21-Cranial Nerve VII & VIII€¦ · Facial Nerve (VII) Mixed cranial nerve Motor Modalities...
Transcript of 21-Cranial Nerve VII & VIII€¦ · Facial Nerve (VII) Mixed cranial nerve Motor Modalities...
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Cranial Nerve VII & VIII
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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.• Review your knowledge of its target organs.• 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.
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Facial Nerve (VII)Mixed cranial nerve
Motor Modalities
• 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 the head
Major motor functions are regulating muscles of facial expression and secretion of saliva and tears
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Facial Nerve (VII)
Sensory Modalities• 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 earAll sensory fibers go to the geniculate ganglion (in facial canal)
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Facial Nerve Nuclei• Main motor nucleus (SVE)
• Location• Connection
• Cortex*• Upper muscles – both sides• Lower muscles – contralateral
innervation*upper motor neuron lesion would affect lower muscles only
• Fibers course• Colliculus facialis
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Facial Nerve Nuclei
• Parasympathetic nuclei (GVE)• Superior salivatory
• Connections • Hypothalamus
• Lacrimal• Connections
• Hypothalamus • Sensory nuclei of V
• Corneal irritation
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Facial Nerve: Sensory Nucleus
• 1st order neuron – geniculate ganglion
• 2nd order neuron –Nucleus of the tractus solitarius (SVA, GVA)• Taste and sensation from palate• Location• Axons cross midline
• 3rd order neuron – PVM of thalamus• Axons → internal capsule → corona radiata → cortex (postcentral gyrus)
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Facial Nerve (VII): Course
• Facial nerve (motor root (SVE) & nervus intermedius(GVE,SVA,GVA,GSA))
• Pons (cerebellopontine angle)
• Internal acuastic meatus
• Facial canal
• Stylomastoid foramen
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Facial Nerve (VII): Branches• Nerve to the stapidius muscle (SVE)
• Posterior auricular n. (SVE)• Stylohyoid & posterior belly of digastric
• Five terminal branches (SVE)
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Facial Nerve (VII): Branches
• Greater petrosal nerve (GVE, GVA)↔ hiatus of the facial canal ↔ pterygoid canal ↔ pterygpalatine ganglion
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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)
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Facial Nerve (VII): Lesion
• Bell’s palsy: paralysis of facial expression mm. • Unable to show teeth and close eye
• Loss of corneal reflex (efferent limb)
• Loss of taste from the anterior ⅔ of tongue (corda tympani)• Unable to distinguish taste sensations (sweet, bitter, sour & salt)
• Decrease salivation (corda tympani)
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UMN Vs LMN Lesions of Facial Nerve
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Vestibulocochlear Nerve (VIII)• Formerly called the acoustic or auditory nerve
• Brainstem (between pons & medulla) → Internal acoustic meatus
• Mainly a sensory nerve
• Consists of two branches:
Cochlear branch• Associated with hearing• Receptors in the spiral organ in the cochlea • The cell bodies in the spiral ganglion• Axons travel to nuclei in the medulla• if damaged deafness or tinnitus (ringing) is
produced
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Auditory Nuclei/Pathway
• 1st order neuron – spiral ganglion
• 2nd order neurons• Cochlear nuclei
• Anterior & posterior• Location• Relations – inferior cerebellar
peduncles
• Axons cross and uncross midline
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Auditory Nuclei/Pathway• 3rd order neurons
• Posterior nucleus of trapezoid body & superior olivary nucleus
• Axons – lateral lemniscus
• 4th order neurons• Inferior colliculus• Medial geniculate body (5th) → internal capsule → auditory cortex (superior temporal gyrus)
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Vestibulocochlear Nerve (VIII)
Vestibular branch• Associated with equilibrium• Receptors in the semicircular canals; saccule, and utricle
• The cell bodies in vestibular ganglion
• Axons travel to nuclei in the thalamus; some fibers also travel to the cerebellum
• Lesion results in disequilibrium, vertigo, nystagmus, ataxia
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The Vestibular Nuclei/Pathway
• Location – 4th ventricle• Vestibular nuclei (2nd order neurons)• Lateral → vistibulospinal tract• Superior• Medial• Inferior
• Inputs from cerebellum• Axons To spinal cordTo eye muscles nerves (III, IV, VI)To thalamus (VP) → vestibular area in cerebral cortex (postcentral gyrus)