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Gross: 2:00-3:00
Monday, January 12, 2009
Dr. Tubbs
Cranial Nerves
Gross Anatomy
Scribe: Patricia Fulmer
Proof: Sheena Harper
Page 1 of 5
Cranial Nerve = CN
I.
Cranial Nerves [S1]:
a. We will be getting a general introduction to cranial nerves (CN) this hour, and then later we will have the
opportunity to review them further. He’s giving us the essence and functional deficits of each.
II. Considerations [S2]
a. When looking at the CNs, look at the embryologic derivations: does that CN come from forebrain, hindbrain, etc.
b. Do they have a pharyngeal arch associated with them? In the future we will know which CN are associated with
a pharyngeal arch. These are what give rise to gills and certain muscles.
c. Does the CN have autonomic, motor, sensory, or both motor and sensory?
d. “Functional components” is a nomenclature system that lets you know what kind of fibers are travelling in the
CN.
e. Where does that CN come from grossly? The brainstem, spinal cord (1 has a part derived from the cord), or
above the tentorium?
III. Embryological Derivative [S3]
a. We’ve talked about embryological derivative
b. The brain in a developing fetus is a big, long tube with a front called the forebrain, middle called the midbrain,
and back called the hindbrain.
c. Some CNs come off parts other than the hindbrain
IV. Pharyngeal Arch Derivative [S4]
a. Just a term he’s throwing out, we’ll learn more later
V. .Autonomic Fibers [S5]
a. Memorize up front
b. 12 pairs: 3rd (oculomotor), 7th (facial), 9th (glossopharyngeal) and 10th (vagus) all carry autonomic nerve fibers
(GVE fibers = autonomic) GREAT TEST QUESTION!!! – which CNs carry autonomic fibers?
VI. Motor/Sensory/Mixed [S6]
a. Does CN have motor/mixed/sensory?
b. After studying this lecture, we’ll know which have which kind of fibers.
c. CN I (olfactory) is only a sensory nerve, CN XI is only motor, CN IX is mixed
VII. Origin- supratentorial, stem, cord [S7]
a. Does CN come from above the tentorium, from the spinal cord, or from the brainstem?
b. 2 CNs come off above the tentorium- these are not true CNs in the traditional sense, they are outgrowths of that
part of the forebrain
c. The olfactory nerves have little fibers that run in that olfactory bulb and tract and connect to the forebrain
d. The optic nerve is an outgrowth of the forebrain
e. All the others come off the brainstem directly, except part of CN XI
f. [S8] I’ll just show you this picture. You’ll learn all of this when we do neural anatomy.
g. Each CN on the surface is simple, but internally they have a complex relationship
h. Blue shows sensory fibers and red shows motor.
i. There’s high priced real estate in the brainstem- everything’s mixed and mingled.
j. We’ll talk about the nerve as it leaves the brain and skull base.
VIII. Functional Components [S9]
a. If you haven’t already gotten a hand on them, you need to because it makes learning the CNs much easier.
b. If you know what functional components are in each nerve, you’ll be able to pick out the different functions of
each nerve and say these are the GVA fibers or the SVE fibers, etc.
c. The first 4 functional components are in the spinal cord and were mentioned by Dr. Salter.
d. Inside the brainstem and above the tentorium you have to add on 3 more: SSA (special sensory afferent), SVA
(special visceral afferent), SVE (special visceral efferent).
e. In a simplistic way you can look at the brainstem and see that most of the sensory fibers are on the periphery
and motor are more central
f. If you have a tumor pushing in you’ll have a sensory deficit first because the tumor will push on the more
laterally afferent fibers
IX. Olfactory nerve = SVA (special visceral afferent) [S10-11]
a. Start with each CN and beside each he tells us the functional components and what they do
b. The olfactory nerve is easy because it only has one functional component- SVA
c. Smell is SVA.
