BS III CN V - Trigeminal Nerve, CN VII - Facial Nerve, CN VII - Vestibulocochlear Nerve, CN IX - Glossopharyngeal
*CN IX Glossopharyngeal* - Rootlets emerge from *medulla* btw the *olive* & *inferior cerebellar peduncle* - Fibers: innervation? GSA GVE SVA GVA SVE
(GSA) innervates mucosa of - tympanic cavity - auditory tube - root of tongue - oropharynx - fauces - soft palate - skin of auricles (GVE) Preganglionic parasympathetics to the Otic Ganglion (SVA - taste) from posterior 1/3 of tongue (GVA) from carotid body and carotid sinus (SVE) to stylopharyngeus
Major branches of 3 division of CN V - *V1*
(NFL) 1. Nasociliary: deepest of 3 branches, must cut superior rectus & lev. palp to see - enters orbit thru the annular tendon (unique), enters via medial end of superior orbital fissure thru annulus (4 rectus muscles) - suspensory root of the ciliary ganglion comes off of this - *infratrochlear branch*: innervates lacrimal sac & related structures - *anterior & posterior ethmoidal branches*: thru anterior and ethmoidal foramina: *medial, lateral & external nasal branches* of *anterior ethmoidal* help V2 branches innervate nose & forehead. 2. Frontal - *supraorbital branch*: innvervates forehead and scalp skin & frontal sinus - *supratrochlear*: conjunctive, upper lid, forehead, lateral nose 3. Lacrimal: innervates skin near lacrimal gland; conjunctiva - there are long ciliary nerves conveying sensation from the cornea (afferent limb of the *corneal reflex* CN V1 to VII
Major branches of 3 division of CN V - *V2*
(ZIP) - branch extensively in pterygopalatine fossa ZYGOMATIC branches - Zygomaticotemporal - Zygomaticoorbital - Zygomaticofacial INFRAORBITAL - Inferior palpebral branch on face - *Nasal* branch - *Superior labial branch* on face - *Superior alveolar* branches: course along walls of maxillary sinus to form the superior dental plexus, giving rise to dental branches of the apices of the maxillary teeth and gingival branches too *maxillary sinus infection* causes compression of these nerves, leading to referred dental pain (nerves just outside mucosa of sinus) Anterior & middle SA in intraorbital canal, posterior SA from pterygopalatine fossa PALATINE- related (from pterygopalatine fossa) - Nasal cavity innervation: induce secretion, all V2 except ethmoidal n. of V1) - *palatine nerves* 1. *Greater palatine* 2. *Lesser palatine* 3. *Nasopalatine*: terminates by coursing thru incisive canal of hard palate 4. Posterior superior lateral nasal branch of V2
CN VII Lesions - what kind? - produced by? - what's affected? - symptoms - lesion location
*Bell's Palsy*: resulting from a *peripheral (infranuclear) lesion* at or distal to the stylomastoid foramen - infranuclear bc injury was distal to motor nucleus - spontaneous acute unilateral paresis or paralysis of facial muscles from inflammation of CN VII and edema with compression - produced by viral infection/neuronitis or vasospasm - all actions of the ipsilateral facial muscles are affected, wether motivated by voluntary, reflex or emotional input symptoms: - facial asymmetry w/ gravitation sagging of face & scalp due to loss of tonus of facial muscles - inability to wrinking forehead on command due to paralysis of frontalis - failure to retain tears and saliva in orbit and mouth due to paralysis of orbicularis oculi & orbicularis oris, respecitvely - retention of food in oral vestibule due to paralysis of buccinator note: lesion location determines full range of symptoms - symptoms of either LMN or infranuclear lesion of CN VII may be more extensive depending on the exact location of the lesion btw the pons & stylomastoid foramen (in one of the 5 segments described previously): - other symptoms may include dygeusia (messed up taste), hyperacusis (sound sensitivity), reduced lacrimation & salivation - branching pattern of CN VII: diagnostic significance (ex: temporal bone fractures 1. facial & vestibulocochlear nerve affected; peripheral motor facial paralysis, hearing loss (deafness), vestibular dysfunction (dizziness) 2. Peripheral motor facial paralysis, disturbances of taste sensation (chorda tympani), lacrimation, salivation 3. Motor paralysis, disturbances of taste & salivation 4. Peripheral motor paralysis, disturbances of taste & salivation 5. Peripheral motor paralysis CN VIII Vestibulocochlear innervates TMJ (close to ear) so there's an overlap in symptoms if there's a lesion in either area
*CN IX Glossopharyngeal* Afferent Fibers - cell bodies located where?
