brain stem ii basic neuroscience james h. baños, ph.d

Brain Stem IIBrain Stem II

Basic NeuroscienceBasic Neuroscience

James H. Baños, Ph.D.James H. Baños, Ph.D.

Today…Today…

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 medulla, Extends through the central part of the medulla,

pons, and midbrainpons, 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 the CNSInput and output to virtually all parts of the CNS


Can be roughly divided into three Can be roughly divided into three longitudinal zoneslongitudinal zones Midline - Raphe NucleiMidline - Raphe Nuclei Medial Zone - Long ascending and Medial Zone - Long ascending and

descending projectionsdescending projections Lateral Zone - Cranial nerve reflexes Lateral Zone - Cranial nerve reflexes

and visceral functionsand 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 bothSome have bifurcating collaterals that do both Many have large dendritic fields that traverse Many have large dendritic fields that traverse

multiple levels of the brain stemmultiple levels of the brain stem

Reticular Formation Reticular Formation FunctionsFunctions

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


The Terri Schiavo caseThe Terri Schiavo case


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


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

Pause for contemplation!Pause for contemplation! Major recurring theme: Major recurring theme: LOOPSLOOPS

Many brain functions are represented in Many brain functions are represented in loops (usually with a modulatory loops (usually with a modulatory influence)influence)

Muscle toneMuscle tone Reflex loopsReflex loops Pain modulationPain modulation

Pathology and treatment of pathology are Pathology and treatment of pathology are often related to modulating these loopsoften related to modulating these loops

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

Pause for contemplation!Pause for contemplation!

Periaqueductal Grey

Raphe

Spinal Cord Level

Cortex

Hypothal

SpinothalamicTract

Thalamus

Basic Pathway

Modulatory circuitry

……meanwhile, back at the reticular meanwhile, back at the reticular formation…formation…

III. Autonomic reflex circuitryIII. Autonomic reflex circuitry Reticular formation receives diverse input related to Reticular formation receives diverse input related to

environmental changesenvironmental 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.


Damage to the medulla often kills youDamage to the medulla often kills you

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. Involved in control of arousal and IV. 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 thalamus, Ascending pathways from RF project to thalamus,

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

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

Ascending Reticular Activating System (ARAS)Ascending Reticular Activating System (ARAS) ARAS is a functional system, not an anatomically ARAS is a functional system, not an anatomically

distinct structuredistinct structure


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 CN nucleus decussate Fibers for each CN nucleus decussate

at the level of that nucleus (i.e., at the level of that nucleus (i.e., multiple points of decussation) multiple points of decussation)

Cranial Nerves Cranial Nerves and Their Nucleiand Their Nuclei

A word about A word about organization…organization…

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


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 the same Otherwise, structurally and functionally the same

as other muscleas other muscle Autonomic fibersAutonomic fibers


All of these fiber types organize All of these fiber types organize predictably around the sulcus predictably around the sulcus limitanslimitans

Starting from the top…Starting from the top…CN ICN I

Starting from the top…CN I - Starting from the top…CN I - OlfactoryOlfactory

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

Note that there is no brain stem nucleus Note that there is no brain stem nucleus for CNIfor CNI

Olfactory bulb

Cribiform plate

CN I


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


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 Dysomia - Distorted sense of smellDysomia - 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


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

CN III - OculomotorCN III - OculomotorNucleus of III

Edinger-Westphal

Spinothalamic

Medial Lemniscus

Corticospinal

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 muscle of the upper eyelid Levator muscle of the upper eyelid



III7 CN III OculomotorCN III Oculomotor

““Pillars” that hold Pillars” that hold the eye openthe eye open

CN VII FacialCN VII Facial ““Hook” that pulls Hook” that pulls

the eye closedthe eye closed


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 pupilary light reflexpupilary light reflex

Also involved in pupilary Also involved in pupilary accommodationaccommodation


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


Pupillary light reflexPupillary light reflex DirectDirect ConsensualConsensual

II - left

II - right III - right

III - left


CN IV - TrochlearCN IV - Trochlear


Somatic MotorSomatic Motor Superior Oblique - Intorts, depressed, Superior Oblique - Intorts, depressed,

adducts the eyeadducts the eye


Nucleus of IV

CN VI - AbducensCN VI - Abducens


Somatic MotorSomatic Motor Lateral RectusLateral Rectus


III III

IV

VI

IV

VI

Finally, lets add a Finally, lets add a 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?


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)


III III

IV

VI

IV

VI

Learn More…Learn More…

http://cim.ucdavis.edu/eyes/version15/eyesim.html

University of California -- Davis Eye Simulation Website:

Coming Up…Coming Up…

More cranial nervesMore cranial nerves DiencephalonDiencephalon

brain stem ii basic neuroscience james h. baños, ph.d

Documents

spinal neurons

spinal cordnumerous

periaqueductal grey

loopsmany brain functions

complex motor behaviors

descending collateralssome

pain managementpause

transmission of information