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Cranial nerves (L15) Take home points -motor & sensory nuclei for most are in brainstem CN 1 & II are exceptions to this rule -most of these nerves have only 1 function -new modalities will come into play in the cranial nerves General concepts -in most cases, with cranial nerves sensory & motor are carried on separate nerves! -arise from brainstem or upper spinal cord -almost all limited to parts of head & neck major exception? -motor & sensory usu. not carried by the same nerve Fiber types -NEW classifications (old SA/E, VA/E), new SSA, SVA, SVE: special *SA/E – somatic sensory/motor – most of what you have seen so far *VA/E – visceral sensory/motor – autonomic nerves, both sympathetic & parasympathetic -SSA special somatic afferent *sight, CN II Note that all the senses are unique to the *sound, CN VIII head only! Sight, sound, taste -SVA special visceral afferent *sound, CN I *taste, CN VII, CN IX, CN X -CN I actually in nasal cavity, nerve tract is what is seen on the brain -SVE special visceral efferent (voluntary motor!) *motor to muscles of pharyngeal (brachial) arch origin (NOT from scerodermomyotome!) *CN III, CN VII, CN IX, CN X -only 1 CN in the anterior cranial fossa; 5 CNs that will exit via the middle fossa and 1 important artery; 6 CNs that will exit via the posterior fossa and some very important venous stuff Cranial -cribriform plate CN I (anterior cranial fossa) foramina -optical canal CN II, ophthalmic a. -superior orbital fissure ophthalmic branch of CN V, CN II, CN IV, CN VI (these all pass through the cavernous venous sinus before entering the SOF – this is a very important clinical point!) -foramen rotundum maxillary branch of CN V (CN V2) (also passes through the cavernous sinus) ***internal carotid also passes through the cavernous sinus -foramen ovale mandibular branch of CN V (CN V3) -foramen spinoum middle meningeal a (all above through middle cranial fossa) *supplies most of blood to dura mater -internal acoustic (auditory) meatus CN VII, CN VIII, labyrinthine a. -jugular foramen CN IX, CN X, CN XI, sigmoid & inferior petrosal venous sinuses -foramen magnum spinal roots of CN IX, these are entering the cranial cavity, not exiting! *meninges & CFS pass through as well -hypoglossal canal CN XII (all above through posterior cranial fossa) CN I -olfactory SVA fibers -multiple nerves in the olfactory area of the nasal cavity & septum -axons pass though cribriform plate of ethmoid bone; synapse on 2nd order neurons in olfactory bulb *2nd order axons pass through olfactory tract as 2 distinct bands - olfactory striae lateral goes to temporal piriform cortex; medial goes thru anterior commissure to other side -only cranial nerve to enter cerebrum directly CN II -optic nerve & the eye are actually direct extension of the developing brain SSA fibers -retinal receptor cells project their axons as the optic nerves -fibers decussate in the optic chiasm optic tracts terminate in the lateral geniculate nuclei of the thalamus -final axons course widely thru cortex as optic radiations to visual cortex in occipital lobe CN III -has 2 functions GSE – somatic motor to 4 extraocular muscles and levator palpebrae superioris *superior, medial, & inferior recti & inferior oblique *also proprioceptive to these mm. *motor nucleus is in the midbrain -GVE parasympathetic motor to the sphincter pupillae & ciliary mm. *sphincter pupillae constricts pupil to control light input *ciliary changes shape of lens to accommodate changes in distance vision *primary neurons in Edinger-Westphal nucleus in midbrain *synapse in ciliary ganglion – postganglionic axons travel to mm in eye via short ciliary nn. CN IV -only one function & only one muscle to do it to GSE to the superior oblique m; nucleus of trochlear n. is in midbrain, just caudal to oculomotor nucleus CN V -also called the sensory nerve of the face! both deep & surface structures -3 major divisions, each based around a major branch arising from the trigeminal ganglion all 3 divisions carry GSA sensory fibers to sensory nucleus of V – 3 distinct subnuclei *mesencephalic – sensory component of SVE system of V *pontine – primarily touch sensation from face *spinal nucleus – pain & temperature, with some tactile -V3, the mandibular division, also carries SVE motor fibers to the muscles of mastication -SVE motor innervation goes to mm which arise from the embryological structures known as pharyngeal (brachial) arches (from motor nucleus of V) -each division exits the cranial vault thru a different foramen -primarily GSA arises from largest of the brainstem ganglia – from near superior colliculus to upper C-spine -branches of V go everywhere in the face, therefor it is very common for branches of other CNs to “hitch a ride” on the branches of V – including CN VII & CN IX *that means that some branches of V may carry modalities not arising in V – they are always considered part of the original nerve, not V! CN V1- OPHTHALMIC -supplies region above the canthus of the orbit; also supplies the globe with sensory fibers -extends down nose to the tip CN V2- MXILLARY -supplies triangular region between the canthus of the eye & the corner of the mouth -also supplies innervation to the upper teeth and most of the nasal cavity & sinuses CN V3 – MANDIBULAR -supplies region that overlies the mandible; supplies lower teeth -in addition to GSA fibers, also has SVE motor fibers to mm of mastication temporalis, pterygoids, masseter -only CN V branch that has intrinsic SVE motor fibers! CN VI (abducens ) CN VII -only one function & one muscle GSE to