The medulla oblongata is the most caudally located part of the brain and is also known as the medulla. This brain region is best known as the center of respiration, reflexes, and blood circulation. Failures of the medulla oblongata are associated with brain death and can cause bulbar brain syndrome, midbrain syndrome, or apallic syndrome.
What is the medulla oblongata?
The human central nervous system consists of the spinal cord and brain. The latter is composed of different parts, all of which are associated with specific functional fields. One such part is the medulla oblongata, also known as the medulla oblongata, bulbus medullae spinalis or bulbus cerebri. It is the most caudally located part of the brain with localization between the spinal cord and midbrain or mesencephalon. Together with the bridge and the area of the cerebellum, the medulla oblongata forms the rhombencephalon, which is one of the important reflex centers in the human body. The medulla oblongata arises from the myelencephalon, the so-called afterbrain, during the embryonic development period. Functionally, the medulla oblongata part of the brain consists of three distinct areas: Tegmentum, Pyramis and Olive. As is well known, the caudal part of the brain is home to the body’s blood pressure and respiratory centers, in addition to the reflex center.
Anatomy and structure
Cranially, the medulla oblongata is bounded by the bridge. Caudally, the cerebral region merges with the spinal cord and bears spinal nerves at its exit. In the dorsally located tegmentum of the medulla oblongata lie the cranial nerve nuclei. In the ventral portion of the region lie the pyramids and olives. In the tuberculum gracile and tuberculum cuneatum, within the dorsal region, the posterior strands of the spinal cord terminate. The posterior cord nuclei nucleus gracilis and cuneatus lie in this location and form the ends of epicritical sensory nerve fibers. In the ventral portion of the medulla oblongata sit the pyramids of pyramidal tract nerve fibers. The pyramidal tract junction lies immediately below. Lateral to the zone are the olives, which contain core areas of fine motor coordination with the olivary nuclei. The hypoglossal nerve or XII. Cranial nerve emerges between olives and pyramides. On the outer surface lies a depression called the fissura mediana anterior medullae oblongatae.
Function and Tasks
Neuronally important centers of blood circulation, respiration, and reflex motor function are located in the medulla oblongata. Reflexes are automated movements that follow a specific stimulus and cannot be controlled voluntarily. Many human reflexes are so-called protective reflexes, such as the sneeze and cough reflex. In addition, a vital reflex is the breathing reflex. Every reflex movement is preceded by an external or internal stimulus, which is registered by sensory cells of perception and reaches the central nervous system via afferent nerve pathways. In the central nervous system, the reflex arc switches the incoming action potential to efferent nerve pathways, through which the excitation reaches the effector organs. The reflex center of the medulla oblongata plays a crucial role in these processes and is thus relevant, for example, for the swallowing, sucking and coughing reflexes. In addition, the vomiting center is located in the medulla oblongata: another protective mechanism of the human body. In addition, many receptors involved in the regulation of acid-base balance are found in the caudal portion of the brain. These receptors are also known as chemosensors in technical language. Through the medullary brain additionally travel all descending connecting pathways between brain areas such as the cerebrum and the spinal cord. On the other hand, ascending pathways from the spinal cord also pass through the medulla oblongata and are switched in the medulla oblongata, for example, the pathway of the posterior cord. With the aforementioned functions, the medulla oblongata performs most of the work required for human life.
Diseases
As a rule, total failure of the medulla oblongata is associated with the death of the patient. In this case, we are talking about brain death, which, unlike cardiac death, corresponds to absolute death. Total loss of the cerebral portion can occur, for example, in the context of severe spinal cord injuries following a traffic accident. If most of the patient’s cerebrum is still non-functional, this is referred to as partial brain death.A cerebral failure alone does not justify a diagnosis of brain death, since the patient can continue to live at least physically with the help of the medulla oblongata and the bodily functions it regulates. A patient with an intact medulla oblongata does not require artificial respiration even in the case of cerebral deficits. However, the consequence of such a scenario is a deep coma with mostly apallic syndrome. This is a clinical picture caused by severe brain damage and involves a functional failure of the cerebrum, while the diencephalon, brain stem and spinal cord continue to function. Patients appear awake for this reason, but are likely unable to communicate. Failure of brainstem functions within the medulla oblongata is again referred to as bulbar brain syndrome. This symptom complex usually results as a consequence of a midbrain syndrome and begins with ataxic respiration or gasping breathing and even respiratory arrest. The patient falls into a deep coma as it progresses. Muscle tension throughout the body relaxes and the pupils, which are fixed to the light, dilate. Reflexes such as the corneal reflex cease and the eyeballs assume divergent positions. In most cases, the clinical picture is the result of compression. Particularly often the medulla oblongata gets jammed at the cerebellar tonsils. The outcome of this phenomenon is usually fatal.
