a visual field?
tracking
What term is used to describe when the eyes move from one target to the next in high speed movement known as saccades?
scanning
T/F: Of the three CNs (III, IV, & IV), trochlear nerve (CN IV) is the only nerve to exit the brainstem posteriorly.
True
