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Chapter 3
The Biological basis of Behavior
Communication in the Nervous
System
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Hardware:
– Glia – structural support and insulation
– Neurons – communication
– Soma – cell body
– Dendrites – receive
– Axon – transmit away
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Myelin sheath – speeds up
transmission
Terminal Button – end of axon;
secretes neurotransmitters
Neurotransmitters – chemical
messengers
Synapse – point at which neurons
interconnect
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The Neural Impulse: Electrochemical
Beginnings
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Hodgkin & Huxley (1952) - giant squid
– Fluids inside and outside neuron
– Electrically charged particles (ions)
– Neuron at rest – negative charge on inside
compared to outside
– -70 millivolts – resting potential
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The Neural Impulse: The Action
Potential
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Stimulation causes cell membrane to open briefly
Positively charged sodium ions flow in
Shift in electrical charge travels along neuron
The Action Potential
All – or – none law
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Neural Impluse
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Synaptic cleft
Presynaptic neuron
– Synaptic vesicles
– Neurotransmitters
Postsynaptic neuron
– Receptor sites
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When a Neurotransmitter Binds: The
Postsynaptic Potential
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Voltage change at receptor site – postsynaptic
potential (PSP)
– Not all-or-none
– Changes the probability of the postsynaptic neuron firing
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Positive voltage shift – excitatory PSP
Negative voltage shift – inhibitory PSP
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Overview of synaptic transmission
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Signals: From Postsynaptic Potentials
to Neural Networks
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One neuron, signals from thousands of other neurons
Requires integration of signals
– PSPs add up, balance out
– Balance between IPSPs and EPSPs
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Neural networks
– Patterns of neural activity
– Interconnected neurons that fire together or sequentially
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Synaptic connections
– Elimination and creation
– Synaptic pruning
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Neurotransmitters
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Specific neurotransmitters work at specific synapses
– Lock and key mechanism
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Agonist – mimics neurotransmitter action
Antagonist – opposes action of a neurotransmitter
15 – 20 neurotransmitters known at present
Interactions between neurotransmitter circuits
Botox – Ach blocker
Dopamine – substantia nigra – Parkinson disease
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Organization of the Nervous System
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Central nervous system (CNS) – brain and spinal cord
– Afferent = toward the CNS/ Efferent = away from the CNS
Peripheral nervous system – nerves that lie outside the
central nervous system
– Somatic nervous system– voluntary muscles and sensory
receptors
– Autonomic nervous system (ANS) – controls automatic,
involuntary functions
• Sympathetic – Go (fight-or-flight)
• Parasympathetic – Stop
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Figure 3.6 Organization of the human nervous system
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Figure 3.7 – Peripheral Nervous
System – Somatic and Autonomic
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Cranial Nerves
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The Cranial Nerves and Their Function
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1 – Olfactory - smell S
2 – Optic – vision S
3 – Occulomotor – eye movements, control of pupil and lens, tears MP
4 – Trochlear - eye movements M
5 – Trigeminal – facial sensations, chewing SM
6 – Abducens - eye movements M
7 – Facial – facial muscles, salivary glands, taste SMP
8 – Auditory – acoustic branch: audition S verstibular branch: balance S
9 – Glossopharynegeal – throat muscles, salivary glands, taste SMP
10 – Vagus – parasympathetic control of internal organs, sensation from internal
organs, taste SMP
11 – Spinal accessory – head and neck muscles M
12 – Hypoglossal – tongue and neck muscles M
S, sensory; M, motor; P, parasympatheic function
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Studying the Brain: Research
Methods
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Electroencephalography (EEG) –
Damage studies/lesioning
Electrical stimulation (ESB) –
Transcranial Magnetic Stimulation (TMS) –
Brain imaging –
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computerized tomography – CT –
positron emission tomography - PET –
magnetic resonance imaging – MRI –
functional magnetic resonance imaging – fMRI –
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Electroencephalography (EEG)
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PET scan
MRI and fMRI scans
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Positron Emission Tomography –
PET scan
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Magnetic Resonance Imaging - MRI
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Functional MRI images showing reduced
activation of language areas during a
linguistic task in patients with schizophrenia
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Functional MRI images
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Brain Regions and Functions
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Hindbrain – vital functions – medulla, pons, and
cerebellum
Midbrain – sensory functions – dopaminergic
projections, reticular activating system
Forebrain – emotion, complex thought – thalamus,
hypothalamus, limbic system, cerebrum, cerebral
cortex
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The Cerebrum: Two Hemispheres,
Four Lobes
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Cerebral Hemispheres – two specialized halves connected by
the corpus collosum –
– Left hemisphere – verbal processing: language, speech, reading,
writing, sequential
– Right hemisphere – nonverbal processing: spatial, musical, visual
recognition, parallel
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Four Lobes: –
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Occipital – vision
Parietal – somatosensory – phantom limb –
Temporal - auditory
Frontal – movement, executive control systems –
Primary functions and associated functions
– Language – Broca’s and Wernicke’s areas – loss of language –
aphasia –
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The cerebral cortex in humans
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Primary motor cortex with homunculus
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Mirror Neurons
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An area just forward of the primary motor cortex is
where “mirror neurons” were first discovered
accidentally in the mid-1990s.
