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Abducens Nerve Lesion • Right LR Is Disabled

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Abducens Nerve Lesion • Right LR Is Disabled Orbit and Contents Remove orbital plate and expose the periorbita CN V2 CN III, IV, V1, VI, SOV CN II, optic n., ophthalmic a. Orbit and Contents Contents of orbit: • Eyeball and extraocular mm • Nerves to mm and orbital contents • Optic nerve (CN II) – retina; vision • Ciliary ganglion – PS supply to sphincter pupillae and ciliary mm • Ophthalmic artery and veins • Lacrimal gland and ducts • Lacrimal sac and canaliculi • FAT!! Bony Orbit and Walls The orbit is a 4-sided pyramid: Base (orbital margin) – anterolaterally • Frontal, Maxilla, Zygomatic bones Apex - posteromedially Walls: Roof – frontal bone Lateral – zygomatic, greater wing of sphenoid Medial – lesser wing of sphenoid, ethmoid (lamina papyracea), lacrimal, part of maxilla Floor – maxilla (“roof of maxillary sinus”) Three of the four sides are bounded by paranasal sinuses: Superiorly – Frontal sinus (behind eyebrows) Medially – Ethmoidal sinuses (air cells) Inferiorly – Maxillary sinus Bones are thin and vulnerable to “blowout” fractures Bony Orbit and Openings Orbital and Optical Axes and Position of Eyeball in Orbit = visual axis Axes about which movements of the eyeball occur 1. Vertical axis (superior/inferior poles) – rotation of pupil toward nose (=adduction) – rotation of pupil away from nose (=abduction) 2. Transverse axis (mediolateral; at equator) – rotate pupil upward (=elevation) – rotate pupil downward (=depression) 3. Anterior-posterior axis (optical axis, line of sight) – rotate superior pole medially (=intorsion) – rotate superior pole laterally (=extorsion) Only the medial rectus and lateral rectus have pure, singular actions. All others move the eyeball on 3 different axes. Extraocular Muscles Muscle Origin Insertion Innervation Function Levator palpebrae Lesser wing of sphenoid Skin of upper eyelid Oculomotor n. (CN III) Elevates upper eyelid superioris and superior tarsal – superior branch plate Superior rectus Common ring tendon Anterior half of eyeball Oculomotor n. (CN III) Elevates, adducts, and superiorly – superior branch medially rotates eyeball (intorsion) Inferior rectus Common ring tendon Anterior half of eyeball Oculomotor n. (CN III) Depresses, adducts, inferiorly – inferior branch and laterally rotates eyeball (extorsion) Medial rectus Common ring tendon Anterior half of eyeball Oculomotor n. (CN III) Adducts eyeball medially – inferior branch Lateral rectus Common ring tendon Anterior half of eyeball Abducens n. (CN VI) Abducts eyeball laterally Superior oblique Sphenoid, superior and Superolateral part of Trochlear n., (CN IV) Depresses, abducts, medial to optic canal; the posterior quadrant and medially rotates tendon redirected to of eyeball eyeball (intorsion) eyeball via fibrocartilaginous loop (‘pulley’) on frontal bone Inferior oblique Medial floor of orbit Inferolateral part of Oculomotor n. (CN III) Elevates, abducts, and (lateral to nasolacrimal the posterior quadrant – inferior branch laterally rotates groove) of eyeball eyeball (extorsion) Extraocular Muscles and Their Actions Single actions: MR: Adducts LR: Abducts Multiple actions: SO: Depress, Abduct, Intort SR: Elevate, Adduct, Intort IR: Depress, Adduct, Extort IO: Elevate, Abduct, Extort Extraocular Muscles – striated muscle Includes: • Levator palpebrae superioris • 4 recti (superior, medial, lateral, inferior) – attach to common ring tendon • 2 obliques (superior, inferior) LPS - antagonist to orbicularis oculi Levator palpebrae superioris Superior rectus Medial rectus Lateral rectus Superior oblique Inferior rectus Inferior oblique Eyeball occupies anterior ½ of orbit. Actions of Extraocular Muscles Individual actions LR and MR muscles have singular, pure actions; of eye muscles abduction and adduction, respectively. They produce no torsion of the eyeball. Elevates Elevates Abducts Adducts All other muscles move the eyeball simultaneously on Extorts Intorts more than one axis and produce torsion. The key to understanding the functions of eye muscles is to realize that no muscle will be recruited in isolation if its action will produce torsion of the eyeball. It will only be enabled to move the eyeball when its torsion effect is negated (e.g., by first moving the eyeball appropriately). Depresses Depresses Abducts Adducts Direct upward gaze in the primary position of the Intorts Extorts eyeball requires synergism of the SR and IO muscles. Their opposite torsion effects cancel out. Direct downward gaze in the primary position of the eyeball requires synergism of the IR and SO muscles. Their opposite torsion effects cancel out. Clinical Testing of Extraocular Muscles and Nerves Therefore, to isolate the function of and to test the extraocular muscles and their nerve supply, a