Transcript No Slide Title

Chapter 2
Biological Basis of Behaavior
The Nervous System
• Nervous System: transmits messages
throughout the body
• Neuron: specialized cell
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–
basic (smallest) unit of the nervous system
it transmits messages
• Glial cells: provide “support” for neurons
–
form the myelin sheath, remove waste products
Parts of the Neuron
dendrites
soma (cell body)
axon
myelin sheath
nodes of Ranvier
axon
terminal
Parts of the Neuron
• Soma (cell body): cell metabolism
• Dendrites: short fibers on cell body,
receive “incoming” chemical messages
• Axon: single fiber extending from cell
body, carries “outgoing” chemical
message
• Axon Terminal: the end of the axon
• Nerve (tract): group or bundle of axons
Parts of the Neuron
• Myelin Sheath: white fatty covering on
longer axons
–
–
–
composed of Glial cells
“insulates”the axon
helps messages travel further and faster
• Nodes of Ranvier: points where myelin
sheath is “pinched” together
3 Types of Neurons
• sensory (afferent) neurons: carry
messages from sense organs to spinal
cord and brain
• interneurons (association neurons):
carry messages from one neuron to
another
• motor (efferent) neurons: carry
messages from spinal cord or brain to
muscles
Communication Within a Neuron
The Action Potential
The Action Potential
• Action Potential: an “electrical”
message that travels down the axon
causing release of chemicals from axon
terminal (neuron “fires”)
• Ions: charged particles that move in
and out of the axon
–
–
sodium “NA” + is most important
also Potassium “K” + and Chloride “CL” --
Action Potential
Membrane Potential
threshold of excitation
absolute refractory period
relative refractory period
resting
potential
Time (msec)
1. Resting State
• neuron is at rest: more “NA” + is
outside than inside axon
• neuron is “polarized”: difference in
electrical potential between inside and
outside of axon is -- 70 millivolts
+ + + + + + + + + +
soma
+
+
+
+ + + + + + + + + +
terminal
2. Depolarization
•
depolarization: dendrites are chemically
stimulated
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channels open, positive NA + ions enter axon
difference in potential reaches, then exceeds 0 mv
message travels down the axon
+
soma
++++ + +
+
+
+
+ +
+
+
+
+ +
terminal
+ +
3. Neuron fires
• Neuron fires: only if “threshold of
excitation” (firing threshold) is reached
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–
–
now more “NA” + inside than outside the axon
charge inside is (+ 40 mv) relative to outside
signal reaches axon terminal
+
soma
+
+
+ + + + + + ++ + +
+
+
+
terminal
Neuron May Fail to Fire
• threshold of excitation: (firing threshold)
level of “depolarization” that must be
reached for neuron to fire
• graded potential: stimulation of dendrites
was too weak to reach threshold and neuron
fails to fire (depolarization just “fades away”)
+
soma
+
+
+
+
+
+
+
terminal
+
+
+
4. Neuron resets
• return to resting state:
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positive ions now flow back out of axon
as before, more “NA” + is outside than inside
axon
difference in electrical potential between inside
and outside of axon is again - 70 millivolts
+ + + + + + + + + +
soma
+
+
+
+ + + + + + + + + +
terminal
4. Neuron resets (cont.)
• absolute refractory period: right after
firing, neuron will not fire again no
matter how strong the incoming
message
• relative refractory period: after
partially “resetting,”neuron will fire
again but only if the incoming message
is unusually strong
Other facts about the Action Potential
• The entire process has taken only a few
milliseconds!
• All or None Law: strength of the action
potential does not vary. The neuron
either fires or it doesn’t.
