Neuroanatomy

1. Cranial Nerves: III,IV & VI
Presenter: Dr. Md. Saiduzzaman
MD(Neurology)Phase-B
Mymensingh Medical College Hospital
Mymensingh, Bangladesh

2. Cranial Nerve-III(Oculomotor nerve)
It has two motor nuclei: 1) The main motor nucleus, 2)The
accessory parasympathetic nucleus.
 Paired oculomotor nuclei are located in the dorsal midbrain
ventral to the periaqueductal gray matter at the level of the
superior colliculus.
Composition of each nucleus:
 Superior rectus subnucleus providing innervation to the
contralateral superior rectus.
 Inferior rectus, medial rectus, and inferior
oblique subnuclei providing ipsilateral innervation;

3. Cranial Nerve-III(Oculomotor nerve)
 An Edinger–Westphal nucleus supplying preganglionic
parasympathetic output to the iris sphincter and
ciliary muscles.
 A single midline caudal central subnucleus provides
innervation to both levator palpebrae superioris
muscles.

5.  A third nerve fascicle originates from the ventral surface
of each nucleus and traverses the midbrain, passing
through or near to the red nucleus and in close proximity
to the cerebral peduncles before emerging ventrally as
rootlets in the lateral interpeduncular fossa. In the
interpeduncular fossa, the rootlets converge into a third
nerve trunk that continues ventrally through the
subarachnoid space toward the cavernous sinus, passing
between the superior cerebellar artery and the posterior
cerebral artery. It travels parallel to the posterior
communicating artery (PCOM) and is very near to this
vessel at the vessel’s junction with the intracranial
internal carotid artery.

8. Location of cranial nerves in the cavernous sinus viewed
from behind.

10.  In the cavernous sinus, the third nerve is located within
the dural sinus wall, just lateral to the pituitary gland.
From the cavernous sinus, the third nerve enters the orbit
via the superior orbital fissure. Just prior to entry, the
nerve anatomically divides into superior and inferior
divisions in the anterior cavernous sinus.
 Within the orbit, the superior division innervates the
superior rectus and the levator palpebrae superioris, and
the inferior division innervates the inferior and medial
recti, the inferior oblique, and the iris sphincter and
ciliary muscles. Prior to innervating the ciliary and
sphincter muscles as the short ciliary nerves,
parasympathetic third nerve fibers synapse in the ciliary
ganglion within the orbit.

11. Clinical lesions:
 Oculomotor Nucleus
 Brainstem Fascicle
 Interpeduncular Fossa and Subarachnoid Space:
Compression by a PCOM aneurysm.
 Cavernous Sinus
 Orbital Apex
 Isolated Oculomotor Nerve Palsy: Microvascular
ischemia is a common cause.
ischemia,hemorrhage, demyelination,
infectious and noninfectious
inflammation, and neoplasm.

14. Syndromes with 3rd cranial nerve:
 Claude syndrome: Ipsilateral oculomotor nerve palsy
and contralateral hemiataxia.
 Nothnagel syndrome: Combination of ipsilateral
oculomotor
nerve palsy and ipsilateral cerebellar hemiataxia.
 Weber syndrome: Ipsilateral fascicular oculomotor
nerve palsy and contralateral hemiparesis.
 Benedikt syndrome: Ipsilateral oculomotor nerve
palsy and contralateral chorea or tremor.

15. Midbrain fascicular third cranial nerve palsies

16. Fourth nerve (trochlear nerve)
 Only cranial nerve to emerge from the dorsal aspect
of the brain
 Crossed cranial nerve – it means that nerve nucleus
innervates the contralateral superior oblique muscles
 Very long and slender nerve.
 Paired trochlear nuclei lie very close to the dorsal
surface ofthe midbrain just inferior to the inferior
colliculus.
 The nerve fibers, after leaving the nucleus, pass
posteriorly around the central gray matter to reach
the posterior surface of the midbrain.

18.  The trochlear nucleus receives corticonuclear fibers
from both cerebral hemispheres.
 It receives the tectobulbar fibers, which connect it to
the visual cortex through the superior colliculus.
 It also receives fibers from the medial longitudinal
fasciculus, by which it is connected to the nuclei of
the third, sixth, and eighth cranial nerves.

