Brain Stem IIIBrain Stem III

Basic NeuroscienceBasic Neuroscience

James H. Baños, Ph.D.James H. Baños, Ph.D.QuickTime™ and a

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YesterdayYesterday CN ICN I CN IICN II CN IIICN III CN IVCN IV CN VICN VI

TodayToday CN VCN V CN VIICN VII CN VIIICN VIII CN IXCN IX CN XCN X CN XICN XI CN XIICN XII

CN V - TrigeminalCN V - Trigeminal

CN V - TrigeminalCN V - Trigeminal

CN V is the general sensory nerve CN V is the general sensory nerve for the headfor the head TouchTouch ProprioceptionProprioception Pain/temperaturePain/temperature

CN V and its connections are to the CN V and its connections are to the head what dorsal roots and the head what dorsal roots and the spinal cord are to the bodyspinal cord are to the body

Also has a motor componentAlso has a motor component

CN V - TrigeminalCN V - Trigeminal

Trigeminal = “tri” + “geminus”Trigeminal = “tri” + “geminus” Tri = 3Tri = 3 Geminus = at the same birthGeminus = at the same birth

“Three at the same birth”

CN V - TrigeminalCN V - Trigeminal

Peripheral afferent fibers distributed Peripheral afferent fibers distributed in three divisionsin three divisions VV11 - Ophthalmic - Sensory only - Ophthalmic - Sensory only

VV22 - Maxillary - Sensory only - Maxillary - Sensory only

VV33 - Mandibular - Sensory and motor - Mandibular - Sensory and motor

CN V - TrigeminalCN V - Trigeminal

Peripheral sensory afferents Peripheral sensory afferents converge at the trigeminal ganglionconverge at the trigeminal ganglion

This is a homologue of the dorsal This is a homologue of the dorsal root ganglion of spinal sensory root ganglion of spinal sensory nervesnerves

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CN V - TrigeminalCN V - Trigeminal

Discriminative touch and conscious Discriminative touch and conscious proprioceptionproprioception The The main sensory nucleusmain sensory nucleus of V is a of V is a

homologue of dorsal column nuclei homologue of dorsal column nuclei (gracilis and cuneatus)(gracilis and cuneatus)

CN V - TrigeminalCN V - Trigeminal

Spinal Cord:Spinal Cord:

Dorsal ColumnsNG

NC

ThalamusMedial Lemniscus

CN V - TrigeminalCN V - Trigeminal

Trigeminal System:Trigeminal System:

CN VV

Main sensory nucleus of V

Dorsal ColumnsNG

NC

ThalamusMedial Lemniscus

CN V - TrigeminalCN V - Trigeminal

VV

Main sensory nucleus of V

NG NG NCNC

CN V - TrigeminalCN V - Trigeminal

Mesencephalic nucleus of VMesencephalic nucleus of V Actually not a true nucleusActually not a true nucleus Cell bodies of what would otherwise be Cell bodies of what would otherwise be

the ganglionic portion of proprioceptive the ganglionic portion of proprioceptive fibers from the muscles of the jawfibers from the muscles of the jaw

CN V - TrigeminalCN V - Trigeminal

VV

Main sensory nucleus of V

Mesencephalic nucleus of V

CN V - TrigeminalCN V - Trigeminal

Pain and temperaturePain and temperature The The spinal nucleus of Vspinal nucleus of V is a long upward is a long upward

extension of the posterior horn of the extension of the posterior horn of the spinal cordspinal cord

It contains a set of neurons resembling It contains a set of neurons resembling the substantia gelatinosa in the spinal the substantia gelatinosa in the spinal cordcord

The tracts entering the spinal nucleus of The tracts entering the spinal nucleus of V are like an upward extension of the V are like an upward extension of the tract of Lissauertract of Lissauer

CN V - TrigeminalCN V - Trigeminal

Pain and temperaturePain and temperature Trigeminal pain and temperature fibers Trigeminal pain and temperature fibers

descend caudally to enter the spinal descend caudally to enter the spinal nucleus of Vnucleus of V

Fibers from the spinal nucleus of V Fibers from the spinal nucleus of V decussate and join the ascending decussate and join the ascending spinothalamic tractspinothalamic tract

