Transcript Chapter 2: Psychology As a Science

Chapter 4: Neuroscience
Chapter Outline
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How do scientists study the nervous system?
How does the nervous system work?
How do neurons work?
How is the nervous system organized?
Structures of the brain
Evolutionary psychology
Brain side and brain size
Neurological diseases
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How Do Scientists Study the Nervous System?
 Examining autopsy tissue
 Testing the behaviour of patients with brain damage.
 Electroencephalograms (EEG)—recording brain
activity from the surface of the scalp
 Animal studies
 Neuroimaging techniques that show visual images in
awake humans
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The Brain at Work
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How Does the Nervous System Work?
 Neurons (nerve cell)—Main building block of the brain
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Sensory—Gathers sensory information
Motor—Communicates information to the muscles
Interneuron—Carries information between neurons in the brain
and the spinal cord
 Glia—Cells that help support neurons
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Astrocytes—Creates blood-brain barrier, influences communication
between neurons, and helps heal brain damage
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One type of astrocytes is the stem cell, which creates new neurons
Oligodendroglia—Provides myelin to speed up transmission of
neurons
Microglia—Cleans up dead cells and prevents infection in the brain
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The Structure of Neurons
 Cell Body—contains nucleus,
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which provides energy for the
neuron (C)
Dendrites—receive messages
from other neurons (B)
Axon—carries information away
from the cell body (D).
Axon Terminals—transmit
signals to the dendrites (E)
Myelin Sheath—A substance
that speeds up the firing of the
neuron (F)
Nodes of Ranvier—The small
gaps on the neuron that have no
myelin covering (A).
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The Neuron
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How Do Neurons Work?
 Resting potential—When a neuron is at rest
 It
is negatively charged inside and positively
charged outside. This resting charge is maintained
through the actions of sodium-potassium pumps.
 Action potential—When a neuron fires
 Pores
in the neuron (ion channels) open to let the
positive charge come in and the negative charge go
out. This shift in electrical charge triggers the axon
terminals to release neurotransmitters.
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The Action Potential
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Communication Between Neurons
 An action potential triggers the release of neurotransmitters
 Neurotransmitters are chemicals that help neighbouring neurons talk to
each other.
 These chemicals float from the synaptic vessel of one neuron and are
taken up by the neurotransmitter receptors in a neighbouring neuron.
 Synapse—the small space between neurons
 Plasticity—Repeated release of neurotransmitters can cause
permanent change to the neurons
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All-or-None Principle
 Either a neuron is sufficiently stimulated to start an action
potential (all) or it is not (nothing).
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Meaning you cannot have a neuron fire a lot or a little. It fires or it
doesn’t.
If you tap your finger, you cannot feel it as much as if you slam your
finger in the door. Why?
 Refractory period—After firing, a neuron can’t fire for 1000th
of a second.
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Absolute refractory period—a short time after an action
potential, during which a neuron is completely unable to fire again
Relative refractory period—just after the absolute refractory
period, during which a neuron can only fire if it receives a stimulus
stronger than its usual threshold level
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Nodes of Ranvier
The nodes of Ranvier are
the regions of bare axon
that are between areas
wrapped in myelin.
Action potentials travel
down the axon by
jumping from node to
node.
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Neurotransmitter Receptors
 Postsynaptic potentials are electrical events in
postsynaptic neurons that occur when a neurotransmitter
binds to one of its receptors. The electrical response of the
postsynaptic cell is determined by the receptor.
 Depolarized regions of postsynaptic membranes have been
stimulated by excitatory neurochemicals to open their ion
channels and increase the likelihood that the neuron they are
part of will initiate an action potential.
 Hyperpolarized areas of a cell have had their negative
charge increased in an inhibitory fashion, making it less likely
that the cell will generate an action potential.
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Neural Networks
 Neural networks—
clusters of neurons that
communicate with
each other
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How Is the Nervous System Organized?
