CN III, IV, VI Flashcards
CN III controls what?
Eye movement— SR, MR, IR, IO
CN IV controls what?
Eye movement— SO
CN VI controls
Eye movement— LR
nucleus of cn 3
midbrain just ventral to superior colliculi
nucleus of cn 4
midbrain just ventral to superior colliculi
nucleus of cn 6
pons (caudal one half)
Describe the multinuclear arrangement of the CNIII
five different muscles to control so five separate nuclei
Medial nucleus: Superior Rectus
Dorsal Nucleus: Inferior rectus
Intermediate nucleus: Inferior oblique
Ventral nucles: medial rectus
Edinger Westphal nucleus (parasympathetic to the contractor muscles of the iris)
What is the facial colliculus
Where the facial nerve, cranial nerve 7, runs over the top of cranial nerve 6 in the floor of the 4th ventricle
All nuclei of the CN III nucleus serve their respective ipsilateral muscles except for the medial nuclei which serves
contralateral superior rectus
CN IV inervates contralateral or ipsilateral superior oblique?
Contralateral
CN III exits where?
midbrain/pons junction
CN III is subject to compression from injury from vascular anomalies called aneurysms why?
Because it is in close juxtaposition to a bunch of intracranial arteries. not going to list them. see notes.
Know that CN III, IV, and VI and trigeminal 1 and 2 pass through the cavernous sinus along with the internal carotid artery and sympathetics travelling with the ICA. Any kind of hemorrhage, tumor, infection, aneurysm, and/or inflamatory disease may affect the cavernous sinus and and affect these structures
ok…so what passes through
III, IV, VI, V1 and V2, Internal carotid and sympathetics travelling with ICA
CN III inervates the levator palpebrae superioris which leads to
elevation of upper eyelid
Autonomic elevation of the eyelid is accomplished through innervation of what by what?
sympathetic innervation of the tarsal muscle
Ciliary muscle produces
change in lens shape, accomodation
Medial Rectus moves the eye in what way?
Adduction ( towards nose)
Lateral Rectus moves the eye in what direction
Abduction (away from nose)
Inferior rectus moves the eye in what direction
down
superior rectus
up
Superior obliques cause
INTORSION of the eye
Inferior obliques cause?
Extorsion of the eye
Sympathetic pathway to pupilary dilator muscle. Nucleus lies where
Hypothalamus
What is the only cranial nerve that exits the brainstem dorsally
CN IV
Which two cranial nerve nuclei controlling eye movement serve contralateral muscles
The medial nuclei of CN III (superior rectus) and the trochlear nucleus (superior oblique)
The first presenting sign of an aneurysm pressing on the top of CN III will be what?
Unilateral pupilar enlargement due to damage of the parasympathetic constrictor fibers that travel in the upper part of CN III. Unilateral paresis will come on shortly after. This is a neurologic emergency.
Paresis of the muscles served by CN III without enlargement of the pupil means?
occlusion of the blood vessels serving the center of CN III as a result of diabetes. The parasympathetic fibers tend to be protected due to their superficial location.
What is the accomodation reflex
Involves three things:
1) convergence of the eyes
2) Parasympathetic constriction of the pupil via EW
3) Thickening of the lens due to contraction of the ciliary muscle allowing the suspensory ligaments to relax.
What initiates the accomodation reflex
Cortical areas:
- Prefrontal eye fields
- Occipito-parietal eye fields
Can accomodation occur in the face of a lesion of MLF >
yes
What is the medial longitudinal fasciculous
The connection between cranial nerve 6 (LR) and CN III nuclei that allows for horizontal eye movement
Conjugate lateral eye movement is what?
activation of CN VI to cause abduction of the ipsilateral eye will immediately activate the contralateral CNIII nucleus that controls the medial rectus of the oopposite eye
Failure of conjugate eye movement =
double vision
The regulation of conjugate lateral eye movement is regulated by what
PPRF nucleus
Activation of the left PPRF causes what
activation of the left lateral rectus (CNVI) and simultaneous activation of right ventral nucleus to activate CNIII
Saccadic eye movement is under the control of which of the cortical centers ?
frontal eye field
What are the three cortical centers that control eye movement
1) Visual cortex
2) frontal eye fields
3) parietal-occipito temporal areas
The saccadic pathway from the frontal eye field travels with what fibers through the internal capsule
corticobulbar
These fibers that travel with the corticobulbar fibers through the internal capsule head where?
to the ipsilateral superior colliculus and then to the contralateral PPRF.
So the right frontal eye field activates which PPRF
The left. The left PPRF then activates the left abducens nerve and the right ventral nucleus of CNIII (medial rectus) to make they eys look left.
Slow pursuit eye movements are under the control of which of the three cortical centers
POT- parietal occipito temporal area
POT directs eye movement contralaterally or ipsilaterally
ipsilaterally.
