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Neuro: 10:00 - 11:00
Thursday, January 15, 2009
Dr. Banos
I.
II.
III.
IV.
V.
VI.
BrainStem III
Scribe: Taylor Nelson
Proof: Chaz Capra
Page 1 of 5
CN V - Trigeminal [S4]
a. Cranial nerve V is generally speaking the sensory nerve for the head
i. We’re talking touch, proprioception, pain, and temperature
b. It’s the equivalent of the dorsal root and dorsal root ganlia of the spinal cord (though it does contain a little motor
component)
CN - Trigeminal [S5]
a. Trigeminal = “tri” + “geminus”
i. Tri = 3
ii. Geminus = at the same birth
1. “Three at the same birth” or Triplets meaning there will be three of something
b. The different afferent fibers(sensory systems) are distributed into three divisions [S6]
i. V1 - Ophthalmic - Sensory only
ii. V2 - Maxillary - Sensory only
iii. V3 - Mandibular - Sensory and motor
c. The distribution is a dermatome arrangement just like with the spinal cord
d. When you look at the physiologic appearance of CN V you do have a big ganglion with three major branches
coming into the ganglion
CN V - Trigeminal [S7]
a. Homologue of the dorsal root ganglion of the spinal sensory nerves
b. Here we have dorsal root ganglion, this is the sensory nerve coming into the dorsal aspect of the spinal cord so
the sensory information coming into the face this would be the equivalent ganglion (see red arrows on slide)
CN V - Trigeminal [S8]
a. Discriminative touch and conscious proprioception – again these are familiar modalities
i. Mediated by the main sensory nucleus of V is a homologue of dorsal column nuclei (gracilis and cuneatus),
same system
b. Here’s what we have in the spinal cord: dorsal columns, medial lemniscus [S9]
i. Fasiculus cuneatus and gracilis synapse on to our nucleus cuneatus and gracilis, they decussate and
continue to rise as the medial lemnicus up to the thalamus
ii. All we’re really doing is adding CN V to accomplish the same thing for the face [S10]
1. The information is coming in from the face and jaw, synapsing onto the main sensory nucleus of CN
V which then joins those fibers of the medial lemniscus
2. Just adding the head onto the sensory fibers, so by the time it gets to the thalamus you have the
entire body represented
c. [S11] Can see the dorsal columns, medial lemniscus, fasiculus gracilis and cuneatus on to their respective
nuclei decussating up the thalamus (drawn bilaterally), can see CN V coming into the main sensory nucleus
decussating and joining the other fibers – same as the previous slide but on an anatomic framework
CN V - Trigeminal [S12]
a. Mesencephalic nucleus of V
i. Trigeminal has several nuclei
ii. Not really a true nucleus
iii. Cell bodies of what would otherwise be the ganglionic portion of proprioceptive fibers from the muscles of
the jaw and it goes on to the motor nucleus of CN V
iv. It’s not a true nucleus because a true nucleus consists of a nerve coming in, synapsing on another nerve
and transmits to another location, in this case it comes in and the cell body is located there but it is the
same neuron so it’s not synapsing and making a multi-segmented pathway
v. These are proprioceptive fibers so location-wise we’re talking in approximations [S13]
1. We haven’t added the motor nucleus that goes to the jaw yet but a jaw jerk reflex is mediated by this
pathway
CN V - Trigeminal [S14,25]
a. Pain and Temperature – different modalities must be accounted for so it makes sense that we would have these
different nuclei
i. Pain and temperature are associated with the spinal nucleus of CN V
ii. The spinal nucleus of V is a long upward extension of the posterior horn of the spinal horn, contains a set
of neurons resembling the substantia gelatinosa in the spinal cord, extends up into the medulla to be the
portion of the system that takes the pain and temperature information from the face
iii. The tracts entering the spinal nucleus of V are analogous to an upward extension of the tract of Lissauer
Neuro: 10:00 - 11:00
Scribe: Taylor Nelson
Thursday, January 15, 2009
Proof: Chaz Capra
Dr. Banos
BrainStem III
Page 2 of 5
iv. Trigeminal pain and temperature fibers descend caudally to enter the spinal nucleus of V, this is odd in the
nervous system because you don’t see many things that choose to go down when the ultimate destination
is upward
1. Think of how this differs from Clark’s column, the nerves coming in above Clark’s column did not go
down Clark’s column and then back up, they just went up
v. Fibers from the spinal nucleus of V decussate and join the ascending spinothalamic tract, like the dorsal
columns it joins it’s appropriate tract
vi. [S16] We have the spinal nucleus of CN V(again an upward extension of the substantia gelatinosa) the
fibers coming in descend to various levels synapse onto that nucleus and the output is decussating and
