Areas covered in this slide include brain stem reticular formation, corticobulbar tract, and cranial nerves and their nuclei

1. Brain StemBrain Stem
Dr. Shittu LAJDr. Shittu LAJ

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

3. Major Brain Stem ActivitiesMajor Brain Stem Activities
 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 ofRegulation of arousal and level of
consciousnessconsciousness
 Cranial Nerve functionsCranial Nerve functions

4. Integrative Functions-Integrative Functions-
Brain Stem ReticularBrain Stem Reticular
FormationFormation

5. Brain Stem Reticular FormationBrain Stem Reticular Formation
 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 theInput and output to virtually all parts of the
CNSCNS

6. Brain Stem Reticular FormationBrain Stem Reticular Formation

7. Reticular Formation FunctionsReticular Formation Functions
Periaqueductal Grey
Raphe
Spinal Cord Level
Cortex
Hypothal
Spinothalamic
Tract
Thalamus

8. Brain Stem Reticular FormationBrain Stem Reticular Formation
 Can be roughly divided into threeCan be roughly divided into three
longitudinal zoneslongitudinal zones
 Midline - Raphe NucleiMidline - Raphe Nuclei
 Medial Zone - Long ascending andMedial Zone - Long ascending and
descending projectionsdescending projections
 Lateral Zone - Cranial nerveLateral Zone - Cranial nerve
reflexes and visceral functionsreflexes and visceral functions

9. Brain Stem Reticular FormationBrain Stem Reticular Formation
 Connectivity isConnectivity is extremelyextremely complexcomplex
 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 descendingNumerous ascending and descending
collateralscollaterals
 Some have bifurcating collaterals that do bothSome have bifurcating collaterals that do both
 Many have large dendritic fields that traverseMany have large dendritic fields that traverse
multiple levels of the brain stemmultiple levels of the brain stem

10. Reticular Formation FunctionsReticular Formation Functions
 I. Participates in control of movement throughI. Participates in control of movement through
connections with both the spinal cord and cerebellumconnections with both the spinal cord and cerebellum
 TwoTwo reticulospinal tractsreticulospinal tracts originate in the rostral pontine andoriginate in the rostral pontine and
medullary reticular formationmedullary 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 circuitrySome interconnectivity with cerebellar motor control circuitry

11. Clinical CorrelationClinical Correlation
 Pseudobulbar affect (as seen in Amyotrphic LateralPseudobulbar affect (as seen in Amyotrphic Lateral
Sclerosis)Sclerosis)
 Degeneration of descending motor pathways from the cortex toDegeneration of descending motor pathways from the cortex to
the brainstemthe brainstem
 ““Release” of some of complex motor behaviors such as laughingRelease” of some of complex motor behaviors such as laughing
and cryingand 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 hyperreflexiaConceptually analogous to upper motor neuron hyperreflexia
 Disinhibited spinal reflexes are very simpleDisinhibited spinal reflexes are very simple
 Disinhibited brainstem reflexes are very complexDisinhibited brainstem reflexes are very complex

12. Reticular Formation FunctionsReticular Formation Functions
 II. Modulates transmission of information in painII. Modulates transmission of information in pain
pathwayspathways
 Spinomesencephalic fibers bring information about noxiousSpinomesencephalic fibers bring information about noxious
stimuli to thestimuli to the periaqueductal greyperiaqueductal grey
 Periaqueductal grey also receives input from the hypothalamusPeriaqueductal grey also receives input from the hypothalamus
and cortex about behavioral and drive statesand cortex about behavioral and drive states
 Efferents from the periaqueductal grey project to one of theEfferents from the periaqueductal grey project to one of the
raphe nuclei and medullay reticular formationraphe nuclei and medullay reticular formation
 These project to the spinal cord and can suppress transmissionThese project to the spinal cord and can suppress transmission
of pain information in the spinothalamic tractof pain information in the spinothalamic tract

13. Reticular Formation FunctionsReticular Formation Functions
Periaqueductal Grey
Raphe
Spinal Cord Level
Cortex
Hypothal
Spinothalamic
Tract
Thalamus

