Orbit.txt

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emm64
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115781
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Orbit.txt
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2011-11-15 11:19:32
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Orbit HN
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Orbit HN
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  1. orbit description
    • conical cavities which contain the eyeballs and their associated structures.
    • shaped somewhat like a 4-sided pyramid.
    • The bony orbit is described as having a roof, floor, medial & lateral walls, an apex, and a base.
    • It also has two fissures, one canal, and one fossa.
    • A. Roof – sphenoid (lesser wing) & frontal (orbital plate)
    • B. Floor – zygomatic & maxilla (orbital plate)
    • C. Medial Wall – lacrimal, ethmoid, palatine, maxilla
    • D. Lateral Wall – sphenoid (greater wing) & zygomatic
    • E. Fissures, Canals, Grooves, Fossae
    • 1. superior orbital fissure-(CN III, IV, V1, VI, ophthalmic veins)
    • 2. inferior orbital fissure-(infraorbital nerve)
    • 3. infraorbital groove-(infraorbital nerve)
    • 4. optic canal-(CN II, ophthalmic a.)
    • 5. lacrimal fossa- (lacrimal sac)
    • F. Apex – optic canal
    • G. Base – orbital margin
  2. pupil
    • dark area in the center of the eye that is formed by the surrounding iris (colored part of the eye).
    • seen through the transparent cornea
  3. iris
    • contractile diaphragm.
    • seen through the transparent cornea
  4. sclera
    white of the eye is the “sclera”.
  5. bulbar conjunctiva
    transparent layer of tissue that covers sclera & cornea
  6. palpebral conjunctiva
    • inside of the eyelids are covered by a transparent but vascular tissue called the “palpebral conjunctiva.”
    • continuous with the bulbar conjunctiva that covers the sclera.
  7. superior & inferior fornix
    points of reflection of the palpebral and bulbar conjunctiva
  8. plica semilunaris
    medial fold of conjunctiva.
  9. 5 Layers of the Eyelid (from Superficial to Deep):
    • 1. skin
    • 2. subcutaneous layer
    • 3. muscle layer (levator palpebrae, orbicularis oculi)
    • 4. tarsofascial layer (tarsal plates and glands)
    • a. tarsal plates (superior & inferior) – dense connective tissue
    • b. tarsal glands – produce oily substance that prevents eyelids from sticking together
    • 5. conjunctival layer – consists of the palpebral conjunctiva
  10. Lacrimal Apparatus:
    • A. Lacrimal lake - is an area at the medial angle of the eye that serves as a small reservoir of tears.
    • B. Lacrimal caruncle - is a mound of modified skin tissue.
    • C. Lacrimal papillae - are small elevations that accommodate the lacrimal puncta.
    • D. Lacrimal puncta - are openings that allow for tear drainage.
    • E. Lacrimal canaliculi – are “little canals” that lead from the puncta to the lacrimal sac.
    • F. Lacrimal sac – collects tears and leads them into the nasolacrimal duct.
    • G. Nasolacrimal duct – is a passage way that extends from the sac to the nasolacrimal opening in the lateral nasal wall of the inferior meatus in the nasal cavity.
  11. Muscles of the Orbit
    • move the eyeball in general
    • striated, skeletal muscles that DO NOT develop from the branchial arches of the embryo – instead, they develop from “somite-like” structures (thus, they receive SE fibers).
    • These muscles include: levator palpebrae, superior rectus, medial rectus, lateral rectus, inferior rectus, superior oblique and inferior oblique.
    • Most of these muscles are innervated by CN III, except the superior oblique (CN IV) and lateral rectus (CN VI).
  12. eyeball elevators
    • occurs around the horizontal axis (medial-lateral axis)
    • inferior oblique
    • superior rectus
  13. eyeball depressors
    • occurs around the horizontal axis (medial-lateral axis)
    • - superior oblique
    • - inferior rectus
  14. eyeball adductors
    • occurs around the vertical axis (superior-inferior axis)
    • - medial rectus
    • - inferior rectus
    • - superior rectus
  15. eyeball medial rotators
    • occurs around an anterior-posterior axis-
    • superior oblique
    • superior rectus
  16. eyeball abductors
    • occurs around the vertical axis (superior-inferior axis)
    • - lateral rectus
    • - superior oblique
    • - inferior oblique
  17. eyeball lateral rotators
    • occurs around an anterior-posterior axis
    • - inferior oblique
    • - inferior rectus
  18. annulus tendineus
    all the rectus muscles attach proximally to the annulus tendineus (a common tendinous ring).
  19. levator palpebrae superioris
    • unusual muscle. It has a striated, skeletal part (which is innervated by CN III, SE fibers).