joining the spinothalamic tract so we’re adding the head onto the pain and temperature tract
VII. CN V - Trigeminal [S17]
a. Motor - Muscles of mastication
i. The Motor nucleus of V is homologous to ventral horn in the spinal cord – again, everything that is
represented in the spinal cord is re-represented in a specialized way in the Trigeminal system
ii. Corticobulbar upper motor neurons synapse on lower motor neurons originating in this nucleus
iii. [S18] Just adding on the motor nucleus of CN V
1. Corticobulbar tract decussates at multiple points
2. You do still have the upper motor neuron and lower motor neuron representation
3. You can have upper and lower motor neuron signs with your jaw, you can have an exaggerated jaw
jerk reflex
4. If somebody has an exaggerated jaw reflex and everything in the rest of the body is normal than we
know that we have an upper motor neuron lesion where the trigeminal system goes to that muscle
a. The upper motor neuron is providing regulation and supervision that keeps that reflex arc in
check
Student Questions
b. SQ: Inaudible – concerning upper and lower motor neurons
c. A: Know where the different sets of symptoms are occurring, with regards a spinal cord lesion you will not have
all lower motor neuron lesions, or all upper motor neuron lesions there will be a pattern of upper and lower that
will help you narrow down where the lesion is. Also, don’t get caught up with upper and lower extremities and
get that tangled up with upper and lower motor neuron – will have lower motor neuron signs in arms and upper
motor neuron signs in legs etc. so often times it will be the reverse of what you think.
d. SQ: Inaudible – concerning decussation
e. A: The decussation especially when talking about motor neurons since they decussate in the medulla it will not
give you a whole lot about where you are in the spine. Decussation points come in handy for localization when
you have pathways that decussate at different levels. For example: in the corticospinal tract to have a
contralateral deficit you would have to be hitting above the decussation (medulla or above), usually you will
know if you are hitting at the medulla or above from reading the case so you begin looking at other pathways
that decussate at different places. The oddball tends to be pain and temperature, it decussates at every level so
knowing the level of the pain and temperature lesion longitudinally in the neuraxis gives you a lot more localizing
information. Weakness and somatosensory deficits are great for lateralizing each side.
f. SQ: Inaudible
g. A: Sensory level is going to be (sensory level is the spot at which you lose pain and temperature sensation)
extended down a little bit, giving you the best hint for longitudinal location. Motor and somatosensory are going
to be ipsilateral and the pain will be on the contralateral side. Motor weakness and loss of sensation on the left
side of the body and loss of pain sensation for some portion of the right side of the body the lesion will probably
be on the left side – can’t get the weakness and the somatosensory deficit if the lesion is on the same side. You
are expected to use the pathways you are learning to verify where you think a lesion is, so think through the
pathways individually and if a pathway doesn’t fit then reassess your hypothesis.
VIII. Clinical Correlation [S19, 20, 21]
a. The trigeminal nerve is the afferent limb of corneal blink reflex
i. Direct and consensual response arrangement
ii. Photo of a test of the corneal blink reflex
1. Cornea has pain receptors, not a fine touch sensation, anything touching your cornea for the most
part will be perceived as a pain stimulus
b. Jaw muscle weakness can be a symptom of a disfunctioning CN V
i. Jaw deviates toward the weak side upon opening the mouth, so whichever side is disfunctioning the
jaw opens that way
c. Disorders of sensation
i. Trigeminal neuropathy – loss of sensation in the trigeminal system
Neuro: 10:00 - 11:00
Scribe: Taylor Nelson
Thursday, January 15, 2009
Proof: Chaz Capra
Dr. Banos
BrainStem III
Page 3 of 5
ii. Trigeminal neuralgia – extreme pain constantly in the trigeminal system to the point that you may have
surgery to eliminate some of the pain
d. Traumatic brain injury
i. Loss of smell does not include harsh or unpleasant smells, the reason smelling salts work is because they
are essentially a pain stimulus going into the ARAS, sensors in your nose that are part of the trigeminal
system for pain (do not run through the cribiform plate)
ii. This can be a means of detecting “faking” – if they deny smelling things that trigger a different pathway they
are most likely faking
IX. CN VII – Facial [S23]
a. Motor (branchial)
i. Muscles of facial expression via the motor nucleus of VII
ii. Eye closure
