心理学与生活-第24节

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according　to　the　magnitude　of　the　stimulation。　One　graded　potential　is　
often　not　enough　to　cause　a　neuron　to　fire　

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d）　Temporal　Summation　involves　several　excitatory　or　inhibitory　inputs　from　
the　same　source　over　time　

e）　Spatial　Summation　involves　several　excitatory　or　inhibitory　inputs　from　
different　sources　at　the　same　time　

2。　The　Biochemical　Basis　of　Action　Potentials　
a）　An　Action　Potential　begins　when　excitatory　inputs　are　strong　enough　to　
overe　inhibitory　inputs　and　involves　depolarization　of　the　neuron　by　
sodium　ions　rushing　into　the　cell　

b）　Resting　Potential　is　the　slightly　negative　voltage　of　a　neuron　in　a　resting　
state　

c）　Ion　Channels　in　neuron　membranes　respond　to　changes　in　excitatory　and　
inhibitory　input。　Excitatory　input　causes　the　ion　channels　to　allow　sodium　
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　
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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　
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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　identified　this　
deficit　in　his　observations　of　patients　who　had　been　injured　in　the　area　of　the　brain　known　today　as　the　left　
frontal　lobe。　Although　Broca　was　unable　to　cond