Overview of the Medulla Oblongata

Model Brain
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The medulla oblongata is a portion of the hindbrain that controls autonomic functions such as breathing, digestion, heart and blood vessel function, swallowing, and sneezing. Motor and sensory neurons from the midbrain and forebrain travel through the medulla. As part of the brainstem, the medulla oblongata helps transfer messages between parts of the brain and spinal cord.

The medulla contains myelinated (white matter) and unmyelinated (grey matter) nerve fibers. Myelinated nerves are covered with a myelin sheath composed of lipids and proteins. This sheath insulates axons and promotes more efficient conduction of nerve impulses than unmyelinated nerve fibers. A number of cranial nerve nuclei are located in the gray matter of the medulla oblongata.

Location

Directionally, the medulla oblongata is inferior to the pons and anterior to the cerebellum. It is the lowest portion of the hindbrain and is continuous with the spinal cord.

The upper region of the medulla forms the fourth cerebral ventricle. The fourth ventricle is a cavity filled with cerebrospinal fluid that is continuous with the cerebral aqueduct. The lower portion of the medulla narrows to form portions of the spinal cord's central canal.

Anatomical Features

The medulla oblongata is a fairly long structure comprised of many parts. Anatomical features of the medulla oblongata include:

  • Median fissures: Shallow groves located along the anterior and posterior portions of the medulla.
  • Olivary bodies: Paired oval structures on the medulla's surface that contain nerve fibers connecting the medulla to the pons and cerebellum. Olivary bodies are sometimes called olives.
  • Pyramids: Two rounded masses of white matter located on opposite sides of the anterior median fissure. These nerve fibers connect the medulla to the spinal cord, pons, and cerebral cortex.
  • Fasciculus gracilis: A continuation of the bundle of nerve fiber tracts that extend from the spinal cord to the medulla.

Function

The medulla oblongata is involved in several functions of the body relating to the regulation of important sensory, motor, and mental processes, including:

  • Autonomic function control
  • Relay of nerve signals between the brain and spinal cord
  • Coordination of body movements
  • Mood regulation

Above all else, the medulla is the control center for cardiovascular and respiratory system activity. It regulates heart rate, blood pressure, respiratory rate, and other life-sustaining processes that take place without a person having to actively think about them. The medulla also controls involuntary reflexes such as swallowing, sneezing, and gagging. Another major function is the coordination of voluntary actions such as eye movement.

A number of cranial nerve nuclei are located in the medulla. Some of these nerves are important for speech, head and shoulder movement, and food digestion. The medulla also aids in the transfer of sensory information between the peripheral nervous system and the central nervous system. It relays sensory information to the thalamus and from there is sent to the cerebral cortex.

Damage to the Medulla

Injury to the medulla oblongata may result in a number of sensory-related problems. Non-fatal complications include numbness, paralysis, difficulty swallowing, acid reflux, and lack of motor control. But because the medulla also controls vital autonomic functions such as breathing and heart rate, damage to this area of the brain can be fatal.

Drugs and other chemical substances can impact the medulla's ability to function. An opiate overdose can be deadly because these drugs inhibit medulla activity until the body can't regulate essential functions. Sometimes, the medulla oblongata's activity is intentionally and very carefully suppressed. For example, the chemicals in anesthesia work by acting on the medulla to decrease autonomic activity. This results in a lower breathing and heart rate, relaxation of muscles, and loss of consciousness.​ This makes surgery and other medical procedures possible.