CN V - TrigeminalCN V - Trigeminal

VV

Main sensory nucleus of V

VV

Spinal nucleus of V

Spinothalamic tract

Mesencephalic nucleus of V

CN V - TrigeminalCN V - Trigeminal

Motor - Muscles of masticationMotor - Muscles of mastication The The Motor nucleus of VMotor nucleus of V is homologous is homologous

to ventral horn in the spinal cordto ventral horn in the spinal cord Corticobulbar upper motor neurons Corticobulbar upper motor neurons

synapse on lower motor neurons synapse on lower motor neurons originating in this nucleusoriginating in this nucleus

CN V - TrigeminalCN V - Trigeminal

VV

Main sensory nucleus of V

VV Spinal nucleus of V

V V Motor nucleus of V

UMN

LMN

Mesencephalic nucleus of V

Clinical CorrelationClinical Correlation

Afferent limb of corneal blink reflexAfferent limb of corneal blink reflex Direct and consensual responseDirect and consensual response

Clinical CorrelationClinical Correlation

Jaw muscle weaknessJaw muscle weakness Jaw deviates toward the weak sideJaw deviates toward the weak side

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Clinical CorrelationClinical Correlation

Disorders of sensationDisorders of sensation Trigeminal neuropathyTrigeminal neuropathy Trigeminal neuralgiaTrigeminal neuralgia

Traumatic brain injuryTraumatic brain injury Loss of smell does not include harsh or Loss of smell does not include harsh or

unpleasant smellsunpleasant smells This can be a means of detecting This can be a means of detecting

“faking”“faking” Smelling salts and the ARASSmelling salts and the ARAS

CN VII - FacialCN VII - Facial

CN VII - FacialCN VII - Facial

Motor (branchial)Motor (branchial) Muscles of facial expression via the Muscles of facial expression via the

motor nucleus of VIImotor nucleus of VII Eye closureEye closure

Motor (autonomic)Motor (autonomic) To salivary and lacrimal glands from To salivary and lacrimal glands from

superior salivatory nucleussuperior salivatory nucleus

CN VII - FacialCN VII - Facial

Somatic sensorySomatic sensory Skin of the outer ear to spinal Skin of the outer ear to spinal

trigeminal nucleustrigeminal nucleus Visceral SensoryVisceral Sensory

Palate and taste buds on anterior 2/3 of Palate and taste buds on anterior 2/3 of the tongue to the Nucleus of the the tongue to the Nucleus of the solitary tractsolitary tract

CN VII - FacialCN VII - Facial

VII VII

Nucleus of the solitary tract

Superior salivatory nucleus

Motor nucleus of VII

CN VII - FacialCN VII - Facial

Motor nucleus of VIIMotor nucleus of VII Corticobulbar fibers for upper face Corticobulbar fibers for upper face

synapse on the motor nucleus of VII synapse on the motor nucleus of VII bilaterally (most fibers decussate)bilaterally (most fibers decussate)

Fibers bound for the lower face synapse Fibers bound for the lower face synapse on the contralateral nucleus onlyon the contralateral nucleus only

CN VII - FacialCN VII - Facial

VII VII

To upper face

To lower face

To upper face

To lower face

CN VII - FacialCN VII - Facial

VII VII

To upper face

To lower face

To upper face

To lower face

CN VII - FacialCN VII - Facial

VII VII

To upper face

To lower face

To upper face

To lower face

Clinical CorrelationClinical Correlation

Lesions of the cortex or corticobulbar Lesions of the cortex or corticobulbar tracttract Contralateral lower face weaknessContralateral lower face weakness Ex: StrokeEx: Stroke

Lesions of the motor nucleus of VII or Lesions of the motor nucleus of VII or peripheral nerveperipheral nerve Ipsilateral lower and upper face weaknessIpsilateral lower and upper face weakness Ex: Bell’s PalsyEx: Bell’s Palsy

Clinical CorrelationClinical Correlation

CN VII is the efferent limb of the CN VII is the efferent limb of the corneal blink reflexcorneal blink reflex

? - left

? - right VII - right

VII left

Clinical CorrelationClinical Correlation

Corneal blink reflexCorneal blink reflex Afferent fibers originate in the Afferent fibers originate in the

ophthalmic division of CN Vophthalmic division of CN V Synapse on Spinal Nucleus of VSynapse on Spinal Nucleus of V Internerons project bilaterally (via the Internerons project bilaterally (via the

reticular formation) to neurons in the reticular formation) to neurons in the motor nucleus of VIImotor nucleus of VII

