Pons

1. Describe the Dev. of the Pons

   • Derived from?

   • Location

2. Differentiate the dev. of Alar vs Basal Plates

3. Describe formation of Basilar Pons

4. What will axons of these nuclei form?

Pons Development:

• derived from:

  • rhombencephalon (primary brain vesicle)

  • later as part of metencephalon along w/ cerebellum.

• Location:

  • pontine flexure btw metencephalon and myelencephalon.

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Alar vs Basal:

• Alar: sensory-related nuclei associated w/ CNs

  • CN sensory nuclei develop/remain in dorsal and lateral position in the pons

• Basal: midline and dorsal motor components of pontine cranial nerve nuclei

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Formation of Basilar Pons:

• pontine nuclei migrate from part of alar plate → ventrally + medially → basilar pons.

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Axons of these nuclei will form:

• middle cerebellar peduncle that wraps around the brainstem in a lateral position

Describe the two major divisions within the pons

• Location within pons?

• Components? (3) (3)

Pontine Tegmentum:

• Dorsal (and medial) portion

• Components:

  • Cont. of medullary reticular formation/ associated tracts

  • Pontine CN nuclei

  • Ascending sensory tracts

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Basilar Pons

• Ventral (and lateral) portion

• Components:

  • Cortically derived axons

  • corticobulbar (includes corticopontine)

  • Pontine nuclei

    • Projections → cerebellum = middle cerebellar peduncle

Describe the PMJ

• Level of What?

• Nuclei Overlaps?

Ponto Medullary Junction (PMJ):

Level Of:

• CN VIII (SSA) - Cochlear Component

  • nuclei overlap between the pons and medulla, and in some cases is classified as lying in both.

1. Describe PMJ-CN VIII - Cochlear Component

   • Origins

   • Function

   • Synapse @

2. Pathway?

3. What happens to the Info in Contra Lat. Lemniscus?

4. Describe the Accessory Auditory Nuclei in Pons:

   • Function?

   • List/Function

5. Describe the Lat. Lemniscus:

   • Travel up in what position?

   • Clinical Importance?

PMJ-CN VIII - Cochlear Component

• Origin: spiral ganglia of the cochlea

• Function: carry auditory information to the brainstem

• Synapse @ Brainstem:

  • Dorsal/Ventral Cochlear Nucleus

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Pathway:

• Dorsal/Ventral Cochlear Nuelci → Lateral Lemniscus (primary ascending auditory pathway)

  • Axons Leave nuclei in dorsal, intermediate and ventral acoustic stria → Cross @ more rostral levels (there is small ipsilateral component)

    • Trapezoid Body = region in brainstem where axons cross

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Info in Contra Lat. Lemniscus:

• Ascends to:

  • Inferior Colliculus

  • Medial geniculate body (thalamus)

  • Cortex (temporal, transverse gyri of Heschel)

• Some Axons → accessory auditory nuclei adj. to tract

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Accessory Auditory Nuclei in Pons:

• Main Function = Sound processing; particularly dampening and localization

• Primary Ones:

  • Superior olivary nuclear complex

    • sound localization- reflex sound dampening

      • via stapedius muscle (CN VII)and tensor tympanic (CN V)

  • Nucleus of trapezoid body

    • localization of sounds

  • Nucleus of lateral lemniscus

    • sound localization

    • acoustic reflexes (not as well defined)

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Lateral Lemniscus Notes:

• Travels up brainstem in dorsolateral position

• There is some Ipsilateral Components

  • → ipsilateral lesion of tract in pons/midbrain → no noticeable unilateral hearing loss

    • EXCEPTION: unless the nerve or cochlear nuclei are involved.

