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Nuero sheet # 13 (9-5-2011)
We will talk about cranial nerves : #2 , #3, #4, #6
Optic nerve
-2ed cranial nerve
-Purely sensory
-type of fiber ( SSA- special sesory afferent )
but olfactory nerve ( SVA )
-start at optic disc as converge of ganglion cells axons till
optic chiasm – it’s also called optic tract because it’s all lie
inside the brain –
- It’s myelinated and the sheath formed by oligodendrocytes
-exit from the orbit through optic canal.
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*layers of retina in general:
1- Photoreceptors layer (cones & rods)
2-layer of bipolar cells.
3-retinal cells – ganglion cells –
((The axons of retinal cells converge to give optic nerve
which exit through optic canal from optic disc ))
Optic disc : found 3-4 mm nasal to mid line at post part
of orbit .
 in the optic canal , nerve’s sheath surrounded by 4
muscles of recti
 Superior rectus firmly adherent to the optic nerve
sheath .
 Optic nerve perforated by central retinal artery .
optic chiasm
-at the junction of ant wall and floor of 3ed ventricle
- crossroad .
- flat & quadrangular in shape .
- Optic nerves make partial decussating at it .
Ant-lat to it there are2 optic nerves,, post-lat to it there
are 2 optic tracts .
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According to vision retina is divided to :
 nasal part “ medial “
 temporal part “ lateral “
the nasal part make decussating at the optic chiasm
…..I.e. the optic tract at one side made by the temporal
pat at same side and nasal part of the other side
e.g. : left optic tract made by left temporal part anode
right nasal part .
optic tract
start from the optic chiasm and terminate in the lateral
geniculate bodies – at the thalamus –
ipslateral temporal condorateral nasal
make relay :
1- mainly at lateral geniculate bodies “ LGB “ to
continue the path way .
2- some in the superior colliculus for reflexes .
** LGB :
 oval structure at post termination of optic tract ,
found in the thalamus
 Consist of 6 layers of gray matter alternate with white
matter and optic nerve make synapse between these
6 layers .
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( remember ALL sensory tract make relay in the
thalamus EXCEPT olfactory nerve )
 2ed order neuron
After that it continue to optic radiation then to primary
visual area .
optic nerve …> optic chiasm ….. > optic tract ……>
LGB ……> optic radiation ……> primary visual cortex
~ primary visual cortex ( area 17 ) found above and
below calcarine sulcus – y shaped sulcus at medial aspect
of cortex –
~ Association area ( 18 ,19 ) explains and makes
memories about what you see .
** binuclear vision …> by 2 eyes
*** what you see by your right eye goes to your left side
of cortex and via verse .
Images at the cortex are inverted .. how it’s modified ??
… it’s still not well understood mechanism .
The pupillary light reflex is a reflex that controls the
diameter of the pupil, in response to the intensity of light
that falls on the retina of the eye, thereby assisting in
adaptation to various levels of darkness and light,
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The optic nerve, or more precisely, the photosensitive ganglion
cells , is responsible for the afferent limb of the pupillary reflex
- it senses the incoming light. The oculomotor nerve is
responsible for the efferent limb of the pupillary reflex - it
drives the muscles that constrict the pupil
Optic nerve make relay in pretectal nucleus ( at
superior colliculus - in the mid brian - )
Then pre-synapse fibers make another relay – synapse –
in edinger -westphal nucleus
** edinger-westphal nucleus : is Para-sympathetic
nucleus of occlumotor nerve , supplying muscles of iris .
Then Pre-gangelionic fibers make a relay in cillary
nucleus .
Post-ganglionic fibers then innervate via occluomotor
nerve cillary muscles
** Post-ganglionc fibers lie between optic nerve and
latral rectus .
The pupillary reflex pathway begins with the photosensitive retinal
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ganglion cells, which convey information to the optic nerve (via the optic
disc). The optic nerve connects to the pretectal nucleus of the upper
midbrain, bypassing the lateral geniculate nucleus and the primary visual
cortex.
From the pretectal nucleus, axons connect to neurons in the EdingerWestphal nucleus, whose axons run along both the left and right
oculomotor nerves.
