Lec 5: Nerves that Move the Eye CN III, CN IV & CN VI

lateral rectus action?

abducts eye

medial rectus action?

adducts eye

superior rectus action?

elevates eye

inferior rectus action?

depresses eye 

inferior oblique action?

elevation, abduction and extorsion

superior oblique action?

depression, abduction & intorsion

what is visual pathway:

Retina – Optic Nerve – Optic Chiasm – Optic Tract – LGN – Optic Radiations – Primary Visual Cortex – Parietal/Temporal

what is pupillary light reflex path":

Retina – Optic Nerve – Optic Chiasm – Optic tract – Superior Colliculus (pretectal
nucleus) – Bilateral Edinger-Westphal Nucleus – CN III, Parasym – Sphincter Pupillae muscle

what is under focusing for close vision?

• Pupillary Constriction – parasympathetic (Edinger-Westphal Nucleus)

• Accommodation for Near Vision – parasympathetic (Edinger-Westphal Nucleus)

• convergence of eyes

what is Pupillary Constriction?

• parasympathetic (Edinger-Westphal Nucleus)

• By contracting the Sphincter Pupillae muscles

what is Accommodation for Near Vision?

• parasympathetic (Edinger-Westphal Nucleus)

• By contracting the Ciliary muscles

what is convergence of eyes?

Activates both Medial Rectus muscles

• __ receives signals directly from the retina

• __ controls the following (mostly) reflexive actions

  • Head alignment

  • Pupillary Diameter

  • Accommodation for Near Vision

Superior Colliculus

what is horner syndrome?

damage to the pathway of sympathetic signals to the eye
• Ptosis, miosis & Anhidrosis

• Connects to the Oculomotor Nucleus (and E-W nucleus) in the Midbrain

  • Edinger-Westphal Nucleus

    • Parasympathetic Nucleus for Pupillary Constriction & Accommodation

  • Trochlear and Abducens Nuclei are in the Pons

Oculomotor Nerve

Oculomotor Nerve sends motor signals to the:

• Sends motor signals to the:

• Medial rectus, Inferior rectus, Superior rectus & Inferior Oblique

• Ciliary Muscles – Parasym. Accommodation

• Sphincter Pupillae Muscle – Parasym. Constrict Pupil

• Levator Palpebrae Superioris

what is levator palpebrae superioris?

• Palpebra = Eyelid; Superioris = Upper
• Raises upper eyelid

• Levator Palpebrae Superioris Nucleus

• Superior Rectus Nucleus

• Medial Rectus, Inferior Rectus, and Inferior Oblique Nuclei

Oculomotor Nuclei of the Midbrain

what is levator palpebrae superioris nucleus

• sends fibers to both eyes
• facilitating bilateral eye opening

what is superior rectus nucleus?

sends information to the contralateral side

what is Medial Rectus, Inferior Rectus, and Inferior Oblique Nuclei”

project only to the ipsilateral side

Therefore, a patient with a rare unilateral oculomotor nucleus injury could present with symptoms that include:

• Ipsilateral medial rectus, inferior rectus & Inferior oblique paresis
• Contralateral superior rectus paresis
• bilateral ptosis

what is occulomotor 

• Superior Colliculus is the visual reflex center of the brainstem

  • See the Optic Nerve Lecture

• Receives information directly from the retina

•  Also receives auditory and somatosensory signals

• to rapidly guide coordinated and/or reflexive movements in the eye

  • Also Autonomic intraocular actions

    • E.g., Pupillary Light Reflex

• Eye is turned “down and out.”

  • Due to the unopposed action of CN VI and CN IV

  • External Strabismus - Laterally Deviated eye

  • Eye positioned in partial abduction and depression with intorsion

  • Produces Diplopia – double vision

  • Ptosis

  • Dilated pupil

    • or one that responds poorly to light

Cranial nerve III Palsy

Cranial nerve III Palsy: As the nerve continues its journey to the extraocular muscles, it travels alongside the

posterior communicating artery 

is the most common cause of a nontraumatic isolated CN III palsy

aneurysm of the posterior communicating artery

A dilated pupil associated with a CN III palsy is always assumed to be due to an

aneurysm until proven otherwise

• From its origin, CN IV innervates the superior oblique muscle on the contralateral side of the head

• Nucleus in the contralateral midbrain

• The only CN that emerges from the posterior side of the brainstem

• Thinnest cranial nerve

• Has the longest intracranial course before it exits the skull

• Most susceptible to injury, trauma, and increased intracranial pressure

Trochlear Nerve

Superior Oblique Actions:

Intorsion, ADduction and Depression of the eye

• CN IV has extensive connections with the __

  • critical for orientation of the eyes associated with head tilt

vestibular system

When the head is tilted to the right shoulder:

• the right eye intorts slightly
• the left eye extorts slightly

CN IV palsy affects the superior oblique muscle:

• slight extorsion of the eye
• Hyper-deviation or elevation of the eye.
• Each of these actions is due the unopposed actions of the other extraocular muscles

• Diplopia

• Lateral Neck flexion (Head tilt)

  • to bring the good eye in line with the elevated eye

• Many patients present with a subtle __ to compensate for the slight extorsion

head tilt away from the side of the muscle palsy

• supplies the Lateral Rectus

• Abducts the eye

• emerges near the midline at the pontomedullary junction

  • Fold between pons and medulla

• Nucleus in the Pons

Abducens Nerve

Injury to the Abducens Nucleus is usually accompanied by

facial nucleus 

Abducens Nerve Injury Presentation:

• Ipsilateral Internal Strabismus

  • medial deviation due to unopposed action primarily of the medial rectus

• Diplopia

what is gaze?

coordinated movement of both eyes (and the neck) that directs visual stimuli onto the fovea of both retinas

what is horizontal gaze?

• involves synchronous activation of the lateral rectus muscle of one eye and the medial rectus muscle of the other

• Horizontal gaze is controlled by CN VI and its associated paramedian pontine reticular formation (PPRF)

what is saccade?

rapid movement of both eyes, simultaneously in the same direction to a new point of fixation

what is horizontal saccade?

rapid horizontal movement of both eyes in the same direction
• Can be voluntary or reflexive

Horizontal gaze is controlled by the

CN VI Nucleus

2 types of neurons in the Abducens Nucleus:

• motor neurons 

• internuclear neurons 

what are motor neurons

axons of these neurons create the abducens nerve

what is internuclear neurons

• axons of these neurons decussate and ascend contralaterally through the Medial Longitudinal Fasciculus (MLF)
• Synapse with neurons in the Oculomotor Nucleus (specifically those that control the medial rectus)

Activation of the abducens nucleus simultaneously directs __ to deviate both eyes toward the abducting side

ipsilateral abduction and contralateral adduction

Thus the __ drives ipsilateral horizontal gaze

CN VI nucleus

• The signal originates in the frontal eye fields of the Right frontal lobe

• To the Right Superior Colliculus

  • After leaving the SC the signal decussates to the contralateral side of the Pons

• To the Left Pontine Reticular Formation

• To the Left Abducens Nucleus

  • To the Lateral Rectus muscle

  • To the Oculomotor Nucleus for the Medial Rectus

Voluntary Horizontal Saccade