Transverse Sections and Blood Supply of the Medulla Oblongata

Rubbia Khalid July 20, 2024

Transverse Section of the Medulla at the Level of Pyramidal Decussation

At this level, the medulla shows features similar to the spinal cord, with some key differences:

  • Nucleus Gracilis and Nucleus Cuneatus: These appear as narrow projections from the posterior aspect of the central grey matter.
  • Nucleus of Spinal Tract of Trigeminal Nerve: The apex of the posterior horn swells to form this nucleus, which is an upward continuation of the substantia gelatinosa.
  • Spinal Tract of Trigeminal Nerve: A bundle of fibers capping over the nucleus of the spinal tract of the trigeminal nerve.
  • Decussation of Pyramidal Tracts: The most notable feature at this level. About 75% of the fibers of the pyramidal tract cross the midline and move to the lateral white column of the opposite side of the spinal cord, continuing as the lateral corticospinal tract. This process detaches the anterior horns from the central grey matter.
  • Spinal Nucleus of Accessory Nerve and Supraspinal Nucleus of the First Cervical Nerve: Each detached anterior horn forms these nuclei. The nucleus of the accessory nerve extends down to the fifth cervical spinal segment, while the supraspinal nucleus gives off efferent fibers of the first cervical nerve and continues with the hypoglossal nerve nucleus.
  • Reticular Formation: A diffuse zone with a network of fibers and scattered nerve cells located in the lateral white column adjacent to the nucleus of the spinal tract of the trigeminal nerve.

Transverse Section of the Medulla at the Level of Sensory Decussation

At this level, the section shows key features related to sensory pathways and nuclei:

Nuclei and Fibers:

Nucleus Gracilis and Nucleus Cuneatus:

  • Become more pronounced and are separated from the central grey matter.
  • Fibers of the fasciculus gracilis and fasciculus cuneatus occupy the broad posterior white column and terminate in these nuclei.

Internal https://www.cpmrevenuegate.com/wjc09xhc?key=fa1dc1e56dbfc6ceb069c788b1cf82d0 Arcuate Fibers:

  • Arise from the gracile and cuneate nuclei (second-order sensory neurons).
  • Course forwards and medially around the central grey matter.
  • Decussate in the median plane (sensory decussation) and then ascend as the medial lemniscus on the opposite side.
  • Gracile fibers are medial to cuneate fibers in this decussation.

Medial Lemniscus:

  • Represents the body with feet anteriorly and head posteriorly.
  • Fibers relay into the corresponding thalamus.

Adjacent Structures:

Accessory Cuneate Nucleus:

  • Located dorsolateral to the cuneate nucleus.
  • Receives lateral fibers from the cervical segments of the cord.
  • Gives rise to posterior external arcuate fibers that convey proprioceptive impulses to the cerebellum through the inferior cerebellar peduncle.

Spinal Nucleus and Tract of Trigeminal Nerve:

  • Lies ventrolateral to the cuneate nucleus.

Inferior Olivary Nucleus:

  • Lower part is visible.

Pyramids:

  • Positioned on either side of the anterior median fissure.

Central Grey Matter:

Hypoglossal Nucleus:

  • Occupies the ventro-medial position close to the midline.

Dorsal Nucleus of Vagus:

  • Lies dorsolateral to the hypoglossal nucleus.

Nucleus of Tractus Solitarius:

  • Located just dorsolateral to the dorsal nucleus of vagus.

Other Tracts:

Medial Longitudinal Bundle:

  • Lies posterior to the medial lemniscus.
  • A compact tract of nerve fibers connecting cranial nerve nuclei III, IV, VI, VIII, and the spinal nucleus of XI.

Spinocerebellar and Lateral Spinothalamic Tracts:

  • Located in the anterolateral area of the lateral white column.
  • Close to each other and collectively form the spinal lemniscus.

Transverse Section of the Medulla at the Level of Olives

This section cuts across the floor of the fourth ventricle and through the middle of the olives, displaying the following features:

Central Grey Matter:

Nuclei from Medial to Lateral:

  • Hypoglossal Nucleus: Closest to the midline.
  • Nucleus Intercalatus: Intermediate position.
  • Dorsal Nucleus of Vagus: Lateral to nucleus intercalatus.
  • Vestibular Nuclei: Inferior and medial vestibular nuclei are more lateral.

Nucleus of Tractus Solitarius: Lies ventral to the vestibular nuclei.

Nucleus Ambiguus: Deep within the reticular formation; originates motor fibers for cranial nerves IX, X, and XI.

Paramedian Region Structures (Dorsal to Ventral):

  • Medial Longitudinal Fasciculus: A tract connecting various cranial nerve nuclei.
  • Tectospinal Tract: Involved in reflex movements of the head and neck.
  • Medial Lemniscus: Carries sensory information from the body.
  • Pyramidal (Corticospinal) Tract: Contains motor fibers from the cerebral cortex.

Arcuate Nuclei:

  • Located on the anteromedial aspect of the pyramids.
  • Receive fibers from the cerebral cortex and send efferent fibers to the cerebellum through anterior external arcuate fibers.

Prominent Lateral Structures (Dorsal to Ventral):

  • Inferior Cerebellar Peduncle: Occupies the posterolateral part.
  • Inferior Olivary Nucleus: The largest mass of grey matter in this section, with a crumbled, bag-like appearance.
  • Medial and Dorsal Accessory Olivary Nuclei: Located close to the main nucleus.

Transverse Section of the Medulla Just Inferior to the Pons (Ponto-Medullary Junction)

In this section, there are no major changes in the distribution of grey and white matter compared to the section at the level of olives. However, the following features are observed:

Lateral Vestibular Nucleus:

  • Replaces the inferior vestibular nucleus seen at the level of olives.

Cochlear Nuclei:

  • Dorsal Cochlear Nucleus: Located on the dorsolateral aspect of the inferior cerebellar peduncle.
  • Ventral Cochlear Nucleus: Located on the ventrolateral aspect of the inferior cerebellar peduncle.

Key Features:

  • Central Grey Matter: Hypoglossal Nucleus, Nucleus Intercalatus, Dorsal Nucleus of Vagus, Vestibular Nuclei, Nucleus of Tractus Solitarius, Nucleus Ambiguus.
  • Paramedian Region (Dorsal to Ventral): Medial Longitudinal Fasciculus, Tectospinal Tract, Medial Lemniscus, Pyramidal (Corticospinal) Tract.
  • Arcuate Nuclei: Located on the anteromedial aspect of the pyramids.
  • Lateral Structures (Dorsal to Ventral): Inferior Cerebellar Peduncle, Inferior Olivary Nucleus (including medial and dorsal accessory olivary nuclei).
  • Inferior to the Pons: Lateral Vestibular Nucleus, Cochlear Nuclei (Dorsal and Ventral).

Blood Supply of the Medulla

The medulla oblongata receives its blood supply from several arteries:

Vertebral Arteries:

  • Two vertebral arteries supply the medulla.

Spinal Arteries:

  • Anterior Spinal Artery
  • Posterior Spinal Artery

Inferior Cerebellar Arteries:

  • Anterior Inferior Cerebellar Artery
  • Posterior Inferior Cerebellar Artery

Basilar Artery:

  • Supplies parts of the medulla as well.



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Rubbia Khalid

Posted by Rubbia Khalid

BSc in Biomedical Science & Physiology from UNISA.

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