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BSC 116 Notes Week 11- Lectures 31-33

by: Alexia Acebo

BSC 116 Notes Week 11- Lectures 31-33 BSC 116

Marketplace > University of Alabama - Tuscaloosa > Biology > BSC 116 > BSC 116 Notes Week 11 Lectures 31 33
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A collection of the eleventh week of notes from BSC 116 covering material from lectures 31-33!
Principles Biology II
Jennifer G. Howeth
Class Notes
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This 9 page Class Notes was uploaded by Alexia Acebo on Monday November 9, 2015. The Class Notes belongs to BSC 116 at University of Alabama - Tuscaloosa taught by Jennifer G. Howeth in Summer 2015. Since its upload, it has received 34 views. For similar materials see Principles Biology II in Biology at University of Alabama - Tuscaloosa.

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Date Created: 11/09/15
Lecture  31     •4  keys  stages  to  animal  development:   1.fertilization   2.cleavage   3.gastrulation   4.organogenesis     •fertilization:  union  of  sperm  and  egg   –n  +  n  =  2n   –best  studied  in  sea  urchins;  external  fertilization   •unfertilized  egg   –plasma  membrane  with  species-­‐specific  receptors   –vitelline  layer:  extracellular  matrix   –jelly  coat:  protects  egg  and  attracts  sperm     •contact  triggers  acrosomal  reaction   –acrosome:  vesicle  at  sperm  tip  with  hydrolytic  enzymes  break  down   jelly   –acrosomal  process:  structure  w/  proteins  that  bind  receptors  on  eggs   •matching  species-­specific  receptors  ensures  sperm  matches  egg   –fusion  of  plasma  membranes   –depolarization:  fusion  leads  to  change  in  membrane  potential   •fast  block  to  polyspermy     •fusion  also  initiates  cortical  reaction   –vesicles  in  cortex  (outer  part)  fuse  with  plasma  membrane   –contents  (enzymes,  etc.)  lead  to  fertilization  envelope  and  slow  block  to   polyspermy   •separate  vitelline  layer  from  plasma  membrane   •clips  off  sperm-­‐binding  receptors   •following  cortical  reaction,  the  egg  is  “activated”   –increased  respiration  &  protein  synthesis   –sperm  nucleus  fuses  with  egg  nucleus   –first  cell  division  after  90  minutes   •mammal  fertilization  basically  the  same,  except:   –internal  fertilization   –no  fast  block  to  polyspermy,  only  slow  block   –egg  completes  meiosis  II  after  fertilization   –first  cell  division  after  12-­‐36  hours   •cleavage:  earliest  divisions,  rapid   –cells  divide  by  mitosis,  but  don’t  grow  in  size   –blastomeres:  individual  (smaller),  cells   •blastula:  hollow  ball  of  cells  with  a  blastocoel   •relatively  simple  in  sea  urchins     •development  of  body  polarity  is  well-­‐studied  in  frogs   –because  parts  of  zygote  are  color-­‐coded;  easy  to  follow   •even  before  fertilization,  oocyte  not  just  an  unorganized  blob   –cytoplasmic  determinants:  proteins,  mRNA,  etc.  in  various  places   –yolk:  stored  nutrients   •two  poles  that  determine  first  divisions   –yolk  concentrated  toward  the  vegetal  pole   –opposite:  animal  pole   •some  polarity  set  at  fertilization   –animal-­‐vegetal  axis    anterior-­‐posterior  axis   –area  opposite  sperm  entry  (gray  crescent)    dorsal   •presence  of  yolk  influences  shape  of  blastula   –first  2  divisions,  lead  to  4  blastomeres   rd –3  division:  8  cells;  unequal  offset  by  yolk   –blastocoel  only  in  animal  hemisphere   •during  gastrulation  the  ball  of  cells  turns  into  a  structure  with  2-­‐3  tissue  layers   and  a  gut  (gastrula)   –mass  movement  of  cells   •because  nourished  by  mother,  eutherian  eggs  can  be  smaller:  no  need  for  bulky   yolk   –best  studied  in  mice  and  early  stages  of  human  in  vitro  fertilization   •cleavage  to  8-­‐blastomere  stage:  3  days   –after  six  days,  ready  to  implant  in  uterus;  >100  cells   1.blastocyst:  mammalian  blastula   –trophoblast:  outer  epithelium   –inner  mass  cells:embryonic  stem  cells   2.trophoblast  initiates  implantation   –secretes  enzymes  to  break  down  endometrium   –thickens,  sends  extensions  to  maternal  blood  vessels   –inner  mass  cells  form  epiblast  and  hypoblast   3.once  implanted,  gastrulation  initiated  &    extraembryonic  membranes  form   –placenta  derived  from  trophoblast,  mesoderm  and  endoderm  from   the  epiblast   4.3  layered  embryo  with  4  extraembryonic  membranes   •once  germ  layers  (tissues)  present,  cells  differentiate  to  form  organs:   organogenesis   –cluster  locally   •early  organogenesis   –notochord:  condensation  of  dorsal  cells  above  archenteron   –ectoderm  above  that  becomes  hollow  dorsal  nerve  cord   •neural  plate:  cells  curve  inward  to  form  neural  tube   –becomes  CNS:  brain  and  spinal  cord   •neural  crest  cells:  migrate  to  form  other  nerves   –mesodermal  somites  arranged  segmentally  around  notochord   •become  vertebrae,  ribs,  and  associated  muscles   •organogenesis  continues:  cell  differentiation  and  morphogenesis   –leads  to  adult  organs   •You  have  talked  about  morphogenesis  and  differentiation  in  plants   –cell  walls  don’t  move:  nothing  as  fancy  as  gastrulation   •animal  cells  change  shape  