Oculomotor nerve axons synapse on ciliary ganglion neurons
The eye which is hit directily with light make diect reflex and
Neuron
#4 innervates
the reflex
constrictor
muscle
of the
the other
eye indirect
“ just
names
“ iris
Oculomotor nerve
 3ed cranial nerve
 Start from mid-brain and enter the orbit through
superior fissure
 Purely MOTOR
 Kind of fibers -> GSE “ general somatic efferent “ to
the extra ocular muscles ( 5 in # )
->GVB “ general visceral efferent “
PARASYMPATHETIC to ciliary muscles & pupil constrictor
muscle
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It has 2 nuclei :
 motor : MAJOR ,, give GSE
_ located at the level of superior colliculs of mid-brain ,, ant
to cerebral aqueduct ,, post to MLF _ it’s fibers exit from ant
part of interpedincular fossa,, middle side of cris cerebria
 Edinger-westphal – parasympathetic - ,, give GVE
ooclumotor nerve then enter cavernous sinus “ Latraly “ ,,
then enter the orbit through superior fissure
 cortex affect this nerve by corticobulbar tract (
cortico nucluer )
 also from superior colliculus affected by tectbulbar
– give info about vision –
 MLF: connect between nerves that affect the
movement of eye muscles ( #3, #4 , #6 , #8 ).
****** This is also true for nerves : #4 , #6 , #8
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Main action of the fiber depend on functional
component of the fiber: 1- GSE




Superior recti …> elevation .
Medial rectus …> medial “ adduction “
Inferior rectus …..> depression .
Inferior oplique …> upward and medial .
2-GVE
 Levator palpebrae superiors muscle ..> elevate
upper eyelid
 Sphincter of pupil …..> constriction of the pupil (
part of direct and indirect reflex ).
 Cilliary muscles ….> “ accommodation “ (part of
direct and indirect reflex ) .
Injures
o The muscles supplied by this nerve will not
function
( loss elevation, depression ,, etc )
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so eye moves laterally at rest – because lateral muscle
innervated by abducent nerve – “ external strabismus “
….> external because medial rectus doesn’t function ,, so
the eye goes latrely
“ But when abducent nerve is injuered called …>
internal strabismus ,, the eye goes medialy . “
o Dropping of upper eye lied “ ptosis “
o Their will be no reflex to light and the pupils will
be dilated .
Troclear nerve :
 Purely motor ,,, most cylindrical .
 Exit from the posterior aspect of mid-brain at the level
of inferior colliculus
 It’s the only cranial nerve that exit from posterior
aspect
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 It’s nucleus located anterior to cerebral aqudect then
it’s fibers make duccasation – posteriorly – ( fibers
from left side come from right nerve and vea verse )
 Enter the orbit through superior optic fissure
 Cortex have affect on this nerve through cortico-bulbar
tract
 superior colliculus affected by tectobulbar .
 and through MLF bounded to cranial nerves >> #3, #6 ,
#8 .
>> this nerve inervate …> superior oblique muscle - SO4which depress the eye latraly .
Abducent nerve:
 Cranial nerve #6
 Exit from pons ,, located beneath the facial nucleus
 Enter the eye through superior optic fissure
 Affected by : tectobulbur ,, cortico bulbur ,, MLF _ as
mentioned earlier -
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Function … > abduction of the eye through lateral rectus >>>
as its name imply
Injury of this nerve …. > inernal strabismus means that the
eye moves medially
Introduction of trigeminal nerve :
Largest nerve
 Mixed …. Sensory part and motor part .
 4 Nuclei :
> main sensory nucleus: as a continuation of spinal
nucleus … found laterally to motor nucleus inside the pons .
> motor nucleus . at level of pons medially to sensory
>>> spinal nucleus . as a continuation of stantia gelatinosa of
spinal cord from the lower part of pons through the medulla
till C2
>>> mesencephalic nucleus .
Written by : Eman Z Al Nsour .
Dedicated to : Reem Nsour ,, Abeer Yassin ,,
Ghidaa M3ani ,, Afaf 7adad …… =D