Nervous and Endocrine Systems

29.5Brain Function andChemistryKEY CONCEPT Scientists study the functions and chemistry of the brain.MAIN IDEAS• New techniques improve our understandingof the brain.• Changes in brain chemistry can cause illness.• Drugs alter brain chemistry.VOCABULARYaddiction, p. 893desensitization, p. 893tolerance, p. 893sensitization, p. 893stimulant, p. 894depressant, p. 894Reviewneurotransmitter,action potentialConnect When you take medicine for a headache, the drug alters your brain’schemistry. Aspirin, for example, stops your brain from making certain chemicals.In small amounts, it is beneficial to your health. However, even nonprescriptiondrugs can cause permanent damage to your nervous system if taken incorrectly.CTMRIFIGURE 29.14 Modern technologiesuse computers and sensingdevices to observe the brain withoutthe need for surgery.MAIN IDEANew techniques improve our understanding ofthe brain.For many years, the only way scientists could study brain function was byobserving changes that occurred in people who had accidental brain injuriesor by dissecting the brains of people who had died. A live patient would haveto undergo surgery in order for scientists to learn about brain function.Today, scientists use imaging technologies such as CT, MRI, and PET scansto study the brain in living patients without the need for surgery. Thesemethods use x-rays, magnetic fields, or radioactive sensors and computerprograms to form images of the brain, as shown in FIGURE 29.14.PETComputerized tomography (CT) scans use x-rays to viewthe brain. Magnetic resonance imaging (MRI) uses magneticfields and radio waves. Both CT and MRI scans make imagesthat show the structure of the brain. These scans are used toexamine the brain’s physical condition.Positron emission tomography (PET) scans show whichareas of the brain are most active. During PET scans, a personis injected with radioactive glucose. Recall from Chapter 4 thatcells use glucose for energy. By measuring where the radioactive glucosecollects in the brain, scientists can see which areas of the brain are using themost energy. In the image shown above, the bright red and yellow areas are themost active, and the dark blue areas are the least active.Infer Why are modern technologies for studying the brain safer for the patientsbeing studied?Chapter 29: Nervous and Endocrine Systems 891