Cranial Nerves

Cranial NervesOculomotor NervePresented By:Kiran Suwal

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Cranial NervesCranial 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).Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck.There are 12 pairs of cranial nerves emerging directly from the brain.Sometime there may be a thirteenth cranial nerve, the terminal nerve (nerve O or N), which is very small and may or may not be functional in humansCranial Nerves may be sensory, motor or both and somatic or parasympathetic, or have mixed functions.As a rule, cranial nerves do not cross in the brain.6/12/2016Kiran Suwal2

here may be a thirteenth cranial nerve, the terminal nerve (nerve O or N), which is very small and may or may not be functional in humans2

Types of Cranial Nerves

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Types of Cranial Nerves (Cont...)

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Types of Cranial Nerves (Cont...)

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Location of Cranial NervesThe olfactory and optic nerves arise from the anterior portion of the brain called the cerebrum. The oculomotor and trochlear cranial nerves stem from the midbrain. The trigeminal, abducent, and facial nerves arise in the pons.The vestibulocochlear nerve arises in the inner ears and goes to the pons. The glossopharyngeal, vagus, accessory and hypoglossal nerves are attached to the medulla

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Oculomotor NervesThe 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 ganglioncalled also third cranial nerve

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Origin of Oculomotor Nerves The oculomotor nerve originates from the anterior aspect of the midbrain.It is situate in the ventromedial part of central grey matter of midbrain at the level of superior colliculus.The fibers for the constrictor pupillae and for the ciliaris arise from the Edinger-Westphal nucleus which forms part of the oculomotor nuclear complex.6/12/2016Kiran Suwal11

Pathway of Oculomotor NervesIt 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 theinternal carotid plexus.The nerve leaves the cranial cavity via the superior orbital fissure.At this point, it divides intosuperiorandinferior branches.6/12/2016Kiran Suwal12

Pathway of Oculomotor Nerves (Cont..)6/12/2016Kiran Suwal13Superior 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.

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Functions of Oculomotor NervesGeneral somatic efferent, for movements of the eyeball.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.6/12/2016Kiran Suwal16

Clinical Test of Oculomotor Nerves Cranial nerves III, IV, and VI are usually tested together as part of thecranial nerve examination.Oculomotor nerves can be tested by following two ways:Eye musclesPupillary reflexes

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Disorders of Oculomotor NervesComplete and total paralysis of the third nerve results in: Ptosis, i.e. Drooping of the upper eyelidLateral squintDilatation of the pupil Loss of accommodationSlight proptosis, i.e. Forward projection of the eyeDiplopia or double vision.

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Disorders of Oculomotor Nerves (Contd.)A midbrain lesion causing contralateral hemiplegia and ipsilateral paralysis of the third nerve is known as Weber's syndrome.Supranuclear paralysis of the third nerve causes loss of conjugate movement of the eyes.Compression of III nerve due to extradural haematoma causes dilatation of pupil. Parasympathetic fibers lying superficial get affected first. Pupil dilates on affected side and there s little response to light. 6/12/2016Kiran Suwal22

Treatment of Disorders of Oculomotor NervesSymptomatic cases can be treated with Strabismus surgery.Surgical correction of ptosis: Ptosis surgery6/12/2016Kiran Suwal23

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