Clinical CorrelationClinical Correlation

CN VII is the efferent limb of the CN VII is the efferent limb of the corneal blink reflexcorneal blink reflex

V - left

V - right VII - right

VII left

CN VIII CN VIII VestibulocochlearVestibulocochlear

CN VIII - CN VIII - VestibulocochlearVestibulocochlear

Two divisions - both special sensoryTwo divisions - both special sensory Cochlear (auditory)Cochlear (auditory) VestibularVestibular

CN VIII - CN VIII - VestibulocochlearVestibulocochlear

Cochlear divisionCochlear division Cochlear ganglion to CN VIIICochlear ganglion to CN VIII CN VIII synapses in the cochlear nucleiCN VIII synapses in the cochlear nuclei Cochlear nuclei project to the superior olivary Cochlear nuclei project to the superior olivary

nucleus and inferior colliculusnucleus and inferior colliculus Superior olivary nucleus is also receiving input Superior olivary nucleus is also receiving input

from contralateral cochlear nucleifrom contralateral cochlear nuclei Superior olivary nucleus projects to inferior Superior olivary nucleus projects to inferior

colliculuscolliculus Inferior colliculus projects to thalamusInferior colliculus projects to thalamus

CN VIII - CN VIII - VestibulocochlearVestibulocochlear

Cochlear divisionCochlear division

Cochlear Nuclei

VIII

Sup. Olivary Nuc.

Clinical CorrelationClinical Correlation

Note that auditory information is Note that auditory information is bilaterally represented very early in the bilaterally represented very early in the pathwaypathway

This means that you only have unilateral This means that you only have unilateral hearing loss followinghearing loss following Lesion to CN VIII itselfLesion to CN VIII itself Lesion to the cochlear nuclei on one sideLesion to the cochlear nuclei on one side

Cortical lesions (i.e., Heschel’s Gyrus) will Cortical lesions (i.e., Heschel’s Gyrus) will not result in unilateral hearing loss not result in unilateral hearing loss

CN VIII - CN VIII - VestibulocochlearVestibulocochlear

Vestibular division - inputsVestibular division - inputs Vestibular afferents project toVestibular afferents project to

The cerebellumThe cerebellum Vestibular Nuclear ComplexVestibular Nuclear Complex

InferiorInferior LateralLateral MedialMedial SuperiorSuperior

Vestibular Nuclear Complex also receives afferents Vestibular Nuclear Complex also receives afferents fromfrom

CerebellumCerebellum Contralateral Vestibular Nuclear ComplexContralateral Vestibular Nuclear Complex

CN VIII - CN VIII - VestibulocochlearVestibulocochlear

Vestibular division - inputsVestibular division - inputs

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CN VIII - CN VIII - VestibulocochlearVestibulocochlear

Vestibular division - OutputsVestibular division - Outputs ThalamusThalamus Nuclei of III, IV, and VINuclei of III, IV, and VI Spinal CordSpinal Cord

Lateral Vestibulospinal TractLateral Vestibulospinal Tract Medial Vestibulospinal TractMedial Vestibulospinal Tract

CN VIII - CN VIII - VestibulocochlearVestibulocochlear

Vestibular division - OutputsVestibular division - Outputs ThalamusThalamus Nuclei of III, IV, and VINuclei of III, IV, and VI Spinal CordSpinal Cord

Lateral Vestibulospinal TractLateral Vestibulospinal Tract Medial Vestibulospinal TractMedial Vestibulospinal Tract

CerebellumCerebellum

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CN VIII - CN VIII - VestibulocochlearVestibulocochlear

Medial and Lateral Vestibulocerebellar Medial and Lateral Vestibulocerebellar TractsTracts Part of a system that supports the voluntary Part of a system that supports the voluntary

motor system by providing corrective signals motor system by providing corrective signals to muscles depending on vestibular feedbackto muscles depending on vestibular feedback

Why are there projections to oculomotor Why are there projections to oculomotor nuclei?nuclei?

