Chapter 3: Biological Foundations
Synesthesia = a cross-sensory experience, for example, when a visual image has a
What is the genetic basis of psychological science?
- Heredity involves passing along genes through reproduction
- Genotypic variation is created by sexual reproduction
- Genes affect behavior
- Social and environmental contexts influence genetic expression
- Genetic expression can be modified
- Critical thinking skill: seeking disconfirming evidence
How does the nervous system operate?
- Neurons are specialized for communication
- Action potentials cause neural communication
- Neurotransmitters bind to receptors
- Neurotransmitters influence mind and behavior
What are the basic brain structures and their functions?
- The brain stem houses the basic programs of survival
- The cerebellum is essential for movement
- Subcortical structures control emotion and basic drives
- The cerebral cortex underlies complex mental activity
How are neural messages integrated into communication systems?
- The peripheral nervous systems includes the somatic and autonomic systems
- The endocrine system communicates through hormones
- Actions of the nervous system and endocrine system are coordinated
How does the brain change?
- The interplay of genes and environment wires the brain
- Cultures affect the brain
- The brain rewires itself throughout life
- Critical thinking skill: recognizing understated assumptions
- Females’ and males’ brains are similar and different
- The brain can recover from injury.
Chromosomes = Structures within the cell body that are made up of genes
Gene = the unit of heredity that determines a particular characteristic in an
Dominant gene = A gene that is expressed in the offspring whenever it is present. Recessive gene = A gene that is expressed only when it is matched with a similar gen
from the other parent.
Genotype = the genetic constitution determined at the moment of conception
Phenotype = Observable physical characteristics that result from both genetic and
E.g. Phenylketonuria (PKU) is a disorder in which infants are unable to breakdown
an enzyme, phenylalanine, contained in dairy and other products, such as
aspartame, a sweetener in soft drinks. It can lead to sever brain damage. Providing
children with low-phenylalanine diets until they pass the critical stages of
development greatly helps to reduce brain damage. The phenotype, then, is
modified by diet.
E.g. Industrial melanism is a phenomenon in which areas of the world with heavy
soot or smog tend to have moths and butterflies of darker colors.
E.g. Sickle-cell disease is a genetic disorder that alters the bloodstream’s
processing of oxygen; it can lead to pain, organ and bone damage, and anemia. It
occurs mainly in people of African descent; approximately 9% of whom are
estimated to have the recessive gene for it.
Germline therapy = changing the early embryonic genes, which are incorporated
into all cells of the body and are passed on to future generations.
Eugenics = the science of attempting to improve a group’s gene pool.
>> The study of how genes and environment interact to influence psychological
1) Twin studies – compares similarities between different types of twins to
determine the genetic basis of specific traits
2) Adoption studies – compares the similarities between biological relatives and
Monozygotic twins = result from one zygote dividing in two; each new zygote, and
therefore each twin, has the same chromosomes and the same genes on each
chromosome. i.e. identical twins
Dizygotic twins = result from two separately fertilized eggs developing in the
mother’s womb simultaneously; resulting twins are no more similar genetically than
any other pair of siblings. i.e. fraternal or non-identical twins. Caspi’s study of the influence of environment and genes
Hypothesis: The enzyme monoamine (MAO) may be important in determining
susceptibility to the effects of maltreatment, because low levels of MOA have been
implicated in aggressive behaviors.
- A group of more than 1,000 New Zealanders were followed from birth to
- Researchers measured which children were mistreated by their parents
- Researchers measured the presence of the MAO gene, which comes in two
forms, one that leads to higher levels of MAO and one that leads to lower
- Researchers measured the tendency toward criminal behavior
Results: Those who had the gene for low MAO activity were much more likely than
others to have been convicted of violent crimes if they had been maltreated as
children. The effects of maltreatment had less influence on those with the high-MAO
Conclusion: Nature and nurture work together to affect human behavior.
The Nervous System
Neuron = the basic unit of the nervous system; it operates through electrical
impulses, which communicate with other neurons through chemical signals.
Neurons receive, integrate, and transmit information in the nervous system.
Three types of neurons:
1) Sensory neurons – detect information from the physical world and pass that
information along to the brain, usually via the spinal cord. Ie. Afferent
2) Motor neurons – direct muscles to contract or relax, thereby producing
movement; transmit signals from the brain to the muscles throughout the
body. i.e. efferent neurons.
3) Interneurons – communicate within local or short-distance circuits; integrate
neural activity within a single area rather than transmitting information to
other brain structures or to the body organs.
Somatosensory = the sensory nerves that provide information from muscles.
Dendrites = short, branch-like appendages that increase the neuron’s receptive field
and detect chemical signals from neighboring neurons
Cell body = where the information received from thousands of other neurons is
collected and integrated. Axon = a long narrow outgrowth of neuron by which information is transmitted to
Terminal buttons = small nodules at the axons’ ends, receive the electrical impulses
and release chemical signals from the neuron to an area called the synapse or
Synapse or synaptic cleft = the site for chemical communication between neurons,
which contains extracellular fluid.
Myelin sheath = a fatty material, made up of glial cells, that insulates the axon and
allows for the rapid movement of electrical impulses along the axon.
Nodes of Ranvier = small gaps of exposed axon, between the segments of myelin
sheath, where action potentials are transmitted.
Resting membrane potential = the electrical charge of a neuron when it is not active.
Action potential or neural firing = the neural impulse that passes along the axon and
subsequently causes the release of chemicals from the terminal buttons.
- Excitatory signals depolarize the cell membrane, increasing the likelihood
that the neuron will fire
- Inhibitory signals hyperpolarize the cell, decreasing the likelihood that the
neuron will fire.
- Excitatory and inhibitory signals received by the dendrites are integrated
within the neuron.
- If the total amount of excitatory input from the other neurons surpasses the
receiving neuron’s threshold, an action potential is generated.
- When a neuron fires, the sodium gates in the cell membrane open, allowing
sodium ions to rush into the neuron
- This influx of sodium causes the inside of the neuron to become slightly more
positively charged than the outside
- A fraction of a second later, potassium channels open to allow potassium ions
inside the cell membrane to rush out.
- This change from a negative to a positive one inside the neuron is the basis of
the action potential.
Propagation = when the neuron fires, the cell membrane’s depolarization moves
along the axon like a wave.
Deterioration of the myelin sheath leads to multiple sclerosis (MS), as especially
tragic neurological disorder that begins in young adulthood. The earliest symptoms
are often numbness in the limbs and blurry vision. Since the myelin insulation helps
messages move quickly along axons, demyelination slows down neural impulses.
The axons essentially short-circuit, and normal neural communications is interrupted. Motor actions become jerky, as those affiliated lose the ability to
coordinate motor movements. Over time, movement, sensation and coordination
are severely impaired. As the myelin sheath disintegrates, axons are exposed and
may start to break down.
All-or-none principle = the principle whereby a neuron fires with the same potency
each time, although frequency can vary; it either fires or not, it cannot partially fire.
Neurotransmitter = a chemical substance that carries signals from one neuron to
Receptors = In