Anatomy of 3rd cranial nerve by faslu muhammed

1. ANATOMY
OF
THIRD CRANIAL NERVE
OPTOM FASLU MUHAMMED

2. The cranial nerves 12 in number. Are part of the peripheral nervous
system. The craniocaudal sequence of cranial nerves is as follows
• 1- Olfactory
• 2- Optic
• 3- Oculomotor
• 4- Trochlear
• 5- Trigeminal
• 6- Abducent
• 7- Facial
• 8- Vestibulocochlear
• 9- Glossopharyngeal
• 10- Vagus
• 11- Accessory
• 12- Hypoglossal
 All exit the cranial cavity through foramina or fissures. All originate from
the brain. Contain sensory, motor or both components

4. 1- MOTOR (EFFERENT) PARTS OF
CRANIAL NERVES:
• Arise within brain from group of nerve cells, which
constitute their nuclei of origin.
• They are connected with cerebral cortex by
corticonuclear fibres, these arise from cells of
motor areas of the cortex, descend chiefly in
genicular part of internal capsule to brainstem,
where many but not all cross the median plane and
end by arborizing round nuclei of origin of motor
cranial nerves.

5. 2- SENSORY (AFFERENT) CRANIAL
NERVES:
•Arise from nerve cells outside brain, these nerve cells may be
grouped to form ganglia on trunks of the nerves, or
may be situated in peripheral sensory organs such as the nose, eye
& ear.
•The centrally directed processes of the cells run into brain &
there end by arborizing around nerve cells, which are grouped to
form their nuclei of termination.
• Fibres arise from cells of these nuclei and, usually after crossing
to opposite side, run up to connect the nuclei indirectly with
cerebral cortex.

6. The nuclei of the
cranial nerves. The
sensory nuclei are
illustrated on the
left, and the motor
nuclei
on the right.

7. Dorsal aspect of brain stem showing locations
of Afferent cranial N. nuclei (left) , and
Efferent cranial N.nuclei (right) , in which the
same colours have a common embryological

9. • Third cranial nerve.
• It is the largest of the ocular motor nerves.
• It contains some 15,000 axons, including motor fibers and
parasympathetic motor fibers.
• Entirely motor in function.
• Supplies LPS and all extra ocular muscles except lateral
rectus and superior oblique.
• Also supplies the intraocular muscles namely sphincter
pupillae and ciliary muscle

12. FUNCTIONAL COMPONENTS
• Somatic efferent component is concerned with the
movements of the eyeball – motor supply to muscles
derived from head myotomes-LPS, SR,MR,IR and IO.
• General visceral efferent (parasympathetic) component
of the nerve is meant for accommodation and
contraction of the pupil – motor supply to ciliaris and
sphincter pupillae.
• General somatic afferant component of the nerve is
associated with proprioceptive impulses from the
extraocular muscles supplied by the somatic efferent
component of this nerve.

13. OCULOMOTOR NUCLEAR COMPLEX
• Located in midbrain at the level of superior colliculus, in the
ventromedial part of the central grey matter that surrounds the
cerebral aqueduct.

14. • It is a longitudinal column of about 10mm length.
 RELATIONS:
• Dorsomedial: central grey zone surrounding
aqueduct.
• Ventrolateral: medial longitudinal bundle.
• Superior: approaches floor of third ventricle.
• Inferior: continuous with trochlear nucleus

17. • The nucleus of the third cranial nerve is located in
the inferior periaqueductal gray matter of the
mesencephalon.
• It is a complex of both paired and midline motor
cells.
• These cells are found from the posterior
commissure superiorly to the pontomesencephalic
junction caudally in the dorsal midbrain.

18. • Classically, this complex has been described with four
paired subnuclei supplying innervation to the inferior,
medial, and superior rectus muscles and to the
inferior oblique muscle.
• There is a single caudal, dorsal midline nucleus
providing innervation to the levator muscle.
• Innervation of the extraocular muscle from the paired
nuclei is ipsilateral for the inferior and medial rectus
muscles and the inferior oblique muscle.
• However, innervation of the superior rectus is
contralateral.
• The motor fibers to the superior rectus decussate
within the third nerve nucleus and join the fascicle of
the contralateral oculomotor nerve.

