Download Chapter 3: The Biological Bases of Behavior

Chapter 3: The
Biological Bases of
Behavior
 Central
(CNS)
nervous system
◦ Brain and spinal cord
 Peripheral
(PNS)
nervous system
◦ Carries messages to and from
CNS
Parts of the Nervous System

Afferent neurons (Sensory),
 relay information from the senses to the brain
and spinal cord.
▪ Eyes, ears, nose, mouth, and skin

Efferent neurons (motor),
 send information from the central nervous
system to the glands and muscles,
▪ enables the body to move.

Interneurons
 carry information between neurons
▪ in the brain
▪ in the spinal cord
Types of Neurons
Copyright © Allyn & Bacon 2006
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Structures of a neuron
The cell body
Contains the cell’s Nucleus
◦ Round, centrally located
structure
◦ Contains DNA
◦ Controls protein
manufacturing
◦ Directs metabolism
◦ No role in neural
signaling
Dendrites




Information
collectors
Receive inputs
from neighboring
neurons
Inputs may
number in
thousands
If enough inputs
the cell’s AXON
may generate an
output
Dendritic Growth
Mature neurons
generally can’t
divide
 But new
dendrites can
grow
 Provides room
for more
connections to
other neurons
 New connections
are basis for
learning

Axon
The cell’s output
structure
 One axon per cell, 2
distinct parts

◦ tubelike structure
branches at end that
connect to dendrites
of other cells
Myelin sheath
White fatty
casing on axon
 Acts as an
electrical insulator
 Not present on all
cells
 When present
increases the
speed of neural
signals down the
axon.

Myelin Sheath

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
The Neuron at Rest
Neurons communicate by means of an
electrical signal called the Action Potential
 Action Potentials are based on movements
of ions between the outside and inside of
the cell
 When an Action Potential occurs a
molecular message is sent to neighboring
neurons

How neurons communicate





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
The Action Potential
Figure 3.2 The neural impulse
Neuron to Neuron




Axons branch out
and end near
dendrites of
neighboring cells
Axon terminals are
the tips of the
axon’s branches
A gap separates
the axon terminals
from dendrites
Gap is the Synapse
Dendrite
Axon
Cell
Body
Synapse

axon terminals
contain small
storage sacs
called synaptic
vesicles
vesicles contain
neurotransmitter
molecules
Sending
Neuron
Axon
Terminal
Synapse
Neurotransmitter Release

Action Potential causes vesicle to
open
 Neurotransmitter released into
synapse
 Locks onto receptor molecule in
postsynaptic membrane
Figure 3.3 The synapse
Figure 3.4 Overview of synaptic transmission
Locks and Keys

Neurotransmitter
molecules have specific
shapes
 Receptor molecules have
binding sites
 When NT binds to
receptor, ions enter
positive ions (NA+ )
depolarize the neuron
negative ions (CL-)
hyperpolarize
Some Drugs work on receptors


Some drugs are
shaped like
neurotransmitters
Antagonists : fit the
receptor but poorly
and block the NT
 e.g. beta blockers
 Agonists : fit
receptor well and
act like the NT
e.g. nicotine.
When a Neurotransmitter Binds:
The Postsynaptic Potential

Voltage change at receptor site –
postsynaptic potential (PSP)
◦ Not all-or-none
◦ Changes the probability of the postsynaptic
neuron firing
Positive voltage shift – excitatory PSP
 Negative voltage shift – inhibitory PSP

Neurotransmitters and Behavior

Specific neurotransmitters work at
specific synapses
 Lock and key mechanism
Agonist – mimics neurotransmitter
action
 Antagonist – opposes action of a
neurotransmitter
 More than 40 neurotransmitters known
at present
 Interactions between neurotransmitter
circuits

Types of Neurotransmitters







Acetylcholine
Serotonin
Norepinephrine
Dopamine
Endorphins
GABA
Glutamate
Table 3.1 Common Neurotransmitters and Some of their Functions
Acetylcholine
Found in
neuromuscular
junction
 Involved in muscle
movements

Alzheimer’s Disease
Deterioration of
memory, reasoning
and language skills
 Symptoms may be
due to loss of ACh
neurons


http://www.youtube.com/
watch?v=q1BkfV2h09g
Serotonin
Involved in sleep
 Involved in depression

