A to Z on third cranial nerve ( Oculomotor nerve)

2. 1
2
3
3rd
Nerve
PRESENTATION CONTENT
•Origin &
Insertion
•Relation with eye
•Important supply

3. Embryology
• By the fourth week of development , nuclei
of all cranial nerves are present.
• Parasympathetic (visceral efferent) ganglia
and somatic efferent nuclei are derived
from neural crest cells.

5. Introduction
• 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.

8. 1 2 3 5
FASCICULUS
NUCLEAR COMPLEX BASILAR
INTRACAVERNOUS
PATHWAY OF OCULAR MOTOR NERVE
4
ORBITAL

9. Main parts of the Brain

11. 1. Nucleus and cisternal portion
ORIGIN :
The oculomotor nerve originates from the upper part of
the midbrain/Mesencephalon.
The oculomotor nucleus lies in the deep periaqueductal
grey matter at the level of the superior colliculus anterior
to the cerebral aqueduct.
It is a longitudinal column of about 10mm length.
Two Nucleus :
Oculomotor Nucleus
» somatic motor fibers (general somatic
efferents)
Edinger-Westphal nuclei
» visceral motor fibers (general visceral
efferent)

13. 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 of
superior 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.

14. • 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.

16. • 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

17. From To
Uncrossed
fibers
ipsilateral
oculomotor
nucleus
Medial rectus.
Inferior rectus.
Inferior oblique.
Crossed
fibers
Contralateral
oculomotor
nucleus
Superior rectus.
uncrossed
fibers
oculomotor
nuclei
Levator palpebrae
superioris muscle.
Uncrossed
para-
sympathetic
fibers
Ipsilateral
Edinger
Westphal
nucleus
Constrictor pupliae
muscle.
Ciliary muscle.

19.  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.

20. • In addition to the extraocular muscle motor
fibers, the Edinger-Westphal nuclei supply
the parasympathetic preganglionic neurons
that project to the ciliary ganglion.
• All evidence suggests that these fibers
project ipsilaterally.

21. Oculomotor
Nerve
Somato motor
Four extraocular
muscle
Superior Rectus
Inferior Rectus
Medial Rectus
Inferior Oblique
Levator palpebral
superiosis
Edinger-Westphal
(visceral motor)
constrictor
pupillae
Ciliary muscles
IMPORTANT SUPPLY TO THE EYE

23. 2. FASCICULUS:
The fibers run through the tegmentum, red
nucleus and medial aspect of the
substantia nigra to emerge from the medial
aspect of the cerebral peduncle.
Emerge from the midbrain and pass into
interpeduncular space

24. Mid Brain/ Mesencephalon
Periequedoctor grey
matter

26. 2. The Basilar part :
• Starts as a series of 15-20 rootlets in the
interpeduncular fossa.
• These rapidly 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 below the posterior cerebral
artery, and above the superior cerebellar artery and
running lateral to & parallel with the posterior
communicating artery to reach the cavernous sinus.

29. * Starts Upper part of the mid brain

30. 3. Cavernous sinus part:
• It moves anteriorly, passing the nerve pierces
the dura mater. and enters the lateral aspect of
the cavernous sinus superiorly.
• Within the cavernous sinus, it receives sympathetic
branches from the internal carotid plexus.
• These fibres do not combine with the oculomotor
nerve – they merely travel within its sheath.
• In the anterior part of cavernous sinus, the nerve
divides into superior and inferior branches which
enters the orbit through SOF within the annulus of
zinn.

35. 4. Orbital part:
• The nerve enters the orbit through the
superior orbital fissure in the common
tendinous ring which were already divided
into two branches; one superior and one
inferior.

36. a. Superior branch: Motor innervation to the superior
rectus and levator palpabrae superioris. Sympathetic
fibres run with the superior branch to innervate the
superior tarsal muscle.
b.Inferior branch: Motor innervation to the inferior
rectus, medial rectus and inferior oblique.
Parasympathetic fibres to the ciliary ganglion, which
ultimately innervates the sphincter pupillae and ciliary
muscles.
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.

37. Superior Orbital Fissure

40. 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.

42. • They carry:
Parasympathetic fibres: supply sphincter
pupillae & ciliary muscles (more than 95% of
these fibres are distributed to ciliary muscle
which is much larger in volume).

43. BLOOD SUPPLY

44. • All nerves are supplied with blood from adjacent vessels, which are
usually small and variable.
• 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 Internal Carotid Artery.
• 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.

45. • 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.