• The “Rate of firing” is really what
changes. The neuron is never really
“at rest”
Communication Between Two
Neurons
Synaptic Transmission
A “Chemical” Process
synapse
axon terminal
synaptic vesicle
neurotransmitter
receptor site
on dendrite
The Synapse
• Synapse has three parts:
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1. axon terminal of first neuron
2. synaptic “cleft” or “space”
3. receptor site on dendrite of second neuron
• Neurotransmitters: chemicals released
from the axon terminal
• Synaptic Vescicles: sacs in the axon
terminal that contain neurotransmitter
1. Release
• Action potential reaches axon terminal
of neuron #1
• Vescicles open and release
neurotransmitter in to synaptic space
• neurotransmitter crosses synaptic space
2. Communication
• Neurotransmitter attaches to receptor
site and “stimulates” neuron #2
• Each specific neurotransmitter and its
receptor site fit like a “Lock and Key”
Serotonin molecule -- Will fit >
Dopamine molecule -- Won’t fit >
Serotonin
Receptor site
3. Inactivation
• Neurotransmitter releases from
receptor site, moves back into synaptic
space, and is either:
–
–
1. taken back up into axon #1 terminal for reuse OR
2. “broken down” into basic components and
carried away for disposal
Neurotransmitters can speed
OR slow rate of firing
Excitatory Neurotransmitters:
“increase”firing rate in the neuron they
attach to
Inhibitory Neurotransmitters:
“decrease” firing rate in the neuron
they attach to
(see Summary Table in book)
Neurotransmitters
How Drugs Work
• Acetylcholine (Ach) is an excitatory
neurotransmitter at muscle synapses
• Botulism: prevents Ach release, result is
paralysis
• Black Widow Venom: causes excess Ach
release, result is shaking/tremors
• Curare: blocks (occupies) Ach receptros,
result is paralysis
• LSD visual hallucinations may be due to
blocking of serotonin receptors
Experience and Plasticity
Mark Rosenzweig’s Experiment
• Two groups of rats
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one raised in a boring unstimulating
environment
one raised in a complex stimulating
environment
• The second group had larger neurons
with more synapses
• Plasticity: extent to which the brain will
change in response to experience
The Nervous System
Nervous
System
Central
Nervous
System
Brain
Peripheral
Nervous
System
Spinal
Cord
Somatic
Nervous
System
Autonomic
Nervous
System
Sensory
Neurons
Sympathetic
Nervous
System
Motor
Neurons
Parasympathetic
Nervous System
Central Nervous System (2 parts)
• 1. Brain: has 3 divisions. . . . later
• 2. Spinal Cord: large bundle of
“nerves” which connects the rest of the
body to the brain
Cross-section of
spinal cord, with
numerous nerves
(tracts)
Peripheral Nervous System
• Autonomic Division: carries messages
between the internal organs and CNS
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Sympathetic: arouses, prepares body for “fight or
flight”
Parasympathetic: relaxes body
• Somatic Division: carries messages
between sense organs/muscles and CNS
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messages from CNS to muscles
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“reflex arc” - example of a complete circuit
The Reflexe Arc
The Reflex Arc
• involves 3 neurons
• 1. Afferent (sensory) neuron: carries
sensory information from body to spinal
cord (hit with hammer)
• 2. Efferent (motor) neuron: carries motor
information from spinal cord to muscles
(move leg)
• 3. Association (inter) neuron: connects
the two other neurons
Cross-section of the Brain
Forebrain
Cerebral cortex
Thalamus
Hypothalamus
Midbrain
Hindbrain
Cerebellum
Pons
Medulla
1. Hindbrain (Brainstem)
• The “oldest” part of the brain (3 parts)
• 1. medulla: controls “automatic” functions
such as breathing, heart rate, blood pressure,
ALSO place where many axons “cross
over” from right to left
• 2. pons: links cerebellum to motor areas of
brain and to muscles of body
• 3. cerebellum: balance and movement
Reticular Formation
• Also located in the brainstem, the
reticular formation plays an important
role in controlling alertness and the
“sleep-wake cycle”
2. Midbrain
• A large “relay station”
• Many synapses are located here
• Visual and Auditory information is
relayed here
Limbic System
Group (ring) of structures surrounding the midbrain
1. Amygdala - Self preservation (fear and aggression)
2. Hippocampus - Formation of new memories
3. Forebrain (3 basic parts)
• 1. thalamus: “a relay station” for visual
and auditory sensory information
• 2. hypothalamus: controls “motivated
behaviors”: thirst, hunger, and sexual
behavior
• 3. cerebral cortex: see next slide
Forebrain (cont.)
• 3. Cerebral Cortex: “newest” part of the
brain, consists of TWO hemispheres,
right and left
• Corpus Callossum: bundle of axons
connecting right and left hemispheres
• Convolutions: folds and creases that allow
the cortex to fit in the skull
Lobes of the Brain
• Each hemisphere is divided into four
“lobes”
• 1. Occipital Lobes: interprets visual
information
• 2. Parietal Lobes: sense of touch
(primary somatosensory cortex)
Lobes of the Brain (cont.)