◦ Prozac works by keeping serotonin in the
synapse longer, giving it more time to exert
an effect
Also involved in Obsessive Compulsive
Disorder:
◦ http://www.youtube.com/watch?v=vnKZ4pdSU-s
Norepinephrine
 Arousal
 “Fight
or flight” response
Dopamine
Involved in movement, attention and
learning
 Dopamine imbalance also involved in
schizophrenia
 Loss of dopamine- producing neurons is
cause of Parkinson’s Disease
 http://www.youtube.com/watch?v=ECkP
VTZlfP8

Endorphins
Control pain and
pleasure
 Released in response
to pain
 Morphine and
codeine work on
endorphin receptors
Involved in healing
effects of
acupuncture

Gamma-Aminobutyric Acid
(GABA)
Main inhibitory neurotransmitter
 Benzodiazepines (which include
tranquilizers such as Valium) and alcohol
work on GABA receptor complexes

Glutamate
Major excitatory neurotransmitter
 Too much glutamate (and too little GABA)
associated with epileptic seizures

Integrating Signals
One neuron, signals from thousands of
other neurons
 Neural networks

 Patterns of neural activity
 Interconnected neurons that fire together
or sequentially

Synaptic connections
 Elimination and creation
 Synaptic pruning
Communication in the Nervous System
Glia – structural support and insulation
 Neurons – communication

◦
◦
◦
◦
◦
Soma – cell body
Dendrites – receive
Axon – transmit away
Myelin sheath – speeds up transmission
Terminal Button – end of axon; secretes
neurotransmitters
◦ Neurotransmitters – chemical messengers
Central Nervous System
Brain

Brain and Spinal Cord
Spinal
Cord
Central nervous
system
Peripheral
nervous system
Figure 3.5 Organization of the human nervous system
Sympathetic
CENTRAL NERVOUS SYSTEM SYMPATHETIC





“ Fight or flight” response
Release adrenaline and
noradrenaline
Increases heart rate and
blood pressure
Increases blood flow to
skeletal muscles
Inhibits digestive
functions
Brain
Dilates pupil
Stimulates salivation
Relaxes bronchi
Spinal
cord
Salivary
glands
Lungs
Accelerates heartbeat
Inhibits activity
Heart
Stomach
Pancreas
Stimulates glucose
Secretion of adrenaline,
nonadrenaline
Relaxes bladder
Sympathetic Stimulates ejaculation
ganglia
in male
Liver
Adrenal
gland
Kidney
Parasympathetic
CENTRAL NERVOUS SYSTEM PARASYMPATHETIC
Brain
“Rest and digest”
system
 Calms body to
conserve and
maintain energy
 Lowers heartbeat,
breathing rate,
blood pressure
Contracts pupil

Stimulates salivation
Spinal
cord
Constricts bronchi
Slows heartbeat
Stimulates activity
Stimulates gallbladder
Gallbladder
Contracts bladder
Stimulates erection
of sex organs
Summary of autonomic
differences
Autonomic nervous system controls physiological arousal
Sympathetic
division (arousing)
Pupils dilate
Decreases
Parasympathetic
division (calming)
EYES
Pupils contract
SALVATION
Increases
Perspires
SKIN
Dries
Increases
RESPERATION
Decreases
Accelerates
HEART
Slows
Inhibits
DIGESTION
Activates
Secrete stress
hormones
ADRENAL
GLANDS
Decrease secretion
of stress hormones
Studying the Brain: Research Methods

Damage studies/lesioning
Studying the Brain: Research Methods
 Brain imaging –
 computerized tomography
 positron emission tomography
 magnetic resonance imaging:
 Transcranial magnetic stimulation
(TMS)
Brain has 2 Hemispheres




Left & Right sides are
separate
Corpus Callosum : major
pathway between
hemispheres
Some functions are
‘lateralized’
◦ language on left
◦ math, music on right
Lateralization is never
100%
Corpus Callosum
Right
Hemisphere
Left
Hemisphere
Figure 3.14 The cerebral hemispheres and the corpus callosum
Each hemisphere is
divided into 4 lobes
Frontal
Parietal
Occipital
Temporal
The Cerebrum:
The Seat of Complex Thought

