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UNIT
2:
The Biology of Behavior
Structure of a (typical) Neuron
dendrites
soma
myelin
sheath
synapses
axon
terminal
buttons
The Neural Impulse
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Neural impulse – a brief electric surge that carries the
neuron’s message
All-or-None Law – like a gun, a neuron either fires or it
doesn’t, and it’s impulses are all the same size (a
weaker stimulus will not create a smaller impulse)
Synapse – when an impulse reaches its terminal
buttons, it triggers the release of chemical messengers
(neurotransmitters). The chemicals move across to be
received by the receiving cell (muscle, gland, or
another neuron)
David Suzuki - Neural Impulse & Synapses
Typical Synapse
Copyright © Allyn & Bacon 2007
Otto Lowei (1921)
“Vagusstoff”
(actually Acetylcholine)
Neurotransmitters
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Neurotransmitters –
Chemical messengers that relay neural messages across
the synapse
They can be excitatory (increase likelihood that
following neurons will fire) or inhibitory (decrease
likelihood that following neurons will fire)
They play a key role in everything from muscle
movements to moods and mental health
some 15-20 chemical substances act as
neurotransmitters, each one a specific size/shape to
bind with a particular location
Five Important Neurotransmitters
Dopamine
Serotonin
Norepinephrine
Acetylcholine
Endorphins
Neurotransmitters
Serotonin
Normal Function:
Regulates sleep and
dreaming, mood, pain,
aggression, appetite and
sexual behavior
Problems with Imbalance:
Depression, certain anxiety
disorders, obsessivecompulsive disorder
Substances that Affect:
Prozac, hallucinogenics
(e.g. LSD)
Neurotransmitters
Normal Function:
Norepinephrine
Controls heart rate, sleep,
sexual responsiveness,
stress, vigilance and
appetite
Problems with Imbalance:
High blood pressure,
depression
Substances that Affect:
Tricyclic antidepressants,
beta blockers
Neurotransmitters
Normal Function:
Dopamine
Produces sensations of
pleasure and reward; used
by CNS neurons in
voluntary movement
Problems with Imbalance:
Schizophrenia, Parkinson’s
disease
Substances that Affect:
Cocaine, amphetamines,
Ritalin, alcohol
COCAINE EFFECTS
Neurotransmitters
Acetylcholine
Normal Function:
Primary transmitter used by
neurons carrying messages
from CNS; involved in
some kinds of learning and
memory
Problems with Imbalance:
Certain muscular disorders,
Alzheimer’s disease
Substances that Affect:
Nicotine, botulism toxin,
curare, atropine
Neurotransmitters
Endorphins
Normal Function:
Pleasurable sensations and
control of pain
Problems with Imbalance:
Lowered levels resulting
from opiate addiction
Substances that Affect:
Opiates: opium, heroin,
morphine, methadone
Review
Nervous System Component

dendrite
Metaphor
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neuron
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axon
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
terminal button
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Like the insulation that covers electrical wires
myelin sheath
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like a tree. Also, each branch is a telephone
wire that carries incoming messages to you
synapse
Like a silicon chip in a computer which receives
and transmits information
Like an electrical cable that carries
information
Like the nozzle at the end of a hose, from
which water is squirted
Like a railroad junction, where two trains may
meet