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BIOL 110 (57)

Lectures I and II

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BIOL 110
Christine Dupont

Cranial Nerves Lectures I and II CN I = olfactory • Special sensory nerve of smell • Olfactory nerve = bundle of nerves, located in upper nasal mucosa o 25 million olfactory cells on each side of mucosa o bipolar neuron cells: their deep processes merge to make plexiform network o plexiform network then recombine to give bundles of nerve that give olfactory nerve, proper • Nerves come through cribriform (=sieve like) plate: piece of ethmoid bone o Ethmoid bone: thin, complex bone between orbits o In middle of cribriform plate: cristae galae: where falx cerebri attaches in front o Holes in cribriform plate: where nerves are transmitted into end of anterior portion of endocranial fossa • Nerves are attached to olfactory bulbs, which are then joined to olfactory tracts o Bundles of nerve travel through cribriform to olfactory bulbs where they synapse @ mitral cellsolfactory tracts o Olfactory tracts connected to telencephalon o Olfactory bulbs can break  lost of smell (anosmia) o Olfactory cells: degenerate at 1% a year; regenerate CN II: optic • Special sensory nerve of vision • Nerve begins in retina in back of eyeball o Retina: developmentally is an outgrowth of brain o Retina converges at optic disk to become continuous with optic nerve o Optic nerve is surrounded by meninges because of connexn with retina o Each optic nerve: million of ganglion cells  Ganglion cells synapse at bipolar cells  Bipolar cells lengthen to form rods and cones • Nerve travels through optic canals: oblique openings o Optic canals open at junction between anterior middle cranial fossae • Two optic nerves meet to form optic chiasma: in front of pituitary o Nerve fibers from medial half of retina cross in optic chiasma o Lateral fibers stay on the same side o Effect: carry neurons in related visual field end up in same optic tract o The fibers go back to the thalamus or midbrain (lateral geniculate ganglion or superior colliculi ganglion) CN III: oculomotor o Comes off of midbrain and goes under the lesser wing of sphenoid o Goes through superior orbital fissure: opens into back of orbit o Nerve is lateral to optic nerve o Associated with all muscles of the eye: both smooth and striated o General somatic motor and parasympathetic component o General somatic motor o Supply most (5 out of 7) of the muscles around eyeball that move it o Nerve splits immediately after exit o Superior division:  Superior rectus: moves eyeball  Levator palpebrae superioris: elevator of upper eyelid o Inferior division  Medial and inferior rectus  Inferior oblique  Three extraocular muscles move eyeball o Parasympathetic: third division of CN III o Synapse in ciliary ganglion on way to eye  Postganglion parasympathetics carried in short ciliary nerves o Ciliary nerves fibers pierce eyeball and travel to front to supply two smooth muscles  Pierce sclera and travel between outer and middle coat  Sphincter pupillae: in the iris, controls size of pupil (amount of light)  Ciliary muscle: surrounds the lens, allows up-close focus o Nasociliary nerve from trigeminal suspends ciliary ganglion but does not synapse o All 4 parasymp ganglion suspended by a fiber from trigeminal nerve CN IV: trochlear o Smallest CN o Comes off back of back of midbrain o Passes on side of middle cranial fossa o Exits through superior orbital fissure to travel in medial roof of orbit o Somatic motor nerve to superior oblique muscle that moves the eye o Superior oblique muscle: o Changes direction of pull within the orbit by passing through a fibrocartilage loop in superomedial angle of orbit= trochlea o Origin: apex of orbit o Insertion: above eyeball o Muscles courses along upper medial angle of orbit CN V: trigeminal o Largest cranial nerve o Emerges from pons and goes thru middle cranial fossa o Forms huge semilunar/trigeminal sensory ganglion (medial side of middle cranial fossa) and divides into 3 pieces o Primary somatic sensory nerve of head; also a motor nerve of first pharyngeal arch 1, 2, 3 o Labelin1 scheme: CN V o CN V = ophthalmic, entirely sensory o Goes to superior orbital fissure to join CN III and IV to go to back of orbit o Supplies cornea, conjunctiva, eyeball, lacrimal