The Occulomotor, Trochlear &
Abducent Cranial Nerves
Dr. Nimir
Dr. Safaa
Objectives
• Discuss the central connections of the Occulomotor(III)
nerve.
• Discuss the central connections of the trochlear(IV)
nerve.
• Discuss the central connections of the abducent(III,IV,VI)
nerve.
• Oculomotor Nerve (Cranial
Nerve III)
• Oculomotor nerve is
entirely motor in function.
• Has two motor nuclei:
• Main motor nucleus.
• Accessory parasympathetic
nucleus.
• Main nucleus is anterior to
cerebral aqueduct at level
of superior colliculus.
• It supply all extrinsic
muscles of eye except
superior oblique and
lateral rectus.
• Main nucleus receives
corticonuclear fibers from
both cerebral
hemispheres.
• It receives tectobulbar
fibers from superior
colliculus (information
from visual cortex).
• It is connected to nuclei of
fourth, sixth, and eighth
cranial nerves by medial
longitudinal fasciculus.
• Accessory parasympathetic
nucleus (Edinger-Westphal
nucleus) is posterior to main
nucleus.
• Preganglionic fibers
accompany other
oculomotor fibers to orbit &
synapse in ciliary ganglion.
• Postganglionic fibers pass
through short ciliary nerves
to constrictor pupillae of iris
and ciliary muscles.
• Accessory nucleus receives
corticonuclear fibers for
accommodation reflex and
from pretectal nucleus for
the direct and consensual
light reflexes.
• Course of Oculomotor
Nerve
• Oculomotor fibers passes
through red nuleus and
emerge between cerebral
peduncles & pass forward
between posterior
cerebral and superior
cerebellar arteries.
• It then continues into the
middle cranial fossa in
lateral wall of cavernous
sinus. Here, it divides into
a superior and an inferior
branches, which enter the
orbital cavity through
superior orbital fissure.
• Oculomotor nerve supplies levator palpebrae superioris,
superior rectus, medial rectus, inferior rectus, and inferior
oblique.
• It also supplies, through parasympathetic fibers, constrictor
pupillae of iris and ciliary muscles.
• It is responsible for lifting upper eyelid, turning eye upward,
downward, and medially.
• Constricting pupil and accommodating the eye.
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Trochlear Nerve
Trochlear nerve is entirely
motor in function.
Trochlear Nerve Nucleus:
The trochlear nucleus is
situated anterior to
cerebral aqueduct.
It lies inferior to
oculomotor nucleus at
level of inferior colliculus.
The nerve fibers, after
leaving nucleus, pass
posteriorly to reach
posterior surface of
midbrain.
• The trochlear nucleus
receives corticonuclear
fibers from both cerebral
hemispheres.
• It receives tectobulbar
fibers, which connect it to
visual cortex through
superior colliculus.
• It also receives fibers from
medial longitudinal
fasciculus, by which it is
connected to nuclei of
third, sixth, and eighth
cranial nerves.
• Course of the Trochlear Nerve
• Trochlear , most slender cranial
nerves and the only one to
leave posterior surface of
brainstem.
• Emerges from midbrain and
immediately decussates with
that of opposite side.
• Trochlear nerve passes forward
through middle cranial fossa in
lateral wall of cavernous sinus
and enters orbit through
superior orbital fissure.
• Trochlear nerve supplies
superior oblique muscle of
eyeball.
• Trochlear nerve assists in
turning eye downward and
laterally.
• Abducent Nerve (Cranial Nerve
VI):
• It is entirely motor in function.
• Abducent has small motor
nucleus situated beneath floor
of upper part of fourth
ventricle, close to midline and
beneath facial colliculus.
• The nucleus receives afferent
corticonuclear fibers from both
cerebral hemispheres.
• Nucleus receives tectobulbar
tract from superior colliculus, by
which connected to visual
cortex.
• It also receives fibers from
medial longitudinal fasciculus,
by which it is connected to the
nuclei of third, fourth, and
eighth cranial nerves.
• Course of the Abducent
Nerve
• Abducent fibers pass
anteriorly through pons and
emerge in groove between
lower border of pons and
medulla oblongata.
• It passes forward through
cavernous sinus, lying below
and lateral to internal
carotid artery.
• The nerve then enters orbit
through superior orbital
fissure.
• Abducent supplies lateral
rectus muscle and,
therefore, is responsible for
turning eye laterally.