Superior medulla oblongata
Pars superior medullae oblongatae
- Latin synonym: Pars aperta meudllae oblongatae
- Synonym: Upper medulla oblongata; Open medulla oblongata
Definition
The superior medulla oblongata (upper medulla) and inferior medulla oblongata (inferior medulla) exhibit unique anatomical differences. These can be summarized as follows:
Central Canal:
Superior medulla oblongata | Inferior medulla oblongata | ||
In the upper medulla, the central canal expands to form the fourth ventricle, which is a part of the ventricular system of the central nervous system. | In contrast, in the lower medulla, the central canal narrows and continues downward as the spinal (or central) canal of the spinal cord. | ||
Gray Matter Nuclei in the dorsal part of medulla oblongata:
Superior medulla oblongata | Inferior medulla oblongata | ||
In the upper medulla, the dorsal column nuclei (nucleus gracilis and nucleus cuneatus) decussate as internal arcuate fibers and ascend as the medial lemniscus, which is positioned medially and ventrally, directly behind the pyramids. Consequently, the nucleus gracilis and nucleus cuneatus are absent in the upper medulla oblongata. Instead, additional gray matter nuclei can be found in the dorsal region beneath the floor of the fourth ventricle, arranged from medial to lateral. These include the hypoglossal nucleus, dorsal motor nucleus of vagus, nucleus of tractus solitarius, vestibular nuclei, and cochlear nuclei. | In the lower medulla, the nucleus gracilis and nucleus cuneatus are located dorsally, visible as the gracile and cuneate tubercles. White matter tracts, namely the fasciculus gracilis and fasciculus cuneatus, feed into these nuclei, forming the first-order sensory neurons of the dorsal column-medial lemniscal pathway. | ||
Spinal Nucleus and Tract of Trigeminal Nerve (CN V):
The spinal nucleus of CN V is elongated, extending through both upper and lower sections of the medulla. Its lower end transitions into the substantia gelatinosa of the cervical spinal cord's posterior gray horn (lamina 2).
The spinal tract of CN V is positioned laterally to the nucleus in both parts of the medulla.
Spinocerebellar Tracts and Inferior Cerebellar Peduncle:
The spinocerebellar tracts (anterior and posterior) are laterally positioned in both the upper and lower medulla. In the superior medulla oblongata, the inferior cerebellar peduncle transmits proprioceptive information from these tracts to the cerebellum.
Rubrospinal and vestibulospinal (motor) tracts:
The rubrospinal and lateral vestibulospinal tracts run laterally and continue into the lateral funiculus of the spinal cord without significant differences between the superior and inferior medulla oblongata.
Spinothalamic tracts:
The spinothalamic tracts are located laterally in both parts; however, in the superior medulla oblongata, they are lateral to the decussating medial lemniscus fibers, while in the inferior medulla oblongata, they are lateral to the decussating corticospinal tracts at the pyramidal decussation.
Midline Structures:
Superior medulla oblongata | Inferior medulla oblongata | ||
In the upper medulla, key midline structures–from front to back–include the pyramids, medial lemniscus, tectospinal tract, and medial longitudinal fasciculus. Arcuate nuclei are found further anterior to the pyramids. | In the lower medulla, the pyramids decussate to form the lateral corticospinal tract, disrupting the anterior median fissure. The gracile and cuneate nuclei and fasciculi are notably visible at the dorsum of the medulla. | ||
Cranial Nerves:
Superior medulla oblongata | Inferior medulla oblongata | ||
In the upper medulla, cranial nerves such as the hypoglossal nerve (emerging from the preolivary sulcus), and the vagus, glossopharyngeal, and cranial part of the accessory nerves (emerging from the retroolivary sulcus), can be seen. All these nerve traverse the reticular formation prior to emerging from the brainstem surface. | In the lower medulla, the spinal part of the accessory nerve is visible in the retroolivary sulcus. | ||
References
Snell, R.S. (2010). ‘Chapter 5: The Brainstem', in Clinical Neuroanatomy. (7th ed.) Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, pp. 199-206.
Iordanova R, Reddivari AKR. Neuroanatomy, Medulla Oblongata. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK551589/
