Brain Stem III
Basic Neuroscience
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James H. Baños, Ph.D.
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Yesterday
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CN I
CN II
CN III
CN IV
CN VI
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Today
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CN V
CN VII
CN VIII
CN IX
CN X
CN XI
CN XII
CN V - Trigeminal
CN V - Trigeminal
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CN V is the general sensory nerve for the
head
Touch
 Proprioception
 Pain/temperature
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CN V and its connections are to the head
what dorsal roots and the spinal cord are
to the body
Also has a motor component
CN V - Trigeminal
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Trigeminal = “tri” + “geminus”
Tri = 3
 Geminus = at the same birth
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“Three at the same birth”
CN V - Trigeminal
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Peripheral afferent fibers distributed in
three divisions
V1 - Ophthalmic - Sensory only
 V2 - Maxillary - Sensory only
 V3 - Mandibular - Sensory and motor
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CN V - Trigeminal
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Peripheral sensory afferents converge at
the trigeminal ganglion
This is a homologue of the dorsal root
ganglion of spinal sensory nerves
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CN V - Trigeminal
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Discriminative touch and conscious
proprioception
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The main sensory nucleus of V is a
homologue of dorsal column nuclei (gracilis
and cuneatus)
CN V - Trigeminal
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Spinal Cord:
Medial Lemniscus
Dorsal Columns
NG
NC
Thalamus
CN V - Trigeminal
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Trigeminal System:
Medial Lemniscus
Dorsal Columns
Thalamus
NG
NC
CN V
V
Main sensory nucleus of V
CN V - Trigeminal
Main sensory nucleus of V
V
NC NG
V
NG NC
CN V - Trigeminal
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Mesencephalic nucleus of V
Actually not a true nucleus
 Cell bodies of what would otherwise be the
ganglionic portion of proprioceptive fibers
from the muscles of the jaw
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CN V - Trigeminal
Mesencephalic nucleus of V
Main sensory nucleus of V
V
V
CN V - Trigeminal
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Pain and temperature
The spinal nucleus of V is a long upward
extension of the posterior horn of the spinal
cord
 It contains a set of neurons resembling the
substantia gelatinosa in the spinal cord
 The tracts entering the spinal nucleus of V are
like an upward extension of the tract of
Lissauer
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CN V - Trigeminal
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Pain and temperature
Trigeminal pain and temperature fibers
descend caudally to enter the spinal nucleus
of V
 Fibers from the spinal nucleus of V decussate
and join the ascending spinothalamic tract
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CN V - Trigeminal
Mesencephalic nucleus of V
Main sensory nucleus of V
V
V
Spinal nucleus of V
Spinothalamic tract
CN V - Trigeminal
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Motor - Muscles of mastication
The Motor nucleus of V is homologous to
ventral horn in the spinal cord
 Corticobulbar upper motor neurons synapse
on lower motor neurons originating in this
nucleus
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CN V - Trigeminal
UMN
Mesencephalic nucleus of V
Main sensory nucleus of V
LMN
VV
VV
Motor nucleus of V
Spinal nucleus of V
Clinical Correlation
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Afferent limb of corneal blink reflex
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Direct and consensual response
Clinical Correlation
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Jaw muscle weakness
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Jaw deviates toward the weak side
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Clinical Correlation
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Disorders of sensation
Trigeminal neuropathy
 Trigeminal neuralgia
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Traumatic brain injury
Loss of smell does not include harsh or
unpleasant smells
 This can be a means of detecting “faking”
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Smelling salts and the ARAS
CN VII - Facial
CN VII - Facial
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Motor (branchial)
Muscles of facial expression via the motor
nucleus of VII
 Eye closure
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Motor (autonomic)
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To salivary and lacrimal glands from superior
salivatory nucleus
CN VII - Facial
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Somatic sensory
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Skin of the outer ear to spinal trigeminal
nucleus
Visceral Sensory
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Palate and taste buds on anterior 2/3 of the
tongue to the Nucleus of the solitary tract
CN VII - Facial
Nucleus of the solitary tract
Superior salivatory nucleus
Motor nucleus of VII
VII
VII
CN VII - Facial
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Motor nucleus of VII
Corticobulbar fibers for upper face synapse
on the motor nucleus of VII bilaterally (most
fibers decussate)
 Fibers bound for the lower face synapse on
the contralateral nucleus only
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CN VII - Facial
To upper face
To upper face
VII
To lower face
VII
To lower face
CN VII - Facial
To upper face
To upper face
VII
To lower face
VII
To lower face
CN VII - Facial
To upper face
To upper face
VII
To lower face
VII
To lower face
Clinical Correlation
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Lesions of the cortex or corticobulbar tract
Contralateral lower face weakness
 Ex: Stroke
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Lesions of the motor nucleus of VII or
peripheral nerve
Ipsilateral lower and upper face weakness
 Ex: Bell’s Palsy
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Clinical Correlation
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CN VII is the efferent limb of the corneal
blink reflex
? - left
? - right
VII left
VII - right
Clinical Correlation
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Corneal blink reflex
Afferent fibers originate in the ophthalmic
division of CN V
 Synapse on Spinal Nucleus of V
 Internerons project bilaterally (via the reticular
formation) to neurons in the motor nucleus of
VII
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Clinical Correlation
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CN VII is the efferent limb of the corneal
blink reflex
V - left
V - right
VII left
VII - right
CN VIII Vestibulocochlear
CN VIII - Vestibulocochlear
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Two divisions - both special sensory
Cochlear (auditory)
 Vestibular
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CN VIII - Vestibulocochlear
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Cochlear division
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Cochlear ganglion to CN VIII
CN VIII synapses in the cochlear nuclei
Cochlear nuclei project to the superior olivary nucleus
and inferior colliculus
Superior olivary nucleus is also receiving input from
contralateral cochlear nuclei
Superior olivary nucleus projects to inferior colliculus
Inferior colliculus projects to thalamus
CN VIII - Vestibulocochlear
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Cochlear division
Sup. Olivary Nuc.