Gross: 2:00-3:00
Scribe: Patricia Fulmer
Monday, January 12, 2009
Proof: Sheena Harper
Dr. Tubbs
Gross Anatomy
Page 2 of 5
d. The olfactory nerve comes up from the ceiling of the nasal cavity through the cribriform plate and gains access
to the olfactory bulb and tract
e. 18-20 little nerves on each side
f. Smell goes to the hypothalamus, which has to do with primitive drives: sex, hunger, and thirst, and to the part of
the brain for memory
g. This is why we buy perfume and cologne- it stimulates the memory part of the brain and takes us back to some
place you liked or it stimulates the hypothalamus’s sex part
X. Optic Nerve = SSA [S12]
a. Has special sensory afferent fibers: period
b. Can talk about it and the retina as a whole class or several lectures; just doing the very beginning of optic nerve
as it goes through skull base carrying visual fibers
c. It’s an outgrowth of the forebrain and runs through the optic canal to the receptors on the retina (back of the
orbit)
XI. Oculomotor Nerve = GSE, GVE; Trochlear/Abducens = GSE [S13]
a. These next three critters (oculomotor, trochlear, and abducens) all go to muscles that move your eye around:
external ocular muscles
b. GSE fibers innervate the extraocular muscles (will learn their functions more in orbit lecture)
c. Oculomotor nerve (CN III) in addition also carries GVE (autonomic) fibers, which has a ganglion it synapses on
and postganglionic fibers leave the ganglion and act upon the effectors to make something happen (different
from other nerves with beginning and end, no intermediate ganglion)
d. You can see the ganglion associated with CN III here, the ciliary ganglion
e. If you stimulate the oculomotor nerve, it moves the majority of the extraocular muscles
f. The trochlear (CN IV) makes the superior oblique muscle move only; the lateral rectus muscle only is moved by
the abducens (CN VI)
g. Autonomics are parasympathetic nerves for the cranial nerves; if you have a parasympathetic nerve it must
have a ganglion
h. The postganglionics go out to the muscles around the iris to help constrict the pupil
i. Someone who is “fixed and dilated” has lost function of the oculomotor nerve (it’s being compressed) so it
cannot constrict the pupil and the sympathetic fibers are dilating it.
j. The GVE fibers will make the lens accommodate to read up close
k. All of these branches (CN III, IV, and VI) come from the brainstem and go through the superior orbital fissure
from the brainstem to gain access to the orbit
l. Each of these (CN III, CN IV) come off the midbrain and the abducens comes from the lower part of the pons
m. [S14] The interesting thing about the trochlear nerve is that it is the only CN that comes off the posterior aspect
of the brainstem (can see it in this image)
n. All the others exit anteriorly, but the trochlear exits posteriorly and wraps around the midbrain, then goes
through the superior orbital fissure to reach the superior oblique muscle
o. [S15] This is looking if you enucleated (removed) the eyeball you see the bare optic nerve and ophthalmic
artery.
p. Here’s the superior orbital fissure with the CN III, IV, and VI coming out of the various extraocular muscles and
making them move
XII. Third Nerve Palsy [S16]
a. This is a typical patient with a CN III injury
b. On her right side, she has a dilated pupil. This means the GVE fibers in CN III are not working properly and can’t
constrict the pupil. The left side is working fine so the pupil constricts.
c. The oculomotor injured side can’t come over medially. It stays in the lateral part of the orbit, and you see a lot of
sclera here medially. It is hung down and out typical oculomotor nerve lesion
XIII. Fourth Nerve Palsy [S17]
a. Fourth nerve injury is hard to pick up but you’ll notice the pupils are equal because there are no GVE fibers
running in the trochlear nerve
b. He also has trouble coming to the medial and down position. Up and out laterally are fine.
XIV.
Sixth Nerve Palsy [S18]
a. Here’s an abducens nerve and he’s very easy to pick out because he can’t look out laterally.
b. Abducens is very commonly injured after a motor vehicle accident.