*GSA, GVA, SVA* - cell bodies all located in the *superior & inferior ganglia of CN IX* - central processes of the pseudounipolar sensory neurons in the 2 ganglia project as follows: *SVA* -> solitary nucleus (rostal) *GVA* -> solitary nucleus (caudal) *GSA* -> spinal trigeminal Nucleus
Pharyngeal branches of CN IX provide sensory innervation of mucosa lining the walls of the oropharynx. Mechanical stimulation of the oropharyngeal wall produces...
*Gag reflex* 1 Pharyngeal constriction 2 Palatal elevation 3 Glottis closure 4 Tongue thrust 5 Mouth opening
CN XII is vulnerable to...
*Iaotrogenic injury* in the increasingly common procedure known *Carotid Endarectomy* & *Carotid Artery Dissection
What transmits CN VII and VIII?
*Internal Acoustic Meatus* transmits CN VII and CN VIII via similar courses *Both vulnerable formation of acoustic neuromas (vestibular schwannomas) as they enter the meatus* - Benign encapsulated by perineurium - Compromise acoustic perceptions - Cause dizziness - May lead to facial muscle weakness - If it grows large enough it can also compress CN V
*CN IX Glossopharyngeal* Efferent Fibers
*SVE* - LMV cell bodies in the nucleus amiguus of the medulla *GVE* - preganglionic parasympathetic neurons in the inferior salivary nucleus
Tonsilar & lingual branches of CN IX maybe lesioned during a...
*tonsillectomy* eliminating ALL sensation from the ipsilateral posterior 1/3 tongue
Summary: 5 distinct segments of CN VII (defined within facial canal)
- *Labyrinthe*: passes above the labyrinth housing the vestibular system - *External Genu*: includes the geniculate ganglion - *Tympanic*: travels posteriorly & laterally along the medial wall of the middle ear cavity - *Mastoid*: descending gives rise to the nerve to stapedius and the corda tympani - *Trunk*: gives rise innervation of mimetic muscles and stylohyoid & posterior digastric
*CN V* Trigeminal ganglion (no proprioceptive sensors here) -> GSA fibers -> single, long sensory nucleus of CN V (2/3 portions): these have 2ndary neurons receiving input from primary neurons in the trigeminal ganglion:
- *Pontine trigeminal (principal sensory) nucleus* - touch sensation from the face - *Spinal trigeminal tract & nucleus* - pain & temperature
*CN V* Spinal trigeminal tract & nucleus - pain & temp
- Also receives GSA inputs from CN VIII, IX, and X - 3 components rostral -> caudal thru brainstem 1. *nucleus oralis* (face touch) - receives tactile inputs from face, scap, oral cav, nasal cav 2. *nucleus interpolaris* (tooth pulp pain) - pain & temp from tooth pulp 3. *nucleus caudalis* (face pain & temp) - pain & temp from face, scalp, oral cav, nasal cav, supratentorial dura - caudal medulla -> upper cervical spinal cord - rostral (1) -> caudal (5) 4. 3/3 portion of *sensory nucleus of CNV*: mesencephalic nucleus - proprioception (impt in TMJ) - only primary sensory neurons here - neural crest-derived - highest, most rostral, closest to midbrain of all trigeminal nuclei in brainstem - note: trigeminal ganglion has no proprioceptive neurons; it uses ones form here
GVE Parasympathetics of CN VII Facial Nerve - origin - nerves (2) - where do they enter?