46. Small arteries
supply blood
→peripheral
nervous system

47. CLINICALLY
APPLIED
ASPECTS

48. 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 :

49. 1. Ptosis - paralysis of LPS muscle.
2. Deviation – out, down and intorted – unopposed
action of LR and SO.
4. Pupil is fixed and dilated – paralysis of sphincter
pupillae muscle.
5. Accommodation is completely lost – paralysis of
ciliary muscle.

54. 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.

55. FEATURES AND CAUSES OF THIRD
NERVE LESIONS AT VARIOUS LEVELS
1. Nuclear lesions
• Lesions involving purely the third nerve nucleus are relatively
uncommon.
• Common causes include ; vascular diseases, demyelination,
primary tumors and metastasis
• Lesions involving 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.

56. 2. 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.
Nothnagel 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
Nothnagel syndromes

58. COMMON CAUSES OF NUCLEAR AND
FASICULAR THIRD CRANIAL NERVE
CHILDREN
Congenital
- with neurological abnormalities
- with aberrant rennervation
- with cyclic oculomotor spasm
Vascular ( AV
malformations )
Primary tumour
Metastatic tumour
YOUNG
ADULTS
Demyelinating
Vascular
(hemorrhage or
infarction)
Tumor
OLDER
ADULTS
Vascular
(infarction)
Tumour

59. 3. Lesions involving basilar part of the
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. Head trauma: 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.

63. 4. Lesions involving intracavernous part
of the nerve:
• Because of its close proximity to other
cranial nerves, intracavernous 3rd nerve
palsies are usually associated with
involvement of the 4th and 6th nerves, and
the 1st division of trigeminal nerve.

64. • Important Causes :
1. Diabetes may cause vascular palsy.
2. Pituitary apoplexy – may cause a third
nerve palsy (after child birth), if the gland
swells laterally & extension into cavernous
sinus.
3. Intracavernous lesions – aneurysms,
meningiomas, carotid-cavernous fistulae
and Tolosa-Hunt syndrome
(granulomatous inflammation)

65. 5. 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, trauma and
vascular diseases.

66. 6. 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.

68. • Surgical lesions such as aneurysms,
trauma and uncal herniation
characteristically involve 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 associated
with these diseases involves the vasa
nervorum, causing infarction of the main
trunk, but sparing the superficial pupillary
fibres.

69. In ISOLATED THIRD NERVE PALSY 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.

71. Multiple
choice
Questions

72. 1. Which of the following statements regarding the origin and course
of III is/are correct except?
a) It emerges as a number of rootlets from a nucleus lying level with the superior
colliculus
b) It leaves the brainstem after passing through the red nucleus
c) It runs below and lateral to the free margin of the tentorium cerebelli
d) It pierces the dura midway between the anterior and posterior clinoid processes
e) Its branches cross the same part of the superior orbital fissure as VI
2. A patient suffers damage to the orbit in a road traffic incident
resulting in damage to the third cranial nerve. Which of the
following signs will be present?
a) Pupillary constriction and a medial strabismus
b) Pupillary dilatation and a medial strabismus
c) Pupillary constriction and a lateral strabismus
d) Pupillary dilatation and a lateral strabismus

73. 3. Regarding the distribution of fibres from III
a) Levator palpebrae superioris only receives a motor supply from the superior
division of III
b) It innervates all the muscles at the junction of their middle and posterior thirds
c) The parasympathetic supply to the iris is conveyed via the short ciliary nerves
d) Superior rectus is innervated ipsilaterally
e) Levator palpebrae superioris contralaterally represented at the level of the
oculomotor nuclei
4. Which of the following statements regarding III is correct?
a) The parasympathetic fibres lie centrally in the precavernous sinus portion of the
nerve
b) A third nerve palsy causes the eye down and out.
c) Accommodation is unaffected by such a palsy
d) Compression of the nerve causes a partial ptosis
e) The Edinger-Westphal nucleus lies ventral to the main oculomotor nucleus

74. 5. All of the following are characteristics of oculomotor nerve except:
a) Carries parasympathetic nerve fibers
b) Supplies inferior oblique muscle
c) Enters orbit through the inferior orbital fissure
d) Causes constriction of pupil
6. The following structure(s) synpase(s) in the ciliary ganglion:
a) Nasociliary nerve fibres
b) Parasympathetic nerve fibres from oculomotor nerve
c) Sympathetic nerve fibres from the carotid plexus
d) Parasympathetic nerve fibres form the facial nerve abducent nerve fibres.

75. Thank You