PSY100H1: Chapter 3 Textbook Notes: Biological Foundations
Synesthesia: A cross-sensory experience in which, for example a visual image has a taste. It tends to run
in families, it may help us to understand how heredity affects the way we experience the world. Maybe
related to creativity. One portion of the brain may have adopted the role of another portion: cross-
The Genetic Bases of Psychological Science
Genetics: How physical characteristics are passed on to offspring through inheritance. Also refers to the
process of turning genes “on” and “off”; this reveals that the environment affects our genes- how they
are expressed and how they influence our thoughts, feelings and behavior.
The Human Genome Project is the attempt to map the entire structure of human genetic material.
First step: map out the entire structure of DNA to identify the order of molecules that make up
each of the thousands of genes on each of the 23 pairs of human chromosomes
We have less than 30,000 genes
Goal: understand how genes and their variations interact to affect health and illness.
Within almost every cell is the genome for making the entire organism- the blueprint
It provides detailed instructions for every part of the body- different genes are turned on and
off; the genome provides the option and the environment determines which option is taken.
Chromosomes are structures within the cell body that are made up of genes. Typically, humans have 23
pairs of chromosomes (46 individual), half of each pair coming from each parent.
Genes are components of DNA which specify an exact instruction to manufacture a distinct
Proteins are the basic chemicals which make up the structure of the cells and direct their
A Gene is a segment of DNA which is involved in producing a protein to carry out a specific task.
Cells become distinct from another depending on which of their genes are expressed.
The environment determines which proteins are produced and when they are produced (Ex:
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
Genotype: The genetic constitution determined at the moment of conception. The genetic makeup.
Phenotype: Observable physical characteristics that result from genetic and environmental influences. Phenylketonuria (PKU) is an example of how the environment can influence a phenotype. It is a disorder
in which infants are unable to break down an enzyme (phenylalanine) that is contained in dairy and
other products. It can lead to severe brain damage. This phenotype is modified by diet.
A characteristic is polygenic when it is influenced by many genes (and the environment). A population
displays a range of variability for a certain characteristic such as height or intelligence.
Example: The variety of skin colour is not the result of a single dominant/recessive gene pairing,
but it shows the effects of multiple genes.
Mutations are errors in cell division. They usually have little influence on the organism but can
occasionally produce a selective advantage or disadvantage in terms of survival or reproduction- they
can be adaptive or maladaptive.
Genes Affect Behaviour
Behavioural genetics is the study of how genes and the environment interact in order to influence
psychological activity. Two methods are used to assess the degree to which traits are inherited.
1. Twin studies compare similarities between different types of twins to determine the genetic
basis of specific traits.
Monozygotic twins or identical twins result from one zygote (fertilized egg) dividing into
two. Therefore each twin has the same set of chromosomes and genes.
Dizygotic twins or fraternal twins result from two separately fertilized eggs developing
simultaneously. Have different genes just as any other siblings.
The Minnesota Twin Project: observed two sets of twins: one who grew up together and
one who were separated at birth. Twins raised apart may be more similar than those
2. Adoption studies compare the similarities between biological relatives and adoptive relatives
They will have similar home environments but different genes.
Heritability: a statistical estimate of the variation, caused by differences in heredity, in a trait within a
population. It refers to populations, not individuals. Estimates of heritability are only concerned with the
extent that people differ in terms of their genetic makeup within the group.
How Does the Nervous System Operate?
Neurons are the basic units of the nervous system. They are cells that specialize in communication. They
operate through chemical impulses and communicate with other neurons through chemical signals
(Excitable). They have three functions.
1. Taking in information from neighbouring neurons (reception)
2. Integrating those signals (conduction)
3. Passing signals to other neurons (transmission) The three basic types of neurons are:
Sensory neurons: They detect information from the physical world and pass that information along to
the brain, usually via the spinal cord.
They are often called afferent neurons, meaning they carry information to the brain.
Somatosensory are the sensory nerves that provide information from muscles. This is
the general term for sensations experienced within the body.
Motor neurons: They direct muscles to contract or relax, producing movement.
They are efferent neurons because they transmit signals from the brain to the muscles
throughout the body.
Interneurons: They communicate within local of short-distance circuits. They integrate neural activity
within a single area rather than transmitting information to other brains structures or to the body
The basis of all psychological activity consists of the complex networks of thousands of neurons which
send and receive signals.
Neurons do not communicate randomly or arbitrarily- they selectively communicate with other
neurons to form circuits or neutral networks which develop through maturation and experience.
There are four structural regions of a neuron which are involved in its communicational functions.
1. The dendrites are short, branchlike extensions of the neuron that detect information from other
neurons. They increase its receptive field and detect chemical signals from neighbouring
2. In the cell body, the information is received from thousands of other neurons in order to be
collected and processed.
3. The axon is where information is transmitted by electrical impulses to other neurons after
information has been integrated in the cell body.
