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Cranial Nerve 2,3,4,6 function, loci.pdf
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- 2. Sight • Is notonly dependent on the cerebal cortex but also on cranial nerves • Perception is a function of the retina, optic nerve, tract, radiation and cortex • The optic pathway transmits impulses from the retina to the brain
- 3. CN 2: Optic •A CNS Tract • Primary sensory neurons are bipolar and confined to the retina • Axons of the secondary sensory neurons form the optic nerve, chiasm and tract • Pathway from the eyeball to the optic chiasm • Purely sensory
- 4. CN 2:Optic • Retina •Two Layers: Neural and pigment • Neural layer: rods and cones • Terminal portioin of the neural layer is in contact with the pigment layer • Rods and cones synapse with the bipolar cells • Bipolar cells synapse with the ganglion cells • Axons of the ganglion cells form the optic nerve
- 5. Optic Nerve • Passesposteriorly from the eyeball • Surrounded by meninges, subarachnoid space and CSF • Passes through the common tendinous ring and leaves the orbit through the optic canal • Nerve is surrounded by the tube like extension of the 3 meningeal layers and CSF • The Paired optics communicate at the chiasm • Nasal Portion of the nerve decussate at the chiasm • From the chiasm the optic tract extend to the lateral geniculate body
- 6. Optic Nerve • Fromthe LGB some axons bifurcate sending signals to the midbrain from the pupillary light reflex • Inferior optic radiations pass through the temporal lobe (Meyers loop) • Superior optic radiations pass by the parietal lobe • Majority of axons from the LGB make its way to the occipital lobe as the optic radiation
- 7. Optic Nerve • Connectionto the midbrain • To the pretectal nuclei of the midbrain to facilitate pupillary light reflex • Connected to the superior colliculus and medial longitudinal fasciculus to facilitate eye accommodation and conjugate eye movement
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- 9. Papilledema • Optic nervein the orbit is surrounded by the subarachnoid space containing CSF leading to compression of the nerve if intracranial pressure rises • Compression will occlude the central vein before the artery, this will engorge the retina with blood leading to the ooptic disc to bulge into the retina • Papilledema is a reliable sign of increased ICP
- 10. Cranial Nerves: 34 6 • Innervate the extraocular muscles which move the eyeball • Function in conjugate eye movement
- 11. Occulomotor Nerve • Innervatethe levator palpebra superioris • Innervate the superior, inferior, medial and inferior oblique • Through its parasympathetic component it constricts the pupil
- 12. Occulomotor Nerve • Occulomotornucleus is located at the midbrain at the level of the superior colliculus • Peripheral axons pass ventrally in the tegmentum, penetrate the red nucleus and peduncles to emerge between posterior cerebral and superior cerebellar arteries in the interpeduncular fossa • After penetrating the dura, it courses laterally along the wall of the cavernous sinus, and enters the orbit through the superior orbital fissure • Passes through the annulus of zinn
- 13. Parasympathetic component • Originate fromthe Edinger Westphal nucleus, consist of pre ganglionic parasympathetic fibers • The fibers synapse in the ciliary ganglion • The ciliary nerves supply the ciliary and constrictor pupillae muscles which facilitate accommodation and constriction
- 14. Pupillary Light Reflex • LightStimulus elicits pupillary constriction
- 15. Accommodation Reflex • Partof the adaptation of the eyes to near vision • Afferent limb terminates in the visual cortex • Efferent limb terminates in the pupillary constrictors, medial rectus and ciliary muscles via the pretectal region • Constriction, convergence and change in lens size
- 16. Occulomotor Nerve palsy • Inhibitionof medial and vertical gaze leading to diplopia • Drooping of upper eyelid • Mydriasis • Absent Pupillary light reflex • No accommodation reflex
- 18. Trochlear Nerve • Nucleuslocated in the midbrain caudal to the oculomotor nucleus at the level of the inferior colliculus • Exit dorsally passing through the cavernous sinus and into the superior orbital fissure, peripheral fibers decussate • Supplies the superior oblique muscle- inward rotation and downward movement
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- 20. Abducens Nerve • Nucleusis located in the pons just beneath the 4th ventricle • This nucleus is draped by the facial nerve dorsally which forms the facial colliculus • Emerges between the pons and the pyramids, courses the cavernous sinus, lateral to the ICA and through the superior orbital fissure • Innervates the lateral rectus muscle
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- 22. Horizontal conjugate eye movement •Combination of voluntary and involuntary eye movement that help us track objects in space • Initiated by the frontal eye field, whose fibers traverse the posterior limb of the internal capsule and the cerebral peduncle to terminate in the paramedian pontine reticular formation • PPRF sends signals to the ipsilateral abducens and via the medial longitudinal fasciculus to the contralateral oculomotor nerve