1. Central Nervous System—Neurons in the brain and
spinal cord
2. Peripheral Nervous System—Neurons in the rest of the
body
a) Somatic Nervous System—All the neurons that take in
sensory information (touch and pain) from all over the
body and deliver it to the spinal cord and brain
b) Autonomic Nervous System
i. Sympathetic Nervous System—Controls fight-orflight function
ii. Parasympathetic Nervous System—Controls
digestive and other organ function
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Organization of the Nervous System
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Pain Reflex Circuit of the Spinal Cord
 Allows for rapid motor reactions to pain and controls
pain reflexes without any communication with the
brain
 Consists of three neurons:
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A sensory neuron, whose cell body is located in the periphery
but whose axon travels into the spinal cord
A connecting neuron, called an interneuron
A motor neuron, whose cell body is located in the spinal cord
and whose axon travels out to the body
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Reflex Circuit of the Spinal Cord
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Structures of the Brain
 Hindbrain
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Pons, reticular formation,
cerebellum, medulla
 Midbrain
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Thalamus, hypothalamus,
hippocampus, substantia
nigra, pituitary gland
 Neocortex
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Visual, auditory, motor,
sensory, cognitive
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Hindbrain
 Function
 Regulates basic life functions
 Location
 Part of the brain closest to the spinal cord
 Parts of Hindbrain
 Reticular formation—regulates sleep/wake cycle
 Main source of the neurotransmitter serotonin, which is important
for mood and activity levels
 Pons—sends signals to and from the forebrain and cerebellum
 Important for sleep, breathing, swallowing, eye movements, and
facial sensation and expression
 Locus coeruleus uses neurotransmitter norepinephrine, which is
important for arousal and attention.
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Hindbrain
 Parts of Hindbrain (continued)
 Medulla—regulates heartbeat, breathing, sneezing, and coughing
 Cerebellum—important for motor coordination and certain types of
learning that involve movement, such as learning to play the piano
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The Cerebellum
 The cerebellum has
many folds on its
surface, shown here in
this fluorescent image
of a slice through this
part of the brain.
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Midbrain
 Function
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A large variety of functions (see below)
 Location
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Right on top of the brainstem (middle of the brain)
 Parts of Midbrain
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Thalamus—serves as a relay station for incoming sensory
information
Hypothalamus—important for motivation, basic drives, and
control of the endocrine system
Pituitary Gland—regulates hormones
Hippocampus—important for certain types of learning and
memory
Amygdala—involved in processing information about emotions,
particularly fear
 The thalamus, hypothalamus, amygdala, and hippocampus
form the limbic system.
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Midbrain
 Parts of Midbrain (continued)
 Straitum—produces fluid movements and helps with learning
and memory that does not require conscious awareness
 Nucleus accumbens—important for motivation, reward,
and addiction
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The HPA Axis
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Neocortex
 Location
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Top part of the brain, with many
convolutions
 Four lobes
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Frontal lobe (front of brain)—
higher intellectual thinking
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Broca’s area—speech production
Prefrontal cortex—memory, morality,
mood, planning
Occipital lobe (back of brain)—vision
Temporal lobe (sides of brain)—
speech comprehension, recognizing
complex visual stimuli (like faces)
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Wenicke’s area—language
comprehension
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Speech
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Vision: Crossed Pathway
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Parietal Lobe
 Located at the top of the
brain—perception of
touch and complex visual
information, particularly
about locations
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Somatosensory strip
contains neurons that
register the sensation of
touch
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The Brain’s Body Map
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Localization of Function
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Areas of the Neocortex
 Sensory Cortex—registers sensory neurons (touch)
 Motor Cortex—registers the motor neurons
(muscles)
 Association Cortex—registers complex functions,
including higher-order sensory processing,
integrating information from different senses,
thinking, planning
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Parallel Processing
 Parallel processing—Air
traffic controllers must react
to an array of sensory
stimuli and make quick
decisions. Communication
among the association
cortex within and between
the lobes of the brain allows
us to perform such complex
functions simultaneously.
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Corpus Callosum
 Function
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Dense bundle of neural fibres
(axons) that allow
communication of
information from one side of
the brain to the other
 Location
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Connects the two brain
hemispheres
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Evolutionary Psychology
 Evolutionary psychology examines how the
process of evolution has shaped the body and brain
via the interaction of our genes and the environment
to produce our thoughts and behaviours.
