BrainBrain stemstem
PonsPons (bridge)(bridge) CNSCNS divisionsdivisions BrainstemBrainstem divisionsdivisions
Midbrain Mesencephalon
Pons Cerebellum Metencephalon
Medulla Myelencephalon VentralVentral brainbrain stemstem
cerebral peduncle
middle cerebellar peduncle
pyramid DorsalDorsal brainbrain stemstem
Superior Cranial Nerve IV colliculus
Inferior colliculus
Middle Fourth ventricle cerebellar peduncle VentralVentral brainbrain stemstem
Basilar Pons
Cranial Nerve V
Cranial Nerve VI
Cranial Nerve VII
Cranial Nerve VIII BrainstemBrainstem –– macroscopicmacroscopic overviewoverview
Dorsal view Ventral view
Bulbopontine sulcus NeuralNeural tubetube foldingfolding
Day 21 → → day 26 OriginOrigin ofof CNSCNS subdivisionssubdivisions Primary/secondary brain vesicles & flexures that separate them Primary vesicles Cervical flexure Embryo axis Cephalic flexure
Cephalic flexure
Pontine flexure Cervical flexure
Secondary vesicles NeuralNeural tubetube foldingfolding –– pontinepontine flexureflexure
Neural tube folding (5 th -8th wk) AlarAlar vs.vs. BasalBasal plateplate derivativesderivatives -- medullamedulla
dorsal
somatic Alar plate = afferent = sensory visceral
Basal plate = efferent = motor visceral somatic infeior olivary nucleus ventral AlarAlar vs.vs. BasalBasal plateplate -- ponspons
Spinal cord Medulla
Pons AlarAlar vs.vs. BasalBasal plateplate derivativesderivatives -- ponspons
Pontine nuclei somatic are alar plate Alar plate = afferent = sensory visceral precursors migrated Basal plate = efferent = motor visceral ventrally somatic
The basal plate → primarily efferent nuclei (CN V, VI, VII, superior salivatory nuclei) The alar plate → somatic and visceral sensory nuclei (CN V, VIII, pontine nuclei) EstimatedEstimated timetime ofof developmentdevelopment ofof variousvarious brainbrain regiregionsons
Modified from Bayer SA et al. Neurotoxicology 14:83–144, 1993 LongitudinalLongitudinal zoneszones inin thethe brainbrain stemstem cranial tectum Structures in Pons: Nuclei → neuronal tegmentum bodies Reticular formation → neuronal bodies basis Tracts = white matter → neuronal axons passing through ending in pons
caudal LevelLevel ofof CNCN VV -- PonsPons
Superior Cerebellar Peduncle
4th Ventricle
Middle Cerebellar Peduncle LevelLevel ofof CNCN VI,VI, VIIVII -- PonsPons
Superior Cerebellar Peduncle
Facial Colliculus
Middle Cerebellar Peduncle
Pyramids (beginning) TheThe brainstembrainstem isis connectedconnected toto thethe cerebellumcerebellum viavia thethe cerebellarcerebellar pedunclespeduncles
superior cerebellar peduncle (SCP) Brachium conjunctivum MidbrainMidbrain ↔↔ CerebellumCerebellum
middle cerebellar peduncle (MCP) Brachium pontis PonsPons →→ CerebellumCerebellum MCP is the principal input path of the cerebellum (it has no output)
inferior cerebellar peduncle (MCP) MedullaMedulla oblongataoblongata ↔↔ CerebellumCerebellum AfferentAfferent cerebellarcerebellar pathwayspathways inin brainstembrainstem
Saggital view Dorsal view StructuresStructures inin basisbasis pontispontis
CorticoCortico --pontoponto --cerebellarcerebellar fibersfibers CorticospinalCorticospinal fibersfibers CorticobulbarCorticobulbar fibersfibers ((cortexcortex →→ cranialcranial nervenerve nucleinuclei )) directdirect cc orticobulbarorticobulbar indirectindirect cc orticoortico --reticuloreticulo --bulbarbulbar (( cortexcortex →→ RFRF →→ CNCN nucleinuclei )) NucleiNuclei pontispontis (gray(gray matter)matter) CorticopontocerebellarCorticopontocerebellar fibersfibers constituteconstitute thethe largestlargest groupgroup ofof fibersfibers inin thethe basisbasis pontispontis
