## Oculomotor nerve
<ul>
 <li>Largest extraocular nerve</li>
 <li>Nucleus in midbrain at level of the superior colliculus</li>
 <li>2 types of nuclei</li>
 <ul>
 <li>
 5 complexes of somatic efferent nuclei containing cells of neurones that directly supply EOMs
 </li>
 </ul>
</ul>
<HotTopic>
 
 The nucleus for each EOM supplies the ipsilateral muscle except the nucleus for superior rectus
 which has contralateral innervation
 
</HotTopic>
<ul>
 <li>
 The levator has a centrally located, fused nucleus (the central caudal subnucleus) and is{' '}
 bilaterally innervated. Hence a lesion of the levator nucleus causes a
 bilateral ptosis
 </li>
</ul>
<ul>
 <li>
 These motor nuclei are connected to the fourth and sixth nerve nuclei via the medial
 longitudinal fasciculus
 </li>
 <li>
 General visceral efferent nuclei (Edinger-Westphal) nuclei containing preganglionic
 parasympathetic neurone cell bodies
 </li>
 <li>The parasympathetic nucleus lies posterior to the motor nucleus</li>
</ul>
<ClinicalCorrelate>
 
 A lesion of the left third nerve nucleus will affect the left medial rectus, inferior rectus,
 inferior oblique, the right superior rectus and both levators.
 
</ClinicalCorrelate>
Course
<ul>
 <li>
 The nerve emerges from midbrain at the level of the superior colliculus (at the border of the
 midbrain and the pons) in the interpeduncular fossa
 </li>
 <li>Passes between the posterior cerebral artery and superior cerebellar artery</li>
 <li>Travels parallel to posterior communicating artery</li>
 <li>Enters dural roof of cavernous sinus</li>
 <li>Travels in upper lateral wall of cavernous sinus</li>
 <li>
 Enter orbits through superior orbital fissure within the tendinous ring. Divides into superior
 and inferior branches prior to entering orbit
 </li>
 <li>Smaller superior branch supplies superior rectus and pierces it to supply levator.</li>
 <li>Larger inferior division gives small branches to medial rectus and inferior rectus</li>
 <li>
 Thick inferior branch passing alongside inferior rectus reaches inferior oblique and contains
 preganglionic parasympathetic fibres
 </li>
 <ul>
 <li>These pass to the ciliary ganglion and synapse</li>
 <li>
 Second order neurones then travel to iris (sphincter pupillae), choroid, CB muscle in short
 ciliary nerves
 </li>
 </ul>
 <li>Branches to EOMs enter the muscles approx 1/3rd along muscle length</li>
 <li>Parasympathetic fibres travel most superficially within the nerve</li>
</ul>

## Trochlear nerve
<ul>
 <li>Longest intracranial course</li>
 <li>Pure motor nerve: has fewest nerve fibres of all the cranial nerves</li>
 <li>
 Nucleus lies at the level of the inferior colliculus (midbrain, caudal to third nerve nucleus)
 </li>
 <li>Decussates before exiting brainstem</li>
 <ul>
 <li>Therefore supplies contralateral superior oblique</li>
 </ul>
 <li>Nerve exits the posterior aspect of the midbrain&nbsp;</li>
 <ul>
 <li>The only motor nerve to do this</li>
 </ul>
 <li>Wraps around crus of midbrain</li>
 <li>Passes between PCA and superior cerebellar artery</li>
 <li>Initially below CNIII</li>
 <li>Enters lateral wall of cavernous sinus</li>
 <li>On exiting the sinus it is above and lateral to CNIII</li>
 <li>Enters orbit outside of tendinous ring</li>
 <li>Travels beside the origin of the levator towards superior oblique.</li>
</ul>
<ClinicalCorrelate>
 
 Isolated damage to the trochlear nerve causes difficulty looking down especially in adduction
 (since SO is only depressor in adduction)
 
</ClinicalCorrelate>
<ul>
 <li>
 Patients demonstrate a contralateral head tilt to make up for torsion of unopposed inferior
 oblique
 </li>
</ul>
<ul>
 <li>Trochlea:</li>
 <ul>
 <li>Composed of fibrocartilage (not bone)</li>
 <li>Attached to the frontal bone</li>
 <li>Contains a synovial sheath that surrounds the tendon of superior oblique</li>
 <li>Medial to supraorbital nerve</li>
 <li>Divides the preaponeurotic fat into the medial and lateral fat pads</li>
 </ul>
</ul>
<ClinicalCorrelate>
 
 The nerve lies outside the orbital cone and so is not generally affected by retrobulbar
 anaesthesia
 
</ClinicalCorrelate>

## Abducens nerve
<ul>
 <li>Longest intradural course</li>
 <li>Pure motor nerve</li>
 <li>Nucleus in floor of fourth ventricle (pons)</li>
 <li>
 Emerges from midpons beneath facial colliculus at junction between medulla and pons
 (cerebello-pontine angle)
 </li>
 <ul>
 <li>Arises from a nucleus close to the facial nerve</li>
 </ul>
 <li>
 Anterior inferior cerebellar artery crosses at origin and fixes the nerve to the brainstem
 </li>
 <li>Passes upwards in pontine cistern</li>
 <li>
 Changes to horizontal orientation at upper border of petrous temporal bone where it penetrates
 the dura
 </li>
</ul>
<ClinicalCorrelate>
 
