Ventral (Anterior) Surface
In the center of the anterior surface runs the anterior median fissure (fissura mediana ventralis), which is a direct continuation of the corresponding fissure of the spinal cord. In its upper part, this fissure is interrupted by the pyramidal decussation (decussatio pyramidum).
On either side of the central fissure lie two longitudinal elevations called the pyramids (pyramides medullae oblongatae). Further laterally are oval bulges known as the olives (oliva).
| Structure | Limiting Sulci | Note |
|---|---|---|
| Olive | Medially: ventrolateral sulcus (sulcus ventrolateralis). Laterally: retroolivary sulcus (sulcus retroolivaris) | Appears as an elongated elevation |
| Pyramid | Laterally: ventrolateral sulcus | Contains descending motor fibers |
Dorsal (Posterior) Surface
On the posterior side along the midline runs the posterior median sulcus (sulcus medianus dorsalis). Flanking it are the posterior funiculi (funiculus posterior), continuous with those of the spinal cord. The outer boundary of the posterior funiculus is the dorsolateral sulcus (sulcus dorsolateralis).
Each posterior funiculus is divided by an intermediate sulcus into two parts:
- Gracile fasciculus (fasciculus gracilis) — located medially.
- Cuneate fasciculus (fasciculus cuneatus) — located laterally.
In the upper parts of the medulla oblongata, these fasciculi terminate in expansions: the tubercle of the gracile nucleus (tuberculum gracile) and the tubercle of the cuneate nucleus (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. Fibers that cross over form the lateral corticospinal tract. The remaining uncrossed fibers form the anterior corticospinal tract.
Hidden beneath the olivary elevation is the inferior olivary nucleus (nucleus olivaris inferior), featuring a hilum (hilum nuclei olivaris inferioris). Adjacent to it lie the medial and dorsal accessory olivary nuclei. This entire olivary complex is connected to the cerebellum via the specific olivocerebellar tract.
Arcuate nuclei and the accessory cuneate nucleus are also present within the brain substance, giving rise to external arcuate fibers (fibrae arcuatae externae). These are divided into anterior and posterior groups and incorporate 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 houses the nuclei of several cranial nerve pairs:
- Portions of the nuclei of CN V and VIII.
- Nuclei of the glossopharyngeal (CN IX, nervus glossopharyngeus), vagus (CN X, nervus vagus), accessory (CN XI, nervus accessorius), and hypoglossal (CN XII, nervus hypoglossus) nerves.
The emergence of rootlets from the brain is strictly ordered: fibers of CN IX, X, and XI emerge from the dorsolateral sulcus, while rootlets of CN XII emerge from the ventrolateral sulcus.
The reticular formation (formatio reticularis*0 is located in the dorsomedial zone. Its cells group paramedially to form the raphe nuclei (*nuclei raphae), while the central core of gray matter directly forms the raphe of the medulla oblongata (raphe medullae oblongatae).