These functions

These functions of the nervous system are performed mainly by the basal regions of the brain, which together are loosely called the limbic system, meaning the border system. ActivatingDriving Systems of the Brain Without continuous transmission of nerve signals from the lower brain into the cerebrum, the cerebrum becomes useless. In fact, severe compression of the brain stem at the juncture between the mesencephalon and cerebrum, as sometimes results from a pineal tumor, often causes the person to go into unremitting coma lasting for the remainder of his or her life. Nerve signals in the brain stem activate the cerebral part of the brain in two ways: by directly stimulating a background level of neuronal activity in wide areas of the brain and by activating neurohormonal systems that release specific facilitory or inhibitory hormonelike neurotransmitter substances into selected areas of the brain. Control of Cerebral Activity by Continuous Excitatory Signals from the Brain Stem Reticular Excitatory Area of the Brain Stem Figure shows a general system for controlling the level of activity of the brain. The central driving component of this system is an excitatory area located in the reticular substance of the pons and mesencephalon. This area is also known by the name bulboreticular facilitory area. We also discuss this area in Chapter because it is the same brain stem reticular area that transmits facilitory signals downward to the spinal cord to maintain tone in the antigravity muscles and to control levels of activity of the spinal cord reflexes.