 The nerve can easily be severed against the crest of the petrous temporal bone in head injury
 
</ClinicalCorrelate>
<ul>
 <li>
 Passes within cavernous sinus (therefore more vulnerable as not protected by
 dura in lateral wall)
 </li>
 <li>Lies lateral to ICA: atheroma can compress nerve here</li>
 <li>Enters orbit within tendinous ring</li>
 <li>Short course to enter lateral rectus 1/3rd along its medial surface</li>
</ul>

 Note: lateral rectus has two origins: one from tendinous ring, other from greater
 wing of sphenoid.


## Trigeminal nerve
<ul>
 <li>Largest cranial nerve</li>
 <li>Nucleus extends throughout brainstem but the main sensory nucleus is in the pons</li>
 <ul>
 <li>
 Mesencephalic nucleus extends up into midbrain: sensory info from muscles of mastication,
 facial expression and EOMs.
 </li>
 <li>
 Spinal nucleus extends down to medulla: tactile, nociceptive, thermal info from face
 (responsible for mainly pain and temperature)
 </li>
 <li>Main sensory nucleus responsible for touch and pressure</li>
 </ul>
</ul>
<ul>
 <li>
 Emerges from brainstem in posterior cranial fossa as large sensory root and smaller motor root
 </li>
 <li>Trigeminal ganglion (aka semilunar ganglion)</li>
 <ul>
 <li>Crescentic shape</li>
 <li>Lies in Meckel&rsquo;s cave near the apex of the petrous part of the temporal bone</li>
 <li>Within the middle cranial fossa</li>
 <li>Closely related to the motor root</li>
 <li>But is mainly a sensory ganglion (the motor root passes beneath the ganglion)</li>
 </ul>
 <li>3 branches emerge from flattened anterolateral surface of ganglion</li>
 <li>Ophthalmic lies in lateral wall of cavernous sinus</li>
 <ul>
 <li>See Sensory Nerves chapter for more details</li>
 </ul>
 <li>Maxillary: purely sensory</li>
 <ul>
 <li>Lies in lateral wall of cavernous sinus</li>
 <li>
 Passes through foramen rotundum into pterygopalatine fossa where it supplies pterygopalatine
 ganglion
 </li>
 <li>Becomes infraorbital nerve as enters inferior orbital fissure</li>
 <li>Passes through infraorbital groove, canal and foramen</li>
 <li>Gives zygomatic branch: zygomaticofacial and zygomaticotemporal branches</li>
 <li>
 Note: within the orbit they pass beneath periorbita/periosteum so not technically intraorbital
 </li>
 <li>
 Infraorbital supplies: maxillary sinuses, incisor, premolar and canine teeth, skin of cheek,
 lower eyelid, cheek, upper lip)
 </li>
 </ul>
</ul>

Oculomotor nerve Largest extraocular nerve Nucleus in midbrain at level of the superior colliculus 2 types of nuclei 5 complexes of somatic efferent…

Neuroanatomy

Extraocular Nerves

Intro

FRCOphth Part 1 Study Notes

Orbit and ocular adnexae

Orbit

Extraocular Muscles

Orbital Blood Vessels

Paranasal Sinuses

Lacrimal Glands

Tear Film

Eyelids

Blinking

Anterior segment - ocular surface

Conjunctiva

Conjunctivitis

Sclera

Cornea

Corneal Structure And Development

Corneal Physiology

AC to Lens

Angle

Ciliary Body

Aqueous Humour Dynamics

Iris

Pupil

Lens

Posterior segment

Choroid

Vitreous

Retinal Macrostructure

Neurosensory Retina

Retinal Pigment Epithelium

Venous Sinuses

Cerebral Ventricles

Cerebral Blood Supply

Supranuclear Gaze Pathways

Head And Neck Autonomic Nervous Supply

Head And Neck Glands

Osteology

Nerves

Muscles And Pharyngeal Arches

Sensory Nerves

Physiology

Physics Of Blood Flow

Neuronal Control Of Blood Vessels

Oxygen-Haemoglobin Dissociation Curve

Cytochrome p450

Pituitary Gland

Thyroid Hormone Production

Insulin

Glucagon

Parathyroid Hormone

Corticosteroids

Catecholamines

Cardiac Cycle

Renal Physiology

Fluid Balance

Acid-Base Balance

Muscle Physiology

Sensory Fibres

Cutaneous Receptors

Endocytosis

Glycosaminoglycans

Condensed Ocular Biochemistry

Eye Movements

Accomodation

Vision

Visual Cycle And Phototransuction

Visual Pathway

Visual Acuity

Colour Vision

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Pathology

Collagen

Tissue Damage

Inflammation

Disease Entities

Wound Healing

Thrombosis / Atherosclerosis

Cell Growth

Neoplasia

Histopathology

Nystagmus

Free Radicals And Antioxidants

Immunology

Ocular Immunology

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Protozoa

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Multifactorial Inheritance