Brainstem cranial nerve

Brain Stem Brain Stem

Dr. Shittu LAJDr. Shittu LAJ

Learning outlineLearning outline Brain Stem Reticular FormationBrain Stem Reticular Formation Corticobulbar tractCorticobulbar tract Cranial nerves and their nucleiCranial nerves and their nuclei

Major Brain Stem Major Brain Stem ActivitiesActivities

ConduitConduit Ascending and descending pathwaysAscending and descending pathways

Integrative functionsIntegrative functions Complex motor patternsComplex motor patterns Respiratory and cardiovascular activityRespiratory and cardiovascular activity Regulation of arousal and level of Regulation of arousal and level of

consciousnessconsciousness Cranial Nerve functionsCranial Nerve functions

Integrative Functions-Integrative Functions-Brain Stem Reticular Brain Stem Reticular

FormationFormation

Brain Stem Reticular Brain Stem Reticular FormationFormation

Reticular = “netlike”Reticular = “netlike” Loosely defined nuclei and tractsLoosely defined nuclei and tracts Extends through the central part of the Extends through the central part of the

medulla, pons and midbrainmedulla, pons and midbrain Intimately associated withIntimately associated with

Ascending/descending pathwaysAscending/descending pathways Cranial nerves/nucleiCranial nerves/nuclei

Input and output to virtually all parts of Input and output to virtually all parts of the CNSthe CNS


Reticular Formation Reticular Formation FunctionsFunctions

Periaqueductal Grey

Raphe

Spinal Cord Level

Cortex

Hypothal

SpinothalamicTract

Thalamus


Can be roughly divided into Can be roughly divided into three longitudinal zonesthree longitudinal zonesMidline - Raphe NucleiMidline - Raphe NucleiMedial Zone - Long ascending Medial Zone - Long ascending

and descending projectionsand descending projectionsLateral Zone - Cranial nerve Lateral Zone - Cranial nerve

reflexes and visceral functionsreflexes and visceral functions


Connectivity is Connectivity is extremelyextremely complex complex Many different types of neuronsMany different types of neurons

Innervate multiple levels of the spinal cordInnervate multiple levels of the spinal cord Numerous ascending and descending Numerous ascending and descending

collateralscollaterals Some have bifurcating collaterals that do Some have bifurcating collaterals that do

bothboth Many have large dendritic fields that Many have large dendritic fields that

traverse multiple levels of the brain stemtraverse multiple levels of the brain stem


I. Participates in control of movement through I. Participates in control of movement through connections with both the spinal cord and connections with both the spinal cord and cerebellumcerebellum Two Two reticulospinal tractsreticulospinal tracts originate in the rostral pontine originate in the rostral pontine

and medullary reticular formationand medullary reticular formation Major alternate route by which spinal neurons are controlledMajor alternate route by which spinal neurons are controlled Regulate sensitivity of spinal reflex arcsRegulate sensitivity of spinal reflex arcs Tonic inhibition of flexor reflexesTonic inhibition of flexor reflexes Mediates some complex “behavioral” reflexesMediates some complex “behavioral” reflexes

YawningYawning StretchingStretching Babies sucklingBabies suckling

Some interconnectivity with cerebellar motor control Some interconnectivity with cerebellar motor control circuitrycircuitry

Clinical CorrelationClinical Correlation Pseudobulbar affect (as seen in Amyotrphic Pseudobulbar affect (as seen in Amyotrphic

Lateral Sclerosis)Lateral Sclerosis) Degeneration of descending motor pathways from the Degeneration of descending motor pathways from the

cortex to the brainstemcortex to the brainstem ““Release” of some of complex motor behaviors such as Release” of some of complex motor behaviors such as

laughing and cryinglaughing and crying Usually uncontrollable, not consistent with moodUsually uncontrollable, not consistent with mood May laugh when angry, cry at sad things, etcMay laugh when angry, cry at sad things, etc Conceptually analogous to upper motor neuron Conceptually analogous to upper motor neuron

hyperreflexiahyperreflexia Disinhibited spinal reflexes are very simpleDisinhibited spinal reflexes are very simple Disinhibited brainstem reflexes are very complexDisinhibited brainstem reflexes are very complex


