Laith Sorour. Facial nerve (vii):

Size: px

Start display at page:

Download "Laith Sorour. Facial nerve (vii):"

Emmeline Griffin
6 years ago
Views:

1 Laith Sorour Cranial nerves 7 & 8 Hello, there are edited slides please go back to them to see pictures, they are not that much important in this lecture but still, and yes slides are included :p Let s goooooooooooooooooooooooooooooooooooooo! Facial nerve (vii): It s a mixed cranial nerve which means it has a Motor modality and Sensory modality. First, The Motor modalities: 1-Motor fibers (SVE) and originate from the pons and innervate facial expression muscles (facial, scalp muscles) 2-Parasympathetic innervation (GVE) are via pterygopalatine and submandibular ganglia and they innervate various glands in the head like The salivary glands (secretion of saliva) (sublingual and submandibular + small salivary glands but NOT the parotid gland although it pierces it through its course) and the Lacrimal Gland (secretion of tears) ***so lesions to motor modalities of facial nerve will lead to facial palsy and defect in salivation and lacrimation. Secondly, Sensory modalities: **All sensory fibers go to the Geniculate ganglion in facial canal. *Ganglion=gray matter outside CNS. We have 3 types of sensory fibers: 1-SVA from the taste buds of the anterior 2/3 of the tongue and external 2-GVA from soft palate and beginning of oropharynx 3-GSA from external ear (many nerves sense the external ear because its embryological formation is from more than one arch) Now lets about Facial nerve nuclei: 1-The main motor nucleus (SVE): located deep in the reticular formation in the lower part of the pons, it connects with the cortex and then innervates the upper

2 muscles of facial expression bilaterally (from both sides) and the lower muscles contralateral (left hemisphere innervate right side and like this). *so any lesion in UMN will affect the lower muscles of the contralateral side but the upper muscles will not be affected. -Fibers go posteriorly looping around abducent nucleus and this gives us Colliculus facialis and will combine with the other nerves and give Facial nerve which ascends between pons and medulla until it inters Internal acoustic meatus 2- Parasympathetic nuclei (GVE) **Superior salivatory which connects with hypothalamus **Lacrimal which connects with hypothalamus and Sensory nuclei of Trigeminal (v) \but why?? Because trigeminal nerve innervates the sensation of the eyeball so as reflex lacrimal glands will secrete tears (Corneal irritation will secrete tears) *crying in the corner because life is hard* 3-Sensory nucleus 1st order neuron geniculate ganglion (as we said before all fibers go here) 2nd order neuron Nucleus of the tractus solitarius (SVA, GVA) They are responsible for Taste and sensation from palate, the nucleus located in the posterolateral region of the medulla and the Axons cross midline 3rd order neuron PVM of thalamus Axons internal capsule corona radiata cortex (postcentral gyrus) ** Facial nerve has two roots 1- motor root (SVE) & nervus intermedius which contains the sensory and parasympathetic fibers of the facial nerve (GVE,SVA,GVA,GSA) The facial nerve course it begins In the Pons ( cerebellopontine angle) Internal acoustic meatus then will reach the middle ear and will go in facial canal and move on medial wall and then posterior wall until it exits through stylomastoid foramen into infratemporal fossa. *so because of its complicated course it can be easily affected, like in otitis media.

3 Now lets talk about Facial nerve branches: 1-Nerve to stapidius muscle (SVE) from facial canal from posterior wall of the tympanic cavity to stapedius muscle where it originates in the middle ear \\ so the lesion may affect hearing. 2-Posterior auricular n. (SVE) It innervates Stylohyoid muscles & POSTERIOR belly of digastric muscle *Ant belly of digastric is innervated by mandibular branch of trigeminal n. 3-** important I think : IT gives 5 terminal branches ( SVE) in the Parotid gland *****The facial nerve pierces the parotid gland dividing it into superficial and deep and splits into five terminal branches innervating the muscles of facial expression (temporal, zygomatic, buccal, marginal mandibular, cervical)**** *so any injury to parotid gland or a parotid tumor may cause palsy *FACIAL nerve does NOT innervate parotid gland it just pierces it. 4-Greater petrosal nerve (GVE,GVA)(mainly parasympathetic lacrimal and small salivary glands) Exits from hiatus of facial canal which opens into cranial cavity near foramen lacerum goes to pterygoid canal where it fuses with deep petrosal nerve (sympathetic) and gives nerve of pterygoid canal pterygopalatine ganglion (parasympathetic ganglion) it distributes post-ganglionic neurons like zygomatic branch goes to cranium an lacrimal gland and other branches to nasal cavity and palate *we took these is Respiratory system with Dr. Abd Al-Amir. 5-Chorda tympani n. (GVE submandibular & sublingual glands) (SVA ant. 2/3 of the tongue\taste) (GVA) Chorda tympani leaves the facial nerve within facial canal in posterior wall of tympanic cavity canal in the petrotympanic fissure (*almost outside of auditory meatus ) foramen at the spine of sphenoid and combines with lingual nerve (V3) of trigeminal

4 Lesions of facial nerve : 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) less lacrimation and worsening of hearing because it innervates stapedius muscle *Slide 14: it was explained previously but please go back to edited slides to understand it better since it is a picture with notes. Vestibulocochlear Nerve (VIII) It has two branches: 1-vestibular 2-cochlear Formerly called the acoustic or auditory nerve Brainstem (between pons & medulla) Internal acoustic meatus and will inter inner ear. Mainly a sensory nerve but cochlear has an efferent for ulduar hair cells 1-Cochlear branch Associated with hearing Receptors in the spiral organ in the cochlea The cell bodies in the spiral ganglion at base of spinal lamina Axons travel to nuclei in the medulla if damaged deafness or tinnitus (ringing) is produced Auditory Nuclei/Pathway: 1st order neuron spiral ganglion 2nd order neurons Cochlear nuclei: it is located with the vestibular nuclei In the lateral side?? fossa between pons and medulla Two nuclei Anterior & posterior Relations inferior cerebellar peduncles Axons cross and uncross midline

5 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) 2-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 4th ventricle *Vestibular nuclei (2nd order neurons) have 4 nuclei that connects mainly with cerebellum and the lateral connects with spinal cord Lateral vistibulospinal tract Superior Medial Inferior Inputs from cerebellum Axons (so when you move your head eyes move too) in cerebral cortex (postcentral gyrus) Sorry for any mistakes and the last slides doctor didn t explain well because he explained them in the previous lecture. PEACE OUT

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