ABSTRACT
The brain comes into the world with innumerable potential patterns of detailed organization, as reflected in the infinite combinations through which its cells could connect up with each other. This highly interconnected set of brain structures, most of which lie deep within the brain, comprises the limbic system. The brain is an organ, but it is not an isolated organ. It is connected in various ways with the other organs of the body. The brain is interposed between the outer and inner worlds of the body. The brain is made up of neurons, together with a range of nonnervous cells that act in support of neurons and help to maintain their survival. Brain functions dependent on information derived from the external world are primarily channel-dependent functions. The brainstem is a direct extension of the spinal cord into the skull, and it is phylogenetically the most ancient part of the brain.