XV. Trigeminal Nerve [S19]
a. 3 pronged look to it
b. Comes off lateral pons here (can also see the optic and oculomotor nerves, and the trochlear nerve coming from
the posterior brainstem, all heading toward the orbit)
Gross: 2:00-3:00
Scribe: Patricia Fulmer
Monday, January 12, 2009
Proof: Sheena Harper
Dr. Tubbs
Gross Anatomy
Page 3 of 5
c. The trigeminal nerve has a swelling called the trigeminal ganglion that contains neuronal cell bodies for GSA
fibers that go out to something somatic like skin
d. As trigeminal nerve unfolds you see most of the skin on the face is innervated by this nerve
e. V1, V2, V3 are the 3 parts
f. V1 travels through the superior orbital fissure, V2 through the foramen rotundum, V3 through the foramen ovale
g. All the branches have sensory fibers in them, so they go to a patch of skin for example; they also all go to the
dura mater, which is GSA fibers
h. Some of the fibers in the V3 are SVE- motor fiber, special visceral efferent; so innervates a muscle that derives
from a pharyngeal arch (SVE=pharyngeal arch)
i. The pharyngeal arch muscles are muscles of mastication (chewing) primarily- lose ability to masticate if injured
j. [S20] This show’s you very nicely the trigeminal nerve leaving the brainstem
k. V1 branches into a multitude of branches in the orbit
l. [S21] We talked about the cavernous sinus and the relationship of the V1 in the cavernous sinus
m. [S22] This is a diagrammatic picture that shows you that the trigeminal nerve is a sticky nerve to get your hands
around because each branch branches further
n. Simplistically you can say each of these branches (V1-3) are associated with a parasympathetic ganglion that
the oculomotor, glossopharyngeal, and facial nerve use
o. You also see that V1, 2, 3 end on a patch of skin on the face
p. [S23] Here’s an inside out view, and we do this dissection toward the end of the course
q. This shows the trigeminal ganglion with V1, 2, and 3 with the parasympathetic ganglion that are suspended
along the way from the branches
r. [S24] Just to show you you’re going to learn all the branches when you do the orbit
s. [S25] That’s what it will look like when you start to do that dissection by removing the floor of the interior cranial
fossa
t. [S26] We’ll step down and see the trigeminal nerve has V1 that runs in the upper part of the orbit, V2 runs in the
floor of the orbit (they both end on the skin in different places)
u. V2 supplies the sensation to the upper teeth
v. V1 has fibers associated with the ciliary ganglion
w. V2 is structurally related to the pterygopalatine ganglion but has no functional association with it. This ganglion
will receive fibers from the facial nerve, which will synapse here and travel along V2 branches to V1 branches
then end on the lacrimal gland (how we get facial parasympathetic fibers with postganglionic fibers to the
lacrimal gland to lacrimate)
x. [S27] Now sensory wise, this shows you nicely the trigeminal places that receive sensory information
y. If you pinprick the anterior part of your tongue you feel it with trigeminal nerve and the inside of the nasal cavity
(some of the paranasal air sinuses) are all innervated with branches of the trigeminal nerve
z. [S28] This you really have to commit to memory because this shows the dermatome pattern or patches of the
skin that receive specific innervation from the branches of the trigeminal nerve (V1 in green, V2 in blue, V3 in
purple)
aa. If you were to pinprick just lateral to the nose and below the eye, you’re testing for sensation of the V2 branch
bb. [S29] Now if you were to take the skin off of the prior picture and look at the little nerves that contribute to the
patches, this is what it would look like (we will learn all these branches and how they contribute to the
dermatomes he refers to the ones that make up V2 as an example)
cc. [S32] V3 travels in foramen ovale in the middle cranial fossa, and as it does so, it has already innervated dura in
the cranium. It has multiple branches. It will give supply to the anterior part of the tongue for sensation and
supply the muscles of mastication. It will end through various foramina sometimes on the skin of the face.
dd. [S33] Now those are color coded muscles of mastication; all of these muscles receive innervation from V3, the
mandibular part, and each help move the jaw around (for example the temporalis muscle and pterygoid muscles
we’ll be learning)
XVI.