b. Motor (autonomic)
i. To salivary and lacrimal glands from superior salivary nucleus
X. CN VII – Facial [S24]
a. Somatic sensory
i. Skin of the outer ear go to spinal trigeminal tract
b. Visceral Sensory
i. Palate and taste buds on anterior 2/3 of the tongue to the nucleus of the solitary tract
ii. As we get to CN VII and below we will start to see a lot of these extra neuclei that work with a couple of
different cranial nerves and solitary tracts is one of them
c. Visceral Motor (Autonomic)
i. Superior Salivary Nucleus to salivary glands
XI. CN VII – Facial [S25]
a. Photo:
i. Motor nucleus of VII
ii. Superior salivary nucleus
iii. Nucleus of the solitary tract
XII. CN VII – Facial [S26]
a. Motor nucleus of VII
i. The fibers that go from the motor nucleus of VII to the face are arranged somatotopically in that the fibers
going to the upper muscles of the face are the top part of the nucleus and the fibers going to the muscles of
the lower part of the face are in the lower part of the nucleus
ii. The corticobulbar fibers for upper face synapse on the motor nucleus of VII bilaterally (most decussate)
iii. The fibers bound for the lower face synapse on the contralateral nucleus only, this leads to a clinically
useful phenomena
iv. [S27, 28] Corticobulbar fibers synapse bilaterally to the upper face and contralateral to the lower face
v. [S29] If a lesion occurs at the lightning bolt:
1. Contralateral lower face weakness
2. The muscles of the upper face are still intact
XIII. Clinical Correlation [S30]
a. Classic cortical stroke – ability to move forehead is retained and muscle weakness will occur in the contralateral
lower face
b. If the lesion is the motor nucleus itself or the peripheral nerve then the entire side of the face is affected, so
usually if the entire side of the face is weak Bell’s palsy is the term you hear if the pathology just involves the
nerve itself
c. The less serious lesion has more prominent symptoms with an entire side of the face being weak and the more
serious lesion (cortical stroke) will generate a less prominent symptom with only a quarter of the face being
weak
XIV.
Clinical Correlation [S31]
a. CN VII is the efferent limb of the corneal blink reflex with the afferent limb being the CN V
i. So you should have a direct response and a consensual response
XV. CN VIII Vestibulochochlear [S35]
a. Two divisions - both special sensory
i. Cochlear (auditory)
ii. Vestibular
iii. Each function is related to the ear, inner ear is the balance (vestibular part), cochlea (hearing part)
b. Tomorrow in lab the nerve will look like a pair of wires running together
Neuro: 10:00 - 11:00
Scribe: Taylor Nelson
Thursday, January 15, 2009
Proof: Chaz Capra
Dr. Banos
BrainStem III
Page 4 of 5
XVI.
CN VIII Vestibulochochlear [S36]
a. Cochlear division – Will build this later in more detail, slide is more for flavor now
i. Cochlear ganglion to CN VIII
ii. CN VIII synapses in the cochlear nuclei
iii. Cochlear nuclei project to the superior olivary nucleus and inferior colliculus
iv. Superior olivary nucleus is also receiving input from contralateral cochlear nuclei
v. Superior olivary nucleus projects to inferior colliculus
vi. Inferior colliculus projects to thalamus
XVII. CN VIII Vestibulochochlear [S38]
a. The important thing to know right now is that auditory information is bilaterally represented very early in the
pathway, unlike a lot of things that may travel for a while before they decussate you have immediate bilateral
representation
i. This means that it is very hard to have unilateral hearing loss following a central nervous system lesion
1. If you have a lesion to CN VIII itself or a lesion to the cochlear nuclei on one side you could have
unilateral hearing loss
2. Cortical lesions (i.e., Heschel’s Gyrus, primary auditory cortex) will not result in unilateral hearing
loss
3. This can be very critical localizing information
XVIII. CN VIII Vestibulochochlear [S39, 41]
a. Vestibular division – inputs
i. Vestibular afferents project to:
1. The cerebellum
2. Vestibular Nuclear Complex
a. Inferior, lateral, medial, superior
3. Vestibular Nuclear Complex also receives afferents from:
a. Cerebellum
b. Contralateral Vestibular Nuclear Complex
b. This is a very complex system
c. Vestibular division - Outputs
i. Thalamus
ii. Nuclei of III, IV, and VI
iii. Spinal Cord
1. Lateral Vestibulospinal Tract
2. Medial Vestibulospinal Tract
d. [S43] Medial and Lateral Vestibulocerebellar Tracts
i. Part of a system that supports the voluntary motor system by providing corrective signals to muscles
depending on vestibular feedback
ii. Part of what the vestibular system is doing (along with the cerebellar system, and others) is giving feedback
to the muscles to correct balance
iii. Why are there projections to the occulomotor nuclei?