WWideide areasareas ofof cortexcortex →→ ipsilateralipsilateral pontinepontine nucleinuclei →→ contralateralcontralateral cerebellumcerebellum viavia MCPMCP (some(some 10%10% -- ipsilatipsilat .).) NumberNumber ofof fibersfibers -- 1919 millionmillion onon eacheach side/numberside/number ofof pontinepontine nucleinuclei neuronsneurons –– 2323 millionmillion onon eacheach sideside (~1:1)(~1:1) PrincipalPrincipal corticalcortical inputinput –– primaryprimary sensorimotorsensorimotor areasareas →→ correctioncorrection ofof movementsmovements AllAll projectionprojection ss areare somatotopicallysomatotopically organizedorganized CorticopontocerebellarCorticopontocerebellar pathwaypathway
Purves, et al, Neuroscience, 3rd ed. Corticopontine tract – upper pons
Origin: Premotor, primary motor, and primary somatosensory cortex Course: Internal Capsule (A/P), cerebral peduncles, Pons Termination: Pontine nuclei Laterality: Ipsilateral Fibers will then synapse on Corticopontine tract pontine nuclei, which then decussate in the transverse fibers of the pons and enter the MCP…
Pontine Nuclei
Origin: Premotor, primary motor, and primary somatosensory cortex Course: Internal Capsule (A/P), cerebral peduncles, Pons Termination: Pontine nuclei Laterality: Ipsilateral Inputs,Inputs, MCPMCP PontocerebellarPontocerebellar TractTract
preprogram of fine motor movements, esp. upper extremity
Origin: Pontine Nuclei Course: Immediately decussates and enters MCP Termination: granule cells of the cerebellar hemispheres Laterality: Contralateral CCorticospinalorticospinal andand corticobulbarcorticobulbar tractstracts CorticospinalCorticospinal tracttract –– upperupper ponspons
Origin: Primary motor cortex (BA 4) Course: Post Limb IC, Pyramids Termination: Spinal cord ventral horn Laterality: CONTRA (lateral), IPSI (anterior) CorticospinalCorticospinal tracttract –– lowerlower ponspons
Origin: Primary motor cortex (BA 4) Course: Post Limb IC, Pyramids Termination: Spinal cord ventral horn Laterality: CONTRA (lateral), IPSI (anterior) CorticobulbarCorticobulbar tractstracts
MotorMotor inputinput to:to: ReticularReticular formationsformations –– pontinepontine CranialCranial NerveNerve motormotor nucleinuclei –– V,V, VI,VI, VII,VII, VIIIVIII
Note – No direct connections from the primary motor cortex to CN VI; this nucleus gets input from frontal and parietal cortex StructuresStructures inin thethe tegmentumtegmentum pontispontis
CranialCranial nervenerve nucleinuclei –– CNCN V,V, VI,VI, VII,VII, VIIIVIII ReticularReticular formationformation -- nucleusnucleus locuslocus ceruleusceruleus && otherother CrossingCrossing pathwayspathways ascending (sensory) – basal part of tegmentum lemniscal spinothalamic anterior spinocerebellar tract descending (motor) central tegmental tract (basal ganglia /midbrain → inferior olive ) rubrospinal tract tectospinal tract other – sympathetic fibers from hypothalamus; medial longitudinal fasciculus PositionPosition ofof ascendingascending toto descendingdescending fibersfibers inin tegmentumtegmentum
ascending – ventral part of tegmentum descending – dorsal part of tegmentum DescendingDescending brainbrain stemstem pathwayspathways (to(to spinalspinal cord)cord)
(tectospinal)
Purves, et al, Neuroscience, 3rd ed. CranialCranial nervenerve nucleinuclei inin brainbrain stemstem
Name Nerve Nuclei
Oculomotor III Oculomotor, Edinger–Westphal midbrain Trochlear IV Trochlear Trigeminal V Main sensory, spinal (descending), mesencephalic, motor (masticatory) Abducens VI Abducens pons Facial VII Facial, superior salivatory, gustatory (solitary)** Vestibulocochlear VIII Cochlear (2 nuclei), vestibular (4 nuclei) Glossopharyngeus IX Ambiguus*, inferior salivatory, solitary** Vagus X Dorsal motor, ambiguus**, solitary* medulla Accessory XI Spinal accessory (C1–5), ambiguus** Hypoglossal XII Hypoglossal
