Published on June 16, 2016
1. Innervation of the Extraocular Muscles Tukezban Huseynova, MD Specialist in Strabismus and Refractive Cornea, Briz-L Eye Clinic, Baku, Azerbaijan Tukezban@gmail.com
2. • The third, fourth, and sixth cranial nerves innervate six extraocular muscles in each orbit.
3. a Oculomotor Nerve
5. Anatomy Origin: From 2 nuclei in the rostral midbrain: 1. Oculomotor nucleus: General Somatic Efferrent fibers to superior, medial, and inferior recti muscles, to the inferior oblique muscle, and to the levator palpebrae superioris muscle. 2. Edinger- Westphal nucleus: General Visceral Efferent preganglionic fibers to the ciliary ganglion.
7. • The Oculomotor Nerve supplies all the extra ocular muscles except Lateral Rectus and Superior Oblique. • Has 2 components: Somatomotr: Extraocular Muscles Visceromotor: Ciliary Gamglion Anatomy
10. Pathway • Scheme showing central connections of the optic nerves and optic tracts.
11. Pathway Within the orbit: - Superior ramus (to the superior rectus and levator muscles) - Inferior ramus (to the medial and inferior rectus muscles, and the ciliary ganglion). - Postganglionic fibers from the ciliary ganglion innervate the sphincter pupillae muscle of the iris as well as the ciliary muscle.
13. Lesion results in: • Paralysis of the 3 rectus muscles and the inferior oblique muscle(causing the eye to rotate downward and slightly outward) Lesions
14. Lesions • Paralysis of elevator palpebrae superious muscle (drooping of the eyelids).
15. Lesions • Paralysis of Sphinkter pupillae and ciliary muscles (so that the pupil will remain dilated and the lens will not accommodate).
16. Lesions Lesion due to: • Transtentorial uncal herniation(tumor/hematoma) • Aneurysms: Carotid and Posterior communicating arteries. • Cavernous sinus Thrombosis • Diabetis Mellitus.
17. - Abducens Nerve
18. Nucleus • There are two cell populations within the sixth nerve nucleus. - One group of cell bodies contains motor neurons that innervate the ipsilateral lateral rectus. - The other group of cell bodies produces axons, which decussate and enter the contralateral medial longitudinal fasciculus. - There they ascend via the medial longitudinal fasciculus to the oculomotor nerve complex, forming synapses in the region of the medial rectus subnucleus.
20. Fascicle • The abducens fascicle courses ventrally, laterally, and caudally to emerge at the junction of the pons and medulla. • During its course, the fascicle is in close proximity to the facial nerve nucleus, the facial nerve fascicle, motor and sensory nuclei of the trigeminal nerve, and the pyramidal tract.
21. Nerve • The nerve exits the brainstem just lateral to the pyramid. It ascends in the subarachnoid space along the clivus, passing near the inferior petrosal venous sinus and then beneath the petrosphenoid ligament . This space is called Dorello's canal.
22. • The abducens nerve, or abducent nerve, is a motor nerve. It innervates the lateral rectus muscle (responsible for lateral gaze, i.e., moving the eyeball outwards) of the ipsilateral orbit.
23. Lesion • Due to its long path inside the skull, the abducens nerve is often damaged in fractures of the base of the skull, or by a disorder, such as a tumor, that distorts the brain. Such damage may give rise to double vision or a squint.
24. Lesion Abducens nerve palsy
25. Trochlear Nerve
26. Nucleus • The nuclei of the trochlear nerve are a paired group of motor cells located in the floor of the cerebral aqueduct. They are positioned just caudal to the oculomotor nerve complex in the midbrain.
28. Fascicle • About 2,100 axons emerge from each nucleus, passing first laterally and then dorsally to converge and decussate over the roof of the cerebral aqueduct just caudal to the inferior colliculi, where they exit the brainstem . The short fascicular course makes it clinically difficult to separate nuclear from fascicular involvement.
29. Nerve • The trochlear nerve has the longest subarachnoid course of the ocular motor nerves. • Within the cavernous sinus, the nerve is positioned in the lateral wall just below the third cranial nerve and above the ophthalmic division of the trigeminal nerve. • The nerve continues forward, passing through the superior orbital fissure above and medial to the annulus of Zinn to reach the superior oblique muscle. It is the only ocular motor nerve that does not pass through the annulus of Zinn
31. Lesion • Fourth (trochlear) nerve palsy
32. Development. • The oculomotor, trochlear, and abducens nerve nuclei develop from specific neuronal populations in the hindbrain (rhombencephalon). Abnormal development of extraocular muscle innervation produces a number of complex strabismus syndromes, known collectively as the “congenital cranial dysinnervation disorders. These disorders have been considered myopathic in origin, but recent work suggests that many may be of neuropathic origin.
33. Thank You
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