physician must first ask the patient to move their eyes outward or inward on the horizontal plane to bring the axis of the eyeball into alignment with the long axis of the muscles being tested. Right eyeball Intraocular Muscles Smooth muscle of the eyeball contained within: • Iris: Dilator pupillae and sphincter pupillae - control pupillary diameter • Ciliary body: Ciliary muscle – controls thickness of lens for Pupil accommodation/near vision Iris Ciliary muscle Lens Dilator pupillae Sympathetic innervation Zonular fibers (Suspensory ligament of the lens) Normal Sphincter pupillae Parasympathetic innervation Cranial nerve palsies Impairments of extraocular muscle(s) may cause the visual axis of one eye to deviate from its normal position. This produces a “double image” called diplopia. Right abducens nerve lesion • Right LR is disabled. Affected eye is adducted due to unopposed pull by MR Cranial nerve palsies Right trochlear nerve lesion • SO is disabled. Affected eye is directed medially and superiorly Cranial nerve palsies Right oculomotor nerve lesion • SR, IR, MR, and IO are disabled • Eyeball is abducted and depressed due to unopposed actions of LR and SO • There is complete ptosis of upper eyelid (loss of LPS) • The pupil is dilated and unreactive to light due to unopposed action of dilator pupillae Nerves of the Orbit Special Sensory: General Somatic Sensory: Frontal nerve (Special Somatic Afferent, SSA): Optic nerve, CN II - Vision Lacrimal nerve Motor: Nasociliary nerve Oculomotor nerve Trochlear nerve Abducens nerve Nerves of the Orbit Nerve Functional Fiber Type(s) Function/Targets Optic n., CN II Special Somatic Afferent Vision • Develops as a tract of the forebrain • Surrounded by meninges Oculomotor n., CN III General Somatic Efferent Motor to: LPS, SR – Superior division MR, IR, IO – Inferior division General Visceral Efferent Preganglionic PS fibers to ciliary ganglion via inferior division Postganglionic PS fibers via short ciliary nn to: sphincter pupillae m. (smooth muscle in iris) and ciliary muscle (smooth muscle of accommodation for near vision) Trochlear n., CN IV General Somatic Efferent Motor to: • Smallest CN Superior oblique m. (whose tendon passes through a pulley or • Has longest intracranial course ‘trochlea’) • Only CN to arise from posterior surface of brainstem Nerves of the Orbit Nerve Functional Fiber Type(s) Function/Targets Ophthalmic n., CN V1 General Somatic Afferent Sensory to/via: Lacrimal n. – lacrimal gland and skin of upper, lateral eyelid; receives communicating branch from zygomatic branch of CN V2 consisting of postganglionic PS secretomotor fibers to lacrimal gland Frontal n. – divides into supraorbital branch (skin of upper eyelid, forehead, and anterior scalp) and supratrochlear branch (skin of forehead in midline) Nasociliary n. – supplies branches to eyeball and cornea, sphenoid and ethmoidal sinuses, and parts of nasal cavity, skin of dorsum of nose Abducens, CN VI General Somatic Efferent Motor to: Lateral rectus (the muscle that abducts the eyeball) Nerves and Vessels Passing Through the Common Ring Tendon • Optic nerve • Ophthalmic artery • Oculomotor n., superior and inferior divisions • Abducens nerve • Nasociliary nerve Lacrimal n. Ophthalmic veins Frontal n. Trochlear n. out Sensory branches of Ophthalmic Nerve; ‘NFL’ brs Lacrimal nerve • Courses along upper border of lateral rectus to the lacrimal gland and lateral part of upper eyelid • Receives a communicating branch from the zygomatic nerve conveying postganglionic parasympathetic fibers to the gland Lacrimal nerve View you will see in dissection. Sensory branches of Ophthalmic Nerve; ‘NFL’ brs Frontal nerve • Courses anteriorly superficial to the LPS muscle just deep to the periorbita • Divides into: o Supraorbital n. – to skin of upper eyelid, forehead, anterior scalp, and mucosal lining of frontal sinus o Supratrochlear n. – to skin of upper eyelid and portion of midline of forehead View you will see in dissection. Sensory branches of Ophthalmic Nerve; ‘NFL’ brs Frontal nerve • Courses anteriorly superficial to the LPS muscle just deep to the periorbita • Divides into: o Supraorbital n. – to skin of upper eyelid, forehead, anterior scalp, and mucosal lining of frontal sinus o Supratrochlear n. – to skin of upper eyelid and portion of midline of forehead View you will see in dissection. Sensory branches of Ophthalmic Nerve; ‘NFL’ brs Nasociliary nerve • Courses superior to the optic nerve (below SR) • In a lateral to medial direction. Gives rise to: o Long ciliary nerves to eyeball and cornea; contain postganglionic sympathetic fibers to dilator pupillae muscle o Sensory root to ciliary ganglion o Anterior ethmoidal n. – to ethmoidal air cells, nasal cavity, dorsum of nose to tip o Posterior ethmoidal n. – to ethmoidal air cells and sphenoid sinus o Infratrochlear n.
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