Medulla Oblongata

Brainstem
The brainstem consists of the midbrain, pons, and medulla. MedicalRF.com/Getty Images

What Is the Medulla Oblongata?

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 a part of the brainstem, the medulla oblongata helps in the transferring of messages between various parts of the brain and the spinal cord.

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

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

Function

The medulla oblongata is involved in several functions of the body including:

  • Control of Autonomic Functions
  • Relay of Nerve Signals Between the Brain and Spinal Cord
  • Coordination of Body Movements
  • Regulation of Mood

The medulla is the control center for cardiovascular and respiratory system activity.

It regulates heart rate, blood pressure, and respiratory rate. The medulla also controls involuntary reflex actions such as swallowing, sneezing, and gag reflex. Another major function of the medulla is the control and coordination of voluntary 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.

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.

Features

Some anatomical features of the medulla oblongata include:

  • Median fissures - shallow groves located along the anterior and posterior portions of the medulla.
  • Olive - paired oval structures on the medulla surface that contain nerve fibers which connect the medulla to the pons and cerebellum.
  • Pyramid - two rounded masses 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 - continuation of the bundle of nerve fiber tracts that extend from the spinal cord to the medulla.

Injury to the Medulla

Injury to the medulla oblongata may result in a number of sensory related problems. These includes numbness, paralysis, difficulty swallowing, acid reflux, and lack of movement control.

Because the medulla 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 and the body becomes unable to perform vital functions. The chemicals in anesthesia work by acting on the medulla to decrease autonomic activity. This results in a lower breathing rate and heart rate, relaxation of muscles, and loss of consciousness.

Images

Divisions of the Brain

  • Forebrain - encompasses the cerebral cortex and brain lobes.
  • Midbrain - connects the forebrain to the hindbrain.
  • Hindbrain - regulates autonomic functions and coordinates movement.