20. • In addition to the extraocular muscle motor
fibers, the Edinger-Westphal nuclei supply the
parasympathetic preganglionic neurons that
project to the ciliary ganglion.
• These nuclei are positioned dorsal and medial to
the muscle motor nuclei.
• They are composed of two cell groups, a medial
unpaired column and a lateral paired column.
• All evidence suggests that these fibers project
ipsilaterally.

22. OCULOMOTOR NERVE NUCLEI:
Include two motor nuclei:
Main Motor Nucleus:
 Site : ventral part of central grey matter "surrounding the
cerebral aqueduct", of midbrain, at the level ofsuperior
colliculus, close to median plane.
 Supply : all extrinsic muscles of the eye except superior
oblique & lateral rectus. The levator palpebrae superioris
muscles of both sides are supplied by single central group
of cells "central caudal nucleus". The superior rectus
muscle is supplied by contralateral oculomotor nucleus.
The remaining muscles are innervated by ipsilateral
oculomotor nucleus.

23. • It is composed of subnuclei supplying individual
extraocular muscles as follows :
1. Dorsolateral Nucleus : Ipsilateral Inferior Rectus
2. Intermedial Nucleus : Ipsilateral Inferior Oblique
3. Ventromedial Nucleus : Ipsilateral Medial Rectus
4. Paramedial (Scattered) Nucleus : Contralateral Superior
Rectus
5. Caudal Central Nucleus : Bilateral Levator Palpebrae
Superioris

24. Warwick's arrangement of the III cranial
nerve subnuclei, illustrating the pattern of
motor cells in the brain stem that sends
fibers to each of the extraocular muscles
in the oculomotor nuclei

27.  Accessory parasympathetic (EDINGERWESTPHAL) nucleus:
 Site : it lies dorsal to the main motor nucleus.
 Supply : the axons, which are preganglionic accompany other
oculomotor fibres to relay within ciliary ganglion in orbit and
supply sphincter pupillae & ciliary muscles via short ciliary
nerves.
 It consists of a median and two lateral components.
 Perhaps, the cranial half of the nucleus is concerned with light
reflexes and the caudal half with accommodation.
 The median part is fork-shaped (Nucleus Of Perlia) and its role
in convergence is questionable.

29. FASCICLE
• The fascicular portion of the oculomotor nerve descends as its
moves ventrally and laterally through the mesencephalon.
• The fascicles pass through the medial longitudinal fasciculus,
the red nucleus, and the medial portion of the cerebral
peduncle.
• During the passage through the ventral midbrain, there
appears to be topographic organization of the fascicles so that
a divisional paresis is possible even with intrinsic lesions.
• The oculomotor nerve exits the brain stem into the
interpeduncular fossa as a horizontal arrangement of multiple
fiber bundles that rapidly coalesce to form the subarachnoid
portion of the third cranial nerve.

30. Cross-sections of the brain stem. (A) Through superior colliculus, showing
cranial nerve III nuclei with intramedullary fibers.

31. CONNECTIONS
1. Cerebral cortex
• Motor cortex (precentral gyrus) of both sides
through corticonuclear tracts.
• Visual cortex through the superior colliculus and
the tactobulbar tract.
• Frontal eye field.
2. Nuclei of 4th, 6th and 8th cranial nerves through the
medial longitudinal bundle.
3. Pretectal nucleus of both sides (for light reflex)
4. Vertical and torsional gaze centers through the
medial longitudinal bundle.
5. Cerebellum through the vestibular nuclei.

32. DEEP ORIGIN :
• The oculomotor fibres run forwards from nuclear complex
passing through MLF, tegmentum, red nucleus & medial part of
substantia nigra, forming series of curves with lateral convexity.
• They emerge from sulcus oculomotorius on medial side of
cerebral peduncle.

33.  SUPERFICIAL ORIGIN:
• The nerve emerges as 10-15 rootlets at sulcus oculomotorius close to
upper border of pons, near termination of basilar artery.
• As it emerges from brain it is invested by piamater & lies in the
subarachnoid space.
• It passes between superior cerebellar & posterior cerebral arteries.
• Between the two nerves is the posterior perforated substance (fig. N4).

34. COURSE
AND
DISTRIBUTION

35. Fascicular
Basilar
Intracavernous
Intraorbital

36. The Fascicular part :
• Fasciculus consists of efferent fibres which pass
from the third nerve nucleus through the red
nucleus and the medial aspect of the cerebral
peduncle
• They then emerge from the midbrain and pass
into the interpedencular space

39. Oculomotor nerve. Axial oblique 0.8-mm-thick SSFP MR image shows the
nerve (small arrows) where it emerges from the interpeduncular cistern
(large arrow), which lies medial to the cerebellar peduncle (p).

