-----start 11.04.96 anatomy cranial nerves---------------

no slides technical difficulties.
handout wasn't given to us either for some bizarre unknown reason.


don't get hung up on different location/foramen will see that in lab.

objectives: understand nomenclature and types of nerve fibers in cranial 
nerves
			know general location of cranial nerves
			know the names and numbers of the cranial nerves
			know what nerves are either sensory only, motor only, or mixed
			don't have to memorize all the other kinds of fibers
			understand clinical significance of each nerve
Today's lecture is focusing on the NERVE ONLY. There are OTHER clinical 
signs or location in the brainstem that can alter these things.  When we 
take neuro we may learn things which modify what we've learned today. 
Some nerves have many functions but are not clinically significant. If 
you can't see, examine, or test it, it isn't clinically significant and 
might not be on the exam.

BREAKDOWN of terminology

nerves are categorized in one major level as EFFERENT or AFFERENT:

EFFERENT: effectors. from CNS out to periphery. motor function 

AFFERENT: to the brain. most/all sensory function.

The a or the e is usually the last letter of the nomenclature

General Somatic Afferent: gsa.

First letter is G for GENERAL or S for SPECIAL. 

GENERAL: everything that isn't special
SPECIAL: things that are special: senses, vision, smell, etc, all special 
nerves are in the cranial nerve system.

Middle letter is a V or an S

VISCERAL: everything that isn't somatic. some ectodermal derivatives.
SOMATIC: all those things innervated that are derived from somites: 
muscles, etc.

If someone said "give an example of a general somatic afferent"  you 
should eventually be able to .

Those nerves that have single function:

SENSORY ONLY

Cranial I: olfactory SVA
II: optic SSA
VIII vestibular cochlear SSA

MOTOR ONLY

III: oculomotor GSE
IV: abducens GSE
VI: trochlear GSE

XI: accessory SVE innervates muscles from brachial arteries rather than 
somites
XII: hypoglossal GSE

MIXED

V: trigeminal GSA (sensory) and GVE (motor)
VII: facial GSA sensory;          GVE motor
IX: glossopharyngeal
X: vagus

I: primary function is olfaction, smelling. nerve in nasal cavity, 
travels through tribiform plate. clinical significance is questionable. 
most lesions are on one side, it's hard to ask an animal to smell w/one 
nostril. If TOTALLY affected, eg bilaterally, smell not possible

II optic, sensory only, special somatic afferent. in the retina/optic 
canal. is actually part of the brain: it's enclosed by meninges, has 
subarachnoid space, CSF; myelin is laid down by oligodendrocytes. so 
brain diseases affect this nerve. this nerve is clinically significant. 
blindness is seen secondary to damage of this nerve. blindness clinically 
will be partially dilated pupil that doesn't constrict when exposed to 
light. however, since the optic nerve decisates - at optic chiasm is 
crosses over, a portion of fibers cross to other side of the brain - 
different degree in diff species. so, say L nerve is affected, L pupil 
will still constrict if you stimulate right side, because the reflex arc 
picks up info on the good side

III oculomotor: motor only. GSE and GVE. The GSE innervates ocular 
muscles. GVE is the parasympathetic innervation to the eye. the pupil is 
governed by symp and parasympathetic nerves. parasympathetic stimulation 
constricts the pupil. So with damage to nerve III, pupil will not 
constrict at all. In this case, it doesn't matter which side you 
stimulate, because you need to motor function to constrict the pupil. 
only superior oblique and lateral rectus are left unaffected. you would 
see a ventrolateral strabismus with damage to this nerve.
most important: has parasympathetic fibers that constrict the pupil and 
it innervates most of the extrinsic ocular muscles.

IV and VI: trochlear and abducens: both GSE motor nerves. IV/trochlear 
constricts the dorsal oblique muscle of the eye. the only time you see 
this, it's not really clinically significant, but most eyes have a vein 
that may be deviated if this nerve is damaged. VI/abducens innervates 
lateral rectus muscle


III, IV, and VI all exit through orbital fissure.

V: trigeminal: sensory and motor. opthalmic branch, maxillary branch, 
mandibular.

Vi: ophthalmic: GSA very clinically significant, sensory to the forehead 
and medial orbit. with this nerve but separate runs a sympathetic branch 
to the pupil that we won't be held responsible for, but which dilates the 
pupil.
in orbital fissure

Vii: maxillary branch: GSA. sensory to the lateral head, nose and upper 
jaw. 
in foramen rotundum

Viii: mandibular branch: GSA and SVE. SVE is motor innervation to 
temporal and maceter (?) muscles. because these muscles are derived from 
brachial arches, not somites, which may account for TMJ myositis...
this nerve also responsible for proprioception in this region: ability to 
know where parts of your body are w/o having to look.
in oval foramen.
this nerve is VERY clinically significant. Can see temporomandibular 
muscle atrophy. ..if both sides affected you would assume that left and 
right nerve are damaged, and that would mean the brainstem would be 
affected.
unilateral: peripheral disease. neuritis. when you see nerve disease, the 
innervated muscle atrophies w/in days.

