M02.02.003 The medulla oblongata

The medulla, also known as the medulla oblongata, is the lowest part of the brainstem and is responsible for several vital functions necessary for survival. Let’s explore the external and internal structure of the medulla, including its pyramids, lemnisci, and olives:

1. External Structure:
   • Location: The medulla is located between the pons superiorly and the spinal cord inferiorly.
   • Shape and Size: It has a conical shape and gradually narrows as it descends into the spinal cord.
   • Anterior Surface: The anterior surface of the medulla contains two prominent longitudinal ridges called pyramids. These pyramids are formed by bundles of descending motor fibers known as corticospinal tracts.
   • Lateral Surface: On each side of the medulla, there is an oval-shaped swelling called the olive. The olive contains underlying structures related to motor coordination.
   • Posterior Surface: The posterior surface of the medulla forms part of the floor of the fourth ventricle.
2. Internal Structure:
   • Nuclei: The medulla contains various nuclei involved in vital functions, including:
     • Cardiovascular Centers: Nuclei within the medulla regulate heart rate, blood pressure, and blood vessel diameter.
     • Respiratory Centers: The medulla houses nuclei that control the rhythm and depth of breathing.
     • Nuclei of Cranial Nerves: The medulla contains the nuclei of several cranial nerves, including IX (glossopharyngeal), X (vagus), XI (spinal accessory), and XII (hypoglossal), which control functions such as swallowing, speech, and neck movements.
   • Decussation of Pyramids: As the corticospinal tracts descend through the medulla, the majority of the fibers cross over to the opposite side of the spinal cord. This crossover, known as the decussation of pyramids, allows for the contralateral control of voluntary movements.
3. Lemnisci:
   • Medial Lemniscus: The medial lemniscus is a bundle of ascending sensory fibers that carry information related to touch, proprioception (sense of body position), and vibration from the body to the brain. It runs through the medulla.
   • Lateral Lemniscus: The lateral lemniscus is involved in the transmission of auditory information from the cochlea to the brainstem and runs through the medulla.
4. Olives:
   • Inferior Olivary Nucleus: Each olive contains the inferior olivary nucleus, which is involved in motor coordination and learning. The olives play a role in relaying information to the cerebellum for fine-tuning motor movements.

The medulla also receives its blood supply from various arteries, including branches of the vertebral arteries and posterior inferior cerebellar arteries.

Understanding the external and internal structure of the medulla, including the pyramids, lemnisci, and olives, is essential for comprehending its functions and the consequences of any abnormalities. Lesions or disorders affecting the medulla can lead to severe neurological deficits, such as disturbances in cardiovascular and respiratory functions. Diagnosis and treatment often involve neuroimaging techniques like MRI, as well as careful assessment of cranial nerve function and other medulla-related symptoms.