What is the medulla oblongata?
The medulla oblongata (myelencephalon, afterbrain) is the lowest and rearmost area of the brain. After transition from the spinal cord, it thickens in an onion shape and ends at the bridge. The myelencephalon contains cranial nerve nuclei and is thus the origin of cranial nerves VII to XII, which emerge from the anterior surface of the medulla oblongata.
In addition to a fissure running down the middle, at the anterior surface of the medulla oblongata lies the pyramid, which tapers downward and pulls partly into the lateral cord, partly crosses over the midline, and another part pulls into the anterior cord. In addition to the pyramid, at the front of the medulla oblongata there is the olive, which contains the olive nucleus, gray matter, in its interior.
On the posterior side of the myelencephalon continues the posterior cord, which has split in two in the cervical medulla. Both strands become progressively wider and form two thickenings in the medulla oblongata containing the posterior strand nuclei. These are the switching stations to a neuron of the posterior cord pathways.
What is the function of the medulla oblongata?
The medulla oblongata contains important regulatory centers for respiration and blood circulation, as well as reflex centers for the swallowing and sucking reflex, the coughing, sneezing and gagging reflex, and the vomiting center.
Breathing
Breathing movements are controlled by groups of neurons in the medulla oblongata. Rhythmic respiratory activity occurs through a complex circuitry of respiratory neurons in the medulla oblongata that promote and inhibit each other. A basal breathing rhythm is ensured by the respiratory center, which can be adapted to the respective needs by higher brain centers and the body periphery.
For example, during physical activity one has to breathe more strongly in order to be able to meet the increased oxygen demand. So information is fed to the respiratory center in the medulla oblongata via mechanoreceptors in the joints and muscles to increase respiratory drive.
Sympathetic and parasympathetic nervous system
Peripheral nerves have a basic activity, sympathetic tone. This is determined by pathways originating in the medulla oblongata and extending into the spinal cord via the posterior cords. If this control center of the sympathetic nervous system in the medulla oblongata is stimulated, sympathetic nerves and the associated organs are activated accordingly. This results, for example, in an increase in blood pressure.
Conversely, inhibition of this control center leads to a decrease in activity in the sympathetic nerves, resulting in a drop in blood pressure, for example.
Digestion in the small intestine is regulated, among other things, by the muscle tone of the intestinal wall and nerve fibers in the intestinal wall. Fibers of the parasympathetic nervous system draw to excitatory and inhibitory ganglia. Which function – excitatory or inhibitory – predominates is determined in nerve nuclei of the medulla oblongata (and in the lower spinal cord).
Circuit
Chewing and swallowing
The medulla oblongata contains the centers that control chewing and swallowing and thus food intake. Superior to these are two centers, the eating center and the satiety center in nuclei of the hypothalamus. Chewing and the beginning of swallowing are controlled by cranial nerves that emerge from the medulla oblongata (trigeminal nerve, hypoglossal nerve, and vagus nerve).
Acid-base balance
The medulla oblongata contains chemosensitive receptors that regulate the body’s acid-base balance.
Other
Descending pathways connecting the cerebrum to the spinal cord pass through the myelencephalon and ascending pathways are switched here.
The nerve fibers for epicritic sensibility – fine sensations of temperature and touch, sense of movement and position, sense of force and shape recognition – terminate in the posterior cord nuclei nucleus gracilis and nucleus cuneatus.
The olive nuclei of the medulla oblongata coordinate fine motor skills.
Where is the medulla oblongata located?
What problems can medulla oblongata cause?
A medulloblastoma is a malignant tumor of the cerebellum that grows rapidly and is undifferentiated. It displaces the medulla oblongata due to its growth in size. Medulloblastoma develops preferentially in childhood and adolescence, especially in the seventh to twelfth years of life. Leading symptoms are vomiting and a disorder of movement coordination (ataxia) with a tendency to fall backwards.
An infarction of the medulla oblongata can be caused by an occlusion of an important blood vessel (Arteria cerebelli inferior posterior) at the transition of the bridge into the medulla oblongata. Possible symptoms include headache, rapid heartbeat, shortness of breath, rotary vertigo and tendency to fall, eye tremor, gait disturbance, swallowing and speech disturbance, and sensory disturbances due to trigeminal palsy.
Disturbance of blood flow in the medulla oblongata, such as occurs in cerebral ischemia, leads to activation of the sympathetic nervous system. The same occurs when sudden hemorrhage demands space in the brain and displaces brain tissue: Sympathetic activity increases, and blood pressure rises (Cushing’s reflex).
