SEMINAR PRESENTATION
ON
CRANIAL NERVE III
(OCCULOMOTOR NERVE)
BY
MGBACHI KAREN CHIMDALU
2018 284 088
&
EZEMENAKA ELIZABETH
NNEAMAKA
2018 284 087
INTRODUCTION
The oculomotor nerve is the third cranial nerve (CNIII),
and one instance in which the name is a clear indication
of the function of the nerve (Oculo = pertaining to the
eye, motor = producing movement). Simply from the
name then, it is easy to know that the oculomotor nerve
will innervate muscles that move the eye itself or
components of the eye. It is the movement producing
functions of the nerve that make it a useful indicator of
brain injury.
ORIGIN
It is first important to understand the distinction between
the direction that motor and sensory information travel in
the nervous system.
Sensory information will be traveling towards the spinal
cord and parts of the brain (afferent information) for
processing and identification and thus will typically
originate outside of the brain.
Motor information on the other hand, will originate in,
and then travel from parts of the brain out to target
muscles (efferent information). The motor nerves will
interact with the target muscles via the neuromuscular
junction.
All cranial nerves with motor functions will originate from
and thus have their nuclei located within either the
brainstem (medulla, pons, or midbrain) or the spinal cord
(the spinal accessory nerve/CNXI). The oculomotor nerve
is no exception. The cell bodies of the oculomotor nerve
are located within two nuclei positioned close to one
another, posteromedially in the midbrain, the most
superior component of the brainstem. The cell bodies
and their somatic motor nerve fibers, or axons, that will
innervate skeletal muscles associated with the eye, arise
from the oculomotor nucleus. The cell bodies and their
visceral motor nerve fibers, or axons, that innervate
muscles within the eye itself, arise from the EdingerWestphal nucleus.
FUNCTIONS Occulomotor nerve comprises of two major
functions which include: Somatic motor function and
Visceral motor function.
• SOMATIC MOTOR FUNCTION:- These nerve axons will
arise from the oculomotor nucleus and innervate
skeletal muscles associated with the eye. There are
seven extrinsic eye muscles (muscles that lay outside of
the eye itself) that move the superior eyelid and the
eyeball. Five of them are innervated by the oculomotor
nerve.
VISCERAL MOTOR FUNCTION:- The visceral motor axons
of the oculomotor nerve are part of the autonomic
nervous system, specifically the parasympathetic division.
They will arise from the Edinger-Westphal nucleus and
innervate two separate intrinsic muscles within the eye.
These will constrict the pupil and cause accommodation
of the lens of the eye respectively.
MUSCLES INNERVATED BY THE OCCULOMOTOR
NERVE
EXTRINSIC EYE MUSCLE (SOMATIC MOTOR FUNCTION):These muscles are located outside of the eye itself. There are seven in total but the oculomotor
nerve supplies five of them. The first four mentioned here will move the eyeball; the last one will
move the upper eyelid.
•SUPERIOR RECTUS
Origin
Superior part of the common tendinous ring
Insertion
Sclera on the top of the eyeball, posterior to the
corneoscleral junction
Action
*Elevation, adduction, medial rotation of the
eyeball
•INFERIOR RECTUS
Origin
Inferior part of the common tendinous ring
Insertion
Sclera on the bottom of the eyeball, posterior to the
corneoscleral junction
Action
*Depression, adduction, lateral rotation of the eyeball
•MEDIAL RECTUS
Origin
Medial part of the common tendinous ring
Insertion
Sclera on the medial aspect of the eyeball, posterior
to the corneoscleral junction
Action
*Adduction of eyeball
•INFERIOR OBLIQUE
Origin
Anterior aspect of the floor of the orbit
Insertion
Sclera of the eyeball, deep to the insertion of the
lateral rectus on the lateral aspect of the eyeball
Action
Abduction, elevation, lateral rotation of the eyeball
NOTE :The common tendinous ring is a
fibrous ring of tissue that
surrounds the optic canal in the
posterior aspect of the orbit and
provides a point of origin for all
four recti muscles of the eye
(superior, inferior, medial and
lateral recti).