Draw out the Cochlear component pathway

1. Describe PMJ-CN VIII - Vestibular Component

   • Origins

   • Function

   • Innervates? (4)

   • Central Nuclei projections? (3)

2. List and describe function of the 4 CN VIII - Vestibular Related Pathways

PMJ-CN VIII - Vestibular Component

• Origins: vestibular ganglion;

• Function:

  • Transmits afferent information from vestibular apparatus

• Innervates:

  • four nuclei in dorsal and lateral part of the PMJ

    • Medial Vestibular Nucleus

    • Lateral Vestibular Nucleus (Deiter’s nucleus)

    • Superior Vestibular Nucleus

    • Inferior Vestibular Nucleus

• Central Nuclei Projections:

  • → Cerebellum via juxtarestiform body (balance coordination)

  • Some direct connections to:

    • flocculonodular lobe

    • deep cerebellar nuclei.

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CN VIII - Vestibular Related Pathways

• Oculomotor nuclei:

  • via medial longitudinal fasciculus (MLF)-

• Thalamus:

  • via MLF:

  • → cortex to give conscious perception of equilibrium and orientation.

• From SC:

  • Lateral vestibulospinal tract

    • from lateral vestibular nucleus (Deiter's nucleus),

    • Function: excitatory to extensor spinal alpha motor neurons.

  • Medial vestibulospinal tract (a.k.a. MLF)

    • Descends in Spinal Cord

    • Function:

      • Inhibitory to neck and upper trunk muscles

      • Contributes to head- righting reflexes in relation to vision, etc

What is rostral to nuclei of CN VIII

rostral to nuclei of CN VIII @ PMJ:

• caudal pons contains nuclei for Cranial Nerves VI/VII

  • exit from nuclei in ventral and slightly caudal direction to exit @ PMJ

Describe CN VII:

• Exits brainstem @?

• Nerve Includes?

Describe the CNVII Motor Branch:

• Internal nerve course

• What is the Facial Colliculus:

• Cortical Innervation?

Facial Nerve - CN VII

• Exits brainstem:

  • anterior to VIII @ PMJ

• nerve includes

  • motor root

  • smaller intermediate nerve lateral to it.

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CNVII Motor Branch:

• Internal nerve course

  • axons loop around (internal genu of facial nerve) the nucleus of CN VI Nucleus → exit ipsilaterally

  • Note: axons forming 'loop' = from the motor nucleus.

• Facial Colliculus:

  • bump on floor of 4th ventricle

  • Shows presence of CNVI nucleus and axons of CN VII surrounding it

• Cortical Innervation:

  • Bilateral: nucleus innervating muscles of the forehead

  • Contralateral: nucleus for muscles of the lower face

  • NOTE: This means that after a cortical or corticonuclear lesion function to the forehead may remain, but not to the lower face.

1. Describe PONS - CN VII - Intermedius Branch

   • Functions (3)

2. Describe the Superior Salivatory Nucleus- (GVE):

   • Location

   • Axon Pathway

3. Describe the Central autonomic connections to GVE:

   • Pathway

   • Function

   • Brainstem reflex circuits

4. Describe the pathway of Solitary Nucleus

Functions:

• Parasympathetic functions (GVE):

  • lachrymal qlands

    • via pterygopalatine ganglion

  • mucous membranes of nose, hard and soft palates

  • salivary qlands-

    • via submandibular ganglion

    • submandibular, sublingual

• Taste: (SVA)

  • anterior 2/3 of tongue

  • hard and soft palates

  • via geniculate ganglion.

• GSA:

  • skin of ear wall of acoustic meatus and external tympanic membrane

    • Geniculate Ganglion → Nervus intermedius → Spinal Nuceus and tract of CNV

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Superior Salivatory Nucleus- (GVE)-

• Location:

  • in dorsolateral reticular formation

  • dorsolateral to descending limb of facial nerve

• Axons:

  • transverse geniculate ganglion → pterygopalatine and submandibular ganglia (cholinergic).

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Central autonomic connections to GVE:

• NOTE: this means Higher Brain systems → Intermedius Branch

• Pathway:

  • limbic system and olfactory areas → hypothalamus → brainstem

    • via dorsal longitudinal fasciculus.

• Functions

  • emotional responses

  • weeping

  • mouth watering to odors etc.