14. Clinical CorrelationClinical Correlation
 Pain ManagementPain Management
 Periaqueductal grey has high concentration of opiatePeriaqueductal grey has high concentration of opiate
receptorsreceptors
 Natural pain modulation relies on endogenousNatural pain modulation relies on endogenous
opiatesopiates
 Exogenous opiates are used for pain managementExogenous opiates are used for pain management

15. LOOPSLOOPS
Many brain functions are represented inMany brain functions are represented in
loops (usually with a modulatoryloops (usually with a modulatory
influence)influence)
 Muscle toneMuscle tone
 Reflex loopsReflex loops
 Pain modulationPain modulation
 Pathology and treatment of pathology arePathology and treatment of pathology are
often related to modulating these loopsoften related to modulating these loops
 Many of the basic pathways are supplementedMany of the basic pathways are supplemented
by more complex pathways that complete thisby more complex pathways that complete this
modulated loop architecturemodulated loop architecture

16. the reticular formation…the reticular formation…

III.III. Autonomic reflex circuitryAutonomic reflex circuitry
 Reticular formation receives diverse input related toReticular formation receives diverse input related to
environmental changesenvironmental changes
 Also receives input from hypothalamus related toAlso receives input from hypothalamus related to
autonomic regulationautonomic regulation
 Output toOutput 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.

17. Clinical CorrelationClinical Correlation
 Damage to the medulla often kills youDamage to the medulla often kills you
 Horner’s SyndromeHorner’s Syndrome
 Interruption of descending pathways to theInterruption of descending pathways to the
intermediolateral cell columnintermediolateral 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

18. Reticular Formation FunctionsReticular Formation Functions
 IV.IV. Involved in control of arousal andInvolved 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 andThalamus is important in maintaining arousal and
“cortical tone”“cortical tone”
 This system is loosely defined, but referred to as theThis 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 anatomicallyARAS is a functional system, not an anatomically
distinct structuredistinct structure

19. 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

20. The Corticobulbar TractThe Corticobulbar Tract

21. The Corticobulbar TractThe Corticobulbar Tract
 Corticospinal tractCorticospinal tract
 Descending motor pathways to ventral hornDescending motor pathways to ventral horn
of the spinal cordof the spinal cord
 Includes only fibers for torso, arms, legs (i.e.,Includes only fibers for torso, arms, legs (i.e.,
headless HAL)headless HAL)
 Decussates at a single point in the pyramidsDecussates at a single point in the pyramids
of the medulla (pyramidal decussation)of the medulla (pyramidal decussation)

22. The Corticobulbar TractThe Corticobulbar Tract
 Corticobulbar tractCorticobulbar tract
 Descending motor pathways to cranial nerveDescending motor pathways to cranial nerve
nucleinuclei
 Includes descending fibers for HAL’s headIncludes descending fibers for HAL’s head
 Fibers for each Cranial nucleus decussate atFibers for each Cranial nucleus decussate at
the level of that nucleus (i.e., multiple pointsthe level of that nucleus (i.e., multiple points
of decussation)of decussation)

23. Cranial Nerves andCranial Nerves and
Their NucleiTheir Nuclei

24. organizationorganization
 Sensory and motor spinal nerves can beSensory and motor spinal nerves can be
divided intodivided into
 Sensory (dorsal)Sensory (dorsal)
 Somatic - pain, temperature, mechanical stimuliSomatic - pain, temperature, mechanical stimuli
 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

25. organizationorganization
 Cranial Nerves also include:Cranial Nerves also include:
 Special Sensory fibersSpecial Sensory fibers
 Hearing, equilibrium, etcHearing, equilibrium, etc
 Special motor fibersSpecial motor fibers
 Branchial motorBranchial motor
 Muscles of the head and faceMuscles of the head and face
 Different embryologic origin andDifferent embryologic origin and
locationlocation
 Otherwise, structurally and functionallyOtherwise, structurally and functionally
the same as other musclethe same as other muscle
 Autonomic fibersAutonomic fibers

26. organizationorganization
 All of these fiber types organizeAll of these fiber types organize
predictably around the sulcus limitanspredictably around the sulcus limitans