** The solitary nucleus is common for CN VII, IX, and X * The ambiguus nucleus is common for CN IX, X, and XI Cranial nerves – sensory nuclei Cranial nerves – motor nuclei CNCN V:V: TrigeminalTrigeminal CNCN V:V: TrigeminalTrigeminal
The “level” of CN V is determined by where the nerve fibers * exit * *
* AAfferentfferent andand efferentefferent rootsroots ofof CNCN VV
Mesencephalic nucleus is homologous to the dorsal root ganglion but centrally placed
Trigeminal JawJaw jerkjerk reflexreflex –– CNCN VV
Proprioceptive fibers to the mesencephalic nucleus convey pressure and kinesthesia from the teeth, periodontium, hard palate, and joint capsules as well as impulses from stretch receptors in the muscles of mastication. The mesencephalic nucleus is concerned with mechanisms that control the force of the bite. CNCN V:V: TrigeminalTrigeminal -- mesencephalicmesencephalic
The mesencephalic Origin: Mesencephalic nucleus and tract run Nucleus of V above the level of CN V Course: Mesencephalic tract of V Termination: Motor Nucleus of V Laterality: Bilateral CNCN V:V: TrigeminalTrigeminal motormotor andand chiefchief sensorysensory (level(level ofof CNCN V)V)
Chief Sensory Motor nucleus nucleus of V of V
R A L L A A S A B
Alar → sensory Basal → motor CornealCorneal reflexreflex
CN V
CN VII
Touching the cornea elicits reflex closure of the eye → might be disrupted in pontine lesions CNCN V:V: TrigeminalTrigeminal SpinalSpinal nucleusnucleus andand tracttract atat levellevel ofof VI/VIIVI/VII
Neuron #1 Origin: Trigeminal (Gasserian) Ganglion Course: All branches of Trigeminal Nerve, Spinal Trigeminal tract Termination: Spinal Nucleus of V Laterality: Ipsilateral CNCN VI:VI: AbducensAbducens
Origin: Abducens Nucleus Course: Exit PM Jxn, ascend through Dorello’s canal, cavernous sinus, sup orb fissure Termination: Lateral Rectus Laterality: Ipsilateral CNCN VI:VI: AbducensAbducens CNCN VI:VI: AbducensAbducens -- paralysisparalysis
Left eye can’t look to left. CNCN VII:VII: FacialFacial Origin: Geniculate Ganglion (sensory), Motor Nucleus of VII (motor), Salivatory Nucleus (autonomic) Course: CNVII, through IAC, temporal bone, exit stylomastoid foramen Termination: Nucleus Solitarius (taste), Muscles of facial expression, stapedius, post belly digastric, Parasympathetic ganglia (sublingual, lacrimal, submandibular) Laterality: Ipsilateral CNCN VII:VII: FacialFacial Motor
Sensory visceral somatic
sol
CN VI Solitarius Motor
Motor VII
Salivatory TheThe unusualunusual coursecourse ofof facialfacial motormotor nucleusnucleus axonsaxons CNCN VII:VII: FacialFacial –– BellBell ’’ss palsypalsy CNCN VIII:VIII: VestibulocochlearVestibulocochlear
Cochlear Portion Origin: Spiral Ganglion Course: CNVIII, through internal auditory meatus Termination: Cochlear Nucleus Laterality: Ipsilateral
Vestibular Portion Origin: Scarpa’s Ganglion Course: CNVIII, through internal auditory meatus Termination: Vestibular Nucleus Laterality: Ipsilateral CNCN VIII:VIII: VestibulocochlearVestibulocochlear cochlear nuclei vestibular nuclei CNCN VIIIVIII -- nucleinuclei
Cochlear nuclei ventral cochlear nucleus dorsal cochlear nucleus Vestibular nuclei superior vestibular nucleus (Bechterew) inferior vestibular nucleus (Roller) medial vestibular nucleus (Schwalbe) lateral vestibular nucleus (Deiters) VestibularVestibular SystemSystem
Superior Vestibular Nucleus
Medial Vestibular Nucleus
Lateral Vestibular Nucleus VestibularVestibular SystemSystem
Medial Longitudinal Fasciculus UpperUpper ponspons ((levellevel ofof locuslocus ceruleus)ceruleus)
medial longitudinal fasciculus UpperUpper ponspons ((levellevel ofof locuslocus ceruleus)ceruleus) MidMid --PonsPons ((levellevel ofof CNCN V)V)
tegmentum
basis LowerLower PonsPons
Corpus trapezoideum BBloodlood supplysupply ofof thethe ponspons –– basilarbasilar arteryartery
dorsal tegmentum
basis + ventral tegmentum
Anterior inferior cerebellar lateral artery (AICA) tegmentum