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Cranial Nerve VII & VIII

Cranial Nerve VII & VIII. Lecture Objectives. Follow up the course of facial nerve from its point of central connections, exit and down to its target areas. Follow up the central connections of the facial nerve. Discuss the various modalities of its fibers.

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Cranial Nerve VII & VIII

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  1. Cranial Nerve VII &VIII

  2. LectureObjectives • Follow up the course of facial nerve from its point of central connections, exit and down to its targetareas. • Follow up the central connections of the facial nerve. • Discuss the various modalities of itsfibers. • Review your knowledge of its targetorgans. • Follow the course of the VIII nerve down to its point of entry to the brain. • Follow up the central connections of the VIII nerve.

  3. Facial Nerve(VII) • Mixed cranialnerve MotorModalities • Motor fibers (SVE) originate from the pons and innervate facial, scalp muscles • Parasympathetic innervation (GVE) (via the pterygopalatine and submandibular ganglia) to various glands in thehead • Major motor functions are regulating muscles of facial expression and secretion of saliva andtears

  4. Facial Nerve(VII) • SensoryModalities • Sensory fibers (SVA) from the taste buds of the anterior ⅔ of the tongue • Sensory fibers (GVA) from soft palate • Sensory fibers (GSA) from external ear • All sensory fibers go to the geniculate ganglion (in facial canal)

  5. Facial NerveNuclei • Main motor nucleus(SVE) • Location • Connection • Cortex* • Upper muscles – bothsides • Lower muscles – contralateral innervation • *upper motor neuron lesion would affect lower musclesonly • Fibers course • Colliculusfacialis

  6. Facial NerveNuclei • Parasympathetic nuclei (GVE) • Superior salivatory • Connections • Hypothalamus • Lacrimal • Connections • Hypothalamus • Sensory nuclei ofV • Cornealirritation

  7. Facial Nerve: SensoryNucleus • 1st order neuron – geniculate ganglion • 2nd order neuron –Nucleus of the tractus solitarius (SVA, GVA) • Taste and sensation frompalate • Location • Axons crossmidline • 3rd order neuron – PVM of thalamus • Axons → internal capsule→ corona radiata → cortex (postcentralgyrus)

  8. Facial Nerve (VII):Course • Facial nerve (motor root (SVE) & nervus intermedius (GVE,SVA,GVA,GSA)) • Pons (cerebellopontineangle) • Internal acuasticmeatus • Facialcanal • Stylomastoidforamen

  9. Facial Nerve (VII): Branches • Nerve to the stapidius muscle (SVE) • Posterior auricular n.(SVE) • Stylohyoid & posterior belly of digastric • Five terminal branches(SVE)

  10. Facial Nerve (VII): Branches • Greater petrosal nerve (GVE, GVA)↔ hiatus of the facial canal ↔ pterygoid canal ↔ pterygpalatineganglion

  11. Facial Nerve (VII): Branches • Chorda tympani n. (GVE, SVA,GVA) ↔ canal in the tympanic cavity ↔ canal in the petrotympanic fissure ↔ foramen at the spine of sphenoid ↔ lingual nerve(V3)

  12. Facial Nerve (VII): Lesion • Bell’s palsy: paralysis of facial expressionmm. • Unable to show teeth andclose eye • Loss of corneal reflex (efferent limb) • Loss of taste from theanterior • ⅔ of tongue (cordatympani) • Unable to distinguish taste sensations (sweet, bitter, sour & salt) • Decrease salivation (corda tympani)

  13. UMN Vs LMN Lesions of FacialNerve

  14. Vestibulocochlear Nerve(VIII) • Formerly called the acoustic or auditory nerve • Brainstem (between pons & medulla) → Internal acousticmeatus • Mainly a sensorynerve • Consists of twobranches: • Cochlearbranch • Associated withhearing • Receptors in the spiral organ in thecochlea • The cell bodies in the spiralganglion • Axons travel to nuclei in themedulla • if damaged deafness or tinnitus (ringing) is produced

  15. AuditoryNuclei/Pathway • 1st order neuron – spiral ganglion • 2nd orderneurons • Cochlearnuclei • Anterior &posterior • Location • Relations – inferior cerebellar peduncles • Axons cross and uncrossmidline

  16. AuditoryNuclei/Pathway • 3rd orderneurons • Posterior nucleus of trapezoid body & superior olivarynucleus • Axons – laterallemniscus • 4th orderneurons • Inferiorcolliculus • Medial geniculate body (5th) → internal capsule → auditory cortex (superior temporalgyrus)

  17. Vestibulocochlear Nerve(VIII) • Vestibularbranch • Associated withequilibrium • Receptors in thesemicircular canals; saccule, andutricle • The cell bodies investibular ganglion • Axons travel to nuclei in the thalamus; some fibers also travel to thecerebellum • Lesion results in disequilibrium, vertigo, nystagmus,ataxia

  18. The VestibularNuclei/Pathway • Location – 4thventricle • Vestibular nuclei (2nd order neurons) • Lateral → vistibulospinaltract • Superior • Medial • Inferior • Inputs fromcerebellum • Axons • To spinalcord • To eye muscles nerves (III, IV,VI) • To thalamus (VP) → vestibular area in cerebral cortex (postcentralgyrus)

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