    • ut it also has a smooth muscle part called “the superior tarsal muscle” – which is innervated by symp/post fibers and functions during the flight or fight response to widen the eyelids.
  20. Vessels of the Orbit
    • arteries are branches of the ophthalmic artery.
    • The ophthalmic artery is the only branch of the internal carotid artery.
    • After the ophthalmic artery enters the orbit through the optic canal (along with the optic nerve), it gives rise to a number of branches: the central a. of the retina, lacrimal a., posterior ciliary as., supraorbital a., posterior & anterior ethmoidal as., and supratrochlear a.
    • These arteries have corresponding veins. These veins, along with the inferior opthalmic vein, then drain into the superior ophthalmic vein.
  21. Ophthalmic Artery Branches
    • 1. Central Artery of the Retina – pierces the meninges of CN II and travels in the middle of CN II to the retina.
    • 2. Lacrimal Artery – to lacrimal gland and lateral eyelids
    • 3. (Short and Long) Posterior Ciliary Arteries – to back of eyeball
    • 4. Supraorbital Artery – to superior face and scalp
    • 5. Posterior Ethmoid Artery – to posterior ethmoidal air cell
    • 6. Anterior Ethmoid Artery – to anterior ethmoidal air cell
    • 7. Dorsal Nasal Artery – one of the two terminal branches of the ophthalmic a.; goes to lacrimal sac and dorsum of nose
    • 8. Supratrochlear Artery – one of the two terminal branches of the ophthalmic a.; goes
    • to skin and muscles of forehead
  22. Veins of the Orbit
    • The superior & inferior ophthalmic veins are the main veins of the orbit.
    • The superior ophthalmic vein receives tributaries (little veins) which correspond to the branches of the ophthalmic artery.
    • The inferior ophthalmic vein usually drains into the superior ophthalmic vein.
  23. Nerves of the Orbit
    • CN II, III, IV, V1, and VI and/or their branches.
    • CN II enters the orbit through the optic canal (along with the ophthalmic a.). It carries special sense (SS) fibers for vision.
    • CN III, IV, V1, and VI enter the orbit through the superior orbital fissure.
    • CN III carries VE-para/pre fibers to the ciliary ganglion and SA and SE fibers to all the muscles of the eyeball except for superior oblique (CN IV) and lateral rectus (CN VI).
    • CN V1 will divide into various sensory (SA) branches to supply the face and mucosa of the ethmoidal air cells.
  24. CN II (optic n.)
    • enters the orbit via the optic canal (along with the ophthalmic artery).
    • It carries special sensory (SS) fibers for vision.
    • The optic nerve is like an extension of the brain and is covered by the same 3 meninges.
  25. CN III (oculomotor n.)
    • enters the orbit via the superior orbital fissure (along with the CN IV, V1, and VI).
    • It will innervate most of the ocular muscles (except the superior oblique and lateral rectus).
    • It carries SA & SE fibers.
    • It also carries VE-para/pre fibers to the ciliary ganglion.
    • As CN III enters the orbit, it divides into a superior division and inferior division.
    • Each division will innervate certain muscles (SA & SE).
    • The VE-para/pre fibers of CN III will follow the inferior division to the ciliary ganglion.
  26. CN IV (trochlear n.)
    • enters the orbit via the superior orbital fissure and innervates a single muscle in the orbit – the superior oblique.
    • It carries SA & SE fibers.
  27. CN V1
    • enters the orbit via the superior orbital fissure and divides into 3 major branches: the frontal nerve, lacrimal nerve, and nasociliary nerve.
    • The frontal nerve then divides into the supraorbital and supratrochlear nerves.
    • CN V1 branches are all sensory (SA) nerves. The SA cell bodies are in the trigeminal ganglion.
    • The nasociliary nerve courses from lateral to medial over the optic nerve and gives rise to the long ciliary ns., posterior & anterior ethmoidal nerves, then changes names to become the infratrochlear n. All these branches are sensory (SA). (Note: the anterior ethmoidal n. gives rise to the external nasal n.).
    • The nasociliary nerve also has a connection to the ciliary ganglion (forming its sensory root).
  28. Summary of V1 Branches:
    • Lacrimal Nerve
    • Frontal Nerve
    • -Supraorbital N.
    • -Supratrochlear N.
    • Nasociliary Nerve
    • -Long Ciliary Nerves
    • -Posterior Ethmoidal N.
    • -Anterior Ethmoidal N.
    • -Infratrochlear N.
    • -Sensory Root to Ciliary Ganglion
  29. CN VI (abducens n.)
    enters the orbit via the superior orbital fissure and innervates a single muscle in the orbit – the lateral rectus. It carries SA & SE fibers.
