Download Cranial nerves (L15)

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