27. Cranial nerve-ICranial nerve-I

28. CN I - OlfactoryCN I - Olfactory
 Fiber types:Fiber types:
 Special Sensory -- SmellSpecial Sensory -- Smell
 The olfactory bulb and tract aren’t really CNIThe olfactory bulb and tract aren’t really CNI
 The fibers of CNI originate in the olfactoryThe fibers of CNI originate in the olfactory
mucosa of the nasal cavity, pass through themucosa of the nasal cavity, pass through the
cribriform plate, and synapse onto the olfactorycribriform plate, and synapse onto the olfactory
bulbbulb
 Note that there is no brain stem nucleus for CNINote that there is no brain stem nucleus for CNI

29. Olfactory bulb
Cribiform plate
CN I

30. Clinical CorrelationClinical Correlation
 Olfactory nerve dysfunction is oftenOlfactory 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

31. 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 smellHyperosmia - Exaggerated sense of smell
 Dysosmia - Distorted sense of smellDysosmia - Distorted sense of smell
 Olfactory hallucinations - Associated withOlfactory hallucinations - Associated with
seizuresseizures

32. CN II - OpticCN II - Optic

33. 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 visualThalamus (lateral geniculate nucleus) -- Primary visual
pathwaypathway
 Superior colliculus -- Reflexes involving vision and lightSuperior colliculus -- Reflexes involving vision and light
 Hypothalmus -- Light-dependent behavioral cyclesHypothalmus -- Light-dependent behavioral cycles
 Does not have a specific nucleus in the brainDoes not have a specific nucleus in the brain
stemstem

34. CN III - OculomotorCN III - Oculomotor

35. CN III - OculomotorCN III - Oculomotor
 Somatic Motor - Eye movementSomatic 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 pupillaryEdinger-Westphal nucleus to pupillary
sphinctersphincter

36. CN III - OculomotorCN III - Oculomotor
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Nucleus of III
Edinger-Westphal

37.  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
CN III - OculomotorCN III - Oculomotor

38. CN III - OculomotorCN III - Oculomotor
III
 CN III-Oculo-motorCN III-Oculo-motor
““Pillars” that holdPillars” that hold
the eye openthe eye open
 CN VII- FacialCN VII- Facial
““Hook” that pullsHook” that pulls
the eye closedthe eye closedLR6SO4O3
7

39. CN III - OculomotorCN III - Oculomotor
 Edinger-Westphal nucleusEdinger-Westphal nucleus
 Receives bilateral projections fromReceives bilateral projections from
superior colliculi (which had receivedsuperior colliculi (which had received
unilateral projections from CN II)unilateral projections from CN II)
 This is the efferent component of theThis is the efferent component of the
pupillary light reflexpupillary light reflex
 Also involved in pupillaryAlso involved in pupillary
accomodationaccomodation

40. 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

41. II - left
II - right III - right
III - left
Clinical CorrelationClinical Correlation
 Pupillary light reflexPupillary light reflex
 DirectDirect
 ConsensualConsensual

42. II - left
II - right III - right
III - left
Clinical CorrelationClinical Correlation

43. II - left
II - right III - right
III - left
Clinical CorrelationClinical Correlation

44. II - left
II - right III - right
III - left
Clinical CorrelationClinical Correlation

45. CN IV - TrochlearCN IV - Trochlear

46. CN IV - TrochlearCN IV - Trochlear
 Somatic MotorSomatic Motor
 Superior Oblique - Intorts, depressed, adductsSuperior Oblique - Intorts, depressed, adducts
the eyethe eye

47. CN IV - TrochlearCN IV - Trochlear
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Nucleus of IV

48. CN VI - AbducensCN VI - Abducens

49. CN VI - AbducensCN VI - Abducens
 Somatic MotorSomatic Motor
 Lateral RectusLateral Rectus

50. CN VI - AbducensCN VI - Abducens
III III
IV
VI
IV
VI

51. pathwaypathway
 What muscles are being used when weWhat muscles are being used when we
look left or right?look left or right?
 What cranial nerves?What cranial nerves?
 Is the same thing happening on each side?Is the same thing happening on each side?

52. Pathway-IIPathway-II
 During horizontal conjugate eyeDuring horizontal conjugate eye
movements, each eye is doing themovements, 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 wiring” theThis is accomplished by “cross wiring” the
nuclei via thenuclei via the medial longitudinal fasciculusmedial longitudinal fasciculus
(MLF)(MLF)

53. Pathway-IIIPathway-III
III III
IV
VI
IV
VI