Facial Nerve [S35]
a. Facial nerve (CN VII)- it has parasympathetic autonomic fibers (represented by GVE fibers) that go to 2 main
areas: the lacrimal glands and 2 glands that help you salivate
b. So when you tear or salivate, those are contributed to by stimulation of the facial nerve
c. Each have to have a ganglion for the preganglionic fibers to synapse on
d. SVE fibers mean pharyngeal arch, and the facial nerve is a pharyngeal arch nerve
e. The primary muscles that the SVE fibers innervate are all the little muscles under the skin of the face that we
collectively call the muscles of facial expression (these are unique to humans, we can make expressions by
stimulating the facial nerve)
f. There are very few GSA fibers innervated by the facial nerve; an example is some skin in your ear
Gross: 2:00-3:00
Scribe: Patricia Fulmer
Monday, January 12, 2009
Proof: Sheena Harper
Dr. Tubbs
Gross Anatomy
Page 4 of 5
g. SVA fibers means that they’re taste fibers in that nerve; specifically, the facial nerve gives taste fibers to the
anterior 2/3 of your tongue (the general sensation fibers are from the trigeminal nerve, but the taste fibers are
from the facial nerve)
h. [S36] Now the facial nerve has 2 parasympathetic ganglion that are involved in motor responses and a sensory
ganglion- the geniculate ganglion
i. The sensory fibers from the little part of the ear that the facial nerve innervates will terminate in the geniculate
ganglion
j. Here’s the internal auditory meatus that’s been opened and we see facial nerve coming in and just beyond that
the geniculate ganglion
k. [S37] Here again is our facial nerve; it’s a descending portion that goes out the base of the skull
l. If the mastoid process is not well developed, like in a neonate, you can injure the facial nerve because without
the mastoid process the facial nerve is exposed
m. [S38] Now one of the facial nerve branches we’ll learn about (see it in the middle here and in the infratemporal
fossa) is the fiber that carries 2 different types of fibers called the chorda tympani
n. We see it coming off the facial nerve, entering the middle ear, and comes down medial to the lower jaw and
hitchhikes along a branch of V3 and goes down into the oral cavity
o. In the chorda tympani there are fibers going down that will make you salivate and fibers coming back that bring
taste fibers back to the brain
p. Here’s a ganglion that we get the best view of here- the otic ganglion that is associated with CN IX and the
fibers from that ganglion go out to your parotid gland
q. [S39] The 2 ganglion associated with the facial nerve are shown in this slide
r. This ganglion in the back of the nasopharynx is called the pterygopalatine and the other is in the oral cavity and
is called the submandibular ganglion. Fibers from the facial nerve go to both of these.
s. If they go to the pterygopalatine, they mainly make your lacrimal gland secrete tears
t. If they go to the submandibular, they make 2 of your salivary glands secrete saliva
u. [S40] You may have a patient come in with a facial nerve injury or paralysis that is complaining that normal
sounds are too loud or exaggerated (hyperacusis) the reason for this is because the stapedius muscle
(smallest in body) in the middle ear is innervated by the facial nerve. It attaches on the stapes and dampens
loud sounds by disengaging or stabilizing the ear bones. If the facial nerve is injured, the muscle may not work
and so sounds come across louder. Normal sounds seem exaggerated.
XVII. Vestibulocochlear Nerve [S41]
a. Has 1 functional component-SSA fibers
b. These fibers are associated with the cochlea, which is the organ of hearing (where hearing is 1 st established),
and the group of semicircular canals that have to do with balance and equilibrium (why you feel off balance and
dizzy when you have an inner ear infection)
c. So the nerves from the cochlea and semicircular canals combine to form the vestibulocochlear nerve (if you cut
just the cochlear part, you’d lose hearing on that side)
d. [S42] There are 2 sensory ganglia: cochlear and vestibular ganglia
e. Those are where the neuronal cell bodies for each modalities live
f. Here’s a nicer view of the semicircular canals and the cochlea is seen too
XVIII. CNs IX, X, XI [S43]
a. We’ll lump the last 3 together; most go through the jugular foramen in the base of the skull
b. CN XI has a catch
XIX.
