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Lec 22- Optic Nerve
Question | Answer |
---|---|
The optic nerve is a collection of what that exits the eye? | axons of the retinal ganglion cells |
Where does the optic nerve exit the eye? | through the lamina cribrosa within the posterior scleral foramen |
Approx. how many axons make up the optic nerve? | 1.2 million |
What structure of what bone does the optic nerve after it passes through the orbit? | the optic canal of the lesser wing of the sphenoid bone |
What is the optic nerve referred to after it passes the optic canal? | intracranial portion |
What does the optic nerve merge with afte rit passes the optic canal? | the optic chiasm |
Ganglion cells within the optic nerve are enveloped by what? | myelin sheath |
Where is myelin sheath derived from? | oligodendrocytes |
Axons of the retina ganglion cells within the eye are unmyelinated. What structure must it pass to acquire myelin sheath? | lamina cribrosa |
What 3 meningeal sheaths surround the optic nerve? | tough dura mater (outermost), delicate arachnoid (intermediate), and vascular pia (innerpost) |
Where do the 3 meningeal sheaths fuse at? | the sclera |
What is the subarachnoid space? | the space b/w the arachnoid membrane and pia mater |
What happens to the subarachnoid space when ICP increases? | the cerebrospinal fluid in the subarachnoid space will exert pressure on the nerve |
Why does the lamina cribrosa give a convex appearance? | this is due to the cerebrospinal fluid that places pressure on the nerve |
What happens if ICP increases too much? | It will compress the central retina; venous engorgement; papilledema |
What 4 divisions can the optic nerve be divided into? | intraocular portion, intraorbital portion, intracanalicular portion, intracranial portion |
What structures does the intraocular portion include? | the optic disc and the portion of the nerve that lies within the sclera |
Clinically, what is the prelaminar zone of the optic nerve referred to as? | the optic disc |
What is the shallow depression that is observed within the disc known as? | the optic cup |
The optic cup is lined by a glial plaque known as? | tissue of Kuhnt or meniscus of Kuhnt |
What is the Bergmeister's papilla? | an over-esaggerated tissue of Kuhnt |
What is the meniscus of Kuhnt continuous with? | the inner limiting membrane of Elschnig |
Both the meniscus of Kuhnt and the inner limiting membrane of Elschnig are composed of what neuroglial cell? | astrocytes |
What is the vascularized region b/w the optic cup and the outermost edge of the optic disc? | the rum of the optic disc |
What envelopes the nerve fiber bundles in the intraorbitral portion? | septa that is formed from pial sheath |
The length of the intraorbital portion of the optic nerve is 6mm longer than the distance b/w the posterior surface of the eye and the optic canal. How is this advantageous to the eye? | it gives the eye greater movement |
what surrounds the intraorbital portion of the optic nerve? | orbital fat |
what is embedded in orbital fat? | ciliary vessels and nerves |
What 2 structures does the parasympathetic ciliary ganglion lie between? | the lateral border of the optic nerve and the lateral rectus muscle |
Arterial supply of the optic nerve is supplied from? | short posterior ciliary arteries |
some of the short posterior ciliary arteries will enter the sclera and form an anastomotic arterial circle with what? | the circle of zinn-haller |
vessels from the zinn-haller will supply what? | most of the capillaries lying within the lamina cribrosa and the pial vasculature |
describe the capillaries in the optic nerve? | they are nonfenestrated and have zonula occludens |
what nourishes the prelaminar portion of the optic disc? | retinal capillaries |
what supplies blood to the intraorbital portion of the nerve? | branches of the pial plexus (it extends into the nerve via pial septa) |
what supplies the pial plexus with blood? | branches of the ophthalmic artery |
the pial plexus supplies what structures with blood? | the intracanalicular and intracranial portion of the optic nerve |
venous drainage of the optic nerve is through the? | central retinal vein |