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PART ONE REVISION. > NEUROANATOMY - Nerves > Flashcards

NEUROANATOMY - Nerves Flashcards

1
Q

How long is each optic nerve segment?
1. intraocular
2. orbital
3. intracanalicular
4. intracranial

A
  1. 1mm (1squared)
  2. 25mm (5 squared)
  3. 6-9mm (3 squared)
  4. 16mm (4squared)
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2
Q

Which nerve is not covered by the neurilemma? What is this nerve covered by?

A

optic nerve, covered by the meninges

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3
Q

What is the average diameter of the optic nerve head? What happens at level of the sclera?

A

1.5mm. At the level of sclera it doubles to 3mm as there is now myelination of the fibres

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4
Q

What are the 4 subregions of the intraocular part of the optic nerve? What is their blood supply?

A
  1. Surface nerve fibre layer - nerve fibres (95%) plus astrocytes (5%)
    –> branches of central retinal artery
  2. Prelaminar region: higher number of astrocytes and neurons
    –> short posterior ciliary artery
  3. Laminar region : passing through lamina cribrosa through fenestrations
    –> short posterior ciliary artery + arterial circle of zinn
  4. Retrolaminar region: astrocytes decrease and oligodendrocytes increase to form myelin
    –> pile plexus (centripetal branches) + centrifugal branches
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5
Q

When does the central retinal artery and vein enter the intraorbital part of the nerve?

A

About 10mm from the eyeball and passes inferomedially.

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6
Q

Where is the internal carotid artery in relation to the intracranial part of the optic nerve

A

Runs inferiorly and laterally to the optic nerve

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7
Q

What is the blood supply of the surface nerve fibre layer region of the optic nerve?

A

branches of CRA.

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8
Q

What is the ocular blood supply of the prelaminar region of intraocular part of optic nerve?

A

short posterior ciliary artery

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9
Q

What is the ocular blood supply for the laminar region of the intraocular part of the optic nerve?

A

Laminar region : passing through lamina cribrosa through fenestrations
–> short posterior ciliary artery + arterial circle of zinn

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10
Q

What is the ocular blood supply for the retrolaminar region of the optic nerve?

A

pile plexus (centripetal branches) + centrifugal branches

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11
Q

How thick are the optic nerve fibres?

A

2-10 microns

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12
Q

What is the route of the optic nerve?

A

Intraocular part passes through sclera and passes through lamina cribrosa, chorod and appears inside as the optic disc.

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13
Q

What is the average diameter of the optic nerve head? Why does it expand behind the sclera?

A

1.5mm, 3mm behind sclera due to presence of oligodendrocytes (which form myelin)

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14
Q

What is the route of the intraorbital part of the optic nerve?

A

extends from back of eyeball to the optic foramina. Sinous path (curved) to allow extraocular movement.

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15
Q

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?

A

10mm posterior to eyeball. Passes inferomedially to nerve.

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16
Q

What are the structures that pass between optic nerve and lateral rectus muscle? (5)

A
  1. Ciliary Ganglion
  2. superior/inferior divisions of CN3
  3. Nasociliary nerve
  4. Sympathetic nerve
  5. CN6
17
Q

What are the close relations of the intracanalicular part of optic nerve?

A
  1. ophthalmic artery
  2. sphenoid and ethmoid sinus
  3. thin bony lamina separates sinus from intracanalicular part
18
Q

Where does the larger lateral root of the optic tract terminate?

Where does the smaller medial root of the optic tract terminate?

A

lateral root: LGN
medial root: subcortical targets (1) superior colliculus, (2) pretectal nucleus (3) suprachiasmatic nucleus (4) pulvinar nucleus (5) parvocellular reticular formation (6)

19
Q

In the intracranial part of the optic nerve, what are its relations to the..
1) internal carotid artery
2) ophthalmic artery
3) anterior cerebral artery

A

1) ICA - medial
2) ophthalmic artery - superomedial
3) anterior cerebral artery - inferior

20
Q

What is are the two routes of the optic nerve after the optic chiasm?

A

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)

21
Q

What are the layers of optic radiations?

A

1, 4, 6 - contralateral fibres synapse
2, 3, 5 - ipsilateral fibres synapse

22
Q

Where is the ciliary ganglion situated?

A

Between optic nerve and lateral rectus muscle.

23
Q

Name the structures.

A
24
Q

What are the 3 roots of the ciliary ganglion?

A
  1. Sensory
  2. Sympathetic
  3. Parasympathetic
25
Q

is the ciliary ganglion a sympathetic or parasympathetic ganglion?

A

parasympathetic - only parasympathetic fibres SYNAPSE in the ganglion.

26
Q

What is the sympathetic pathway of the sympathetic root of ciliary ganglion?

A

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.

27
Q

What is the sensory route of the ciliary ganglion?

A

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
28
Q

What is the parasympathetic route of the ciliary ganglion?

A

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

29
Q

What is the function of the parasympathetic pathway from ciliary ganglion?

A
  1. sphincter pupillae - pupil constriction
  2. ciliary muscle - accomodation
30
Q

What happens when ciliary ganglion is affected?

A

Causes adie-tonic pupil –> slow constriction to pupil to light reflex but good reaction to accomodation.

sympathetic function is preserved as long ciliary nerve bypasses ciliary ganglion

31
Q

What is the oculocardiac reflex?

A

Trigemino-vagal reflex causes reduction in HR by > 20% following globe pressure or traction of extraocular muscle

32
Q

WHat is the afferent limb of the oculocardiac reflex?

A

stretch receptors in ocular tissues –> short/long ciliary nerve –> ciliary ganglion (no synapse) –> V1 –> trigeminal ganglion –> trigeminal nucleus –> CNS.

33
Q

What is the efferent limb of the oculocardiac reflex?

A

internuerons between trigeminal sensory nucleus and visceral motor nucleus of vagus nerve –> myocardium to synapse –> sinoatrial node –> vagal motor response (bradycardia).

PART ONE REVISION. (84 decks)

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