Download CHAPTER 3 3.1 The nervous system is the interacting network of

CHAPTER 3
3.1 The nervous system is the interacting network of nerve cells that underlies all psychological
activity. Neurons are the basic units of the nervous system. Sensory (afferent) neurons carry
sensory information from sensory receptors to the brain. Motor (efferent) neurons transmit
commands from the brain to the glands and muscles of the body. Interneurons connect neurons
with one another. Neurons generally have a cell body, dendrites which receive information from
other neurons, an axon that carries information down the neuron, and terminal branches which
trasmit information to adjacent neurons. Neurons connect at synapses.
3.2 When a neuron is at rest (its resting potential of -70 mVs), it is polarized, with a negative
charge inside the cell membrane and a positive charge outside. When a neuron is stimulated by
another neuron, its cell membrane is either depolarized or hyperpolarized. The spreading voltage
changes along the cell membrane that occur as one neuron is excited by other neurons are called
graded potentials. If the cell membrane is depolarized by enough graded potentials (to about
-50 mVs), the neuron will fire, sending the information down its axon to potentially transmit to
other neurons. This depolarization process is called an action potential, or nerve impulse.
3.3 Within the terminal buttons of the presynaptic neuron are neurotransmitters, such as
glutamate, GABA, dopamine, serotonin, acetylcholine, and endorphins. Neurotransmitters
transmit information from one neuron to another as they are released into the synapse from the
synaptic vesicles. They bind with receptors in the membrane of the postsynaptic neuron, which
produces graded potentials that can either excite or inhibit the postsynaptic neuron from firing.
Levels of neurotransmitters affect behavior and cognitions such as sleep and memory.
Medications can affect neurotransmitter levels in a number of ways.
3.4 The nervous system consists of the central nervous system (CNS: the brain and spinal
cord) and the peripheral nervous system (PNS: neurons in the rest of the body). Neurons of
the PNS carry messages to and from the CNS. The PNS has two subdivisions: the somatic
nervous system and the autonomic nervous system. The somatic nervous system consists of
sensory neurons that carry sensory information to the brain and motor neurons that direct mostly
voluntary actions of skeletal muscles. The autonomic nervous system controls basic, mostly
involuntary life processes such as the beating of the heart, workings of the digestive system, and
breathing. It consists of two parts, the sympathetic nervous system, which is activated primarily
in response to threats (but is also involved in general emotional arousal) readying the body for
flight or fight, and the parasympathetic nervous system, which is involved in more routine
activities such as maintaining the body’s energy resources and restoring the system to an even
keel following sympathetic activation.
3.5 Scientists can study the brain by using brain scans. EEGs read electrical activity (brain
waves), PET scans show activity in different regions, and CT scans and MRIs are primarily used
to identify tumors and other structural abnormalities. The central nervous system (CNS) consists
of the brain and spinal cord. The spinal cord carries out reflexes (automatic motor responses),
transmits sensory information to the brain, and transmits messages from the brain to the muscles
and organs. Each of its 31 paired segments controls sensation and movement in a different part
of the body. Because the spinal cord is the source of communication between the brain and the
body, severance of the cord results in paralysis at all levels below the injury.
3.6 The hindbrain includes the medulla oblongata, the cerebellum, and parts of the
reticular formation. The medulla regulates vital physiological functions, such as heartbeat,
circulation, and respiration, and forms a link between the spinal cord and the rest of the brain.
The cerebellum is the brain structure involved in movement (in particular, fine motor
movements), but parts of it also appear to be involved in learning and sensory discrimination.
The reticular formation is most centrally involved in consciousness and arousal. The midbrain
consists of the tectum and tegmentum. The tectum is involved in orienting to visual and auditory
stimuli. The tegmentum is involved in, among other things, movement and arousal.
3.7 The subcortical forebrain consists of the hypothalamus, thalamus, the limbic system, and
the basal ganglia. The hypothalamus helps regulate a wide range of behaviors, including eating,
sleeping, sexual activity, and emotional experience. Among its other functions, the thalamus
processes incoming sensory information and transmits this information to higher brain centers.