- Both nerves originate in the *superior salivatory nucleus* of the *pons* GREATER PETROSAL NERVE - enters pterygoid canal and is joined by the *deep petrosal nerve* (from autonomic plexus of ICA, postganglionic sympathetic fibers) to form the *nerve of the pterygoid canal/vidian canal* - conveys secretomotor fibers that synapse in the *pterygopalatine ganglion* and then innervates baby fluids via branches of *CN V2*: 1. Lacrimal Gland (zygomatic branch) 2. Nasal and Paranasal Mucosa (posterior lateral nasal/nasal palatine branches) 3. Palatine Glands (greater & lesser palatine branches) CORDA TYMPANI - conveys secretomotor fibers that synapse in the submandibular ganglion and innervate via the lingual n. of CN V3: *submandibular & sublingual salivary glands
4 PS-ganglia of head all suspended from CN V branches - Ciliary ganglion - Otic ganglion - Pterygopalatine Ganglion - Submandibular Ganglion
- Ciliary ganglion - CN III (inferior oculomotor) via CN V1 (short ciliary nn.) - Otic ganglion - CN IV (lesser petrosal) via CN V3 (auriculotemporal) - Pterygopalatine Ganglion - CN VII (greater petrosal) via CN V2 branches - Submandibular Ganglion - CN VII (corda tympani) via CN V3 (lingual)
*CN V* GSA - Afferent sensations from...
- Face & anterior scalp skin - Most dura - Cornea & conjunctive - Nasopharyngeal mucosa - Oral, nasal, & paranasal mucosa - Lingual body mucosa (anterior 2/3) - *teeth, gingiva, periodontium* - pain & proprioception from PA1 muscles & TMJ Dermatome borders are sharp, unlike spinal nerve dermatomes
CN VIII- Taste/Gustatory (SVA) vs. General Sensory (GSA)
- Gustatory receptors (SVA) on anterior 2/3 of tongue convey info via Corda Tympani -> *geniculate ganglion* -> nucleus solitarius - General sensory (GSA) input from filliform papillae of anterior 2/3 is conveyed via the *Lingual Nerve (V3)* Note: some sources claim the greater petrosal nerve also carries taste fibers from mucosa of soft palate & other sources suggest the Corda Tympani conveys these fibers too
Additional CN V lesions
- Herpes zoster infection - Ischemic lesions (branch of cavernous ICA) - Gradenigo syndrome (petrous apicitis - petrous apex infection, more common in pre-antibiotics era) - Dental and facial trauma (laforte fracture) - Neoplasm (trigeminal schwannomas, cerebellopontine angle tumors, perineural spread from face, cavities, or sinuses (retrograde metastasis in CN V & VII) - Hansen's Disease/Leprosy
*CN V* GSA Fibers - From lateral midpons in posterior cranial fossa via...?
- Large sensory root - Small motor root
CN V LMN lesions (SVE)
- Paralysis and atrophy of masticatory muscles - Ipsilateral deviation of jaw upon protusion - Contralateral deviation of soft palate & uvula
Selected major *cutaneous* branches of CN V (GSA): - V1 - V2 - V3 Note: testing GSA fiber integrity can be differentiated: - Light touch - rounded lucite tube - Pain - sharp object, prick skin
- V1: thru supraorbital foramen (supraorbital, supratrochlear, palpebral branch of lacrimal, infratrochlear, external nasal branch of anterior ethmoidal) - V2: thru infraorbital foramen (infraorbital, zygomaticofacial, zygomaticotemporal) - V3: thru mental foramen (mental, buccal, auriculotemporal)
Bc the *vestibular system* primarily provides sensory inputs about the head on the body, the CNS also relies on other sensory modalities to determine overall body position and movement
- Visual inputs convey info about mvmt w/ the environ & direction of vertical (CN II + III inputs combine) - *VOR-Vestibulocular Reflex* coordinates eye movements to compensate for movements of the head so that *visual fixation* upon a chosen object may be maintained even as the head moves - *vestibulo-reticular outputs* mediate *motion-sickness - sense of disequilibrium: nausea, vomiting, pallor, systemic hypotension - Proprioceptors convey inputs about joint position and muscle stretch, providing info concerning relative alignment of body segments to each other & the support surface. - Postural Control via innervation of the extensors of the posterior neck, back and lower limb to support the body against the pull of gravity.
*CN V* SVE - Brachial motor nerves - innervates? - where? - manifestation?
