Medulla 1/2

Describe the Medulla Oblongata

• Structure?

• Derived from?

• Contains?

• Most caudal brainstem, conical in shape

• Derived from the Rhombencephalon

• Contains primary nuclei for autonomic control of respiration, heart rate, blood pressure.

What two long tracts decussate in the Medulla Oblongata

two distinct long tract

• dorsal column-medial lemniscal system

• corticospinal tract

Describe the boundaries of the Medulla Oblongata

Boundaries:

• Caudal Ventral Boundary: pyramidal decussation

• Rostral Boundary: Obex

• No definitive rostral ventral boundary or caudal boundary exist

• Closed portion of the medulla containing the central canal.

Describe the Pyramidal (Motor) Decussation

• Location

• Fiber Destiy

• Somatotopy of Decussation

• Location:

  • ventral surface of the medulla; disruption of the anterior median fissure

• Fibers Destiny Here:

  • 80-90 percent of corticospinal tract fibers decussates (L CST)

    • 8% descend ipsilaterally → anterior funiculus → decussate segmentally (Anterior CST)

    • 2% descend ipsilaterally to contribute to the lateral corticospinal tract (tract of Barnes)

• Somatotopy of Decussation:

  • Upper Extremity fibers: Rostrally

  • Lower Extremity fibers: Caudally

  • THUS: iscrete lesions in the pyramidal decussation may produce different and somewhat unusual patterns of weakness.

What happens @ the level of Pyramidal Decussation (2) (besides CST decussation)

@ Level Pyramidal Decussation:

• Fibers within fasciculus gracilis + fasciculus cuneatus synapse @ Nucleus Gracilis and nucleus cuneatus, respectively.

• spinal trigeminal nucleus (pars caudalis) + tract take place of gray matter of dorsal horn and tract of Lissauer, respectively.

Describe the Spinal Trigeminal Nucleus and Tract

• Location

• Receives

• Pathway of Afferent?

Describe the tuberculum cinereum (or trigeminal tubercle)

• Arise from?

• Location?

Describe the 3 parts of Spinal Trigeminal Nucleus and Tract

• Location

• Function

Describe the Somatotopic Organization of the Medulla

Spinal Trigeminal Nucleus and Tract

• Location:

  • within the lateral medulla

  • Extends caudal pons → upper cervical spinal cord.

• Receives:

  • GSA conveying from Face/External Ear

    • Pain

    • Temperature

    • Crude Touch

• Pathway of Trigeminal Afferents:

  • Enters Brainstem @ level of CNV → Descends in Spinal Trigeminal Tract (located lateral to spinal nucleus) → synapse @ Trigeminal Nucleus along its rostral caudal extent

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tuberculum cinereum (or trigeminal tubercle):

• Arise from spinal trigeminal nucleus and tract

• Located lateral to the cuneate tubercle and tract

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3 parts of Spinal Trigeminal Nucleus and Tract

• Pars Oralis

  • Location: rostral pole of hypoglossal N. → caudal end of principal sensory nucleus (Pons))

  • Function: Tactile input (crude touch)

• Pars Interpolaris

  • Location: level of obex → rostral pole of hypoglossal nucleus)

  • Function: Dental pain

• Pars Caudalis

  • Location: (C3 → obex)

  • Function: Pain and temperature

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Somatotopic Organization:

• V1 synapses ventrally

• V2 and V2 synapses progressively more dorsal.

***NOTE: Sensory fibers from the external ear travel in CN VII, IX, and X to synapse in the dorsal most part of the caudal subnucleus (Pars Caudalis)***

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Onion Skin Pattern of Somatotopic Organization

• Nociceptive afferents from the circumoral (around mouth) region: rostral part of the pars caudalis

• More Posterior/Lateral Parts: progressively more caudal parts of the caudal subnucleus

Describe the Accessory Nucleus @ level of Pyramid Dessucation

• Location

• Route

• Innervates

• Cortical Input to Neurons

Accessory Nucleus @ level of Pyramid Dessucation:

• Location of GSE from Accessory Nucleus:

  • lateral portion of the ventral horn

  • SC +medulla junction → C5/6

• Route of Rootlets:

  • exit to form a trunk → ascends through foramen magnum

• Innervates: trapezius and SCM.