The limbic system includes the septal area, amygdala, and hippocampus. The precise functions
of the septal area are unclear, although it appears to be involved in learning to act in ways that
avoid pain and produce pleasure. The amygdala is crucial to the experience of emotion. The
hippocampus plays an important role in committing new information to memory. Basal ganglia
structures are involved in the control of movement and also play a part in “automatic” responses
and judgments that may normally require little conscious attention.
3.8 The cerebral cortex is convoluted and comprises 80 percent of the brain’s mass. The
“hills” are referred to as gyri and the valleys as sulci. It includes primary areas, which usually
process raw sensory data (except in the frontal lobes), and association areas, which are involved
in complex mental processes such as perception and symbolic thinking. The cortex consists of
the right and left hemispheres, each of which has four lobes. The occipital lobes are involved in
vision. The parietal lobes are involved in the sense of touch, perception of movement, and
location of objects in space. The frontal lobes serve a variety of functions, such as coordinating
and initiating movement, attention, planning, social skills, abstract thinking, memory, and
aspects of personality. Sections of the temporal lobes are important in hearing, language, and
recognizing objects by sight. Damage to Broca’s area, located in the left frontal lobe causes
Broca’s aphasia (difficulty speaking language). Damage to Wernicke’s area, located in the left
temporal lobe, causes Wernicke’s aphasia (difficulty understanding language).
3.9 Some psychological functions are lateralized, or processed primarily by one hemisphere.
Although both hemispheres are involved in the processing of all information, the left is more
involved in processing verbal and analytic information, and the right is more involved in
processing nonlinguistic functions, such as recognizing faces and forming visual maps. The
corpus collosum is responsible for communication between the two hemispheres. Split-brain
studies (on patients in whom the corpus collosum has been severed) have provided a wealth of
information about lateralization. Although the differences tend to be relatively small, female
brains tend to show less lateralization than males.
3.10 Positive psychology defines happiness as subjective feelings of well-being which appear to
involve activation of the frontal cortex. Frequent feelings of well-being are associated with
career success, more satisfactory and stable romantic relationships, and improved physical
health. Psychologists interested in genetics study the influence of genetic blueprints (genotypes)
on observable qualities (phenotypes). Genes are arranged along chromosomes and consist of two
alleles (one each from the biological mother and father). Usually dominant alleles (R) are
dominant over recessive (r) alleles. Behavioral genetics research often involves comparing
monozygotic (MZ) twins (who share 100% of their genetic material) and dizygotic (DZ) twins
(who share about 50% of their genetic material). Research in behavioral genetics suggests that a
surprisingly large percent of the variation among individuals on psychological attributes such as
intelligence and personality reflects genetic influences, which interact with environmental
variables in very complex ways. Heritability refers to the proportion of variability among
individuals on an observed characteristic (phenotypic variance) that can be accounted for by
genetic variability (genotypic variance).
3.11 Evolution refers to a change in gene frequencies over many generations. Evolutionary
theory examines the adaptive significance of human and animal behavior. Known for his
conceptualization of evolutionary theory, Charles Darwin proposed natural selection as the
mechanism through which changes in organisms’ appearance and behavior change over time.
As evolutionary theory has taken root, its applications to a number of phenomena within
cognitive psychology (e.g., language acquisition) and other areas within psychology have
flourished.
3.12 The design of the human nervous system, like that of other animals, reflects its evolution.
Early precursors to the first vertebrates (animals with spinal cords) probably reacted with
reflexive responses to environmental stimulation at specific points of their bodies. The most
primitive vertebrate brain, or brain stem, included a forebrain (specialized for sensing nearby
stimuli, notably smells and tastes), a midbrain (specialized for sensation at a distance, namely
vision and hearing), and a hindbrain (specialized for control of movement). This rough division
of labor persists in contemporary vertebrates, including humans. The forebrain of humans and
other contemporary vertebrates includes an expanded cerebrum, with a rich network of cells
comprising its outer layers or cortex, which allows much more sophisticated sensory, cognitive,
and motor processes. While a sheep has been successfully cloned (duplicated in genetic
material), the system has not been perfected; thus the clone was recently euthanized because of
health problems. Human cloning has not yet been successful and poses a number of ethical
considerations.