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Chapter 3

PSY100H1 Chapter Notes - Chapter 3: Twin, Gene Expression, Zygote

Course Code
Michael Inzlicht

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Key Terms
chromosomes Structures within the cell body that are made up of genes.
gene The unit of heredity that determines a particular characteristic in an organism.
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 gene
from the other parent.
genotype The genetic constitution determined at the moment of conception.
phenotype Observable physical characteristics that result from both genetic and
environmental influences.
monozygotic twins Twin siblings who result from one zygote splitting in two, and
therefore share the same genes (i.e., identical twins).
dizygotic twins Twin siblings who result from two separately fertilized eggs (i.e.,
fraternal twins).
heritability A statistical estimate of the fraction of observed measure of the overall
amount of difference among people in a population that is caused by differences in
neuron The basic unit of the nervous system that operates through electrical
impulses, which communicate with other neurons through chemical signals. Neurons
receive, integrate, and transmit information in the nervous system.
dendrites Branchlike extensions of the neuron that detect information from other
cell body In the neuron, where information from thousands of other neurons is
collected and processed.
axon A long narrow outgrowth of a neuron by which information is transmitted to
other neurons.
terminal buttons Small nodules at the ends of axons that release chemical signals
from the neuron to an area called the synapse.
synapse The site for chemical communication between neurons.
sensory neurons One of the three types of neurons, these afferent neurons detect
information from the physical world and pass that information along to the brain.
PSY100 CH3 Genetic and Biological Foundations

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motor neurons One of the three types of neurons, these efferent neurons direct
muscles to contract or relax, thereby producing movement.
interneurons One of the three types of neurons, these neurons communicate only
with other neurons, typically within a specific brain region.
action potential The neural impulse that passes along the axon and subsequently
causes the release of chemicals from the terminal buttons.
resting membrane potential The electrical charge of a neuron when it is not active.
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.
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.
synaptic cleft The small space between neurons that contains extracellular fluid.
neurotransmitter A chemical substance that carries signals from one neuron to
receptors In neurons, specialized protein molecules on the postsynaptic membrane
that neurotransmitters bind to after passing across the synaptic cleft.
reuptake The process whereby the neurotransmitter is taken back into the
presynaptic terminal buttons, thereby stopping its activity.
enzyme deactivation The process whereby the neurotransmitter is destroyed by an
enzyme, thereby terminating its activity.
autoreceptors A neuron!s own neurotransmitter receptors, which regulate the
release of the neurotransmitters.
agonist Any drug that enhances the actions of a specific neurotransmitter.
antagonist Any drug that inhibits the action of a specific neurotransmitter.
acetylcholine (ACh) The neurotransmitter responsible for motor control at the
junction between nerves and muscles; also involved in mental processes such as
learning, memory, sleeping, and dreaming.
PSY100 CH3 Genetic and Biological Foundations
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