Ventral (anterior) surface
Along the center of the anterior surface runs the anterior median fissure (fissura mediana ventralis), which is a direct continuation of the same fissure of the spinal cord. In the upper part, this sulcus is interrupted by the pyramidal decussation (decussatio pyramidum).
On both sides of the central fissure lie two longitudinal elevations — the pyramids (pyramides medullae oblongatae). Further away from the center (laterally) are oval elevations called olives (oliva).
| Structure | Limiting sulci | Note |
|---|---|---|
| Olive | Medially: ventrolateral sulcus (sulcus ventrolateralis). Laterally: retroolivary sulcus (sulcus retroolivaris) | Represents an oblong elevation |
| Pyramid | Laterally: ventrolateral sulcus | Contains descending motor fibers |
Dorsal (posterior) surface
On the posterior aspect along the midline runs the posterior median sulcus (sulcus medianus dorsalis). On either side of it lie the posterior funiculi (funiculus posterior), extending from the spinal cord. The outer boundary of the posterior funiculus is the posterolateral sulcus (sulcus dorsolateralis).
Each posterior funiculus is divided by an intermediate sulcus into two parts:
- Fasciculus gracilis (fasciculus gracilis) — located medially.
- Fasciculus cuneatus (fasciculus cuneatus) — lies laterally.
In the upper parts of the medulla oblongata, these fasciculi end in expansions: the tuberculum gracile (tuberculum gracile) and tuberculum cuneatum (tuberculum cuneatum).
Internal structure: pathways and olives
Inside the medulla oblongata, gray matter is represented by nuclei, and white matter by nerve tracts.
The pyramidal tract is a complex of longitudinal bundles. Those fibers that cross over form the lateral corticospinal tract. The remaining uncrossed fibers form the anterior corticospinal tract.
Hidden beneath the elevation of the olive is the inferior olivary nucleus (nucleus olivaris inferior), which has a hilum (hilum nuclei olivaris inferioris). Near it lie the medial and posterior accessory olivary nuclei. This entire olivary complex is connected to the cerebellum by a special olivocerebellar tract.
Arcuate nuclei and the accessory cuneate nucleus are also present within the substance of the medulla, giving rise to external arcuate fibers (fibrae arcuatae externae). They are divided into anterior and posterior, and they blend into the inferior cerebellar peduncles. Cells of the gracile and cuneate nuclei give rise to internal arcuate fibers, which transition into the medial lemniscus (lemniscus medialis).
Cranial nerve nuclei and reticular formation
The tissue of the medulla oblongata localizes the nuclei of several pairs of cranial nerves:
- Nuclei of cranial nerves V and VIII are partially involved.
- Nuclei of the glossopharyngeal (IX pair, nervus glossopharyngeus), vagus (X pair, nervus vagus), accessory (XI pair, nervus accessorius), and hypoglossal (XII pair, nervus hypoglossus) nerves.
The exit of rootlets from the brain is strictly ordered: fibers of nerves IX, X, and XI emerge from the posterolateral sulcus, while rootlets of nerve XII emerge from the ventrolateral sulcus.
In the dorsomedial zone lies the reticular formation (formatio reticularis). Its cells are grouped paramedially, forming raphe nuclei (nuclei raphae), whereas the central core of gray matter forms the raphe of the medulla oblongata itself (raphe medullae oblongatae).
Briefly: answers to topical questions
What vital autonomic centers are located in the reticular formation of the medulla oblongata?
The reticular formation of the medulla oblongata houses the following vital autonomic centers:
- Respiratory center — determines rhythmic breathing, consisting of inspiratory and expiratory neurons. Its activity is controlled by neurons of the pontine pneumotaxic center.
- Vasomotor center — responsible for vascular reactions, involved in forming the cortico-subcortical complex of sustained excitation in cardiovascular system pathologies.
What triangles are located on the dorsal surface of the medulla oblongata in the region of the rhomboid fossa?
On the dorsal surface of the medulla oblongata, within the inferior triangle of the rhomboid fossa, lie two triangles.
- Hypoglossal trigone (trigonum n. hypoglossi) — located medially; the motor nucleus of the hypoglossal nerve projects to this area.
- Vagal trigone (trigonum n. vagi) — located inferiorly and laterally; the funiculus separans (funiculus separans) runs along its edge.
What afferent pathways pass through the inferior cerebellar peduncles?
The following afferent pathways pass through the inferior cerebellar peduncles:
- Posterior spinocerebellar tract (tractus spinocerebellaris posterior) — conducts proprioceptive sensitivity from muscle and tendon receptors to the cortex of the cerebellar vermis.
- External arcuate fibers (fibrae arcuatae externae) — transmit proprioception from the nuclei of the gracile and cuneate fasciculi to the cerebellum.
To avoid confusing rootlet exits: the hypoglossal nerve (XII pair) "comes forward" from the ventrolateral sulcus, while a whole group (IX, X, XI pairs) "hides" posteriorly — in the posterolateral sulcus.
Class and exam questions
Where does the border between the medulla oblongata and the spinal cord run?
The anatomical border is drawn conventionally: either at the level of the pyramidal decussation or at the site of exit of the upper rootlet filaments of the first cervical nerve (C1).
What structures form the posterior funiculi?
The posterior funiculi include the medially located fasciculus gracilis and the laterally lying fasciculus cuneatus. Superiorly, they terminate in similarly named tubercles.
What is contained inside the pyramids of the medulla oblongata?
Longitudinal bundles of the corticospinal (motor) tracts run inside the pyramids. Some of their fibers form a decussation.
What are the olivary nuclei associated with?
The inferior olivary nucleus and its accessory nuclei are functionally closely connected to the cerebellum. This connection is provided via the olivocerebellar tract.
What else to study on this topic
- Topography of the nuclei of the bulbar group of cranial nerves
- Projection of the reticular formation nuclei
- Course of the fibers of the medial lemniscus
- Formation of the inferior cerebellar peduncles
- Connections of the accessory cuneate nucleus
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