lateral rectus muscle; nucleus of abducens n. is in the pons, near the median plane -important! carries multiple modalities *SVE motor to mm of facial expression, etc. – facial motor nucleus *GVE (para) to pterygopalatine & submandibular ganglia – superior salivatory nucleus *GSA to small region posterior to ear – geniculate ganglion *SVA (taste) to anterior 2/3 of tongue – nucleus solitaries (gustatory nucleus) -exits the cranial vault with CN VIII -3 principle branches facial nerve proper (SVE & GSA); greater (superficial) petrosal nerve (GVE); chorda tympani nerve (GVE & SVA) -many smaller branches -arises from two roots *motor root – from nucleus in pons – SVE *sensory root – nervus intermedius – GVE from pons, GSA, SVA from geniculate ganglion -in temporal bone, has sensory ganglion – geniculate ganglion *cell bodies only – non synapses – WHY? -2 branches arise split at geniculate ganglion *greater (superficial) petrosal nerve – parasympathetic to pterygopalatine ganglion; to salivary glands *facial nerve proper 2 branches – nerve to stapedius (SVE), chorda tympani (SVA, GVE) -facial nerve proper exits through stylomastoid foramen -5 main branches from here all motor (SVE) *temporal *zygomatic *buccal *marginal mandibular *cervical -also small posterior auricular branch – SVE to occipitalis & GSA to small area posterior to ear CN VIII -two ganglia associated vestibular & cochlear -vestibular SSA fibers *input from semicircular canals, utricle, & saccule *sense linear movement of head *ganglia in medulla medial to inferior cerebellar peduncle -cochlear SSA fibers *input from cochlea *sense sound vibrations – like the dulcet tones of my voice *ganglia in medulla lateral to ICP CN IX -carries multiple modalities *SVA taste to posterior 1/3 of tongue (tractus solitaries) *SVE to 1 muscle – stylopharyngeus (nucleus ambigus) *GVE (para) to parotid gland via otic ganglion (inferior salivatory nucleus) *GSA to middle ear space, pharynx, posterior tongue & soft palate (trigeminal nucleus; gag reflex n.) -arises from medullary nuclei; exits cranial vault with CN X & CN XI (and jugular bulb) -forms part of the pharyngeal plexus of nerves, with CN X & sympathetics -has numerous branches – all after exiting from jugular foramen *tympanic – GSA to middle ear; also gives rise to lesser petrosal nerve – GVE to otic ganglion, postganglionic fibers run with auriculotemporal branch of V3 *glossal – SVA, GSA to posterior tongue *pharyngeal – GSA to pharynx, SVE to 1 muscle *carotid – GSA to carotid body (chemoreceptor) and carotid sinus (baroreceptor) -plays a major role in gag reflex – clinical importance? -innervates only 1 muscle? TEST QUESTION CN X -multiple modalities *GSA – lower pharynx, larynx, & root of tongue ( trigeminal nuclei) *GVA – thoracic & abdominal organs (tractus solitaries) *SAV – epiglottic taste buds (tractus solitaries) *SVE – motor to soft palate, pharyngeal mm, laryngeal mm (nucleus ambiguous) *GVE – (para) to thoracic & abdominal organs (dorsal vagal nucleus) -widest distribution of any nerve in the body -most is inferior to the head & neck – parasympathetic innervation to thoracic & abdominal viscera -distribution in neck pharyngeal branch to muscles of pharynx & pharyngeal mucosa; superior laryngeal – sensory to upper larynx, motor to 1 muscle; recurrent laryngeal – sensory to lower larynx, motor to rest of laryngeal mm -distribution most is to thoracic & abdominal viscera – this will be covered in blocks 4 & 5 – most of this is GVE/A, parasympathetic -important branches in neck *pharyngeal – SVE to pharyngeal mm (nucleus ambiguous) *superior laryngeal – SVE to 1 muscle (nucleus ambiguous), GSA to upper larynx (trigeminal nucleus) & SVA (taste) to epiglottic region (tractus solitaries) *recurrent (inferior) laryngeal – SVE to all other mm of larynx (nucleus ambiguous) & GSA to inferior larynx (trigeminal nucleus) CN XI -only 1 function & two muscles nucleus in upper 5-6 cervical segments of the spinal cord; jointed by a branch of CN X while exiting the skull -GSE to sternocleidomastoid & trapezius mm. CN XII -important relationship to carotid artery – typically found at or very near to the bifurcation of the carotid -major motor nerve -GSE to 3 pairs of extrinsic tongue muscles & all intrinsic tongue muscles -nucleus in medulla origin is numerous small fibers that coalesce into single nerve Autonomic notes -head & neck region is the only place we find discrete, grossly visible parasympathetic ganglia -ciliary located in orbit, adjacent to CN III *parasympathetic 2ndary neurons from CN III; project to sphincter pupillae & ciliary mm -otic located in infratemporal fossa, adjacent to auriculotemporal branch of V3 *parasympathetic 2ndary neurons from CN IX (lesser petrosal nerve); project to parotid gland -pterygopalatine located later to posterior nasal cavity, receives fibers form 3 different nerves for distribution to nasal cavity, sinuses & palate *parasympathetic 2ndary fibers from CN VII (greater petrosal nerve); project to mucosa of nasal cavity & sinuses -submandibular located in floor of oral cavity, adjacent to root of tongue, adjacent to lingual branch of CN V3 *parasympathetic 2ndary neurons from CN VII (chorda tympani); project to sublingual & submandibular glands -where we have parasympathetics, we must have sympathetics is the converse true? -sympathetics in head & neck *primarily arising from the superior cervical ganglion (SCG); 2ndary neurons at the uppermost end of the sympathetic trunks *2ndary processes travel to carotid artery & ten distribute by riding with branches of both internal & external carotid