gland, forehead, nose, upper eyelid, frontal and ethmoid sinuses o Emerges in forehead from frontalis o Branches  Lacrimal: small, lateral • provides somatic sensory to lacrimal gland, adjacent eyelid and conjuncitva (doesn’t control secretions)  Frontal (supraorbital, supratrochlear): both travel to upper medial corner of eye through foramen • Terminal branches on forehead: sensory  Nasociliary • Under levator palpebrae superioris and superior rectus • Four branches o Suspends ciliary ganglion with sensory root: see above  Fibers are considered part of short ciliary nerves  Short ciliary • Parasympathetic • To back of eyeball, pierce sclera and travel on eyeball • May contain some sympathetic fibers o Long ciliary nerves:  Follows same course as short ciliary  Sensory to eye  Primary carrier of sympathetics to ciliary body, iris • dilate muscles Side note: sympathetics travel in sympathetic trunk into neck where there are 3 cervical ganglion • superior cerv. Ganglion o base of skull, above of carotids o where sympathetics of head will synapse o fibers form plexuses around internal and external carotid o fibers can come up with internal carotid and contribute to CNs o Ethmoidal and nasal: from ethmoidal and sphenoidal sinuses, nasal cavity and front and tip of nose  pierces medial wall of orbit  Supplies mucosa  Pierces forward to supply nasal cavity: nasal nerves o Infratrochlear: from superomedial corner of orbit below trochlea  Just sensory o CN V =maxillary, entirely sensory o Goes thru foramen rotundum (a round hole behind the medial angle of the superior orbital fissure, that goes forward in skull) o Takes a bent course to go to floor of orbit; travels the infraorbital fissure and thru infraorbital canal and out the infraorbital foramen o Sensory innervation of cheek; sensory for everything from floor of orbit to roof of mouth  Upper jaw, maxillary sinus, nasal cavity, middle of face, middle ear cavity, auditory tube and dura o Branches  Supends pteryogopalantine ganglion (CN VII) • To reach ganglion, travels vertically along pteryogomaxillary canal • Fibers pass thru then go medially along nasal cavity to palate  Zygomatic: from cheek • Sends sensory thru lateral wall of orbit onto cheek  Nasal branches: from mucous membranes of nasal sinuses  Palatine branches (lesser, greater, nasopalatine) • Fibers pass through pteryogpalatine ganglion • Descend through palatine canal and exit respective foramen • Sensory nerves to palate  nasopalatine nerve • supplies nasal septum • goes to front of palate and exits out opening behind upper incisors (incisor foramen) • sensory to front of palate  Superior alveolar branches from upper teeth, gums, maxillary sinus • Maxillary sinus: hollow cavity from floor of orbit to roof of mouth; lined with mucosa  infraorbital: terminal branch  sensory between orbit and mouth  meningeal: from middle and anterior cranial fossae • given off before exiting foramen rotundum • supplies dura around area  pharyngeal: passes thru ganglion • from middle ear cavity and auditory tube • upper part of pharynx (back of throat) • connection to middle ear o CN V = mandibular, sensory and motor o Largest division o Exits skull thru foramen ovale (postero lateral from foramen rotundum; oval opening); exits at lower jaw o Supplies sensory to lower jaw (tongue, lower teeth, chin, cheek, floor of mouth, anterior 2/3 of tongue, tympanic membrane, salivary glands) o Also supplies motor innervation for mastication  Branchiomotor: associated with first branchial/pharyngeal arch  Striated muscles are supplied  Branches to muscles of mastication • Temporalis, masseter, medial and lateral pterygoids  Branches to floor of mouth: mylohyoid, digastric (anterior belly), tensor veli palatine (tenses roof of palate) and tensor tympani (tenses ear drum) o Branches after motor branches  Buccal • Sensory from cheek, internal and external • Pierces buccinator to mucus membranes and skin  Auriculotemporal • Sensory from external acoustic meatus and tympanic membrane, temporal region and temperomandibular junction • Suspends otic ganglion (CN IX)  Lingual • Sensory for anterior 2/3 of tongue, floor mouth, mandibular gums • Joined by piece of chorda tympani of facial nerve • Suspends submandibular ganglion (CN VII)  Inferior a
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