It is a long, narrow outgrowth, that may vary in size from a millimetre to a metre
A nerve refers to a bundle of axons that carry from the brain to other body parts
4. The terminal buttons are small nodules at the ends of an axon which receive electrical impulses
and release chemical signals from the neuron to an area called the synapse or synaptic cleft
which is the site for chemical communication between neurons. Contain extracellular fluid
The neuron’s membrane is its boundary and regulates the concentration of electrically
charged molecules that are the basis of the neurons electrical activity.
Electrical signals travel down the axon because of the fatty myelin sheath that insulates
it. Between the gaps in an exposed axon (nodes of Ranvier) are ion channels which allow
negative and positively charged ions to pass through the cell when the neuron transmits
signals down the axon.
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. Deterioration leads to multiple sclerosis.
Nodes of Ranvier: Small gaps of exposed axon, between the segments of myelin sheath where action
potentials are transmitted
Action Potential: Also called a neural firing, is the electrical signal that passes along the axon and causes
the release of chemicals from the terminal buttons that transmit signals to other neurons. (Pg. 99 left
Resting membrane potential: the electrical charge of a neuron when it is not active; how the inside and
outside of a neuron differs electrically when it is not active.
Due to the ratio of negative to positive ions is greater inside the neutron than outside of it.
Polarization is when this different electrical charge is changed- it creates the electrical energy to
power the firing of the neutron.
A neuron at rest is polarized
Sodium and Potassium ions contribute to a neuron’s resting potential membrane
All-or-none Principle: Principle whereby a neuron fires with the same potency each time, although
frequency can vary; it either fires or not- it cannot partially fire. How often it fires depends on the
strength of stimulation
A neurotransmitter is a chemical substance, located inside each terminal button’s vesicle that carries
signals from one neuron to another, across the synaptic cleft.
It can bind with only one particular type of receptor on the postsynaptic neuron
Receptors: Specialized protein molecules located on the postsynaptic membrane that neurotransmitters
bind to after passing the synaptic cleft.
This binding produces an excitatory or inhibitory signal for the postsynaptic neuron, thus
encouraging or discouraging neural firing.
Three major events that terminate the transmitters; influence in the synaptic cleft are reuptake, enzyme
deactivation and auto reception
Reuptake occurs when the neurotransmitter molecules are taken back into the presynaptic
Enzyme deactivation occurs when an enzyme destroys the transmitter substance in the synaptic
cleft. Auto receptors monitor how much neurotransmitter has been released into the synapse.
Neurotransmitters Influence Mind and Behavior
Agonist: any drug that enhances the actions of a specific neurotransmitter
Antagonist: any drug that inhibits the action of a specific neurotransmitter.
Drugs and toxins can also mimic neurotransmitters and bind with their receptors as if they were the real
Types of Neurotransmitters
All nine neurotransmitters are important in understanding how we think, feel and behave.
1. Acetylcholine (ACh): Responsible for motor control at the junctions between nerves and
muscles. Also involved in mental processes such as learning, memory, sleeping and dreaming.
2. Epinephrine: Responsible for adrenaline rushes, bursts of energy caused by its release
throughout the body. It is found throughout the body, with small amounts in the brain
3. Norepinephrine: involved in the states of arousal and alertness. Important for the heightened
sensitivity for what is going on around you (vigilance)
4. Serotonin: Involved in many diverse behaviors; emotional states, impulse control and dreaming.
Selective serotonin reuptake inhibitors (SSRIs) are drugs that target serotonin to treat
depression. Example: Prozac
5. Dopamine: Serves brain functions such as motivation and motor control. May communicate
with activities that are rewarding.
Parkinson’s disease develops as a result of dopamine depletion; it is marked by muscular
rigidity, tremors and difficulty with voluntary action.
6. GABA (Gamma-amino butyric acid): Primary inhibitory transmitter in nervous system. Without
the inhibitory effect of GABA, synaptic excitation might get out of control and spread through
the brain chaotically.
Epileptic seizures may occur due to low GABA levels
7. Glutamate: Primary excitatory transmitter in the nervous system, involved in fast-acting neural
transmission throughout the brain.
8. Endorphins A: Involved in natural pain reduction and reward
9. Substance P: Involved in pain perception as well as mood states and anxiety
The Basic Brain Structures and Their Functions
The nervous system is divided into two parts which are responsible for everything we think, feel and do.
The Central Nervous System (CNS): Consists of the spinal cord and the brain The Peripheral Nervous System (PNS): All other nerve cells in the body. It includes the somatic and
autonomic nervous systems.
The Study of Gage (metal rod through the brain guy) provided the basis for the first modern theories of
the role of a part of the brain called the prefrontal cortex in personality and self-control.
Issues with social phenomena such as recognizing social norms, understanding what other
people are thinking and feeling emotionally connected to other people.
Phrenology: Idea that the brain operates through functional localization; the practise of assessing
personality traits and mental abilities by measuring bumps on the human skull.
First Idea steamed through Broca’s Area: the left fronta