Cochlear Nuclei
VIII
Clinical Correlation
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Note that auditory information is bilaterally
represented very early in the pathway
This means that you only have unilateral hearing
loss following
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Lesion to CN VIII itself
Lesion to the cochlear nuclei on one side
Cortical lesions (i.e., Heschel’s Gyrus) will not
result in unilateral hearing loss
CN VIII - Vestibulocochlear
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Vestibular division - inputs
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Vestibular afferents project to
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The cerebellum
Vestibular Nuclear Complex
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Inferior
Lateral
Medial
Superior
Vestibular Nuclear Complex also receives afferents from
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Cerebellum
Contralateral Vestibular Nuclear Complex
CN VIII - Vestibulocochlear
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Vestibular division - inputs
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CN VIII - Vestibulocochlear
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Vestibular division - Outputs
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Thalamus
Nuclei of III, IV, and VI
Spinal Cord
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Lateral Vestibulospinal Tract
Medial Vestibulospinal Tract
CN VIII - Vestibulocochlear
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Vestibular division - Outputs
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Thalamus
Nuclei of III, IV, and VI
Spinal Cord
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Lateral Vestibulospinal Tract
Medial Vestibulospinal Tract
Cerebellum
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CN VIII - Vestibulocochlear
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Medial and Lateral Vestibulocerebellar Tracts
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Part of a system that supports the voluntary motor
system by providing corrective signals to muscles
depending on vestibular feedback
Why are there projections to oculomotor nuclei?
Clinical Correlation
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Vestibuloocular Reflex (VOR)
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Fixation of gaze despite head movement
Stabilizes image on the retina
Reflexive, not a pursuit movement
Works in the dark
Works if unconscious
Clinical Correlation
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Doll’s eye maneuver
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Can be used to test the integrity of the brain stem in
an unconscious patient
CN IX - Glossopharyngeal
CN IX - Glossopharyngeal
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Glossopharyngeal means “tongue and
throat”
Numerous afferents from
Carotid sinus
 Walls of the pharynx
 Mucous membranes
 Taste bud from posterior 1/3 of the tongue
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CN IX - Glossopharyngeal
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Sensory
Taste bud afferents travel to the nucleus of the
solitary tract
 Pain from the pharynx and posterior 1/3 of the
tongue likely go to spinal trigeminal nucleus
 Some sensory fibers likely reach the main
sensory nucleus of V
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CN IX - Glossopharyngeal
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Motor
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Stylopharyngeus
Swallowing (with X anf XII)
 Elevates the pharynx while swallowing and
speaking
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These fibers arise from the nucleus
ambiguus, a poorly differentiated nucleus in
the medullary tegmentum
Clinical Correlation
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Afferent of the Gag Reflex
CN X - Vagus
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Principal parasympathetic nerve
Widely distributed (vagus = “wandering”)
Some overlap with CN IX
Preganglionic parasympathetic fibers to
the thoracic and abdominal viscera
Arise in the dorsal motor nucleus of the vagus
 Fibers to the heart originate in the nucleus
ambiguus
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CN X - Vagus
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Visceral sensory information from
Thoracic and abdominal viscera
 Taste buds of the epiglottis
 Most project to nucleus of the solitary tract
 Some may project to spinal nucleus of V
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Clinical Correlation
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Hoarseness (larynx)
Dysarthria
Paralysis of the soft palate
Dysphagia
Uvula deviates away from weakness
Loss of cough reflex (anesthesia of pharynx and
larynx)
Clinical Correlation
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Efferent of the gag reflex
IX
X
Clinical Correlation
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Vagal nerve stimulator
 Implantable device
 Treatment for seizures
CN XI - Spinal Accessory
CN XI - Spinal Accessory
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Motor only - neck and shoulder muscles
Sternocleidomastoid
 Part of the trapezius
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Accessory Nucleus (cervical spinal cord)
CN XII - Hypoglossal
CN XII - Hypoglossal
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Motor - Muscles of the tongue
Hypoglossal Nucleus
Clinical Correlation
Which side of the tongue is weak?
Clinical Correlation
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The tongue deviates to the weak side
when protruded
Coming Up…
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Diencephalon
Thalamus
 Hypothalamus
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