•LEVATOR PALPEBRAE SUPERIORIS
Origin
Anterior and superior to the optic canal on the
lesser wing of the sphenoid bone
Insertion
Superior tarsus and skin of the upper eyelid
Action
Elevation of the upper eyelid
NOTE:
Superior rectus and levator
Palpebrae superioris are supplied
by the superior branch of the
oculomotor nerve, the inferior
branch supplies inferior rectus
and inferior oblique
• INTRINSIC EYE MUSCLE (VISCERAL MOTOR
FUNCTION)
• These muscles are located within the eye itself
and are both supplied by parasympathetic fibers
of the oculomotor nerve. They are actually the
anterior extensions of the vascular layer of the
eyeball. As such they don’t conform to the
typical organization of other muscles with well
defined origins and insertions. Moving from
posterior to anterior within the vascular layer we
have the choroid (the vascular component of the
layer), ciliary body, and the iris.
BLOOD SUPPLY
• The blood supply to the oculomotor nerve can be more
easily understood if the nerve is broken down into
intracranial and extracranial (i.e. in the orbit) segments.
• INTRACRANIAL SUPPLY
• The initial portion of the nerve is supplied by branches of
the posterior cerebral artery, the thalamoperforating
arteries. Arteries arising directly from the posterior cerebral,
posterior communicating, superior cerebellar, and basilar
artery will also supply blood to this segment of the nerve.
The middle and distal portions of the nerve are typically
supplied by a branch of the internal carotid artery as it
passes
through
the
cavernous
sinus,
the
meningohypophyseal trunk.
EXTRACRANIAL SUPPLY
• Once the oculomotor nerve passes through the superior
orbital fissure into the orbit, both the superior and inferior
branches are supplied by arteries arising from the
ophthalmic artery.
CLINICAL ANATOMY
• The symptoms of oculomotor nerve-related injury can differ
based on the location of damage within the oculomotor and
Edinger-Westphal nuclei in the midbrain, and whether it
occurs inside or outside of the brainstem.
• DAMAGE WITHIN THE MIDBRAIN NUCLEI:• Within the brainstem, organization of the oculomotor and
Edinger-Westphal nuclei in the midbrain can mean quite
specific localization of damage. More anterior lesions within
the oculomotor nucleus would tend to damage motor
supply to the ipsilateral inferior rectus, and the sphincter
pupillae and ciliary muscles (Edinger-Westphal nucleus).
Lesions occurring more posteriorly and laterally would affect
the nerve supply to the ipsilateral medial rectus and inferior
oblique muscles, whereas as more medially located lesions
might affect the supply to the contralateral superior rectus
muscle. The nerve supply to the superior rectus is the only
case in which the input comes from the contralateral side of
the oculomotor nucleus.
• DAMAGE WITHIN THE BRAINSTEM Injury within the midbrain at the
level of the oculomotor nucleus can result in two different syndromes:
• Moritz Benedikt syndrome - Is a lesion of the oculomotor nerve fibers
as they pass through the red nucleus. A lesion here will result in a
contralateral tremor, due to damage to the superior rectus input, and
the typical oculomotor nerve lesion symptoms:
• Deviation of the ipsilateral eye downward and outward (due to action
of the intact superior oblique and lateral rectus muscles)
• A drooping of the ipsilateral eyelid (ptosis) due to a lack of levator
palpabrae superioris action
Diplopia (double vision)
• Ipsilateral loss of accommodation and light reflexes due to lack of
sphincter pupillae and ciliary muscles
• Dilation of ipsilateral pupil (unopposed due to lack of sphincter pupillae
action)
• Weber syndrome - This syndrome results due to damage located more
anteriorly than in Moritz Benedikt syndrome, just before the nerve
fibers exit the brainstem. In this case, the typical oculomotor nerve
lesion symptoms are present but the contralateral tremor progresses to
a contralateral upper motor neuron paralysis affecting the superior
rectus.
• DAMAGE OUTSIDE THE BRAINSTEM
• Damage to the oculomotor nerve after it leaves the
brainstem results in a collection of symptoms known as
oculomotor nerve palsy. Symptoms include:
• Deviation of the ipsilateral eye out downward and outward
• Ptosis
• Double vision
• Ipsilateral pupil dilation
• Unresponsive light and accommodation reflexes in the
ipsilateral eye
• Recall that as the oculomotor nerve fibers exit the brainstem
they pass between the posterior cerebral and superior
cerebellar arteries. This makes the oculomotor nerve
susceptible to aneurysms that may press on the nerve, or
aneurysm rupture, which will manifest as a sudden headache
and symptoms of an oculomotor nerve lesion.
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