- innervates 8 PA1 muscles - Only in V3 mandibular division: arise from LMNs in the motor/masticator nucleus of CN v in the tegmentum of the pons (btw mesencephalic and pontine/principal nuclei of GSA fibers of CN V) *Jaw jerk reflex*: tap mandible at downward angle on chin when mouth is slightly open, and masseter contracts - reflex normally absent/weak - *exaggerated/brisk response: UMN pyramidal tract lesion about the motor/masticator nucleus* - a true monosynaptic stretch reflex initiate by stimulation of muscle spindle proprioceptors (not a dramatic response)
Muscular branches of 3rd division of CN V - *V3*
- only division with branchial motor fibers (PA1 muscles) - V2 SVE fibers innervate: * 4 muscles of mastication: * tensor tympani * tensor veli palatini * mylohyoid *anterior digastric muscular branches: *deep temporal*: ascend side of head btw muscle & neurocranial wall, *surgeons often take trans-zygomatic approach to spare these nerves innervating temporalis* - masseteric - lateral pterygoid - nerve to mylohyoid (mylohyoid, anterior digastric, nerve to tensor tympani, nerve to tensor veli palatini, medial pterygoid nerve)
CN XII Lesions (5) A unilateral CN VII lesion: ? (How do you test it?)
1 Genioglossus protrudes the tongue via contraction of paired muscles at tongue base - Unilateral CN XII lesion: patient will "lick her wounds. Test integrity of CN XII to protrude tongue. - Ipsilateral atrophy on all muscles on affected side - Fibrillation and fasciculations (twitching) - Dysarthria (mild) - Oral transport weakness 2 *Tumors/Meningiomas* of the posterior cranial fossa or nasopharynx 3 *ICA Aneurysm* or dissection below the skull base 4 *IJV puncture* below skull base Lesions w/n sublingual space or tongue: - *Neoplasm (SCC) - *Infection* or *Iatrogenic* from oral surgery along floor of the mouth
4 trigeminal nuclei - names & innervation
1 Mesencephalic nucleus of trigeminal nerve - proprioception of face 2 Trigeminal motor nucleus 3 Principle (pontine) sensory nucleus of trigeminal nerve - touch & proprioception of the jaw 4 *Spinal nucleus* - touch, temp, pain, proprioception of face
CN VII - Facial Nerve - Roots?
2 Roots 1. *Nervus Intermedius* - smaller, complex - Preganglionic parasympathetics (GVE) arise from the salivatory nucleus (where 1st order PSNS neurons are carried) - Afferent fibers arise from primary cell bodies in *geniculate ganglion/external genu* in the temporal bone. Special sensory (SVA - taste, taste fibers terminate in the rostal end of the *nucleus solitarius (gustatory nucleus)* CN VII, IX, X all have afferent taste fibers sent here. General sensory (GSA) - terminate in *spinal nucleus of CN V* 2. *Motor root* - largest part of the nerve - Branchial motor fibers (SVE) of PA2 musc - Arise from *motor nucleus of the facial nerve*, axons of motor neurons exiting the nucleus wrap around the *abducent nucleus* forming the *internal genu* of the facial (external genu, geniculate ganglion is seen when exiting the brainstem to enter the temporal bone)
Cranial Nerves VII & VIII emerge from the brainstem @...
@ Inferior Pontine Sulcus in line w/ the postolivary sulcus of the medulla (in angle btw lateral pons & inferior aspect of cerebellum - cerebello pontine angle)
Major branches of 3 division of CN V - *V3* *sensory* branches
BAIL 1. Buccal: long, head to buccinator or enters buccinators in some areas but doesn't innervate (CN VII does) 2. Auriculo-temporal: formed by 2 root that surround *middle meningeal artery* as it approaches *foramen spinosum* - *vulnerable to condylar neck fracture* 3 Inferior Alveolar - dental branches (plexiform) - mental nerve 4 Lingual - anterior descendant of mandibular - general sensation (GSA) to: presulcal (ant 2/3) tongue mucosa, floor of mouth, mandibular gingivae - corda tympani of CN VII joins lingual nerve in infratemporal fossa - corda tympani also mediates sensation (SVA) from anterior 2/3 of tongue with lingual n. (GSA) - cord tympani also have GVE fibers that synapse in the SubM ganglion -> SubM& SubL salivary glands