– May play a role in the acquisition of new motor skills,
• the imitation of others,
• the ability to feel empathy for others,
• and dysfunctions in mirror neuron circuits may underlie the
social deficits seen in autistic disorders.
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The Plasticity of the Brain
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The brain is more “plastic” or malleable than widely
assumed
– Aspects of experience can sculpt features of brain structure
– Damage to incoming sensory pathways or tissue can lead
to neural reorganization
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Adult brain can generate new neurons –
neurogenesis
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Visual input with split-brain – Roger Sperry and others
Split-brain research
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The Endocrine System: Glands and
Hormones
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Hormones – chemical messengers in the
bloodstream
– Pulsatile release by endocrine glands
– Negative feedback system
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Endocrine glands
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Pituitary – “master gland,” growth hormone
Thyroid - metabolic rate
Adrenal - salt and carbohydrate metabolism
Pancreas - sugar metabolism
Gonads - sex hormones
Use of steroids
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The endocrine system
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Genes and Behavior: The
Interdisciplinary Field of Behavioral
Genetics
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Behavioral genetics = the study of the influence of
genetic factors on behavioral traits
Basic terminology:
Chromosomes – strands of DNA carrying genetic
information
– Human cells contain 46 chromosomes in pairs (sex-cells –
23 single)
– Each chromosome – thousands of genes, also in pairs
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Dominant, recessive
Homozygous, heterozygous
Genotype/Phenotype and Polygenic Inheritance
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Research Methods in Behavioral
Genetics
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Family studies – does it run in the family?
Twin studies – compare resemblance of identical
(monozygotic) and fraternal (dizygotic) twins on a
trait
Adoption studies – examine resemblance between
adopted children and their biological and adoptive
parents
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Modern Approaches to the Nature vs.
Nurture Debate
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Molecular Genetics = the study of the
biochemical bases of genetic inheritance
– Genetic mapping – locating specific genes - The
Human Genome Project
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Behavioral Genetics
– The interactionist model
– Richard Rose (1995) – “We inherit dispositions, not
destinies.”
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Evolutionary Psychology: Behavior in
Terms of Adaptive Significance
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Based on Darwin’s ideas of natural selection
– Reproductive success key
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Adaptations – behavioral as well as physical
– Fight-or-flight response
– Taste preferences
– Parental investment and mating
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Parental Investment and Mating
Systems - sociobiology
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Polygyny – high female, low male – based on a study by
Buss (1994) found in 84 % of human cultures
Polyandry – high male, low female – rare but examples have
been found for example in the Pahari of Nepal and India,
and Tibet and other limited places in the world. The system
in Tibet was based on class and land considerations.
http://www.case.edu/affil/tibet/booksAndPapers/pahari.html
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Monogamy – shared parental investment but not always
equal. There are few exclusively monogamous species – 15
% of human cultures (Buss, 1994)
Polygynadry – group parental investment and very rare – in
chimpanzees mating is promiscuous for males and females
Incest – universal taboo – increased genetic diversity
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– brain
asymmetry and
speech
localization –
use of Wadi
technique and
TMS
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