Flashcards in Neuro - Cranial Nerves CN III, IV, and VI Deck (19):
Identify the location of the cell body of origin and the course of the abducens nerve.
cell body of origin in the pontine tegmentum -> rootlets exit anteriorly -> longest intracranial course -> lateral rectus muscle -> abducts eye
What structure is innervated by the abducens nerve?
lateral rectus muscle
List the signs and symptoms seen following a lesion of the abducens nerve.
- diplopia (double vision) at rest since affected eye looks medially
- diplopia (double vision) when asked to look lateral on the lesioned side
- compensatory head-turn away from side of lesion
Identify the location of the cell body of origin and the course of the trochlear nerve.
cell body of origin in the midbrain tegmentum -> rootlets exit posteriorly -> superior oblique muscles
Name the structure innervated by the trochlear nerve.
superior oblique muscle
List the signs and symptoms seen following a lesion of the trochlear nerve.
- extorsion of eye (top of eye is tipped laterally)
- accompanying vertical double vision (diplopia)
- weakness during attempted downward medial gaze
- compensatory head-tilt toward intact shoulder
Identify the location of the cell body of origin of both components and the course of the oculomotor nerve.
- GVE cell body of origin in the midbrain tegmentum -> rootlets exit into interpeduncular fossa -> Edinger-Westphal nucleus -> ciliary ganglion
- SE cell body of origin in the midbrain tegmentum -> rootlets exit into interpeduncular fossa -> oculomotor nucleus -> all extraocular muscles and levator palpebrae muscle except SO and LR
Name the structure(s) innervated by the oculomotor nerve.
- intrinsic muscles of the eye
- medial rectus, inferior oblique, inferior rectus, superior rectus, and levator palpebrae muscles
List the signs and symptoms seen following a lesion of the oculomotor nerve.
- SE functional component
- ptosis - paralysis of levator palpebrae muscle makes eyelid droop
- eye position - down and out
- GVE functional component (parasympathetic)
- dilated, fixed pupil
- paralysis of accommodation
How does ptosis due to a lesion of the oculomotor nerve differ from that seen in Horner syndrome?
in Horner's syndrome, the drooping of the eyelid is much less severe (?)
What is the significance of unequal pupil size?
it could be used to signal if a person has an uncal herniation since the parasympathetic fibers of CN III (which are one of the controls of pupil size) are unmyelinated and easily damaged by an uncal herniation (?)
Define diplopia. How can the patient minimize diplopia?
- diplopia - double vision
- can be compensated for by tilting the head so that both eyes align
Name the neuroanatomical structure that corresponds with the center for lateral gaze.
abducens nucleus controls eye movements in the horizontal plane (center for lateral gaze); loss of the abducens nucleus results in paralysis of lateral gaze
Name the tract that contains the axons that arise from the internuclear neurons of the abducens nucleus.
medial longitudinal fasciculus
Name the source of the axons that terminate in the ciliary ganglion.
Edinger-Westphal nucleus in the midbrain -> ciliary ganglion
Name the muscle innervated by the oculomotor nerve that holds the upper eyelid up.
levator palpebrae muscle
Describe the anatomical basis of paralysis of lateral gaze.
- abducens nucleus controls the lateral rectus muscle
- abducens nucleus is also connected to the oculomotor nuclear complex via internuclear neurons
- abducens nucleus controls eye movements in the horizontal plane (center for lateral gaze)
- loss of the abducens nucleus results in paralysis of lateral gaze
Describe the anatomical basis of internuclear ophthalmoplegia.
- paralysis of the contralateral medial rectus muscle because the internuclear neuron (neuron connecting abducens and oculomotor nuclei) is cut
- medial rectus does not contract on attempted ipsilateral horizontal gaze
- medial rectus does not contract during accomodation
- nystagmus (quivering) in abducting eye contralateral to lesion