Clinical CorrelationClinical Correlation

Vestibuloocular Reflex (VOR)Vestibuloocular Reflex (VOR) Fixation of gaze despite head movementFixation of gaze despite head movement Stabilizes image on the retinaStabilizes image on the retina Reflexive, Reflexive, notnot a pursuit movement a pursuit movement Works in the darkWorks in the dark Works if unconsciousWorks if unconscious

Clinical CorrelationClinical Correlation

Doll’s eye maneuverDoll’s eye maneuver Can be used to test the integrity of the brain Can be used to test the integrity of the brain

stem in an unconscious patientstem in an unconscious patient

CN IX - GlossopharyngealCN IX - Glossopharyngeal

CN IX - GlossopharyngealCN IX - Glossopharyngeal

Glossopharyngeal means “tongue Glossopharyngeal means “tongue and throat”and throat”

Numerous afferents fromNumerous afferents from Carotid sinusCarotid sinus Walls of the pharynxWalls of the pharynx Mucous membranesMucous membranes Taste bud from posterior 1/3 of the Taste bud from posterior 1/3 of the

tonguetongue

CN IX - GlossopharyngealCN IX - Glossopharyngeal

SensorySensory Taste bud afferents travel to the Taste bud afferents travel to the

nucleus of the solitary tractnucleus of the solitary tract Pain from the pharynx and posterior 1/3 Pain from the pharynx and posterior 1/3

of the tongue likely go to spinal of the tongue likely go to spinal trigeminal nucleustrigeminal nucleus

Some sensory fibers likely reach the Some sensory fibers likely reach the main sensory nucleus of Vmain sensory nucleus of V

CN IX - GlossopharyngealCN IX - Glossopharyngeal

MotorMotor StylopharyngeusStylopharyngeus

Swallowing (with X anf XII)Swallowing (with X anf XII) Elevates the pharynx while swallowing and Elevates the pharynx while swallowing and

speakingspeaking These fibers arise from the These fibers arise from the nucleus nucleus

ambiguus, ambiguus, a poorly differentiated a poorly differentiated nucleus in the medullary tegmentumnucleus in the medullary tegmentum

Clinical CorrelationClinical Correlation

Afferent of the Gag ReflexAfferent of the Gag Reflex

CN X - VagusCN X - Vagus

Principal parasympathetic nervePrincipal parasympathetic nerve Widely distributed (vagus = Widely distributed (vagus =

“wandering”)“wandering”) Some overlap with CN IXSome overlap with CN IX Preganglionic parasympathetic fibers Preganglionic parasympathetic fibers

to the thoracic and abdominal viscerato the thoracic and abdominal viscera Arise in the dorsal motor nucleus of the Arise in the dorsal motor nucleus of the

vagusvagus Fibers to the heart originate in the Fibers to the heart originate in the

nucleus ambiguusnucleus ambiguus

CN X - VagusCN X - Vagus

Visceral sensory information fromVisceral sensory information from Thoracic and abdominal visceraThoracic and abdominal viscera Taste buds of the epiglottisTaste buds of the epiglottis Most project to nucleus of the solitary Most project to nucleus of the solitary

tracttract Some may project to spinal nucleus of VSome may project to spinal nucleus of V

Clinical CorrelationClinical Correlation Hoarseness (larynx)Hoarseness (larynx) DysarthriaDysarthria Paralysis of the soft palateParalysis of the soft palate DysphagiaDysphagia Uvula deviates away from weaknessUvula deviates away from weakness Loss of cough reflex (anesthesia of Loss of cough reflex (anesthesia of

pharynx and larynx)pharynx and larynx)

Clinical CorrelationClinical Correlation Efferent of the gag reflexEfferent of the gag reflex

IX X

Clinical CorrelationClinical Correlation Vagal nerve stimulatorVagal nerve stimulator

Implantable deviceImplantable device Treatment for seizuresTreatment for seizures

CN XI - Spinal AccessoryCN XI - Spinal Accessory

CN XI - Spinal AccessoryCN XI - Spinal Accessory

Motor only - neck and shoulder Motor only - neck and shoulder musclesmuscles SternocleidomastoidSternocleidomastoid Part of the trapeziusPart of the trapezius

Accessory Nucleus (cervical spinal Accessory Nucleus (cervical spinal cord)cord)

CN XII - HypoglossalCN XII - Hypoglossal

CN XII - HypoglossalCN XII - Hypoglossal

Motor - Muscles of the tongueMotor - Muscles of the tongue Hypoglossal NucleusHypoglossal Nucleus

Clinical CorrelationClinical Correlation

Which side of the tongue is weak?

Clinical CorrelationClinical Correlation

The tongue deviates to the weak side The tongue deviates to the weak side when protrudedwhen protruded

Coming Up…Coming Up…

DiencephalonDiencephalon ThalamusThalamus HypothalamusHypothalamus