Somepeoplehavelowlevelsoftheneurotransmitterserotoninintheirbrain. Scientiststhink
that this is one cause of depression. Medications called antidepressants help bring
serotonin levels back to normal. For many people with depression, antidepressants
control the symptoms of their depression and help them lead happy, productive lives.Central Nervous System
Thecentral nervous system (CNS)is the largest part of the nervous system. As shown
inFigure20.4, it includes the brain and the spinal cord. The brain is protected within
the bony skull. The spinal cord is protected within the bones of the spine, which are called
vertebrae.
Figure 20.4: The brain and spinal cord make up the central nervous system. ( 26 )