tah) is an
enlarged continuation of the spinal cord, extending from the
level of the foramen magnum to the pons (see F g. 11.20).
Its dorsal surface ﬂ attens to form the ﬂ oor of the fourth ven-
tricle, and its ventral surface is marked by the corticospinal
tracts, most of whose F
bers cross over at this level. On each
side of the medulla oblongata is an oval swelling called the
from which a large bundle of nerve F bers arises and
passes to the cerebellum.
The ascending and descending nerve F
the brain and spinal cord must pass through the medulla
oblongata because of its location. As in the spinal cord, the
white matter of the medulla surrounds a central mass of gray
matter. Here, however, the gray matter breaks up into nuclei
separated by nerve F bers. Some of these nuclei relay ascend-
ing impulses to the other side of the brainstem and then on
to higher brain centers. The
for example, receive sensory impulses from F bers
of the fasciculus gracilis and the fasciculus cuneatus and
pass them on to the thalamus or the cerebellum.
Other nuclei in the medulla oblongata control vital vis-
ceral activities. These nuclei include the following:
Peripheral nerves transmit impulses
originating in the cardiac center to the heart, where they
increase or decrease heart rate.
The reticular formation (shown in gold) extends
from the superior portion of the spinal cord into the diencephalon.
) Ventral view of the brainstem. (
) Dorsal view of the brainstem with the cerebellum removed, exposing the fourth