19. Course of the Trochlear Nerve:
 The trochlear nerve,the most slender of the cranial
nerves and the only one to leave the posterior surface of
the brainstem,emerges from the midbrain and
immediately decussates with the nerve of the opposite
side. The trochlear nerve passes forward through the
middle cranial fossa in the lateral wall of the cavernous
sinus and enters the orbit through the superior orbital
fissure.
 The nerve supplies the superior oblique muscle of the
eyeball contralateral to the nucleus of origin. The
trochlear nerve is entirely motor and assists in turning the
eye downward and laterally.
 The superior oblique muscle is an intorter of the eye, as
well as a depressor of the adducted eye.

21. Clinical Lesions:
 Trochlear Nucleus and Fascicle: Both locations will result
in paresis of the contralateral superior oblique muscle.
 Trochlear Palsy Appearance: Trochlear nerve dysfunction
results in impaired intorsion of the eye, impaired
depression of the adducted eye, elevation of the affected
eye (hypertropia), and vertical or oblique diplopia.
 Subarachnoid Space
 Cavernous Sinus
 Orbital Apex
 Isolated Trochlear Nerve Palsy

23. Sixth nerve (abducent nerve):
 Motor
 Supplies the
lateral rectus muscle
 Abduction
of the eye

24.  The small motor nucleus is situated beneath the floor
of the of the fourth ventricle, in the dorsal part of the
pons close to the midline and beneath the colliculus
facialis. The nucleus receives afferent corticonuclear
fibers from both cerebral hemispheres. It receives the
tectobulbar tract from the superior colliculus, by
which the visual cortex is connected to the nucleus. It
also receives fibers from the medial longitudinal
fasciculus,by which it is connected to the nuclei of
the third, fourth, and eighth cranial nerves.

25.  Each nucleus contains abducens motoneurons that
form the abducens nerve, and interneurons that
decussate at the nuclear level and ascend in the
medial longitudinal fasciculus (MLF) to the
contralateral oculomotor medial rectus subnucleus to
facilitate conjugate horizontal gaze in the direction
ipsilateral to the abducens nuclear origin of the
interneurons.

26. Course of the Abducent Nerve:
 The fibers of the abducent nerve pass anteriorly
through the pons and emerge in the groove between
the lower border of the pons and the medulla
oblongata. It passes forward through the cavernous
sinus, lying below and lateral to the internal carotid
artery. The nerve then enters the orbit through the
superior orbital fissure. The abducent nerve is
entirely a motor nerve and supplies the lateral rectus
muscle and, therefore, is responsible for turning the
eye laterally.

28. Sixth nerve (abducent nerve)

29. Clinical Lesions:
 Abducens Nucleus: abducens nuclear lesions cause
conjugate horizontal gaze palsy toward the side of
the lesion.
 Lesions involving both the abducens nucleus and
ipsilateral MLF cause the one-and-a-half syndrome,
with an ipsilateral conjugate gaze palsy and an
ipsilateral internuclear ophthalmoplegia with
impaired adduction of the ipsilesional eye and
abducting nystagmus of the contralateral eye

30. Clinical lesions:
 Abducens Palsy Appearance : Abducens nerve dysfunction
results in impaired ipsilateral abduction of the eye and
deviation of the eyes toward one another (esotropia).
 Brainstem Fascicle: Foville syndrome was the
combination of ipsilateral abducens palsy, ipsilateral
lower motor neuron facial palsy, and contralateral
hemiparesis from corticospinal tract involvement.
Millard-Gubler syndrome is the combination of ipsilateral
abducens and facial palsies with contralateral hemiparesis.
Raymond syndrome is the combination of ipsilateral
abducens palsy and contralateral hemiparesis

31. Clinical lesions:
 Subarachnoid Space and Dorello Canal
 Petrous Apex: Gradenigo syndrome>in combination
with trigeminal ophthalmic division and facial nerve
involvement from a lesion at the petrous apex.
 Cavernous Sinus
 Orbital Apex
 Isolated Abducens Palsy