• Cortical Input to Neurons:

  • To trapezius is crossed

  • To SCM is ipsilateral

  • NOTE: not all sources are in agreement

@ level of pyramidal dessucation, What happen to these other tracts:

• Medial Long. Fasciculus

• Ant./Post. Spinocerebellar Tract

• Anterolateral system (spinal lemniscus)

• Rubrospinal tract

Other Tracts:

• Medial Long. Fasciculus (descending limb - medial vestibulospinal tract) and Tectospinal Tract:

  • Pushed laterally by the decussating CST fibers.

• Ant./Post. Spinocerebellar Tract:

  • Retain position similar to SC

• Anterolateral system (spinal lemniscus)

  • medial to spinocerebellar tracts;

  • Retain position like SC

• Rubrospinal tract

  • associated w/ ALS in caudal brainstem.

  • Retains similar position in the spinal cord.

Describe Sensory Decussation of the Dorsal Columns:

• Pathway? Locations?

• What are the names of the fibers decussating?

Sensory Decussation of Dorsal Column

1. Dorsal Columns → ascend to caudal medulla → synapse @ gracile/cuneate nucleus

   • Location: deep to gracile tubercle (clava) and cuneate tubercle

2. dorsal column nuclei → Decussates @ tegmentum → medial lemniscus → ascend to thalamus (VPL).

   • Fibers Decussating = internal arcuate fibers

   • Fibers ascending in medial lemniscus = somatotopically organized

Describe what happens to Accessory Cuneate Nucleus: @ level of Sensory Decussation

• Location

• Equivalent

• Function

• Pathway of Fibers

Accessory Cuneate Nucleus:

• Location:

  • Lateral to cuneate nucleus

• Equivalent:

  • rostral equivalent of the posterior thoracic nucleus (AKA, Clarke’s Column) (Dorsal N.)

• Function:

  • proprioceptive information from upper extremity that is destined for the cerebellum

• Pathway of Fibers:

  • Large diameter afferents (proprioceptive + exteroceptive info) → cervical/Upper thoracic (perhaps) → ascend in fasciculus cuneatus → synapse @ Accessory (lateral,external) cuneate nucleus (instead of the posterior thoracic nucleus) → cuneocerebellar tract → cerebellum via inferior cerebellar peduncle (restiform body)

Describe what happens to these tracts @ level of sensory dessucation:

• tectospinal tract + medial longitudinal fasciculus

• uncrossed pyamidal tracts

• Spinocerebellar Tract, anterlateral system, rubrospinal tract

• tectospinal tract + medial longitudinal fasciculus

  • located in midline behind medial lemniscis

• uncrossed pyamidal tracts

  • located ventromedially.

• Spinocerebellar Tract, anterlateral system, rubrospinal tract

  • moved to a slightly more posterior position

Describe the Blood Supply of the Lower Medulla

• anterior spinal A

  • off Vertebral Artery

  • Supplies: anteriormedial area of lower medulla

• Vertebral Artery

  • Supplies Lateral Areas

• Posterior Spinal Artery:

  • usually branch of PICA or vertebral Artery

  • Supplies Dorsal Areas

(ADD PIC LATER)

NOTE: At more Rostral areas, PICA supplies lateral areas

Describe the Upper Medulla:

• What is it?

• Boundaries?

Describe Development:

• Where are Sensory/Motor CN nuclei?

• Movement of SVE/GSA column

• What forms the inferior Olive?

Level of Obex:

• associated w/?

• Decussation Characteristics?

• What is a unique Characteristic @ this level? Function?

What is it?

• Open portion of medulla containing caudal half of the fourth ventricle.

Boundaries:

• Dorsal Surface:

  • caudal boundary= obex

  • rostral boundary is the striae medullares

• Ventral Surface:

  • no definitive caudal boundary

  • rostral boundary = inferior pontine sulcus

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Development:

• sensory CN nuclei: dorsolateral position due to dev. of 4th ventricle.

• Motor CN nuclei: ventromedially.

• SVE/GSA column will migrate anterolaterally.

• inferior olive = alar plate derivative.

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Level Of Obex:

• Associated w/ CN XII

• Many of characteristics of level of the sensory decussation are retained.

• Unique characteristics: Area Postrema

  • Circumventrical organ containing sinusoid capillaries

  • Function:

    • Chemosensitive trigger zone for emesis stimulated by blood-borne chemicals

Describe what happens @ level of Obex

• Restiform:

  • Function?

