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ions into the neuron； allowing the neuron to fire。 Inhibitory input causes
the ion channels to keep the neuron negatively charged； preventing the
neuron from firing。
d） The action potential then travels down the axon as adjacent areas of the
axon successively depolarize
e） When the fluid inside the neuron bees positive； the sodium ion
channels close and potassium ion channels open； allowing potassium
ions to exit the cell； restoring negative charge of the neuron。
f） Action potentials obey the All…or…None Law。 The size of the action potential
is not influenced by the intensity of stimulation beyond the threshold level。
g） After firing； neurons enter a Refractory Period； a period during which they
cannot fire or will only fire with more intense stimulation dm normal
C。 Synaptic Transmission
1。 Transmission of neural impulses between neurons involves the movement of
neurotransmitters across the synaptic cleft
a） A Synapse is a small physical gap between neurons
b） Once an action potential reaches an axon terminal button； vesicles release
neurotransmitters into the synaptic gap chemical substances that
stimulate other neurons。 The neurotransmitters then traverse across the
synaptic gap and attach to receptor molecules embedded in the
postsynaptic neuron membrane。
D。 Neurotransmitters and Their Functions
1。 At least 60 substances are suspected to function as neurotransmitters in the brain
2。 Acetylcholine； a neurotransmitter found in both the central and peripheral nervous
systems； is implicated in memory loss associated with Alzheimer’s disease and in
some types of respiratory failure
3。 Gamma…Amino Butyric Acid （GABA） is thought to be related to anxiety； as depressants
bind to receptor molecules sensitive to GABA and cause sedation
4。 Catecholamines such as dopamine and norepinephrine play prominent roles in mood
disturbances and schizophrenia
40
CHAPTER3： THE BIOLOGICAL BASES OF BEHAVIOR
a） Decreased levels of norepinephrine have been related to depression
b） Increased levels of dopamine have been related to schizophrenia
5。 Serotonin is involved in autonomic processes； arousal； and depression
6。 Endorphins are neuromodulators that modify the activities of postsynaptic neurons
and may play an important role in emotional behaviors
DISCUSSION QUESTIONS
1。 A fundamental； yet often overlooked； assumption of this chapter is that Darwin’s Theory of Natural
Selection accurately explains how humans reached our current stage of development。 Indeed； it has
bee so well accepted that few students will stop to wonder how this chapter would be different
if it were incorrect。 But what if it was wrong？ What other possible explanations could be put
forward to explain how we are and how we got this way？ Such questions lie at the heart of
religion； psychology； and what it means to be human。 Just over 100 years ago； Lamark’s theory of
acquired characteristics was relatively well accepted。 Five hundred years ago asking such
questions was blasphemous。 How may we look at human evolution； creation； or development
differently 100 years in the future？
2。 A second important question relating to natural selection is whether humans continue to evolve。
Fewer and fewer genes are being removed from the gene pool as environmental threats are
identified and eliminated。 Because fewer individuals succumb to environmental threats； most
humans are able to survive to reproductive maturity and perpetuate their genes。 What does this
successful elimination of environmental threats portend for the long…term survivability of our
species？
3。 A third related question is what es after natural selection after environmental threats are
eliminated and everyone reproduces？ What forces will shape the development of humans in the
absence of environmental threats？ Social Darwinism？ Cultural evolution？ Technological forces？
Eugenics？
4。 To what extent can individuals be held accountable for their biology？ Should an individual with a
tumor that causes extraordinarily high levels of testosterone to be released receive the same
sentence for a violent crime as someone without such a tumor？ What if the tumor caused a mental
disorder such as schizophrenia？ Could the insanity defense be used？
5。 Parents want what is best for their children。 They often go to such lengths as choosing homes near
good schools and sending their children to all sorts of musical； athletic； and academic lessons。
What if the need for all of these expensive lessons would be eliminated if the parents chose their
children’s genes wisely before the children were born？ What if your parents had selected your
genes so that you were better looking； smarter； more athletic； or more artistically inclined？ Would
such decisions be ethical？ Would you want to make them for your children？ Would you have
wanted your parents to make them for you？ Why or why not？
6。 With the advent of modern brain imaging and scanning technologies； the way in which “death” is
often determined has also changed。 Where as years ago death was determined by the cessation of
breathing and the lack of a pulse； now it is additionally determined by the lack of brain activity。
This has made the determination of when someone has actually died much more plicated in
many cases。 Cases are monly reported of people who have drowned or have been frozen； who
have not breathed for dozens of minutes and who have had no heartbeat when found； who were
revived； and sometimes have made plete recoveries。 On the other hand there are also tragic
41
PSYCHOLOGY AND LIFE
cases of people who have been injured in accidents who are breathing and have a pulse； but are
labeled “brain dead。” You might discuss what “brain death” means and explore both the medical
and moral issues related to these situations。
7。 Have students pick at least one task that they would normally do with their dominant hand； and
have them do it with the other hand。 Writing a short in…class assignment can be fun。 But you can
brainstorm and see what ideas they e up with。 Ask students to discuss what problems they
encountered while trying to do things with the opposite hand。
SUPPLEMENTAL LECTURE MATERIAL
Protecting the Brain
Although the bony skull usually does a good protective job； many brains are still injured in auto and
motorcycle accidents； sports； and even at the hands of parents。 Failure to wear seat belts； motorcycle or
bicycle helmets； or the right protective sports equipment can result in permanent damage to some of the
brain’s functioning。
“Many slow…learning and clumsy children with IQs in the 90s；” says pediatrician John Caffey； might have
been intelligent and normally mobile children with IQs of 120； had they not been habitually shaken and
whiplashed during infancy。” Overenthusiastic bouncing of a baby before its neck muscles are strong
enough to support the head may result in broken vessels that deprive the brain of blood and thus retard the
growth of parts of the brain。 Angry slaps on the head and neck can have similar negative consequences；
even for older children。
Drugs that alter brain functions can have permanent effects if taken in excess。 Some drugs； like the
chemicals in glue； when inhaled can lead to death or a lifetime of mental retardation。 Brains； especially
young ones； need lots of oxygen and good nutrition。 They are adversely affected by pollutants in the
environment； especially when children chew on flakes of paint that contain lead。
Although children sustain head trauma in various ways； the most mon source is from blows to the head
by an adult； followed by falls from bicycles。 Sadly； in a fall from a bicycle or motorcycle； the area of the brain
most likely to be traumatized is the frontal lobe； the area of the brain responsible for planning； organization；
and decision…making。
Aphasias： Frontal and Temporal Lobe Injuries
An aphasia； by definition； is difficulty in producing or prehending speech when that difficulty is not
produced by deafness or a simple motor deficit； but caused by brain damage。 Paul Broca first identif