40. The Basilar part :
• Starts as a series of 15-20 rootlets in the interpeduncular
fossa.
• These coalase to form a large medial and a small lateral
root, which unite to form a flattened nerve, which gets
twisted bringing the inferior fibres superiorly and superior
fibers inferiorly; and thus the nerve becomes a rounded
cord.
• The nerve then passes b/w the posterior cerebral artery and
the superior cerebellar artery and runs forward in the
interpeduncular cistern ( running lateral to & parallel with
the posterior communicating artery) to reach the
cavernous sinus.

42. Major blood vessels
and their relationships
to the ocular motor
nerves. Note the
passage of CN III
between the superior
cerebellar artery below
and posterior cerebral
artery above. The
vascular supply to CN
III comes from
branches off
the posterior
communicating artery,
which is in close
proximity.

43. Oculomotor nerve. Coronal 0.8-mm-thick SSFP MR image shows the oculomotor
nerve (white arrow) in cross section between the posterior cerebral artery (white
arrowhead) and the superior cerebellar artery (black arrowhead), which are distal
branches of the basilar artery (black arrow).

44. The Intracavernous part :
• The nerve enters the cavernous sinus by piercing the posterior
part of its roof on the lateral side of the posterior clinoid process.
• It then descends to the lateral wall of the sinus, where it lies
above the trochlear nerve.
• In the anterior part of the cavernous sinus, the nerve divides into
superior and inferior divisions which enter the orbit through the
middle part of the superior orbital fissure within the annulus of
Zinn.
• In the fissure, the nasociliary nerve lies in b/w the two divisions,
while the abducent nerve lies inferolateral to them.

46. lntracavernous course of the ocular motor nerves. CN IIIand CN IV run in the
lateral wall of the cavernous sinus along with CN V divisions VI and v2. CN VI runs in close
approximation to the carotid artery within the cavernous sinus itself. As the nerves course
toward the anterior aspect of the cavernous sinus and the superior orbital fissure, V1
(ophthalmic) divides into 3 branches: the lacrimal, fron tal, and nasociliary nerves. The
lacrimal and frontal nerves cross over the top of CN III and CN IV. CN III divides into
superior and infe rior divisions, which cross under CN IV to enter the orbital apex through
the annulus of Zinn.

49. The Intraorbital part :
• In the orbit, the smaller superior division ascends on
the lateral side of optic nerve & supplies the superior
rectus and the LPS .
• The larger, inferior division divides into three
branches :
1. Nerve To The Medial Rectus passes inferior to the
optic nerve.
2. Nerve To Inferior Rectus passes downward and
enters the muscle on its upper aspect, and
3. Nerve To Inferior Oblique (longest of the three
branches) passes in b/w the IR & LR and supplies the
IO from its posterior border. It gives off the motor
root to the ciliary ganglion.

53. CILIARY GANGLION
• Description : Peripheral parasympathetic ganglion
and its constituent cells are multipolar.
• Size : Small, about the size of pins head.
• Shape & color : Flat & reddish-grey.
• Site : Near orbital apex in some loose fat between
optic nerve & lateral rectus, lying usually on lateral
side of ophthalmic artery.

54.  Roots : recieves posteriorly three roots or
rami
Parasympathetic
(motor) root
Sympathetic
root
Sensory root

56. Parasympathetic (Motor) Root:
• Carries preganglionic parasympathetic fibres
which arise from cells of Edinger-Westphal
nucleus and run through oculomotor nerve &
its branch to inferior oblique to reach the
ganglion.
• These fibres are relayed in the ganglion and
postganglionic fibres travel in the short ciliary
nerves.

58. Sympathetic Root :
• Is branch from internal carotid plexus which enter
the orbit through SOF and reach the ganglion by
either: (a) joining it directly,
(b) joining the sensory root, or
(c) travel via ophthalmic nerve
& its nasociliary branch.
• It consists of postganglionic fibres from the SCO
which traverse the ciliary ganglion without relayto
emerge through short ciliaries.