  • What dissapears?

  • What contributes?

• CTT:

  • Function?

• VTT:

  • Location

  • Origin

  • Function?

Restiform Body (inferior cerebellar peduncle)

• becomes notable in size.

• Function:

  • Provides major afferent pathway → cerebellum,

    • largely from SC + medulla (inferior olive).

• Relatedly: posterior spinocerebellar tract disappears.

• Cuneocerebellar tract fibers will contribute to restiform body

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Central Tegmental Tract (CTT)

• begins to form

  • far more pronounced in the rostral medulla and above

• Function:

  • local communication pathway W/in brainstem

  • contains a # of different types of fibers; EX:

    • from parvocellar red nucleus,

    • gustatory nucleus (rostral solitary nucleus),

    • etc.

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Ventral Trigeminothalamic Tract (VTT):

• Begins to form

  • lateral to the medial lemniscus

• Origins:

  • in the spinal trigeminal nucleus

• Function:

  • carries pain and temperature from the face

List the Structures/ Pathways retained from Sensorry Decussation?

Structures:

1. Hypoglossal nucleus and nerve

2. Nucleus ambiguus

3. Dorsal motor nucleus of Vagus

4. Solitary nucleus and tract

5. Nucleus gracilis and cuneatus

6. Accessory cuneate nucleus

7. Inferior olive

8. Spinal trigeminal nucleus and tract

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Pathways:

1. Pyramids

2. Medial lemniscus

3. Tectospinal tract

4. Medial longitudinal fasciculus

5. Anterior spinocerebellar tract

6. Anterolateral system

7. Rubrospinal tract •

List the three prominent features found at the midolivary level

Prominent Features

• Inferior olivary complex

• Hypoglossal nerve

  • exits preolivary sulcus

• Vagus nerve

  • exits postolivary sulcus

Describe the Structures found @ Midolivary Level

• Inferior Olivary Complex

  • Constituents (2)?

    • Function?

    • Afferents?

• inferior cerebellar peduncle (AKA?)

  • Function?

Hypoglossal Nucleus

• Location

• Function

• Axon Route

• Cortical Innervation

NA:

• Function

• Location

• Cortical Innervation

DMN:

• Location

• Function (3)

• Axon Route

Solitary nucleus (and tract):

• Location

• Two zones?

  • Function

  • Pathway

Vestibular Nuclei (inferior and medial)

• Location

• Function (3)

• Clinical Importance

Inferior Olivary Complex:

• Constituents:

  • Principle Olivary Nucleus

    • Function:

      • Control of planned or skilled voluntary movement

        • predominantly cortical (and subcortical) afferents

  • Medial/Dorsal Accessory Olive

    • Function:

      • Stereotyped Movement

        • Receives predominantly spinal afferents

• inferior cerebellar peduncle (olivocerebellar tract)

  • inferior olive → cerebellum (contralaterally)

  • Reciprocally connected

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Hypoglossal Nucleus:

• Location:

  • deep to hypoglossal trigone

    • either side of median sulcus in medullary portion of rhomboid fossa

• Function:

  • (GSE) to most of tongue (except palatoglossus; CN X)

• Route of Axons (motor neurons):

  • travel ventrally lateral to medial lemniscus → brainstem in preolivary sulcus.

• Cortical innervation

  • bilateral w/ contralateral preponderance (more contribution from contra side)

    • Ipsilateral input allows for functional recovery in the case of a supranuclear lesion.

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Nucleus Ambiguus (NA)

• Function:

  • (SVE) to all

  • (GVE) to cardiac ganglia

• Location:

  • deep w/in medullary reticular formation

  • btw trigeminal nucleus and inferior olive.

• Cortical Innervation:

  • Bilateral

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Dorsal Motor Nucleus of Vagus (DMN)

• Location:

  • deep to vagal trigone

  • lateral to hypoglossal trigone in the floor of the fourth ventricle.

