Third Cranial Nerve - Anatomy & Applied Anatomy

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Oculomotor Nerve - This presentation is about the anatomy and the applied aspects of the third cranial nerve.

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Oculomotor Nerve:

Oculomotor Nerve Kunal

Functional Components :

Functional Components General Somatic efferent Movements of the eyeball General Visceral efferent Accommodation and contraction of pupil General somatic afferent Proprioceptive impulses from extra-ocular muscles

Nucleus:

Nucleus Ventromedial part of central grey matter of midbrain At the level of superior colliculus Lies in floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle. Longitudinal column of about 10mm length Below it is related to the nucleus of trochlear nerve.

Main Motor Nucleus:

Main Motor Nucleus Dorsolateral Nucleus : Ipsilateal inferior rectus Intermedial nucleus : Ipsilateral inferior oblique Ventromedial nucleus : Ipsilateral medial rectus Paramedial (Scattered) nucleus : Contralateral Superior rectus Caudal central nucleus : Bilateral levator palpebrae superioris

Accessory Motor nucleus (Edinger-Westphal Nucleus):

Accessory Motor nucleus ( Edinger-Westphal Nucleus) Situated posterior to the main oculomotor nucleus Preganglionic parasympathetic fibres Cranial half : Light reflexes Caudal half : Accommodation

Connections:

Connections Cerebral Cortex Motor Cortex of both sides Visual Cortex Nuclei of IV, VI and VIII cranial nerves : Medial longitudinal bundle Pretectal nucleus of both sides (light reflex) Vertical and torsional gaze centres : Medial l ongitudinal bundle Cerebellum : Vestibular nuclei

Course:

Course Fascicular Part Basilar Part Intracavernous Part Intraorbital Part

PowerPoint Presentation:

Intraneural course – Arise from Nucleus & pass ventrally through tegmentum , red nucleus and substanstia nigra Base of brain – Attached to oculomotor sulcus on the medial side of the crus cerebri

PowerPoint Presentation:

Passes between superior cerebellar and posterior cerebral arteries. Runs forward in the interpeduncular cistern, on the lateral side of the posterior communication artery Enters Cavernous sinus by piercing posterior part of roof on the lateral side of posterior clinoid process. It descends to the lateral wall of the sinus where it lies above the trochlear nerve .

PowerPoint Presentation:

In the anterior part of the sinus, divides into Upper & Lower Enter the orbit through middle part of superior orbital fissure. Nasociliary nerve lies in between the 2 divisions; abducent nerve lies inferolateral to them In orbit, smaller upper division ascends on the lateral side of the optic nerve, supplies Superior Rectus and Levator Palpebrae Superioris . The larger lower division divides into 3 branches for medial rectus, inferior rectus and inferior oblique.

PowerPoint Presentation:

Nerve to inferior oblique is the longest. It gives off the motor root to ciliary ganglion. All branches enter the muscles on their ocular surfaces except that for inferior oblique which enters its posterior border.

Ciliary Ganglion:

Ciliary Ganglion It lies near the apex of the orbit between the optic nerve and the tendon of the lateral rectus. It has Motor root: Arises from the nerve to the inferior oblique Contains preganglionic fibres that begin in EWN, they relay in ganglion. Post ganglionic fibres pass through short ciliry nerves and supply sphincter pupillae and ciliaris muscle. Sensory root It comes from nasociliary nerve Contains sensory fibres from the eyeball Do not relay in the ganglion

PowerPoint Presentation:

Sympathetic root Branch from internal carotid plexus Post ganglionic fibres arising from superior cervical ganglion Do not relay in the ciliary ganglion Pass out via short ciliary nerves and supply blood vessels of the eyeball Also supply the dilator pupillae Parasympathetic root Arises from nerve to Inferior Oblique Preganglionic fibres from EWN Fibres relay in ganglion Postganglionic fiibres pass through short ciliary nerves and supply sphincter pupillar and ciliary muscle

Pupillomotor Fibres:

Pupillomotor Fibres Located superficially in the superomedial part Derive blood supply from pial blood vessels Main trunk of 3 rd nerve supplied by Vasa Nervorum Surgical lesions Aneurysms, trauma and uncal herniation involve pupil by compressing pial blood vessels & pupillary fibres Medical Lesions HTN & Diabetes usually spare pupil. Microangiopathy involves vasa nervorum

Applied Anatomy:

Applied Anatomy Total third nerve palsy (Congenital/Acquired) Ptosis Eyeball down & out Ocular movements Pupil is fixed and dilated Accommodation lost Crossed diplopia due to paralytic divergent squint Head posture

Supranuclear Lesions:

Supranuclear Lesions Cerebral cortex and supranuclear pathway Conjugate paresis affecting both eyes equally Relative co-ordination maintained No diplopia

Nuclear Lesions:

Nuclear Lesions Relatively uncommon Causes: Vascular, demyelination, primary tumors and metastasis Entire nucleus involvement : Ipsilateral third nerve palsy with ipsilateral sparing and contralateral weakness of elevation Paired medial rectus subnuclei : Wall-eyed bilateral internuclear ophthalmoplegia (WEBINO) characterized by defective convergence and adduction

Fascicular Lesions:

Fascicular Lesions Benedikt’s Syndrome : Ipsilateral third nerve palsy associated with tremors and jerky movements of the contralateral side. Lesion at the intermediate level of mid-brain. (while passing through red nucleus) Weber’s Syndrome : Ipsilateral third nerve palsy, contralateral hemiplegia and facial palsy of upper motor neuron type. (while passing throug cerebral peduncle)

Basilar part:

Basilar part Isolated : Subarachnoid space of base of skull unaccompanied by any other Cranial Nerves. Causes: Aneuryms (Fixed dilated pupil) Extradural haematomas (Fixed dilated pupil) Diabetes (Sparing of Pupillary reflex)

Intracavernous Part:

Intracavernous Part Close proximity to other cranial nerves (IV, VI and first division of V) Pupil is spared Causes: Diabetes Pituitary apoplexy Aneurysms Meningiomas Carotid cavernous fistulae Tolosa -Hunt Syndrome

Intraorbital part:

Intraorbital part Isolated extraocular palsies Superior/inferior divisions Causes: Orbital tumors Pseudotumors Trauma Vascular diseases

PowerPoint Presentation:

Thank You!

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