II. Modulates transmission of information in pain II. Modulates transmission of information in pain pathwayspathways Spinomesencephalic fibers bring information about Spinomesencephalic fibers bring information about

noxious stimuli to the noxious stimuli to the periaqueductal greyperiaqueductal grey Periaqueductal grey also receives input from the Periaqueductal grey also receives input from the

hypothalamus and cortex about behavioral and drive hypothalamus and cortex about behavioral and drive statesstates

Efferents from the periaqueductal grey project to one of Efferents from the periaqueductal grey project to one of the raphe nuclei and medullay reticular formationthe raphe nuclei and medullay reticular formation

These project to the spinal cord and can suppress These project to the spinal cord and can suppress transmission of pain information in the spinothalamic transmission of pain information in the spinothalamic tracttract


Periaqueductal Grey

Raphe

Spinal Cord Level

Cortex

Hypothal

SpinothalamicTract

Thalamus

Clinical CorrelationClinical Correlation Pain ManagementPain Management

Periaqueductal grey has high concentration of Periaqueductal grey has high concentration of opiate receptorsopiate receptors

Natural pain modulation relies on endogenous Natural pain modulation relies on endogenous opiatesopiates

Exogenous opiates are used for pain Exogenous opiates are used for pain managementmanagement

LOOPSLOOPSMany brain functions are represented Many brain functions are represented

in loops (usually with a modulatory in loops (usually with a modulatory influence)influence)

Muscle toneMuscle tone Reflex loopsReflex loops Pain modulationPain modulation

Pathology and treatment of pathology Pathology and treatment of pathology are often related to modulating these are often related to modulating these loopsloops

Many of the basic pathways are Many of the basic pathways are supplemented by more complex supplemented by more complex pathways that complete this modulated pathways that complete this modulated loop architectureloop architecture

the reticular formation…the reticular formation…

III. III. Autonomic reflex circuitryAutonomic reflex circuitry Reticular formation receives diverse input related Reticular formation receives diverse input related

to environmental changesto environmental changes Also receives input from hypothalamus related to Also receives input from hypothalamus related to

autonomic regulationautonomic regulation Output to Output to

cranial nerve nucleicranial nerve nuclei Intermediolateral cell column of the spinal cordIntermediolateral cell column of the spinal cord

Involved inInvolved in BreathingBreathing Heart rateHeart rate Blood pressureBlood pressure Etc.Etc.

Clinical CorrelationClinical Correlation Damage to the medulla often kills Damage to the medulla often kills

youyou Horner’s SyndromeHorner’s Syndrome

Interruption of descending pathways to Interruption of descending pathways to the intermediolateral cell column the intermediolateral cell column

Ipsilateral Miosis (small pupil)Ipsilateral Miosis (small pupil) Ipsilateral Ptosis (drooping eyelid)Ipsilateral Ptosis (drooping eyelid) Ipsilateral Flushing/lack of sweatingIpsilateral Flushing/lack of sweating


IV. IV. Involved in control of arousal and Involved in control of arousal and consciousnessconsciousness Input from multiple modalities (including pain)Input from multiple modalities (including pain) Ascending pathways from RF project to Ascending pathways from RF project to

thalamus, cortex, and other structures.thalamus, cortex, and other structures. Thalamus is important in maintaining arousal Thalamus is important in maintaining arousal

and “cortical tone”and “cortical tone” This system is loosely defined, but referred to as This system is loosely defined, but referred to as

the Ascending Reticular Activating System the Ascending Reticular Activating System (ARAS)(ARAS)

ARAS is a functional system, not an anatomically ARAS is a functional system, not an anatomically distinct structuredistinct structure

Clinical CorrelationClinical Correlation Normal functionsNormal functions

Sleep/wakefulnessSleep/wakefulness

Loss of ConsciousnessLoss of Consciousness Traumatic brain injuryTraumatic brain injury Smelling salts, sternal rubs, and the ARASSmelling salts, sternal rubs, and the ARAS

ComaComa Can result from extensive damage to cortexCan result from extensive damage to cortex More focal damage to ARASMore focal damage to ARAS

Coma vs Minimally Conscious StateComa vs Minimally Conscious State Intact sleep/wake patterns in brain activityIntact sleep/wake patterns in brain activity