• 3. Temporal Lobes: process auditory
information
• 4. Frontal Lobes: higher mental
processes
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language, personality, problem solving, etc.
motor projection areas control muscles
Hemispheric Specialization
Right and left hemispheres are involved
in specific functions
Left Hemisphere
• right hand touch
• right visual field
• language
• logic / math
Right Hemisphere
• left hand touch
• left visual field
• spatial ability
• art
• fantasy
Path to Occipital Lobe
Split Brain Patients
• In 1950s, cutting the Corpus Callosum
reduced siezures in cases of severe
epilepsy
• This severs the connection between
right and left hemispheres
• Sperry and Gazzaniga discovered some
unusual consequences
Split Brain Research
• Right visual field: what is to the right
of the person
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is directed to left hemisphere
• Left visual field: what is to the left of
the person
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is directed to right hemisphere
• This “crossing over” from right to left
takes place at the “optic chiasm”
Split Brain Research
• Right hand touch: what is felt with the
right hand
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is directed to left hemisphere
• Left hand touch: what is felt with the left
hand
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is directed to right hemisphere
• Remember, language is on the left so the
image stored in the right brain cannot be
verbally identified (if corpus calossum is cut)
Split Brain Research
can pick out hammer with left hand
can’t pick out hammer with right hand
Split Brain Research
can pick out ball with right hand
can’t pick out ball with left hand
Tools for Studying the
Nervous System
• microelectrode recording: a needlelike probe records the functioning of a
single neuron
• macroelectrode recording (eeg):
sensors on scalp measure overall brain
activity
Studying Brain Structure
• Computerized Axial Tomography:
(CAT scan) a computer combines
multiple x ray images forming a 3-D
image
• Magnetic Resonance Imaging: (MRI)
brain is exposed to radio waves in a
magnetic field, release of energy from
cells forms a computer image
Studying Brain Function
• Positron Emission Tomography: (PET
scan) active areas absorb more of a
radioactive substance, release of
particles shows which areas were more
active (e.g., while speaking)
• Magnetoencephalography: (MEG)
records magnetic energy given off by
brain areas which are active
The Endocrine System
• works closely with the nervous system
• glands: produce and release hormones
(e.g., adrenal gland)
• hormones: like neurotransmitters but
travel through the bloodstream (e.g.,
adrenaline)
Behavior Genetics and Heredity
Nature-Nurture Debate: is behavior
determined by genes or experience?
Behavior Genetics: studies how genes
combine with experience to produce
behavior
Terminology of Genetics
• traits: characteristics (e.g., eye color,
personality)
• heredity: transmission of traits from
one generation to the next
• deoxyribonucleic acid (DNA): complex
molecules, building blocks for genes
Genes and Chromosomes
• gene: a chain of DNA molecules that
control a trait
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long chains of genes make up the chromosomes
• chromosomes: pairs of twisting
threadlike structures,
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human cells have 23 pair (except sperm and
ovum which have only 23)
a chromosome looks like a twisting ladder
Laws of Inheritance
• Gregor Mendel: Austrian Monk who
discovered laws of dominant and
recessive inheritance in 1800s
Genes and Inheritance
• Genes come in pairs “alleles” (one
from mom and one from dad)
• Homozygous pair: mom and dad have
contributed identical genes (e.g., eye
color Brown + Brown)
• Heterozygous pair: mom and dad have
contributed different genes (e.g., eye
color Brown + blue)
Genotype vs. Phenotype
• Genotype: underlying genetic code for
a trait (a person does not have blue
eyes but does carry the gene for them)
• Phenotype: actual outward appearance
of a trait (a person has blue eyes)
Dominant and Recessive Genes
• For some traits, one gene “B” is dominant
over the other “b”
• Dominant: trait will usually appear in the
phenotype
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B + B = Brown eyes
B + b = Brown eyes (carries b trait)*
• Recessive: trait will appear in phenotype
ONLY if mom and dad both contributed the
recessive gene
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b + b = blue eyes
Studying Genetics in Animals
• strain studies: “Strains” are almost
identical genetically. If two different
strains are raised in identical environments,
then behavioral differences point to
“genetics”
• selection studies: If a trait is genetic,
breeding animals with a specific trait
should produce many offspring with that
trait
Studying Genetics in Humans
• family studies: If genes influence a
trait, closer relatives should be more
similar on that trait than distant
relatives.
• twin studies: If a trait is genetic,
identical twins (share 100% of genes)
should be more similar on the trait than
fraternal twins (share 50% of genes).
Studying Genetics in Humans
• Adoption Studies:
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If trait is genetic, adopted children
should be more similar to biological
parents
If trait is “learned,” adopted children
should be more similar to adoptive
parents