Unit II: Cranial Nerves IV, VI Flashcards
Where is the trochlear nucleus?
Periaqueductal gray, just caudal to the oculomotor nuclei
What muscle is supplied by cranial nerve IV?
Superior oblique
What is unique about the pathway of the trochlear nuclei?
They decussate as they leave the CNS and head posteriorly to exit from the midbrain just inferior to the inferior colliculi
From which area do the trochlear nuclei receive information?
Bdmn. Area 8, superior colliculus, medial longitudinal fasciculus
After leaving the brainstem on the posterior side, where is cranial nerve IV carried in its pathway?
Cavernous sinus
Cranial nerve IV communicates with what structure while in the cavernous sinus?
Cavernous plexus (postganglionic sympathetic fibers)
Why is cranial nerve IV named trochlear nerve?
For the pulley-like mechanism located on the superomedial aspect of the orbit
What passes through the trochlea located on the superomedial aspect of the orbit?
The superior oblique muscle (not the trochlear nerve)
What muscle is supplied by cranial nerve VI?
Lateral rectus
What is the location of the abducens nucleus (nucleus of origin)?
On the floor of the rhomboid fossa, on the inferior part of the pons
What is the name of the nucleus of origin for cranial nerve IV?
Trochlear nucleus
Cranial nerve VI exits the skull through which structure?
Superior orbital fissure
What occurs with internal strabismus?
Affected eye deviates medially (eyes cross, converge)
What occurs with external strabismus?
Affected eye deviates laterally (eyes are directed away from each other, diverging)
What is the term for double vision?
Diplopia
What is the term for the condition where the eyelid droops due to a weakness of the levator palpebrae superioris?
Ptosis
What could be the cause of ptosis?
Oculomotor nerve lesions
What is the issue when dealing with complaints of diplopia?
It is completely subjective
What is seen with oculomotor paralysis (external opthalmoplegia)?
Ptosis, diplopia, diverging strabismus (external)
What would we see with trochlear paralysis?
Slight converging strabismus, diplopia when looking down (difficulty descending stairs)
Which is the most common visual cranial nerve paralysis?
Abducens paralysis
What is seen with abducens paralysis?
Weak abduction, converging strabismus (internal), diplopia
What is internuclear ophthalmoplegia?
Damage to the medial longitudinal fasciculus
What is the result of internuclear ophthalmoplegia?
Nystagmus when abducting
Internal ophthalmoplegia would result in lack of what functions?
Inability to construct pupil, loss of light and accommodation reflexes
What are possible etiologies associated with oculomotor paralysis?
Uncal herniation, PCA aneurysms, diabetes
What is the most common ocular cranial nerve paralysis?
Abducens paralysis
Bilateral ocular cranial nerve paralyses indicate what overlying issue?
CNS lesion
Are ocular cranial nerve paralyses usually unilateral or bilateral?
Unilateral