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Phylogeny—the development of unique species over time
Mammals evolved from an offshoot of reptiles
All life on earth is interrelated and derives from one common
ancestor, LUCA (last universal common ancestor)
Three super kingdoms—Eucharia (includes humans),
Archea, and Bacteria
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The Missing Link
 Tiktaalik—a fish in the
Canadian Arctic that had a
primitive wrist with fingerlike bones
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Tree of Life
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Evolution of Characteristics of Species
 Homologous traits—characteristics that are similar
between species and can be traced back to a common
ancestor
 Analogous traits—characteristics that have evolved
independently in different species
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Convergent evolution—the development of similar physical
characteristics or behaviours in different species that do not
share a common ancestor (e.g., wings on birds and on bees)
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Charles Darwin
 The father of evolution—
Darwin’s extensive
cataloguing of various life
forms he encountered
during his voyage on the
HMS Beagle led to his
famous book On the Origin
of Species (1859) and to
scientific acceptance of the
theory of evolution.
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Natural Selection
 Evolution by natural selection—animals with
physical and behavioural attributes well suited to
their environment are more likely to survive,
reproduce, and pass on their traits to their offspring
 Fitnessan individual’s ability to successfully grow to
maturity and have offspring
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Natural Selection
 Evolution by natural selection—animals with
physical and behavioural attributes well suited to
their environment are more likely to survive,
reproduce, and pass on their traits to their offspring
 Fitness—an individual’s ability to successfully grow
to maturity and have offspring
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Darwin’s Observations
 Darwin made four important observations:
 Animals were changing over time
 Aspects of species that seem different on the surface, such as a
human hand, a bat’s wing, and a cat’s paw, had structural
similarities underneath
 Selective breeding of captive animals leads to changes in the
appearance of the animal
 Not all animals that are born will survive to maturity and be
able to reproduce
 Survival of the fit enough—As the environment changes the
organisms that successfully live in that environment will also
change, and these changes will be passed on to their offspring
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Different but Similar: Comparative Anatomy
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Evolution of the Brain
 Encephalization factor (EF)—ratio of brain weight to
body weight
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Humans: 7.4–7.8
Mice: 0.5
Elephant: 1.13–2.36
 Size of neocortex is most important
 80% of human brain is neocortex
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Skull Size
 The Australopithecus skull
on the left is about 1/3 the
size of the present-day
human skull on the right.
 It has a much smaller frontal
area, which leads to the
assumption that the frontal
cortex in the
Australopithecus was also
smaller.
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The Evolution of Behaviour
 Behaviours that influence the likelihood of
reproductive success and survival
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Mate Choice
Males prefer younger women who have a greater likelihood of
being able to become pregnant and carry to term viable offspring
 Females prefer males with resources
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Parental Investment
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In order for human offspring to survive and eventually reproduce,
parents spend an enormous amount of time caring for their young
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Brain Side and Brain Size
 Both sides of the brain are involved in everything we do due to
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corpus callosum; the two hemispheres are more similar than
they are different
The left brain can accomplish what the right brain can do, it’s
just less efficient at some tasks and more efficient at others
Split-brain studies show hemispheric localization of some
perceptual and cognitive functions, but these patients show
very few problems in daily life
There is no relationship between brain size and IQ for normal
individuals
Gender differences in brain structure are VERY small and do
not predict much
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Neurological Diseases
 Neurological diseases—structural, biochemical, or electrical
circuit abnormalities of the brain, spinal cord, and nerves
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Multiple sclerosis—loss of myelin on the axons resulting in poor
motor skills, poor sensory capabilities, and pain
Amyotrophic lateral sclerosis (ALS or Lou Gehrig’s disease)—
degeneration of motor neurons in the spinal cord, leading to loss of
movement and eventual death
Parkinson’s disease—dopaminergic neurons die, causing tremors
and muscle rigidity
Huntington’s disease—neurons in the striatum die, which causes
awkward movements and symptoms of psychosis
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Stem Cells
 Some of these disorders may
respond to stem cell
transplants
 Stem Cell—undifferentiated
cell that can divide to replace
itself and create new cells that
have the potential to become
all other cells of the body,
including neurons
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