NERVES OF ORBIT AND CLINICAL ANATOMY (ANATOMY) BDS STUDENT

DESCRIBES NERVES OF ORBIT AND THEIR CLINICAL ANATOMY.

1. NERVES OF ORBIT

2. OPTIC NERVE OPTIC NERVE IS 2 ND CRANIAL NERVE. ALSO KNOWN AS NERVE OF SIGHT. IT CONVEYS AXONS FROM GANGLIONIC CELLS OF THE RETINA. IT TRANSMITS SENSORY IMPULSES IN FORM OF ELECTRICAL IMPULSES FROM EYE TO BRAIN.

3. ORIGIN & COURSE ORIGIN Originates in optic disc(a group of cells in retinal tissue at back of eye. Course Extracranial course leaves bony orbit via optic canal and enters middle cranial fossa Intracranial course Within middle cranial fossa optic nerve from each eye unite to form optic chiasm . then it goes through optic tract. Each optic tract travels through lateral geniculate nucleus( lgn ) Lgn further carry visual information via pathway known as optic radiation.

4. Functional components Special somatic afferent fibres : for vision Afferents : for accommodation reflexes and pupillary light Few efferent fibres : sources of origin and their function remain unsettled

5. BLOOD SUPPLY OF OPTIC NERVE THE ARTERIES ARE DERVIED FROM 2 SOURCES . FROM PLEXUS IN PIAL SHEATH WHICH IS CONTRIBUTED BY SUPERIOR HYPOPHYSEAL ARTERY , OPTHALMIC ARTERY , POSTERIOR CILLIARY ARTERY , AND EXTRA NEURAL BRANCHES OF CENTRAL ARTERY. FROM INTRA NEURAL BRANCHES OF CENTRAL ARTERY. THE VENOUS BLOOD DRAINS INTO THE CENTRAL VEIN.

6. OCCULOMOTOR NERVE 3 rd cranial nerve. Distributed to extraocular as well as intraocular muscles. It is somatic motor nerve. It has 2 divisions superior and inferior, (coordinate and adjust eye positions during movement) Nerve enters through cavernous sinus and leaves through orbital fissure .

7. ORIGIN Originates from 2 nuclei in the midbrain :- Oculomotor nucleus Accessory parasympathetic nucleus (Edinger-Westphal nucleus)

8. Oculomotor nerve originates from oculomotor nucleus(within midbrain of brainstem) Emerges from the anterior aspect of the midbrain, passes inferiorly to a posterior cerebral artery and superiorly to the superior cerebellar artery. The nerve then pierces the dura mater and enters the lateral aspect of the cavernous sinus . The nerve leaves the cranial cavity via the superior orbital fissure Course

9. Parasympathetic Functions Two structures in the eye receive parasympathetic innervation from the oculomotor nerve : Sphincter pupillae   Cilliary muscles   The pre-ganglionic parasympathetic fibers travel in the inferior branch of the oculomotor nerve . Motor Functions The  oculomotor nerve  innervates many of the extraocular muscles. These muscles move the eyeball and upper eyelid . Superior Branch Superior rectus   Levator palpebrae superioris  B. Inferior Branch : Inferior rectus   Medial rectus Inferior oblique  

10. Blood supply of ooculomotor nerve . 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 cerebellar artery . 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. Extracranial supply Once the occulomotor 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.

11. TROCHLEAR NERVE The trochlear nerve is the fourth paired cranial nerve. It is the smallest cranial nerve (by number of axons) It has the longest intracranial course. It has a purely somatic motor function. Supplies only superior oblique muscle. Passes through superior orbital fissure to enter orbit of eye. it is the only cranial nerve to exit from the posterior midbrain).

12. Origin The trochlear nerve arises from the  trochlear nucleus  of the brain. Present within the medial midbrain at the level of the inferior colliculus. The right and left nerves then travel dorsally surrounded by periaqueductal grey matter.

