Brain Tour : Our Brain : The Principal Part of the Brain :

Medulla Oblongata

The medulla oblongata , or simply medulla, has centers that control heart and breathing rates and blood pressure, as well as coughing , sneezing, swallowing, and vomiting.

The medulla is continuation of the spinal cord. The cord forms the interior part of the brain stem.

The medulla contains all sensory and motor nerves running between the spinal cord and other parts of the brain. These tracts (or nerve bundles) constitute the white matter of the medulla. Some tracts cross as they pass through the medulla. This is how the crossing occurs:

In the medulla are two roughly triangular structures call the pyramids. The pyramids contain the largest motor tracts that pass from the outer region of the cerebrum (cerebral cortex, cortex=outer covering) to the spinal cord. Most of the fibres in the left pyramid cross to the right side, and most of the fibres in the right pyramid cross to the left. This crossing is call the decussation of pyramids.

Decussation explains why one side of the cerebral cortex controls the opposite side of the body. Motor fibres that originate in the left cerebral cortex activate muscles on the right side of the body and vice versa. Similarly, most sensory fibres also cross over in the medulla so that nearly all sensory fibres received on one side of the body are perceived in the opposite side of the cerebral cortex.

Also within the medulla are:
1. the cardiovascular centre, which regulated the rate and force of heartbeat and the diameter of blood vessels
2. the medullary rhythmicity area which regulates the basic rhythm of breathing
Other centres in the medulla co-ordinate swallowing, vomiting, coughing, sneezing and hiccuping.

Finally, the medulla contains the nuclei of origin or several pairs of cranial nerves.