Four Lobes:




Occipital – vision
Parietal - somatosensory
Temporal - auditory
Frontal – movement, executive control
systems
•Cerebrum Continued
•Cerebral Cortex
•Higher mental processes of
language, memory, and thinking.
•Left Cerebral Cortex
•Frontal lobe
•Motor cortex
•Broca’s Area
•Parietal lobe
•Somatosensory cortex
•Occipital lobe
•Visual cortex
•Temporal lobe
•Auditory Cortex
•Wernicke’s area
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Copyright © Allyn & Bacon 2006
Broca’s Area: speech production
http://www.youtube.com/watch?
v=KpkH25XVpFU
Wernicke’s area: speech comprehension
Figure 3.16 Language processing in the brain
Brain Regions and Functions



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
Figure 3.12 Structures and areas in the human brain
Figure 3.15 The cerebral cortex in humans
The Limbic System
Hypothalamus
 Amygdala
 Hippocampus

Hypothalamus

Contains nuclei involved in a variety of
behaviors
The four f’s. Feeding, fleeing, fighting,
and…mating.
◦ sexual behavior
◦ hunger, thirst
◦ sleep
◦ water and salt balance
◦ body temperature regulation
◦ circadian rhythms
◦ role in hormone secretion
Hypothalamus and Hormones

Hypothalamus releases
hormones or releasing
factors which in turn cause
pituitary gland to release
its hormones
This is a slower
communication process
than the chemical
communication that occurs
between neurons.
Amygdala

Inputs come from all
senses

Amygdala ‘reads’
emotional significance of
inputs

Output influences such
functions as heart rate,
adrenaline release
Hippocampus

Important in
forming new
memories
Thalamus



Relay station in brain
Sensory and motor
information get processed
here, then sent to the
higher brain centers
Processes most
information to and from
higher brain centers
Hindbrain Structures
Cerebellum
 Brainstem

◦ medulla
◦ reticular formation
◦ pons
The Endocrine System:
Another Way to Communicate
Hormones – chemical messengers in the
bloodstream
 Endocrine glands






Pituitary – “master gland,” growth hormone
Thyroid – metabolic rate
Adrenal – salt and carbohydrate metabolism
Pancreas – sugar metabolism
Gonads – sex hormones
Endocrine System

Pituitary gland—attached to the base of
the brain, hormones affect the function of
other glands
Adrenal glands—hormones involved in
human stress response
 Gonads—hormones regulate sexual
characteristics and reproductive
processes; testes in males, ovaries in
females

Copyright © Allyn & Bacon 2006
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Genes and Behavioral Genetics

Genes: – segments of DNA on chromosomes transmit heredity
traits





Chromosomes – rod shaped and contain all genes that carry
genetic information to make a human being.
Dominant-recessive pattern – a set of inheritance rules for
genes
◦ One dominant gene or two recessive genes required for a trait
to be expressed.
Multifactorial inheritance – an inheritance pattern in which
a trait is influenced by both genes and environmental factors.
Polygenic inheritance – many genes influence a particular
characteristic like skin color.
Sex linked inheritance – involves genes on the X and Y
chromosomes
◦ E.g. male or female body type and red-green color blindness

Behavioral Genetics – a field of research that uses twin and
adoption studies to investigate the relative effects of heredity and
environment
on behavior.
Copyright © Allyn
& Bacon 2006
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Basic Principles of Genetics

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

Polygenic traits
Research Methods in Behavioral
Genetics



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
Figure 3.19 Genetic relatedness
Figure 3.20 Twin studies of intelligence and personality
The Evolutionary Bases of Behavior

Based on Darwin’s ideas of natural
selection
 Reproductive success key

Adaptations – behavioral as well as
physical
The Evolutionary Bases of Behavior
 Adaptations – behavioral as well as physical
 Fight-or-flight response: helpful if a tiger is chasing you,
but chronic stress causes us problems
 Taste preferences: fatty foods pack on calories…but if
food is plentiful, this is no longer adaptive
 Parental investment and mating: increased survival in
offspring where there is more parental investment
“The effects of chronic social stress in juvenile hamsters
makes sense because if they were permanently fearful of
conspecifics, they would not be able to mate and have
offspring.”