a "cortex" is an outer layer of an organ; thus, there is a
cerebral cortex (in the brain) as well as an adrenal cortex
(the outer layer of the adrenal gland), a renal cortex (the
outer layer of the kidney), and so on. However, in common
parlance, "cortex" is usually taken as a shorthand for "cerebral
cortex". Likewise, the adjective "cortical" usually refers
to the cerebral cortex.
The cerebral cortex forms the outer layer
of the brain, including its recognizable gray, wrinkled surface.
The gray substance is actually the cell bodies of nerve cells,
or neurons; underneath
lies the so-called white matter, formed of the output processes
(axons) of these neurons. The wrinkled surface reflects the
fact that, in humans and other primates, the brain has grown
at a faster rate than the skull, and so the surface of the
brain is folded to fit inside the skull. If the human cortex
were smoothed out, it would appear as a sheet about the size
of a tabloid newspaper, about 3 millimeters thick.
The cerebral cortex has left and right halves which, to a
first approximation are mirror images of each other. In most
cases, structures which appear on the left side (or hemisphere)
have an analogous structure on the right side (or hemisphere).
There are a few exceptions: notably, areas of the left hemisphere
are specialized for language processing in most right-handed
people. In general, sensory information from the left side
of the body is processed in the right hemisphere, and vice
versa; motor commands to the left side of the body also originate
from the right hemisphere, and vice versa.
The cortex is often divided into large regions,
called lobes, based on anatomical structure and also on function.
These include the frontal
lobes, the parietal
lobes, the occipital
lobes and the temporal
by Catherine E. Myers. Copyright © 2006 Memory Loss and the Brain
Artwork copyright © 2000 Ann L. Myers