*CN VIII Vestibulocochlear Nerve* has distinct vestibular & cochlear portions Vestibular & cochlear nerves are grouped together in single CN bc both sys evolved from the lateral line system present in all fish (sensory mech to sense current like human hair cells) COCHLEAR (Auditory) NERVE - what kind of fibers? - composed of - components (3) - mechanism
COCHLEAR (Auditory) NERVE - *SSA* fibers for hearing - composed of central processes of neurons in the *spinal ganglion* - sound waves induce vibration of the tympanic membrane & ossicles in the tympanic cavity - cochlea consists of 3 *side-by-side concentrically coiled tubes* which make 2.5 turns around the Modiolus. 2/3 tubes are continuous at the Helicotrema (center of spiral, fluid waves move towards it) - *mechanism*: stapes moves in & out of oval window like a piston, generating pressure waves w/n perilymph of the cochlea > organ of corti > waves in the endolymph > stimulating the hair cells (in organ of corti) > perilymph to round window (dissipates) - central projections from the auditory nerve to cochlear nuclei in the *caudal pons*. Cochlear nuclei are tonotopically organized (vs. somatotopically) - Acoustic inputs project to cortex in the *temporal lobe* along lateral sulcus, but the processing of bilateral acoustic inputs begins in the brainstem. *time of arrival* and *intensity* differences btw left/right ears are analyzed to permit localization of sound sources
CN VIII Lesions - causes - symptoms
Causes - *Viral labyrinthitis* - *Meniere's Disease* (imbalance of endolymph): surgeons try not to incise CN VIII when removing tumors/neuromas bc that can cause this disease - *Acoustic neuroma* (benign tumor of Schwann cells) Symptoms - Sensorineural deafness - Tinnitus (ringing, whistling, booming) - Dizziness - Vertigo (illusory perception of motion) - Nausea & vomit - Nystagmus (rhythmic oscillation of the eyeballs) producing *oscillopsia* (jumping of visual environment)
CN VII SVE - Brachial Motor Components - innervate - branches - tumors
Innervate 2nd arch derivatives: muscles of facial expression, stylohyoid & posterior digastric, stapedius Branches: most SVE fibers ramify w/n the parotid gland at the *parotid plexus* (by ECA and retromandibular vein, 5 of 6 main branches) - "Painfully, two zebras bit my coccyx" - *Posterior Auricular Nerve* doesn't enter parotid, instead heads up & posterior (mostly efferent, some afferent fibers) - *Temporal*: raise eyebrow to test forntalis - *Zygomatic*: shut eye tight to test orbicularis oculis - *Buccal*: pucker lips, bare upper teeth, blow out or whistle to test buccinator - *Marginal Mandibular*: bare lower tooth - *Cervical*: flare skin of neck to test platysma Tumors of the Parotid Gland may compress or destroy facial nerve fibers - extension back toward the stylomastoid foramen and facial canal should be carefully sough fro any parotid mass (retrograde: perineural spread all the way to the cranial cavity - fatal)
Trigeminal neuralgia (tic douloureux)
Pain symptoms: * lacinating (piercing/stabbing) * paroxysmal (violent) * intermittent * unilateral * disabling - Pain freq triggered by moving mandible, smiling/yawing, or by cutaneous or mucosal stimulation - almost always adults; often seniors - usually w/n V2 and V3 (midfacial and lower facial region pain) Etiology: - demyelination or compression of sensory root endocranially (by superior of cerebellar artery) - Post-therapetic neuralgia - Tongue piercing - Idiopathic - Usually not of dental origin Tx: - Analgesics - Anticonvulsants - Surgical decompression - Rhizotomy (sever nerve roots in spinal cord) - Gamma knife ablation (spec destruction of CN V sensory root)
GSA of CN VII Facial Nerve - which nerve?
Posterior Auricular Nerve: in addition to innervation of *occipitalis & some auricular musculature*, also contributes to the complex cutaneous innervation of the external ear (also contains an afferent component) - concha skin (hollow funnel leading to EAM) - small patch of skin behind ear - portion of superficial aspect of *tympanic membrane* (ear drum) - *why it is painful when ruptured*
CN XII lies very deep to the oral mucosa of the floor of the mouth. It runs along the ____________ and is medial to the _____________
Runs along the lingual artery and medial to Hyoglossus
What type of fibers make up the trigeminal nerve?