The Corticobulbar The Corticobulbar TractTract

The Corticobulbar TractThe Corticobulbar Tract Corticospinal tractCorticospinal tract

Descending motor pathways to ventral Descending motor pathways to ventral horn of the spinal cordhorn of the spinal cord

Includes only fibers for torso, arms, legs Includes only fibers for torso, arms, legs (i.e., headless HAL)(i.e., headless HAL)

Decussates at a single point in the Decussates at a single point in the pyramids of the medulla (pyramidal pyramids of the medulla (pyramidal decussation) decussation)

The Corticobulbar TractThe Corticobulbar Tract Corticobulbar tractCorticobulbar tract

Descending motor pathways to cranial Descending motor pathways to cranial nerve nucleinerve nuclei

Includes descending fibers for HAL’s Includes descending fibers for HAL’s headhead

Fibers for each Cranial nucleus Fibers for each Cranial nucleus decussate at the level of that nucleus decussate at the level of that nucleus (i.e., multiple points of decussation) (i.e., multiple points of decussation)

Cranial Nerves Cranial Nerves and Their Nucleiand Their Nuclei

organizationorganization Sensory and motor spinal nerves can Sensory and motor spinal nerves can

be divided intobe divided into Sensory (dorsal)Sensory (dorsal)

Somatic - pain, temperature, mechanical Somatic - pain, temperature, mechanical stimulistimuli

Visceral - from receptive endingsVisceral - from receptive endings Motor (ventral)Motor (ventral)

Somatic - Innervate skeletal muscleSomatic - Innervate skeletal muscle Visceral - To visceral autonomic gangliaVisceral - To visceral autonomic ganglia

organizationorganization Cranial Nerves also include:Cranial Nerves also include:

Special Sensory fibersSpecial Sensory fibers Hearing, equilibrium, etcHearing, equilibrium, etc

Special motor fibers Special motor fibers Branchial motorBranchial motor

Muscles of the head and faceMuscles of the head and face Different embryologic origin and locationDifferent embryologic origin and location Otherwise, structurally and functionally Otherwise, structurally and functionally

the same as other musclethe same as other muscle Autonomic fibersAutonomic fibers

organizationorganization All of these fiber types organize All of these fiber types organize

predictably around the sulcus predictably around the sulcus limitanslimitans

Cranial nerve-ICranial nerve-I

CN I - OlfactoryCN I - Olfactory

Fiber types:Fiber types: Special Sensory -- SmellSpecial Sensory -- Smell

The olfactory bulb and tract aren’t really The olfactory bulb and tract aren’t really CNICNI

The fibers of CNI originate in the olfactory The fibers of CNI originate in the olfactory mucosa of the nasal cavity, pass through mucosa of the nasal cavity, pass through the cribriform plate, and synapse onto the the cribriform plate, and synapse onto the olfactory bulbolfactory bulb

Note that there is no brain stem nucleus for Note that there is no brain stem nucleus for CNICNI

Olfactory bulb

Cribiform plate

CN I

Clinical CorrelationClinical Correlation Olfactory nerve dysfunction is often Olfactory nerve dysfunction is often

reported as altered taste and smellreported as altered taste and smell Conditions affecting CNI include:Conditions affecting CNI include:

Upper respiratory tract infectionUpper respiratory tract infection Traumatic Brain Injury (TBI)Traumatic Brain Injury (TBI) Subfrontal meningiomaSubfrontal meningioma DementiaDementia

Clinical CorrelationClinical Correlation Anosmia - Total loss of smellAnosmia - Total loss of smell Hyposmia - Partial loss of smellHyposmia - Partial loss of smell Hyperosmia - Exaggerated sense of Hyperosmia - Exaggerated sense of

smellsmell Dysosmia - Distorted sense of smellDysosmia - Distorted sense of smell Olfactory hallucinations - Associated Olfactory hallucinations - Associated

with seizureswith seizures

CN II - OpticCN II - Optic

CN II - OpticCN II - Optic Fiber TypesFiber Types

Special Sensory -- VisionSpecial Sensory -- Vision Retinal ganglion cells to: Retinal ganglion cells to:

