80 ❯ STEP 4. Review the Knowledge You Need to Score High
tomography (PET) produces color computer graphics that depend on the amount of
metabolic activity in the imaged brain region. When neurons are active, an automatic
increase in blood flow to the active region of the brain brings more oxygen and glucose
necessary for respiration. Blood flow changes are used to create brain images when tracers
(such as radioactively tagged glucose) injected into the blood of the subject emit particles
called positrons, which are converted into signals detected by the PET scanner. Functional
MRI (fMRI) shows the brain at work at higher resolution than the PET scanner. Changes
in oxygen in the blood of an active brain area alters its magnetic qualities, which is recorded
by the fMRI scanner. After further computer processing, a detailed picture of that local
brain activity emerges. With new brain imaging technology, psychologists can explore far
more about our abilities than ever before, from well-known systems like perception to less
understood systems like motivation and emotion.
A magnetic source image (MSI), which is produced by magnetoencephalography
(MEG scan), is similar to an EEG, but the MEG scans are able to detect the slight magnetic
field caused by the electric potentials in the brain. The images can pinpoint locations of seizures.Organization of Your nervous system
Your patterns of behavior generally involve masses of neural tissue rather than a few neurons. All
of the neurons in your body are organized into your nervous system. Your nervous system has
subdivisions based on location and function. The two major subdivisions are your central nerv-
ous system and your peripheral nervous system. Your central nervous system consists of your
brain and your spinal cord. Your peripheral nervous system includes two major subdivisions:
your somatic nervous system and your autonomic nervous system. Your peripheral nervous
system lies outside the midline portion of your nervous system carrying sensory information
to and motor information away from your central nervous system via spinal and cranial nerves.
Your somatic nervous system has motor neurons that stimulate skeletal (voluntary) muscle.
Your autonomic nervous system has motor neurons that stimulate smooth (involuntary) and
heart muscle. Your autonomic nervous system is subdivided into the antagonistic sympathetic
nervous system and parasympathetic nervous system. Sympathetic stimulation results in
responses that help your body deal with stressful events including dilation of your pupils,
release of glucose from your liver, dilation of bronchi, inhibition of digestive functions, acceler-
ation of heart rate, secretion of adrenaline from your adrenal glands, acceleration of breathing
rate, and inhibition of secretion of your tear glands. Parasympathetic stimulation calms your
body following sympathetic stimulation by restoring digestive processes (salivation, peristalsis,
enzyme secretion), returning pupils to normal pupil size, stimulating tear glands, and restoring
normal bladder contractions. Your spinal cord, protected by membranes called meninges and
your spinal column of bony vertebrae, starts at the base of your back and extends upward to
the base of your skull where it joins your brain. The cord is composed mainly of interneurons
and glial cells, which are all bathed by cerebrospinal fluid produced by your glial cells.The Brain
Your brain, which has the consistency of soft-serve yogurt, is covered by protective
membranes called meninges and is housed in your skull. The evolutionary approach
describes the brain’s evolution from more primitive organisms, reasoning that new types
of behavior developed as each new layer of the brain evolved. According to one evolution-
ary model (triune brain), the human brain has three major divisions, overlapping layers
with the most recent neural systems nearest the front and top. The reptilian brain, which
maintains homeostasis and instinctive behaviors, roughly corresponds to the brainstem,
which includes the medulla, pons, and cerebellum. Developmental psychologists call the