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Chapter 3

PSY100H1 Chapter 3: Nature vs. Nurture (PSY100)


Department
Psychology
Course Code
PSY100H1
Professor
Michael Inzlicht
Chapter
3

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Jan 26, 2016
Lecture 3
PSY100
BIOLOGICAL PSYCHOLOGY: Nature vs. Nurture
HEREDITY VS. HEREDITABILITY
Heredity => the genetic transmission of characteristics from parents to offspring
-Ex. Ada might say that she inherited her blue eyes from her dad
Heritability => an estimate of the genetic proportion of the variation in some specific trait
-Within a particular POPULATION (not individuals)
How much does height (or weight, or intelligence, etc…) vary within the population?
Do related individuals show less variation than unrelated individuals?
Estimate of Heritability => % of the variation that is explained by genetic differences
-Ex. Heritability of intelligence is estimated to be between 40% - 80%
TWIN STUDES & ADOPTION STUDIES
Help researchers study the impact of genetics versus environmental influences
Monozygotic vs. Dizygotic
Monozygotic is when there are 2 sperms and 1 egg = 100% genetic similarity
Dizygotic is when there are 2 sperms and 2 eggs = 50% genetic similarity (they
are no different than regular siblings)
Monozygotic twins raised together vs. raised apart
REMEMBER: BEHAVIOUR IS DETERMINED BY MULTIPLE (INTERACTING) FACTORS
-Behaviour is exceedingly complex
-Single-cause explanations may be accurate, but they are generally always
incomplete
-Behaviour is governed by a complex network of interacting factors:
1. Hereditary
2. Biology
3. Environment
4. Culture

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Jan 26, 2016
Lecture 3
THE NERVOUS SYSTEM
There nervous system is the body’s electrochemical communication circuitry
Central Nervous System (CNS)
Peripheral Nervous System (PNS)
-Somatic Nervous System
-It has mostly to do with the external environment and
sensation
-Autonomic Nervous System
Sympathetic Nervous System
Parasympathetic Nervous System
-It has more to do with things happening in our body
NERUONS
Are the basic unit of the nervous system
Operate through electrical impulses
Communicate with other neutrons through chemical signals
Three Types of Neurons:
1. Sensory Neurons (afferent neurons)
2. Motor Neurons (efferent neurons)
3. Interneurons
HINT: SAME (sensory, afferent, motor, efferent)
WHEN DO NEURONS FIRE?
Excitatory Signals => increase the likelihood that the neuron will fire
Inhibitaory signals => decrease the likelihood that the neutron will fire
-The do this by affecting the polarization of the cell
-Neurons fire (generate an action potential) if the excitatory input reaches a
certain threshold
All or None Principle: A neuron fires the same potency each time (it either fires or
does not fire); but how frequently the neutron fires can vary
Action Potential: The neural impulse that passes along the axon and subsequently
causes the release of chemicals from the terminal buttons

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Jan 26, 2016
Lecture 3
NEUROTRANSMITTERS
Are chemical substances that
carry signals from one neuron to
another
Are stored in vesicles (small
packages) inside the terminal
buttons
Action potentials cause the
vesicles to fuse to the presynaptic
membrane (membrane of the
neuron that is sending the signal)
and release their contents into the
synapse, where they are received
by postsynaptic receptors on the
postsynaptic membrane
(membrane of the neuron that is
receiving the signal)
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