59. Sensory Root :
• contains sensory fibres from the eyeball, which
reach the ganglia via short ciliary nerves and
pass through it without interruption.
• It leaves the ganglion backwards to join
nasociliary nerve near the point where that
nerve enters the orbit.

61. Branches:
• These are the short ciliary nerves, 8-10 delicate
filaments which emerge from the ganglion.
• They run forwards in wavy course in company with
short ciliary arteries, above and below the optic
nerve.
• They subdivide into 15-20 branches which pierce
sclera around optic nerve and pass forwards in
delicate grooves on inner surface of sclera.

62. • They carry:
1. Parasympathetic fibres: supply sphincter pupillae &
ciliary muscles (more than 95% of these fibres are
distributed to ciliary muscle which is much larger in
volume).
2. Sympathetic fibres: distributed to blood vessels of
eyeball and may include the fibres which supply the
dilator pupillae when these fibres do not follow their
usual course in the ophthalmic, nasociliary and long
ciliary nerves.
3. Sensory fibres: supply cornea, iris & choroid.

63. BLOOD SUPPLY
• The blood supply to the medial aspect of the brainstem is from
vessels directly off the Basilar artery.
• Small perforators off circumflex arteries (posterior cerebral,
superior cerebellar artery) may also supply the fascicular portion of
the third nerve as it courses through the ventral midbrain.
• The vascular supply of 3rd nerve in subarachnoid space is via
vascular twigs from the post. Cerebral A., the sup. Cerebellar A.,
and the tentorial and dorsal meningeal branches of the
meningohypophyseal trunk of the ICA.
• In the cavernous sinus, the tentorial, dorsal meningeal, and inferior
hypophyseal branches of the meningohypophyseal trunk supply the
nerve along with branches from the ophthalmic artery.

64. • All nerves are supplied with blood from adjacent vessels, which are usually small and
variable.
• Such a nutrient artery divides into ascending and descending branches which
anastomose in the epineurium with similar branches from others.
• From these epineural vessels fine branches penetrate into the perineurium, with
further anastomoses, and their terminal arterioles enter fasciculi to form rich
longitudinal capillary plexuses along the full length of the nerve.
• These are reinforced by other nutrient arteries, but no part of the intrafascicular
plexus is dominated by any one artery.
• The blood supply of the oculomotor, trochlear and abducent nerves is similarly
arranged, the nutrient arteries being derived from any adjacent smaller arteries.
• Though not often noted, it is obvious that deprivation of this blood supply by spasm,
thrombosis or embolism may produce paralysis or paresis of the muscles supplied.

66. CLINICALLY APPLIED
ASPECTS

67. ANATOMICAL BASIS OF CLINICAL
FEATURES OF THIRD NERVE PALSY
• A complete & a total third nerve palsy is of
common occurrence.
• May be congenital or acquired.
• Clinical features of complete third nerve palsy
include :

68. (b) complete left ptosis;
(a)after manual elevation of
upper left eyelid, we can
observe left exotropia and
hypotropia, and mid-dilated
pupil.

69. 1. Ptosis - paralysis of LPS muscle.
2. Deviation – out, down and intorted – unopposed action of
LR and SO.
3. Ocular movements :
• Adduction – MR
• Elevation – SR and IO
• Depression – IR
• Extorsion – IR and IO
4. Pupil is fixed and dilated – paralysis of sphincter pupillae
muscle.
5. Accommodation is completely lost – paralysis of ciliary
muscle.

73. 6. Crossed diplopia – paralytic divergent squint.
7. Head posture – if the pupillary area is
uncovered, head takes a posture consistent
with the directions of actions of the paralysed
muscles, i.e., head is turned on the opposite
side, tilted towards the same side and chin is
slightly raised.

74. FEATURES AND CAUSES OF THIRD
NERVE LESIONS AT VARIOUS LEVELS
1. Supranuclear lesions
• Lesions of the cerebral cortex and
supranuclear pathway produce conjugate
paresis which affect both eyes equally.
• In supranuclear lesions although position and
movements of the eyes are abnormal, they
maintain their relative co-ordination and
produce no diplopia

75. 2. Nuclear lesions
• Lesions involving purely the third nerve nucleus are
relatively uncommon.
• Common causes include ; vascular diseases,
demyelination, primary tumors and metastasis
• Lesions involving entire nucleus cause an ipsilateral third
nerve palsy with ipsilateral sparing and contralateral
weakness of elevation.
• Lesions involving paired medial rectus subnuclei
(ventromedial nucleus) cause a wall-eyed bilateral
internuclear ophthalmoplegia ( WEBINO ) characterised
by defective convergence and adduction

