Cranial Nerve VII VIII Lecture Objectives Follow up

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. • 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.

Mixed cranial nerve Facial Nerve (VII) 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

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 ear All sensory fibers go to the geniculate ganglion (in facial canal)

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

Facial Nerve Nuclei • Parasympathetic nuclei (GVE) • Superior salivatory • Connections • Hypothalamus • Lacrimal • Connections • Hypothalamus • Sensory nuclei of V • Corneal irritation

Facial Nerve: Sensory Nucleus • 1 st order neuron – geniculate ganglion • 2 nd order neuron –Nucleus of the tractus solitarius (SVA, GVA) • Taste and sensation from palate • Location • Axons cross midline • 3 rd order neuron – PVM of thalamus • Axons → internal capsule → corona radiata → cortex (postcentral gyrus)

Facial Nerve (VII): Course • Facial nerve (motor root (SVE) & nervus intermedius (GVE, SVA, GSA)) • Pons (cerebellopontine angle) • Internal acuastic meatus • Facial canal • Stylomastoid foramen

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

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

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 (V 3)

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)

UMN Vs LMN Lesions of Facial Nerve

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

Auditory Nuclei/Pathway • 1 st order neuron – spiral ganglion • 2 nd order neurons • Cochlear nuclei • Anterior & posterior • Location • Relations – inferior cerebellar peduncles • Axons cross and uncross midline

Auditory Nuclei/Pathway • 3 rd order neurons • Posterior nucleus of trapezoid body & superior olivary nucleus • Axons – lateral lemniscus • 4 th order neurons • Inferior colliculus • Medial geniculate body (5 th) → internal capsule → auditory cortex (superior temporal gyrus)

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

The Vestibular Nuclei/Pathway • Location – 4 th ventricle • Vestibular nuclei (2 nd order neurons) • • Lateral → vistibulospinal tract Superior Medial Inferior • Inputs from cerebellum • Axons To spinal cord To eye muscles nerves (III, IV, VI) To thalamus (VP) → vestibular area in cerebral cortex (postcentral gyrus)