V, VII, and VIII are right next to each other as they exit the brain. 
there is a disease, idiopathic [something] disease: you see signs of VIII 
damage. But if ou also see V damage, it's probably something more like a 
brain tumor or something, since V is near VIII.

VII: motor to face. but sensory to face is V, so a reflex arc has to 
involve both nerves. VII has both sensory and motor - SVE motor to facial 
muscles and GVE parasympathetic innervation to lacrimal glands and 
mandibular salivary glands, and other glands. SVA - rostral 2/3 of tongue 
ability to taste (not clinically significant), and GSA: sensory to 
external auditory meatus.

clinical significance of VII really facial paralysis. you will see many 
cases and need to determine if its an idiopathic benign problem or brain 
tumor. If bilateral, probably not too significant, but if unilateral, not 
sure. need to look for involvement of V and VIII. if involvement of V and 
VIII *could* be peripheral dz, but probably not. *probably* at that point 
it would be a brain problem. VII paralysis: bell's palsy.

VIII: sensory only. vestibular and cochlear portion. both SSAs. 
vestibular = balance. the vestibular system is widespread, diffuse, etc. 
it has to be because it's balance. it gives you your position relative to 
gravity. it's very complex. lots of its energy goes to the eyes. eyes are 
key to balance. the body often seems to "follow" the eyes. so extraocular 
muscles get vestibular innervation. "physiological nystagmus" - turning 
head when walking eyes are fixed - turn-fixed-turn. disease of VIII 
causes pathological nystagmus. Slow phase is TOWARD side of lesion. there 
is a distinct fast and slow phase.

most cats of asian/oriental descent (siamese, burmese, persians) have a 
congenital defect causing eyes to oscillate. this is NOT nystagmus. 
oscillation doesn't have a fast/slow phase. 

a head tilt, circling - severe old dog idiopathic vestibular dz will see 
dogs ROLLING across the room. 

dogs with vestibular dz get better w/no help. people often plan to 
euthanize. most vets treat w/steroids. but you don't need steroids. it's 
self limiting. it probably will even start getting better w/in 24 hrs. 
But you NEED to make sure there is no OTHER nerve involvement.

VIII nerve clinical significance: nystagmus, head tilt, circling. if you 
lift dogs head or straighten the head (to asses type of nystagmus), you 
will see the eye has a ventrolateral strabismus, because the eye no 
longer "knows" the proper position. this also helps to differentiate from 
cerebellar dz.

cochlear nerve: hearing nerve. If it doesn't work, you don't hear, if it 
does, you do. hard to determine unilateral deafness in a dog.....usually 
not a huge deal except in puppies for breeding program. old dogs get 
deaf, age 13 and up. bilateral deafness HAS to be nerve 
damage....otherwise, brainstem, and dog would be dead.

IX: glossopharyngeal nerve. sensory and motor. SVE to pharyngeal and soft 
palate muscles. GVE parasympathetic which causes parotid and zygomatic 
salivary secretions. SVA taste for caudal 1/3 of tongue. GSA sensory skin 
of external auditory meatus. don't get hung up on some of these smaller 
details. clinical significance: not many brain tumors cause problems 
here. an ascending paralysis disease like tick paralysis or guillaume 
barre or botulism will have problems with swallowing secondary to 
paralysis of this nerve. a prehending problem would be getting food into 
the mouth. 

see handout for nerve locations. also see in lab.

X: incredibly important to body but not too clinically significant. 
Sensory and motor. GVE parasympathetics to abdomen thorax and heart. 
innervates organs, smooth muscle, etc. SVE innervates muscles of 
esophagus/pharyngeal/laryngeal areas. GSA sensory to these same areas. 
only clinical sig is swallowing difficulty and maybe slow heart rate, but 
heart rate can be changed by many things so need to be careful

XI: spinal accessory: motor only SVE to trapezius cleidocervicalis 
omotransversarius not clin sig because not commonly damaged but would 
cause atrophy.

XII motor only, GSE, causes problems eating. if damaged, tongue is 
deviated toward the lesion. if tongue TOTALLY doesn't work, you have 
bilateral dz, which isn't seen clinically. will also see tongue atrophy 
with damage to this nerve

all we have time for. Dr miselis will get us handouts.


reflex arc: burn finger: impulse goes to cord, motor back to finger to 
pull finger in.

-----end lecture------