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Textbook Notes – Week 3.pdf

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Ashley Waggoner Denton

PSY  100   Textbook  Notes  –  Week  3     Ch.  3:  pp.  81  –  124,  (biological  foundations)     GENOTYPE  AND  PHENOTYPE:     • Dominant  Genes  vs  Recessive  genes   o Dominant  genes  are  expressed  if  present  in  the  genome   o Recessive  genes  are  only  expressed  if  matched  by  the  same  recessive   gene  in  both  pairs  of  chromosomes   • Existence  of  dominant  and  recessive  genes  mean  that  not  all  genes  are   expressed   • Genotype:  the  genetic  constitution  determined  at  the  moment  of  conception   • Phenotype:  observable  physical  characteristics  that  result  from  both  genetic   and  environmental  influences   o Two  purple  flowers  share  phenotypes,  but  could  differ  in  genotype  –   one  could  have  purple  alleles  in  both  chromosome  pairs,  whereas  the   other  might  have  the  dominant  purple  allele  and  the  recessive  white   allele  but  both  would  express  purple  flower  petals   • Polygenic:  A  trait  determined  by  many  individual  genes,  rather  than  being   determined  by  just  one  single  gene     Genes  Affect  Behaviour     • Behavioural  Genetics:  the  study  of  how  genes  and  environment  interact  to   influence  psychological  activity     BEHAVIOURAL  GENETICS  METHODS:     • With  all  the  variation  that  occurs  with  siblings,  (different  genes,  different   prenatal  environments,  different  upbringings,  different  birth  orders,  etc),   behavioural  geneticists  use  two  methods  to  assess  the  degree  to  which  traits   are  inherited:  twin  studies  and  adoption  studies   o Twin  studies:  compare  similarities  between  different  types  of  twins  to   determine  the  genetic  basis  of  specific  traits.    Monozygotic  twins:  twin  siblings  who  result  from  on  zygote   splitting  in  two  and  therefore  share  the  same  genes,  (identical   twins)    Dizygotic  twins:  twin  siblings  who  result  from  two  separately   fertilized  eggs,  (fraternal  twins)    Comparison  of  monozygotic  twins  who  have  been  raised   together  with  ones  who  were  raised  apart   • Identical  twins,  raised  together  or  not,  were  likely  to  be   similar   PSY  100   o Adoption  Studies:  compare  the  similarities  between  biological   relatives  and  adoptive  relatives.    The  assumption  is  that  similarities  among  nonbiological   adopted  siblings  have  more  to  do  with  environment  than  with   genes    Growing  up  in  the  same  home  turns  out  to  have  relatively  little   influence  on  many  traits,  such  as  personality    After  genetic  similarity  is  controlled  for,  even  biological   siblings  raised  in  the  same  home  are  no  more  similar  than  two   strangers  plucked  at  random  off  the  street     Social  and  Environmental  Contexts  Influence  Genetic  Expression     • Biology  and  environment  are  inextricably  entwined.  You  can  have  a  gene  that   predisposes  you  to  aggressive  behaviour,  but  the  aggressive  behaviour  may   only  present  itself  if  you  experience  abuse  in  your  environment   • As  a  result  of  genes  and  social  contexts  interact,  separating  their  independent   effects  can  be  very  difficult  –  some  argue  that  it  is  impossible     Genetic  Expression  Can  Be  Modified     • Researchers  can  employ  various  gene  manipulation  techniques  to  enhance  or   reduce  particular  genes’  expression  or  event  to  insert  genes  from  one  animal   species  into  embryos  of  another     HOW  DOES  THE  NERVOUS  SYSTEM  OPERATE     Neurons  Are  Specialized  for  Communication     • Neurons:  The  basic  unit  of  the  nervous  system;  it  operates  through  electrical   impulses,  which  communicate  with  other  neurons  through  chemical  signals.   Neurons  receive,  integrate,  and  transmit  information  in  the  nervous  system   • Sensory  Neurons:  One  of  the  three  types  of  neurons,  these  afferent  neurons   detect  information  from  the  physical  world  and  pass  that  information  along   to  the  brain,  via  the  spinal  cord.  AFFERENT  =  CARRYING  INFORMATION  TO   THE  BRAIN   • Motor  Neurons:  One  of  the  three  types  of  neurons,  these  efferent  neurons   direct  muscles  to  contract  or  relax,  thereby  producing  movement.  EFFERENT   =  CARRYING  INFORMATION  FROM  THE  BRAIN  TO  THE  MUSCLES   • Interneurons:  One  of  the  three  types  of  neurons,  these  neurons   communicate  only  with  other  neurons,  typically  within  a  specific  brain   region   • Complex  networks  of  thousands  of  neurons  sending  and  receiving  signals  are   the  functional  basis  of  all  psychological  activity   PSY  100   • Neurons  do  not  communicate  randomly;  they  selectively  communicate  with   other  neurons  to  form  circuits,  or  neural  networks.     • Neural  networks  develop  through  maturation  and  experience,  forming   permanent  alliances  among  groups  of  neurons     NEURON  STRUCTURE:     • Dendrites:  branchlike  extensions  of  the  neuron  that  detect  information  from   other  neurons   • Cell  Body:  In  the  neuron,  where  information  from  thousands  of  other   neurons  is  collected  and  processed   • Axon:  A  long  narrow  outgrowth  of  a  neuron  by  which  information  is   transmitted  to  other  neurons,  (nerve  is  a  bundle  of  axons)   • Terminal  Buttons:  Small  nodules,  at  the  ends  of  axons,  that  release  chemical   signals  from  the  neuron  to  the  synapse   • Synapse,  or  synaptic  cleft:  The  site  for  chemical  communication  between   neurons,  which  contains  extracellular  fluid   • Myelin  Sheath:  A  fatty  material,  made  up  of  glial  cells,  that  insulates  the   axon  and  allows  for  the  rapid  movement  of  electrical  impulses  along  the  axon   • Nodes  of  Ranvier:  Small  gaps  of  exposed  axon,  between  the  segments  of   myelin  sheath,  where  action  potentials  are  transmitted     When  a  neuron  is  resting,  the  inside  and  outside  differ  electrically,  a  phenomenon   referred  to  as  the  resting  membrane  potential.  The  ratio  of  negative  to  positive   ions  is  greater  inside  the  neuron  than  outside  it.  Electrical  charge  is  slightly  more   negative  inside  than  outside.  Changing  this  results  in  polarization,  which  creates  the   electrical  energy  to  fire  the  neuron.     The  two  ions  that  contribute  to  a  neuron’s  resting  membrane  potential  are  sodium   ions  and  potassium  ions   • Ions  pass  through  the  cell  membrane  at  ion  channels,  (specialized  pores   located  at  the  nodes  of  Ranvier),  each  channel  matches  a  specific  type  of  ion   • Flow  of  ions  through  each  channel  is  controlled  by  a  gating  mechanism,  when   a  gate  is  open,  ions  flow  in  and  out  of  the  cell  membrane;  a  closed  gate   prevents  their  passage   • Membrane  also  has  selective  permeability,  which  results  in  only  some  types   of  ions  being  able  to  permeate  the  membrane   o This  results  in  more  potassium  being  inside  the  neuron   • Sodium-­‐potassium  pump  works  to  increase  potassium  and  decrease  sodium   inside  the  neuron     Action  Potentials  Cause  Neural  Communication     • Action  Potential:  the  neural  impulse  that  passes  along  the  axon  and   subsequently  causes  the  release  of  chemicals  from  the  terminal  buttons   PSY  100   • Neuron  receives  chemical  signals  from  the  nearby  neurons  through  its   dendrites,  these  signals  tell  the  neuron  whether  to  fire   o Excitatory:    Depolarize  the  cell  membrane,  increasing  the  likelihood  that   the  neuron  will  fire    If  amount  of  excitatory  signals  surpasses  the  receiving  neurons   threshold,  an  action  potential  is  generated   o Inhibitory:    Hyperpolarize  the  cell,  decreasing  the  likelihood  that  the   neuron  will  fire   • Neuron  fires  >  sodium  gates  in  the  cell  membrane  open,  sodium  rushes  into   the  neuron  >  influx  of  sodium  causes  the  inside  of  the  neuron  to  become   slightly  more  positively  charged  than  the  outside  >  potassium  channels  open   to  allow  the  potassium  ions  inside  to  rush  out  of  the  cell  >  inside  cell  changes   from  negative  to  positive   • When  the  neuron  fires,  the  cell  membrane’s  depolarization  moves  along  the   axon  like  a  wave,  an  action  called  propagation   o Sodium  ion  channels  open  successively,  moving  adown  the  axon  away   from  the  cell  body  to  the  terminal  buttons   • A  neuron  either  fires  or  it  does  not;  it  cannot  partially  fire.   o All-­‐or-­‐none  principle:  The  principle  whereby  a  neuron  fires  with  the   same  potency  each  time,  although  frequency  can  vary;  it  either  fires  or   not  –  it  cannot  partially  fire     • Neurotransmitters:  A  chemical  substance  that  carries  signals  from  one   neuron  to  another,  contained  inside  the  terminal  buttons  in  things  called   vesicles   • Action  potentials  cause  neurons  to  release  chemicals  from  their  terminal   buttons.  These  chemicals  travel  across  the  synaptic  cleft  and  are  received  by   other  neurons’  dendrites.     • The  neuron  that  sends  the  signal  is  called  presynaptic  and  the  one  that   receives  the  signal  is  called  postsynaptic   • Neurotransmitters  then  spread  across  the  synaptic  cleft  and  attach   themselves,  or  bind,  to  receptors  on  the  postsynaptic  membrane   • Receptors:    In  neurons,  specialized  protein  molecules,  on  the  postsynaptic   membrane,  that  neurotransmitters  bind  to  after  passing  across  the  synaptic   cleft   • The  binding  of  a  neurotransmitter  with  a  receptor  produces  an  excitatory  or   inhibitory  signal  for  the  postsynaptic  neuron,  encouraging  or  discouraging   neural  firing   • Three  major  events  that  terminate  the  transmitters’  influence  in  the  synaptic   cleft  are:   o Reuptake:  the  process  whereby  a  neurotransmitter  is  taken  back  into   the  presynaptic  terminal  buttons,  thereby  stopping  its  activity   PSY  100   o Enzyme  Deactivation:  occurs  when  an  enzyme  destroys  the   transmitter  substance  in  the  synaptic  cleft   o Autoreception:  neurotransmitters  can  bind  with
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