SVE (1st PA) and GSA (touch, pain, temp) fibers
*CN VIII Vestibulocochlear Nerve* Membranous Labyrinth
Series of communicating sacs & ducts suspending the body labyrinth w/n the otic capsule of petrous temporal bone - interval separating the membranous labyrinth is filled w/ a CSF-like fluid called perilymph - Membranous labyrinth itself contains *endolymph* - Membranous labyrinth components: utricle, saccule, semicircular canals, cochlear duct
*CN VIII Vestibulocochlear Nerve* - What kind of nerves? - What do they convey? - recall: organs of hearing & balance are embedded w/n the *petrous part of the temporal bone/petrous pyramid* (once CN VIII enters internal acoustic meatus, it never leaves temporal bone) - cartilaginous components laterally are continuous w/ the auricle and lead to the bony...
Special somatic afferent (SSA) convey sensory input concerning - sound from the *cochlea* - equilibrium from the semi-circular canals of the vestibular system cartilaginous components go from auricle to body *external auditory meatus*
CN VIII SVA / Taste
Taste buds are around the gustatory nerve endings CN VII, IX, and X - detect water-soluble tastants - widely distributed: entire lingual dorsum and sides, epiglottis, lingual aspect of soft apalte, posterior oropharynx - most taste buds are found in troughs around circumvallate papillae, anterir & posterior to the sulcus terminalis (some are found on the fungiform & foliate papillae as well, note: filliform papillae (hair-like) have no tastebuds, GSA only)
Course of the Facial Nerve
Thru 1 *Internal Acoustic Meatus* > 2 *Facial Canal* w/n petrous portion of temporal bone (where it forms its external genu/geniculate ganglion, afferent fib in *nervus intermedius*) > CN VII branches extensively in facial canal 3 *Greater Petrosal Nerve* > - complex course - exits temporal bone thru *hiatus of the greater petrosal nerve* into middle cranial fossa - nerve runs toward lateral wall of *foramen lacerum* and goes thru to head anteriorly to *vidian canal* to reach *pterygopalatine ganglion* 3 *Corda Tympani* > - eventually joins facial nerve - named so bc it passes along the lateral wall of the *tympanic cavity* - *iter chordae posterius*: entry point of cord tympani into tympanic cavity - exits cranium thru iter chordae anterius at the medial end of the *petrotympanic fissure (on floor of mandibular fossa of the TMJ) to enter the infratemporal fossa 4 *Nerve to Stapedius* - innervate small muscle: *stapedius*: dampen super loud sound to *prevent damage* - after giving rise to the main branches, the *facial nerve trunk* exits cranial base via the *stylomastoid foramen* - these fibers innervate the *muscles of facial expression* and *stylohyoid & posterior digastric* (temporal, zygomatic, buccal, mandibular, cervical)
What are the branch exit points from cranial fossa: - V1 - V2 - V3 What do all 3 branches contribute to? Note: trigeminal ganglion sits in the trigeminal impression on the floor of the middle cranial fossa in the dural Meckel's Cave
V1: *superior orbital fissure* to orbit V2: *foramen rotundum* to pterygopalatine fossa - V1 & V2 course thru cavernous sinus on its way (like CN III, IV, VI) V3: *foramen ovale* to infratemporal fossa All 3 branches contribute to *meningeal branches* innervating the dura of the anterior and middle cranial fossa, falx cerebri, and tentorium cerebelli (tentorial nerves)
CN XII is inferior to the 2 sensory nerves of the tongue...
V3 Lingual Nerve and CN IX Glossopharyngeal nerve
*CN VIII Vestibulocochlear Nerve* has distinct vestibular & cochlear portions Vestibular & cochlear nerves are grouped together in single CN bc both sys evolved from the lateral line system present in all fish (sensory mech to sense current like human hair cells) VESTIBULAR NERVE - function - composed of - convey inputs from
VESTIBULAR NERVE - responsible for controlling posture, balance and equilibrium - composed of the central processes of bipolar neurons in the *vestibular ganglion* - *vestibular system* enables perception of position and motion in relation to gravity as well as the spatial orientation of both head and body in relation to vertical - peripheral processes of bipolar neurons in the vestibular ganglion convey inputs: 1. from *maculae* of the utricle & saccule, otolithic organs, which detect linear accleration and motion due to gravity and translation mvmt 2. from the *ampullae* of the *semicircular canals* - which detect changes in angular motion and rotary acceleration of the head in any direction relative to the vertical during quiet stance