• Function:

  • GVE component of the vagus nerve

  • receives input from solitary nucleus → baroreceptor refelx (efferent component)

  • plays a role in emesis

• Route of Axons:

  • course ventrally and laterally → exit medulla in postolivary sulcus → travel in vagus nerves → synapse on post. gang para. neurons in terminal ganglia

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Solitary nucleus (and tract):

• Location:

  • lateral to DMN in the medulla

• Two Zones:

  • rostral (and lateral) gustatory zone:

    • Function: taste afferents (SVA) from oral cavity and pharynx via CN VII, IX, & X.

    • Pathway:

      • gustatory nucleus → Thalamus (VPM) in ipsilateral central tegmental tract → gustatory cortex

  • caudal cardiorespiratory zone

    • Function:

      • receives (GVA) input

        • CN IX & X: lungs, trachea, larynx, gastrointestinal tract (X)

        • IX: Carotid Sinus

        • IX,X: Chemoreceptors

        • NOTE: Aortic Arch/Bodies also provide input to solitary nucleus via the vagus nerve

      • baroreceptor reflex (Caudal)

    • Pathway of these Neurons:

      • → DMN, NA, IML of the upper thoracic spinal cord and medullary reticular centers → cardiovascular and respiratory control

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Vestibular Nuclei (inferior and medial)

• Location:

  • W/in rostral, dorsolateral medulla

• Function:

  • Receives input from labyrinth of the inner ear

  • body equilibrium

  • control of eye movements

• Clinical Importance:

  • Damage = vertigo, nausea, and nystaqmus

Describe what happens to these structures @ midolivary Levels:

• Restiform body

• Arcuate nuclei

• Nucleus gracilis/ cuneatus

• Lateral cuneate nucleus

• Rubrospinal, reticulospinal and vestibulospinal tracts

• anterior spinocerebellar tract

• Ventral Trigeminothalamic tract

• Similar Position:

  • Spinal nucleus and tract

  • Pyramidal tract,

  • Medial Lemniscus ,

  • tectospinal tract

  • medial Ionitudinal fasciculus

  • anteroateral system are in similar positions.

Midolivary Levels:

• Restiform body enlarges

• Arcuate nuclei

  • found in the ventral aspect of the pyramid.

  • nuclei = continuous w/ pontine nuclei → cerebellum

    • as ventral external arcuate fibers and the striae medullares.

• Nucleus gracilis/ cuneatus

  • no longer present;

  • vestibular nuclei adopt their position

• Lateral cuneate nucleus

  • may still be present

• Rubrospinal, reticulospinal and vestibulospinal tracts

  • in lateral position.

• anterior spinocerebellar tract

  • present.

• Ventral Trigeminothalamic tract

  • lateral to medial lemniscus still.

• Similar Position:

  • Spinal nucleus and tract

  • Pyramidal tract,

  • Medial Lemniscus ,

  • tectospinal tract

  • medial Ionitudinal fasciculus

  • anteroateral system are in similar positions.

1. Describe the Rostral Medulla

   • @ level?

   • Appearance of?

   • What enlarges?

2. Describe Inferior salivatory nucleus (of IX)

   • Origin of?

   • Receives influences from

3. Structures and relationship to restiform body

   • between restiform body and Inferior olive.

   • Now Part of Restiform Body:

4. Reticular Formation Function

• @ Level of CN IX & VIII

• Appearance

  • dorsal and ventral cochlear nuclei (C.N. VIII)

  • Inferior salivatory nucleus (of IX)

  • Nucleus prepositus:

    • (i.e. c. participates in visual fixation on objects)

• Enlarges:

  • Restiform body

  • Reticular formation

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Inferior salivatory nucleus (of IX)

• Origin of:

  • Parasymp motor fibers to parotid gland.

    • Synapse @ Otic

    • Postgang supply parotid gland

• Receives influences from

  • hypothalamus and olfactory system.

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Structures and relationship to restiform body

• Structure between restiform body and Inferior olive.

  • Spinal trigeminal nucleus (and tract),

  • anterolateral system,

  • rubrospinal tract

  • anterior spinocerebellar tract

• Now Part of Restiform Body:

  • Posterior spinocerebellar tract and cuneocerebellar tract

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Reticular Formation:

• Function:

  • Wide range including consciousness and sleep.

Describe the Blood Supply of the Medulla:

anterior spinal artery

• Medial/Ventral

Vertebral Artery

• Intermediate lateral Area

posterior spinal artery

• Dorsal (caudal) Region

Posterior inferior cerebellar artery

• Dorsolateral