13. COURSE Emerges from the posterior aspect of the midbrain. It runs anteriorly and inferiorly within the  subarachnoid   space  before piercing the dura mater adjacent to the  posterior clinoid process  of the sphenoid bone. The nerve then moves along the lateral wall of the  cavernous sinus  (along with the oculomotor nerve, the abducens nerve , and the internal carotid artery ) before entering the orbit of the eye via the  superior orbital fissure .

14. FUNCTIONAL COMPONENTS General somatic efferent fibers General somatic afferent fibers . Motor Function The trochlear nerve innervates a single muscle – the  superior oblique , which is a muscle of oculomotor. As the fibers from the trochlear nucleus cross in the midbrain before they exit, the trochlear neurons innervate the  contralateral  superior oblique.

15. ABDUCENT NERVE (CN VI) 6 th paired cranial nerve Has a purely somatic motor function Innervated lateral rectus muscle

16. origin Originates from a set of neural cells that are found in the ventral aspect of the pons. Then emerges from the brainstem at the pontomedullary junction to enter subarachnoid space. Coursing upward between Pons and clivus to enter Dorello’s canal.

17. ARISES FROM ABDUCENS NUCLEUS IN PONS OF BRAINSTEM. EXITS BRAINSTEM AT JUNCTION OF PONS AND MEDULLA. THEN ENTERS SUBARACHNOID SPACE AND PEIRCES DURA MATER TO TRAVEL IN AN AREA KNOWN AS DORELLO’S CANAL. IT THEN LEAVES DORELLO’S CANAL AND ENTER CAVERNOUS SINUS . IT TRAVELS THROUGH CAVERNOUS SINUS AND ENTERS BONY ORBIT VIA SUPERIOR ORBITAL FISSURE. THEN IT TERMINATED BE INNERCATING LATERAL RECTUS MUSCLE WITHIN BONY ORBIT . COURSE

18. Clinical anatomy of optic nerve Normal optic disc Edematous optic disc OPTIC NEURITIS DEMYLINATING INFLAMMATION OF OPTIC NERVE CLINICAL CONDITIONS SUDDEN LOSS OF MONOCULAR PARTIAL OR COMPLETE VISION PAIN WITH MOVEMENT OF AFFECTED EYE LOSS OF COLOUR VISION(RED) UHTHOFF’S PHENOMENON TRANSIENT WORSENING OF VISION WITH INCREASED BODY TEMPERATURE

19. What is optic neuritis and what are its causes??

20. Can the optic nerve be regenerated??

21. Clinical anatomy of occulomotor nerve

22. Clinical anatomy of trochlear nerve TROCHLEAR NERVE PALSY IT IS CAUSED BY DISEASE OR INJURY TO 4RTH CRANIAL NERVE. MOST COMMON CAUSE OF TROCHLEAR NERVE PALSY IS HEAD TRAUMA. SUPERIOR OBLIQUE MUSCLE IS AFFECTED. TROCHLEAR NERVE PALSYCAUSES AN IPSILATERAL HIGHER EYE ( HYPERTROPHIA) AND EXCYCLOTORSION(THE AFFECTED EYE DEVIATES UPWARD AND ROTATES OUTWARD )

23. TROCHLEAR NERVE PALSY

24. Clinical anatomy of abducens nerve ABDUCENS NERVE PALSY ABDUCENS NERVE PALSY IS A DISORDER ASSCIATED WITH DYSFUNCTION OF ABDUCENS NERVE(CN VI) IT IS RESPONSIBLE FOR CONTRACTION OF LATERAL RECTUS MUSCLE TO ABDUCT (TURN OUT) THE EYE. THE INABILITY OF AN EYE TO TURN OUTWARD RESULTS IN DIPLOPIA i.e. MOST COMMONLY KNOWN AS DOUBLE VISION. TWO IMAGES APPEAR SIDE BY SIDE IN THIS PALSY .

25. ABDUCENS NERVE PALSY