1. The eyes must be able to compensate and adjust when the body or head is moving, this forms part
of the vestibulooccular reflex
a. [S44] Vestibuloocular Reflex (VOR)
i. Fixation of gaze despite head movement
ii. Stabilizes image on the retina
iii. Reflexive, not a pursuit movement
iv. Works in the dark
v. Works if unconscious
1. Clinical Correlation
a. Doll’s eye maneuver can be used to test the integrity of the
brain stem in an unconscious patient, if a lesion is present in
the brainstem the odds are this system would be affected so
if the VOR is intact and the eyes remain forward most of the
brain stem is most likely reasonably intact
XIX.
CN IX - Glossopharyngeal [S47]
a. Glossopharyngeal means “throat and tongue”
b. Numerous afferents from:
i. Carotid sinus
ii. Walls of the pharynx
Neuro: 10:00 - 11:00
Scribe: Taylor Nelson
Thursday, January 15, 2009
Proof: Chaz Capra
Dr. Banos
BrainStem III
Page 5 of 5
iii. Mucous membranes
iv. Taste bud from posterior 1/3 of the tongue
c. [S48] Sensory
i. Taste bud afferents travel to the nucleus of the solitary tract
ii. Pain from the pharynx and posterior 1/3 of the tongue likely go to spinal trigeminal nucleus (this is not
entirely clear)
iii. Some sensory fibers likely reach the main sensory nucleus of V
1. Big picture: think throat, posterior
d. [S40] Motor
i. Stylopharyngeus
1. Swallowing (with X and XII)
2. Elevates the pharynx while swallowing and speaking
ii. These fibers arise from the nucleus ambiguus, a poorly differentiated nucleus in the medullary tegmentum
e. [S50] Clinical Correlation
i. Afferent of the Gag Reflex
1. Glossopharyngeal, Gag – pneumonic
XX. CN X - Vagus [S51]
a. Does a lot of different stuff
b. Principal parasympathetic nerve
c. Widely distributed (vagus = “wandering”)
d. Some overlap in function with CN IX, when talking about throat and tongue functions start to overlap a bit
e. Preganglionic parasympathetic fibers to the thoracic and abdominal viscera
i. Arise in the dorsal motor nucleus of the vagus
ii. Fibers to the heart originate in the nucleus ambiguus
f. [S52] Visceral sensory information from:
i. Thoracic and abdominal viscera
ii. Taste buds of the epiglottis
iii. Most project to nucleus of the solitary tract
iv. Some may project to spinal nucleus of V
1. Don’t get totally lost in all the different nuclei, take a look at different nuclei and have an idea of what
they do
g. [S53] Clinical Correlation
i. Hoarseness (larynx)
ii. Dysarthria – broad term for speaking difficulty that is not related to neural damage in the brain (cortical
damage), so this is weakness on one side of your face making you mumble etc.
iii. Paralysis of the soft palate
iv. Dysphagia – problems with swallowing
v. Uvula deviates away from weakness
vi. Loss of cough reflex (anesthesia of pharynx and larynx)
vii. [S54] Efferent of the gag reflex
1. IX  X
viii. Vagal nerve stimulator – if you stimulate the vagal nerve you can head off a seizure before it happens, not
clear exactly how it works
1. Now it is showing up for use in treating depression, but the problem remains nobody really knows
how it does what it does
XXI.
CN XI - Spinal Accessory [S57]
a. Motor only - neck and shoulder muscles
i. Sternocleidomastoid
ii. Part of the trapezius
b. Accessory Nucleus (similar to the grey matter in the spinal cord)
c. [S58] Runs as a long row of rootlets
XXII. CN XII - Hypoglossal [S58]
a. Between the pyramid and the olive
b. [S59] Motor - Muscles of the tongue
i. Takes a lot of innervations because the tongue is really complicated
ii. The tongue deviates to the weak side when protruded
[End 40:23]