NEUROANATOMY - Nerves Flashcards
How long is each optic nerve segment?
1. intraocular
2. orbital
3. intracanalicular
4. intracranial
- 1mm (1squared)
- 25mm (5 squared)
- 6-9mm (3 squared)
- 16mm (4squared)
Which nerve is not covered by the neurilemma? What is this nerve covered by?
optic nerve, covered by the meninges
What is the average diameter of the optic nerve head? What happens at level of the sclera?
1.5mm. At the level of sclera it doubles to 3mm as there is now myelination of the fibres
What are the 4 subregions of the intraocular part of the optic nerve? What is their blood supply?
- Surface nerve fibre layer - nerve fibres (95%) plus astrocytes (5%)
–> branches of central retinal artery - Prelaminar region: higher number of astrocytes and neurons
–> short posterior ciliary artery - Laminar region : passing through lamina cribrosa through fenestrations
–> short posterior ciliary artery + arterial circle of zinn - Retrolaminar region: astrocytes decrease and oligodendrocytes increase to form myelin
–> pile plexus (centripetal branches) + centrifugal branches
When does the central retinal artery and vein enter the intraorbital part of the nerve?
About 10mm from the eyeball and passes inferomedially.
Where is the internal carotid artery in relation to the intracranial part of the optic nerve
Runs inferiorly and laterally to the optic nerve
What is the blood supply of the surface nerve fibre layer region of the optic nerve?
branches of CRA.
What is the ocular blood supply of the prelaminar region of intraocular part of optic nerve?
short posterior ciliary artery
What is the ocular blood supply for the laminar region of the intraocular part of the optic nerve?
Laminar region : passing through lamina cribrosa through fenestrations
–> short posterior ciliary artery + arterial circle of zinn
What is the ocular blood supply for the retrolaminar region of the optic nerve?
pile plexus (centripetal branches) + centrifugal branches
How thick are the optic nerve fibres?
2-10 microns
What is the route of the optic nerve?
Intraocular part passes through sclera and passes through lamina cribrosa, chorod and appears inside as the optic disc.
What is the average diameter of the optic nerve head? Why does it expand behind the sclera?
1.5mm, 3mm behind sclera due to presence of oligodendrocytes (which form myelin)
What is the route of the intraorbital part of the optic nerve?
extends from back of eyeball to the optic foramina. Sinous path (curved) to allow extraocular movement.
At what point does the central retinal artery enter the intraorbital part of the optic nerve and where does it pass in relation to optic nerve?
10mm posterior to eyeball. Passes inferomedially to nerve.
What are the structures that pass between optic nerve and lateral rectus muscle? (5)
- Ciliary Ganglion
- superior/inferior divisions of CN3
- Nasociliary nerve
- Sympathetic nerve
- CN6
What are the close relations of the intracanalicular part of optic nerve?
- ophthalmic artery
- sphenoid and ethmoid sinus
- thin bony lamina separates sinus from intracanalicular part
What is are the two routes of the optic nerve after the optic chiasm?
optic tracts —-> lateral geniculate body —-> optic radiation —> terminate at Brodmann area 17 of visual cortex
some fibres bypass LGB and terminate in either:
1) pretectal nucleus (pupillary light reflex)
2) superior colliculus (regulaton of saccadic eye movements)
What are the layers of optic radiations?
1, 4, 6 - contralateral fibres synapse
2, 3, 5 - ipsilateral fibres synapse
Where is the ciliary ganglion situated?
Between optic nerve and lateral rectus muscle.
Name the structures.
What are the 3 roots of the ciliary ganglion?
- Sensory
- Sympathetic
- Parasympathetic
What is the sympathetic pathway of the sympathetic root of ciliary ganglion?
PRE-GANGLIONIC:
1. Hypothalamus
2. Sympaethtic root (ciliospinal of budge)
3. Superior cervical ganglion
POST-GANGLIONIC:
1. pleuxs around ICA
2. sympathetic root –> short ciliary nerve (autoregulation of vascular tone of eye)
3. nasociliary nerve –> long ciliary nerve –> dilator pupillae –> DILATION.
What is the sensory route of the ciliary ganglion?
Trigeminal ganglion (PONS) –> ophthalmic division (V1) –> nasociliary nerve
Nasociliary nerve –> long ciliary nerve
–> sensory route through ciliary ganglion –> short ciliary nerve
SAME FUNCTION --> carry pain touch and temperature sensations of the eye
What is the parasympathetic route of the ciliary ganglion?
edinger westphal nucleus (subnucleus of CNIII in midbrain) –> travel superificially in ocularmotor nerve –> inferior division of CNIII –> relay in ciliary ganglion —> short ciliary nerve –>
—> SPHINCTER PUPILLAE - constriction
—> CILIARY MUSCLE - accomodation for near task
WHat is the afferent limb of the oculocardiac reflex?
stretch receptors in ocular tissues –> short/long ciliary nerve –> ciliary ganglion (no synapse) –> V1 –> trigeminal ganglion –> trigeminal nucleus –> CNS.
What is the efferent limb of the oculocardiac reflex?
internuerons between trigeminal sensory nucleus and visceral motor nucleus of vagus nerve –> myocardium to synapse –> sinoatrial node –> vagal motor response (bradycardia).
What is the route of the abducents nerve from its nucleus to its nnervation? (CN6)
NUCLEUS:
medial to the facial nerve nucleus.
pure motor nucleus to the lateral rectus muscle.
1) the nerve leaves the brainstem at the junction of the pons and medulla and enters the subarchnoid space.
2) It runs upward in the subarachnoid space between the pons and the clivus, and then pierces the dura mater to run between the dura and the skull through Dorello’s canal.
3) At the tip of the petrous temporal bone it makes a sharp turn forward to enter the cavernous sinus. In the cavernous sinus it runs alongside just lateral to the internal carotid artery.
4) It then enters the orbit through the superior orbital fissure and innervates the lateral rectus muscle of the eye.