76. 3. Fascicular lesions
• Causes are similar to nuclear lesions.
Benedikt syndrome involves the fasciculus as it passes
through the red nucleus and is characterised by ipsilateral 3rd
nerve palsy and contralateral extrapyramidal signs such as
hemitremor.
Weber syndrome involves the fasciculus as it passes through
the cerebral peduncle and is characterised by ipsilateral 3rd
nerve palsy and contralateral hemiparesis.
Nothangel syndrome involves the fasciculus and the superior
cerebellar peduncle and is characterised by ipsilateral 3rd
nerve palsy and cerebellar ataxia.
Claude syndrome is a combination of Benedikt and Nothangel
syndromes

77. Lesion in cerebral peduncle , Weber Syndrome (B)
Lesion in red nucleus , Benedikt Syndrome (C)

79. 4. Lesions involving basilar part of the nerve
• As the nerve runs in the subarachnoid space at the base
of skull unaccompanied by any other cranial nerve,
isolated third nerve palsies are frequently basilar.
• Causes :
1. Aneurysms at the posterior communicating artery
cause isolated third nerve palsy with involvement of
pupil.
2. Extradural hematomas which may cause tentorial
pressure cone with downward herniation of the
temporal lobe. This compresses the third nerve as it
passes over the tentorial edge. Initially there occurs
fixed, dilated pupil, which is followed by a total third
nerve palsy.
3. Diabetes causes isolated 3rd nerve palsy with sparing
of the pupillary reflexes.

84. 5. Lesions involving intracavernous part of the nerve
• Because of its close proximity to other cranial
nerves, intracavernous 3rd nerve palsies are
usually assoc. with inv. of the 4th and 6th nerves,
and the 1st division of trigeminal nerve.
• In intracavernous 3rd nerve palsy, pupil is
spared. Sometimes, pupil may be constricted
owing to inv of sympathetics.

85. • Causes :
1. Diabetes may cause vascular palsy.
2. Pituitary apoplexy – may cause a third nerve
palsy as a result of hemorrhagic infarction of a
pituitary adenoma (after child birth), with
lateral extension into cavernous sinus.
3. Intracavernous lesions – aneurysms,
meningiomas, carotid-cavernous fistulae and
Tolosa-Hunt syndrome (granulomatous
inflammation)

86. 6. Lesions of the intraorbital part of the nerve
• May cause isolated extraocular muscle palsies
or may involve either superior division or
inferior division or both.
• Causes : orbital tumors, pseudotumors, trauma
and vascular diseases.

87. 7. Lesions of pupillomotor fibres
• B/w the brainstem and the cavernous sinus,
pupillomotor fibres are located superficially in
the superior median quadrant of the nerve.
• They derive the blood supply from the pial
blood vessels whereas the main trunk of the 3rd
nerve is supplied by vasa nervorum.

89. • Surgical lesions such as aneurysms, trauma and
uncal herniation characteristically inv the pupil
by compressing the pial blood vessels and the
superficially located pupillary fibres.
• Medical lesions such as diabetes and
hypertension usually spare the pupil. This is
because the microangiopathy assoc. with these
diseases involves the vasa nervorum, causing
infarction of the main trunk, but sparing the
superficial pupillary fibres.

90. CAUSES OF ISOLATED THIRD
NERVE PALSY
1. Idiopathic - In about 25% cases
2. Vascular diseases – diabetes and HTN, is the most
common cause of pupil-sparing 3rd nerve palsy. In
most cases spontaneous recovery occurs within 3
months. Diabetic 3rd nerve palsy is often assoc.
with periorbital pain and may occasionally be the
presenting feature of diabetes. The presence of
pain is therefore not helpful in differentiating b/w
aneurysmal and diabetic 3rd nerve palsy.

91. 3. Aneurysm of the PCA at its jn with the ICA is
very imp cause of isolated painful 3rd nerve
palsy with involvement of pupil.
4. Trauma, both direct and secondary to subdural
hematoma with uncal herniation, is also a
common cause.
5. Miscellaneous. Other rare causes include
tumors, vasculitis assoc. with collagen vascular
disorders, syphilis and Tb.

92. THANK YOU ..