• Brainstem reflex circuits

  • reflex lachrymation from V

  • gustatory stimulation of salivation.

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Solitary Nucleus (rostral portion, gustatory nucleus, SVA)

• Pathway:

  • Taste Sensory fibers on tongue/hard/soft palate → Chorda Tympani from geniculate ganglion → Brainstem as part of nervus intermedius → tractus solitarius → synapse in rostral portion of the nucleus → central teqmental tract to thalamus (VP) → Cortext (conscious perception of taste)

Solitary Nucleus

Abducens Nerve

Describe the Abducen Nerve

• @ level?

• Exits?

• Function

• Neuron Location?

• Clinical Importance

• Complex central connection w/? Via? involved in?

Abducens Nerve

• Level of VI & VII

• Exits in the inferior pontine sulcus

• Function: GSE:

  • Ipsilateral Lateral Rectus

• Neuron Location:

  • @ Abducens nerve

    • beneath axons of the facial nerve in the facial colliculus

• Clinical Importance:

  • long intracranial course → one of the most frequently injured of cranial nerves

• Complex central connections with oculomotor nuclei.

  • Via MLF (medial longitudinal fasciculus)

  • Involved in conjugate eye movements.

Abducens Nucleus

Describe the Reticular formation

• Location

• Function (3)

pontine reticular formation

• Location: pontine tegmentum;

  • contains many nuclei that contribute to the reticular formation located over the entire brainstem.

• Function:

  • forms complex connections btw CN nuclei for reflex and visceral functions.

  • rostral projections → thalamus

    • regulate consciousness,

  • caudal projections

    • regulate motor and sensory functions.

Describe the location of major tracts in the Caudal Pons

• CST

• Medial Lemniscus

• ALS

• Rubrospinal tract

• Reticulospinals and vestibulospinals

• spinal nucleus and tract of CN V

• MLF and tectospinal (tectobulbospinal ) tracts

• Others

location of major tracts in the Caudal Pons:

• CST/corticonuclear (bulbar) run through the substance of the basilar pons

• Medial Lemniscus:

  • still in the midline

  • begins to turn → somatotopy shifts → leg areas = more lateral

• anterolateral system

  • still in lateral position w/in pontine tegmentum,

    • @ anterolateral edge w/ formation of middle cerebellar peduncle.

• Rubrospinal Tract:

  • Dorsal to ALS

• Reticulospinals and vestibulospinals

  • still being formed in this area, so they are not clear.

• spinal nucleus and tract of CN V

  • still present as pars oralis

  • just dorsal to the exit of the facial nerve.

• MLF and tectospinal (tectobulbospinal ) tracts

  • dorsal position near the midline.

  • will now carry motor information for eye movements.

• Other Ascending/Descending → displaced into the pontine tegmentum

Draw out CST as it progresses up

Draw out the Medial Lemniscus as it progresses up

Draw out the ALS as it progresses up

Draw out the Spinal Nucleus tract of CNV as it progresses up

Describe the Inferior/Middle/Superior Cerebellar Peduncles

• Locations?

• Importance?

inferior cerebellar peduncle (restiform body, ICP)

• enter cerebellum in dorsal and lateral position.

• Includes:

  • vestibulocerebellar projections called juxtarestiform body

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Middle Cerebellar peduncle:

• between the pons and cerebellum

• will wrap laterally around the inferior peduncle

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superior cerebellar peduncles

• in more rostral sections

• Forms part of roof of 4th ventricle along with superior medullary velum,

  • CT membrane between them.

Draw out the Spinocerebellar tracts as it ascends

Inferior/middle cerebellar peduncle (middle = lateral)

Superior Cerebellar peduncle and superior medullary velum,

What are the Blood Supply to the Caudal Pons

Vertebral

Basilar

Posterior Inferior Cerebellar A

Anterior Inferior Cerebellar A

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Vertebral + medial branches of basilar → Ventral and medial

PICA: Dorsolateral