ANAT 2626 Cranial Nerves - 1 Chapter 9 - Pages 1054 to 1082...

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Chapter 9 - Pages 1054 to 1082 Cranial nerves Olfactory nerve is the first cranial nerve Component is special sensory for smell ( special visceral afferent ) Location of nerve cell bodies are in the olfactory epithelium ( olfactory cells ) Cranial exit is through the tiny foramina in cribriform plate of ethmoid Termination 1. olfactory nerve fibers synapse with mitral nerve cells of the olfactory bulb 2. the axons of these secondary neurons form the olfactory tract 3. each olfactory tract divides into lateral and medial olfactory stria 4. the lateral olfactory stria terminates in the pririform cortex of the anterior part of temporal lobe of cerebrum 5. the medial olfactory stria projects through the anterior commissure Main actions 1. smell from the nasal mucosa of roof of each nasal cavity 2. superior sides of nasal septum and superior concha Clinical Site of lesion - fracture of cribriform plate of ethmoid Abnormal findings Anosmia 1. loss of smell 2. cerebrospinal fluid rhinorrhea Optic nerve is the second cranial nerve Component is special sensory for vision ( special somatic afferent ) Location of nerve cell bodies is in the retina of the eye ( ganglion cells ) Formation from the axons of retinal ganglion cells Cranial exit 1. through the optic canal and forms the optic chiasma 2. here the fibers from the nasal ( medial ) half of retina decussate and form the optic tract 1
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Termination 1. most fibers in the optic tracts terminate in the lateral geniculate bodies of the thalamus 2. from these nuclei, axons are relayed to the visual cortex of the occipital lobe of the cerebrum Main action is the vision from the retina Clinial 1. Sites of lesion a) direct trauma to orbit or eyeball b) fracture involving optic canal Abnormal finding is loss of pupillary constriction 2. Site of lesions 1. presssure on optic pathway 2. laceration or intracerebral clot in temporal, parietal or occipital lobes of brain Abnormal finding is visual field defects Oculomotor nerve is the third cranial nerve, motor nerve of the eye 1. Component is somatic motor ( general somatic efferent ) Location of nerve cell bodies in midbrain Origins 1. from the oculomotor ( somatic motor ) nucleus located in the midbrain, at the level of superior colliculus 2. from the accessory nucleus ( Edinger Westphal ) visceral motor ( parasympathetic ) lies dorsal to the oculomotor nucleus Cranial exit is through the superior orbital fissure , and enters the orbit Termination it divides into a superior and inferior divisions Superior division supplies 1. levator palpebrae superioris 2. superior rectus Inferior division supplies 1. inferior rectus 2. medial rectus 2
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3. inferior oblique Inferior division also carries presynaptic parasympathetic ( visceral efferent ) fibers to the ciliary ganglion Main actions 1. motor fibers to superior rectus, medial rectus, inferior rectus, inferior oblique and levator palpebrae superioris muscles 2. raises the upper eyelid 3. turns the eyeball superiorly, inferiorly and medially
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ANAT 2626 Cranial Nerves - 1 Chapter 9 - Pages 1054 to 1082...

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