3rd, 4th and 6th Cranial nerves

Neuroanatomy

1. C ranial 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.

4. 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.

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

6. 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.

7. 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.

8. Syndromes with 3 rd cranial nerve: Claude syndrome: Ipsilateral oculomotor nerve palsy and contralateral hemiataxia . Nothnagel syndrome: C ombination 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.

9. Midbrain fascicular third cranial nerve palsies

10. 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.

11. 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.

12. 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.

13. 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

14. Sixth nerve ( abducent nerve): M otor S upplies the lateral rectus muscle A bduction of the eye

15. 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 .

16. 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.

17. 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.

18. Sixth nerve ( abducent nerve)

19. 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

20. 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

21. 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