Nervous System

The brain, the spinal cord and the nerves and fibers that extend from the spinal cord to the muscles and internal organs make up the nervous system. All our thoughts, sensations and actions are orchestrated by this system.

* The sciatic nerve is the longest nerve in your body--and sciatica is the popular name given to any disorder that causes pain from that nerve. (To find out how to treat sciatica, and other back pain, see "Sciatica--Pulp Friction" on page 386.)

* A pinched nerve in the back can happen when one of the spongy disks that cushions each part of the backbone bulges or bursts. The swollen or exploded matter can then press against one of the 31 pairs of nerves that spread from the spinal cord. (To keep your spinal disks healthy, read "Dodging Disk Damage" on page 382.)

* The vulnerable neck is just seven small bones, a few little muscles and ligaments and eight pairs of cervical nerves that shout "ouch!" all too often. (To banish the common pain in the neck, see "Basic Neck Rules" on page 253.)

* If you have a sore neck and shoulders plus weakness in your upper arms and back, you might have thoracic outlet syndrome. Women with long, graceful necks develop it the most often. (See "Where Pain and Posture Mix" on page 351.)

* While you can''''t make new brain cells, the ones that you have can grow bigger with exercise. And exercise makes brain cells grow not only in the motor areas but also in other areas of the cerebral cortex and in the temporal lobes, where thinking, learning and memory take place. (See "Pumping Up the Power" on page 49.)

* Scientists have found that many of our memories are stored in the temporal lobes, and memory experts have developed techniques to help you pack in even more. (See "Remember the Alamo [and Everything Else]" on page 50.)

* The ancient seat of emotion and behavior is the limbic system. This is the brain area where researchers have discovered important differences between men''''s and women''''s brains. Because of the difference in the limbic system, women tend to verbalize, while men are more prone to act. (See "More between the Sexes" on page 49.)

The brain unscrambles all the messages that are sent to you by the nerve endings in your body. It also makes sense of language, enables creativity, reasons and stores memories. The major parts of the brain include the cerebrum, where your intellect resides; the cerebellum, which orchestrates muscle action; and the tiny hypothalamus, which controls metabolism, appetite and sexual arousal. A cross-section of the brain reveals a complex arrangement of structures including the fornix, hypothalamus and cingulate gyrus--which help to make up the limbic system.