3. Cranial Nerves
Kiran Suwal
6/12/2016 3
• Cranial nerves are the nerves that emerge directly from the brain (including the brainstem),
in contrast to spinal nerves (which emerge from segments of the spinal cord).
• There are 12 pairs of cranial nerves emerging directly from the brain.
• Cranial Nerves may be sensory, motor or both and somatic or parasympathetic, or have
mixed functions.
4. Oculomotor Nerves
Kiran Suwal
6/12/2016 4
• The oculomotor nerve is the third cranial nerve.
• It offers motor and parasympathetic innervation to many of the ocular structures.
• It is distributed to the extraocular as well as the intraocular muscles.
• Medical Definition of oculomotor nerve : either nerve of the third pair of
cranial nerves that are motor nerves with some associated autonomic fibers, arise
from the midbrain, supply muscles of the eye except the superior oblique and the
lateral rectus with motor fibers, and supply the ciliary body and iris with autonomic
fibers by way of the ciliary ganglion—called also third cranial nerve
6. Origin of Oculomotor
Nerves
Kiran Suwal
6/12/2016 6
• The oculomotor nerve originates from the anterior aspect of the midbrain.
• The oculomotor nerve originates from 2 nuclei in the midbrain;
• Occulomotor nucleus
• Accessory parasympathetic nucleus.
7. Insertion of Oculomotor Nerves
• The oculomotor nerve exits the brainstem near midline at the
base of midbrain just caudal to the mammillary bodies.
• It passes through the cavernous sinus and proceeds through
the supraorbital fissure to reach the orbit of the eye.
8. Course of Oculomotor
Nerves
Kiran Suwal
6/12/2016 8
• It moves anteriorly, passing below the posterior cerebral artery, and above the
superior cerebellar artery.
• The nerve pierces the dura mater and enters the lateral aspects of the cavernous
sinus.
• Within the cavernous sinus, it receives sympathetic branches from the internal
carotid plexus.
• The nerve leaves the cranial cavity via the superior orbital fissure.
• At this point, it divides into superior and inferior branches.
9. Course of Oculomotor Nerves
Kiran Suwal
6/12/2016 9
• 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.
• 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.
11. Functions of Oculomotor
Nerves
Kiran Suwal
6/12/2016 11
• General somatic efferent, for movements of the eyeball.
• All movements except lateral and down-and-out movements.
• General visceral efferent or parasympathetic, for contraction of pupil and
accommodation.
• General somatic afferent column carries proprioceptive fibers from the
extraocular muscles to mesencephalic nucleus of V
.
12. Clinical Test of Oculomotor
Nerves
Kiran Suwal
6/12/2016 12
• Cranial nerves III, IV, and VI are usually tested together as part of
the cranial nerve examination.
• Oculomotor nerves can be tested by following two ways:
Eye muscles
Pupillary reflexes
14. Clinical Significance of
Oculomotor Nerves
Kiran Suwal
6/12/2016 14
• Complete and total paralysis of the third nerve results in:
Ptosis, i.e. Drooping of the upper eyelid(due to
paralysis of voluntry levator pallpeberis superiorus)
Lateral squint(due to paralysis of medial rectud and
inferior oblique)
Dilatation of the pupil(paralysis of parasympathetic
fibers of sphinctr pupillae)
Loss of accommodation(due to paralysis of ciliaris
muscle)
16. Clinical significance of ocumulator
nerve
Slight proptosis, i.e. Forward projection of the eye
Diplopia or double vision.
Pupillary light reflects absent in affected aye due to damage of shincter pupillae.
Pupil dilates and become fixed to light.