Thalamus (lateral geniculate nucleus) -- Primary Thalamus (lateral geniculate nucleus) -- Primary visual pathwayvisual pathway

Superior colliculus -- Reflexes involving vision Superior colliculus -- Reflexes involving vision and lightand light

Hypothalmus -- Light-dependent behavioral Hypothalmus -- Light-dependent behavioral cyclescycles

Does not have a specific nucleus in the Does not have a specific nucleus in the brain stembrain stem

CN III - OculomotorCN III - Oculomotor

CN III - OculomotorCN III - Oculomotor Somatic Motor - Eye movement Somatic Motor - Eye movement

Superior, inferior, medial rectiSuperior, inferior, medial recti Inferior obliqueInferior oblique Levator palpebrae superiorisLevator palpebrae superioris

Autonomic - Pupillary constrictionAutonomic - Pupillary constriction Edinger-Westphal nucleus to pupillary Edinger-Westphal nucleus to pupillary

sphincter sphincter


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Nucleus of IIIEdinger-Westphal

Eye movementEye movement Superior rectus - elevationSuperior rectus - elevation Inferior rectus - depressionInferior rectus - depression Medial rectus - adductionMedial rectus - adduction Inferior Oblique - extorsion/elevationInferior Oblique - extorsion/elevation

Levator palpebrae superiorisLevator palpebrae superioris



III

CN III-Oculo-CN III-Oculo-motormotor““Pillars” that Pillars” that hold the eye hold the eye openopen

CN VII- FacialCN VII- Facial““Hook” that pulls Hook” that pulls the eye closedthe eye closed

LR6SO4O3

7

CN III - OculomotorCN III - Oculomotor Edinger-Westphal nucleusEdinger-Westphal nucleus

Receives bilateral projections from Receives bilateral projections from superior colliculi (which had received superior colliculi (which had received unilateral projections from CN II)unilateral projections from CN II)

This is the efferent component of the This is the efferent component of the pupillary light reflexpupillary light reflex

Also involved in pupillary Also involved in pupillary accomodationaccomodation

Clinical CorrelationClinical Correlation Damage to CN III or nucleus of IIIDamage to CN III or nucleus of III

““Down and out” eyeballDown and out” eyeball DiplopiaDiplopia PtosisPtosis Dilated and fixed pupilDilated and fixed pupil Paralysis of pupillary accommodationParalysis of pupillary accommodation

Can be cause by…Can be cause by… Uncal/transtentorial herniationUncal/transtentorial herniation AneurysmAneurysm

II - left

II - right III - right

III - left

Clinical CorrelationClinical Correlation Pupillary light reflexPupillary light reflex

DirectDirect ConsensualConsensual

II - left


III - left

Clinical CorrelationClinical Correlation

II - left


III - left


II - left


III - left


CN IV - TrochlearCN IV - Trochlear

CN IV - TrochlearCN IV - Trochlear Somatic MotorSomatic Motor

Superior Oblique - Intorts, depressed, Superior Oblique - Intorts, depressed, adducts the eyeadducts the eye

CN IV - TrochlearCN IV - Trochlear

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Nucleus of IV

CN VI - AbducensCN VI - Abducens

CN VI - AbducensCN VI - Abducens Somatic MotorSomatic Motor

Lateral RectusLateral Rectus

CN VI - AbducensCN VI - Abducens

III III

IV

VI

IV

VI

pathwaypathway What muscles are being used when What muscles are being used when

we look left or right?we look left or right? What cranial nerves?What cranial nerves? Is the same thing happening on each Is the same thing happening on each

side?side?

Pathway-IIPathway-II During horizontal conjugate eye During horizontal conjugate eye

movements, each eye is doing the movements, each eye is doing the opposite of the otheropposite of the other Adduction (CN III) on one sideAdduction (CN III) on one side Abduction (CN VI) on the other sideAbduction (CN VI) on the other side

This is accomplished by “cross This is accomplished by “cross wiring” the nuclei via the wiring” the nuclei via the medial medial longitudinal fasciculus (MLF)longitudinal fasciculus (MLF)

Pathway-IIIPathway-III

III III

IV

VI

IV

VI

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Brainstem cranial nerve