Glossopharyngeal Nerve [S44]
a. CN IX is small and has more functional components that any other CN
i. GSA fibers- an example: the posterior fossa dura can be innervated by these fibers from CN IX
ii. SVE fibers (we should think pharyngeal arch)- only one muscle that CN IX innervates that is derived from
the pharyngeal arch: stylopharyngeus muscle (little muscle of the pharynx)
iii. SVA fibers (we should think taste)- the posterior 1/3 of the tongue’s taste fibers are from these
iv. GVE fibers (we should think parasympathetic autonomic)- these travel to a ganglion called the otic
ganglion; those postganglionic fibers go to the largest salivary gland in front of the ear called the parotid
gland (if you stimulate the otic ganglion or CN IX, you’ll salivate)
v. GVA fibers (general visceral afferents)- 2 branches from CN IX: 1 senses a specialized area at the bottom
of the internal carotid artery called the carotid sinus
vi. The carotid sinus monitors blood pressure; if the pressure gets too low in the carotid arteries, carotid sinus
nerve will send info will to the brainstem and tell the heartbeat to pump up and raise blood pressure and
visa versa for high pressure
vii. This carotid sinus nerve sits off CN IX and clinically you can use this for patients that have high blood
pressure that you can’t control
Gross: 2:00-3:00
Scribe: Patricia Fulmer
Monday, January 12, 2009
Proof: Sheena Harper
Dr. Tubbs
Gross Anatomy
Page 5 of 5
viii. You can massage the carotid sinus to trick the nerve into thinking that the pressure has been changed or
altered and it may decrease the pressure and heart rate for you
ix. [S45] Basic areas of sensation that the CN IX carries fibers for you’ll see at the back of the oral pharynx up
to the eustachian tube and some of the soft palate, some of your tonsils, posterior 1/3 of your tongue,
middle ear all carry sensory fibers from CN IX
x. If you have a sore throat, it is usually mediated through fibers of the CN IX; the chloraseptic spray numbs
this nerve
b. [S46] CN IX and X are seen here; they are both in the jugular foramen and have 2 sensory ganglion (a superior
and inferior)
c. The 2 superior ganglion house GSA fibers that go to the dura and skin
d. The lower (inferior) 2 ganglion house GVA and SVA neuronal cell bodies (so taste, etc.)
XX. Vagus Nerve [S48]
a. Vagus nerve is aptly named for a vagabond or vagrant (someone who wanders around and doesn’t stay put)
because it wanders and innervates things in the neck, thorax, abdomen, etc. from the brainstem
b. It is the longest CN
c. They’re parasympathetic fibers (GVE fibers)
d. The ganglion are enteric ganglia because they are near or in the walls of the organs it supplies
e. SVE fibers (pharyngeal arch) so it innervates muscles derived from the pharyngeal arch like those of the larynx
(speak because this nerve works correctly via these fibers)
f. SVA (taste) fibers: the vagus nerve has some distribution on your epiglottis (one of the unpaired cartilages of the
larynx) for its taste fibers
g. [S49] Let’s focus on the vagus nerve in the neck and give some examples of where it goes
h. We can see the inferior ganglion with GVA and SVA fibers (taste for vagus on epiglottis)
i. Up high are pharyngeal branches- supply almost all the muscles of the pharynx
j. As we descend we see additional branches we’ll get into later
k. Recurrent laryngeal nerve (we will hear about this a lot): it’s recurrent because it comes off the vagus around the
subclavian on the right side and the aortic arch on the left side and comes all the way back up to the neck to
innervate the muscles of the larynx, with the exception of one muscle
l. If you injure that nerve with a neck operation or thoracic operation, your patient may have hoarseness
XXI.
Spinal Accessory Nerve [S50]
a. Spinal Accessory nerve is an SVE, some classify it as GSE (we won’t get too bent out of shape about either)
b. It innervates the sternocleidomastoid (mastoid process to sternum: contract them to flex neck, lowers ear to
shoulder with this) and the trapezius (elevates the shoulders with upper trapezius) muscles ONLY
c. This nerve is interesting because some components come off the brainstem but others come off the upper 5
segments of the spinal cord then ascend in the spinal canal to join the parts that come from the brainstem and
leave through the jugular foramen
XXII. Hypoglossal Nerve [S51]
a. Easy one- GSE fibers: only to muscles that move the tongue into and out of the mouth and around in the mouth
b. These fibers will go to the muscle seen here that protrudes the tongue (test this nerve by having patient stick out
tongue
c. [S52] These are a little elementary but nice schematics that show the major paths of some of the CNs
d. You should take this as a baseline to build on as we add more details
SQ: Should GVA be on the Vagus nerve slide?
A: Yes; GVA should also be on the Vagus slide because GVA fibers from CN X also go to the carotid sinus area