  30. Ciliary Ganglion Symp
  31. Ciliary Ganglion
    • located in the orbit between the optic nerve and lateral rectus
    • B. has 3 roots: motor (VE-para/pre), sympathetic (VE-symp/post), and general sensory (SA)
    • 1. motor root – para/pre fibers from CN III (inferior division)
    • 2. sympathetic root – symp/post fibers from superior cervical ganglion via carotid plexus which follow the ophthalmic artery into the orbit
    • 3. sensory root – SA fibers (from the eyeball) which join the nasociliary nerve (br of V1)
    • C. branches: the short ciliary nerves (from the ganglion to the back of the eyeball) carry VE-para/post fibers, symp/post fibers, and general sensory (SA) fibers
    • 1. para/post fibers innervate the sphincter pupillae and ciliary body muscles.
    • a. sphincter pupillae constricts to allow less light in parasymp response
    • b. ciliary body muscles focus the lens
    • 2. symp/post fibers in the short ciliary nerves innervate blood vessels of the eye
    • 3. general sensory fibers (SA) bring info from eyeball to CNS – SA cell bodies are in the trigeminal ganglion.
    • D. The symp/post fibers to the dilator pupillae (which opens the pupil) do not course through the ciliary ganglion. They take a different pathway. They jump off the ophthalmic artery to the nasociliary nerve and then to the long ciliary nerves – which take them to the eyeball and then they course to the dilator pupillae m.
  32. Ciliary Ganglion roots:
    • motor (VE-para/pre), sympathetic (VE-symp/post), and general sensory (SA)
    • 1. motor root – para/pre fibers from CN III (inferior division)
    • 2. sympathetic root – symp/post fibers from superior cervical ganglion via carotid plexus which follow the ophthalmic artery into the orbit
    • 3. sensory root – SA fibers (from the eyeball) which join the nasociliary nerve (br of V1)
  33. Ciliary Ganglion branches
    • the short ciliary nerves (from the ganglion to the back of the eyeball) carry VE-para/post fibers, symp/post fibers, and general sensory (SA) fibers
    • 1. para/post fibers innervate the sphincter pupillae and ciliary body muscles.
    • a. sphincter pupillae constricts to allow less light in parasymp response
    • b. ciliary body muscles focus the lens
    • 2. symp/post fibers in the short ciliary nerves innervate blood vessels of the eye
    • 3. general sensory fibers (SA) bring info from eyeball to CNS – SA cell bodies are in the trigeminal ganglion.
    • D. The symp/post fibers to the dilator pupillae (which opens the pupil) do not course through the ciliary ganglion. They take a different pathway. They jump off the ophthalmic artery to the nasociliary nerve and then to the long ciliary nerves – which take them to the eyeball and then they course to the dilator pupillae m.
  34. Levator Palpebrae Superioris
    • origin: lesser wing of sphenoid
    • insert: upper eyelid
    • nerve: CN III (superior division); superior tarsal muscle is innervated by VE-symp/post fibers
    • action: elevates upper eyelid
  35. Superior Oblique
    • origin: body of sphenoid
    • insert: tendon passes through trochlea & inserts on superior sclera deep to superior rectus
    • nerve: CN IV (trochlear nerve)
    • action: abducts, depresses, & medially rotates eyeball
  36. Inferior Oblique
    • origin: anteromedial floor of orbit
    • insert: sclera inferior to lateral rectus
    • nerve: CN III (inferior division)
    • action: abducts, elevates, & laterally rotates eyeball
  37. Superior Rectus
    • origin: anulus tendineus (common tendinous ring)
    • insert: superior sclera
    • nerve: CN III (superior division)
    • action: elevates, adducts, & medially rotates eyeball
  38. Medial Rectus
    • origin: anulus tendineus (common tendinous ring)
    • insert: medial sclera
    • nerve: CN III (inferior division)
    • action: adducts eyeball
  39. Lateral Rectus
    • origin: anulus tendineus (common tendinous ring)
    • insert: lateral sclera
    • nerve: CN VI (abducens)
    • action: abducts eyeball
  40. Inferior Rectus
    • origin: anulus tendineus (common tendinous ring)
    • insert:inferior sclera
    • nerve: CN III (inferior division)
    • action:depresses, adducts, & laterally rotates eyeball
  41. Lacrimal Gland
    • produces lacrimal fluid (tears)
    • innervated by VE-para/post fibers from the pterygopalatine ganglion.
    • These fibers leave the ganglion, hitchhike along V2 and then the zygomatico-temporal nerve which sends a branch to join the lacrimal nerve at its half-way point.
    • Then they follow the lacrimal nerve to the lacrimal gland.
    • Then, the nerve continues on to the face to provide sensory (SA) innervation.

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