using  cytoskeleton   –e.g.,  formation  of  neural  tube   •microtubules  elongate  cells   •perpendicular  microfilaments  narrow  the  apex:  make  cell  wedge-­‐shaped   •animals  cells  move  using  cytoskeleton   –crawl  much  like  an  amoeba   •cells  form  stable  tissues  using  cell  adhesion  molecules  (CAMs);  usually   glycoproteins  on  cell  surfaces   –allow  cells  to  recognize  others  and  bind  them  with  specific  receptors   •migration  of  cells  also  mediated  by  extracellular  matrix:  mesh  of  macromolecules   outside  of  cells   –migrating  cells  have  receptors  that  bind  matrix:  like  a  track   –matrix  can  also  block  cells  from  going  the  wrong  way   •cells  interact  with  the  extracellular  matrix  and  neighboring  cells  to  control  where   they  are  suppose  to  be     •induction  is  involved  in  pattern  formation  by  providing  positional  information   –e.g.,  limb  development  in  a  chick   •limbs  begin  as  mesodermal  limb  buds,  covered  in  layer  of  ectoderm;  three   axes   1.proximal-­‐distal:  shoulder-­‐to-­‐finger   2.anterior-­‐posterior:  thumb-­‐to-­‐pinkie   3.dorsal-­‐ventral:  knuckle-­‐to-­‐palm   Lecture  32     •Sensory  input  gets  integrated  into  the  central  nervous  system  (brain,  nerve  cord),   response  is  transmitted  by  the  peripheral  nervous  system     •neurons:  specialized  cells  that  conduct  and  store  information  in  the  nervous   system     **  Neurons  have  specialized  structure  and  unique  function**   •the  role  of  a  neuron  is  to  receive  and  transmit  electrical  signals   •what  a  neuron  looks  like:   –cell  body:  houses  most  of  cytoplasm,  nucleus,  etc.   –many  short  dendrites:  branched  extensions  at  receiving  end   –one  long  axon:  extends  from  neuron  to  cell  it  acts  on   •might  be  >1  meter   •axon  hillock:  where  axon  joins  cell  body,  where  signals  are  generated       •what  a  neuron  does:   –becomes  electrically  exited  &  conducts  excitement  down  axon   –synapse  connection  between  neurons   •excitement  passed  chemically   •excited  synaptic  terminal  in  the  presynaptic  cell  releases  neurotransmitters   •postsynaptic  cell  may  (or  may  not)  become  electrically  excited  by  the   neurotransmitters   –connections  among  neurons  can  form  highly  complex  networks   •single  neuron  might  receive  inputs  from  100,000  synapses       •how  a  neuron  works:   –functions  as  an  on-­‐off  switch   –either  the  inside  is  negatively  charge  (not  excited)  or  positively  charged   (excited)   –charge  determined  by  movement  of  ions  across  membrane     **Structural  Diversity  of  neurons  and  the  role  of  glia**   •Sensory  neurons:  transmit  information  from  eyes  and  other  sensors  that  detect       external  stimuli  or       internal  conditions   •Interneurons:  form  the  local  circuits  connecting  neurons  in  the  brain   •Motor  neurons:  transmit  signals  to  muscle  cells,  causing  them  to  contract   •Glial  cells:  nourish,  insulate,  and                regulate  neurons       •membrane  potential:  voltage  difference  across  cell  membrane  as  a  result  of   unequal  ion  distribution   –difference  in  charge  between  inside  &  outside  of  cells   –all  living  cells   •resting  potential:  membrane  potential  of  a  neuron  that  isn’t  excited   –-­‐60  mV  to  -­‐80  mV  (inside  relative  to  outside)   •resting  cell  maintains  a  K -­‐Na  gradient   –ATP-­‐powered  sodium-­potassium  pump   •brings  K  in,  sends  Na  out   –also  ion  channels  that  let  ions  move  down  their  gradients   •many  potassium  ion  channels:  K  always  leaking  out   + •few  sodium  ion  channels:  Na  builds  up  outside   •no  ion  channels:  for  Cl  and  other  anions   –net  movement  of  charge  is  what  creates  voltage  potential   •K  keeps  leaking  out  results  in  negative  charge   •chemical  and  electrical  gradients  balanced:  equilibrium  potential   –pumped  in  at  the  same  rate  that  it  is  leaking  out     **  When  a  neuron  is  excited,  the  membrane  potential  goes  from  negative  to   positive**     •in  addition  to  “regular”  ion  channels,  neurons  have  gated  ion  channels:  respond  to   some  stimulus  by  opening/closing   –voltage-­gated  ion  channels:  respond  to  change  in  membrane  potential   •hyperpolarization:  membrane  potential  more  negative   + •depolarization  (less  negative)  of  membrane  potential  activates  voltage-­gated  Na   channels   –positive  feedback:  leads  to  further  depolarization  and  more  Na  channels   opening   –action  potential:  massive,  rapid  depolarization   •occurs  once  potential  exceeds  threshold  of  -­‐55  mV  (mammalian  threshold)   •all-­or-­nothing  response   –action  potential  very  brief:  1-­‐2  msec   + •gated  Na  channels  only  active  for  a  short +time   •rapid  depolarization  opens  voltage-­gated  K  channels:  results  in  rapid   hyperpolarization   –“undershoots”  normal  resting  potential     **Action  potentials  are  propogated  along  axons**   •during  the  falling  phase  and  undershoot,  Na  channels  inactivated   –refractory  period:  time  between  action  potentials,  Na+  closed,  AP  not   possible   –sets  maximum  frequency  of  action  potentials   –helps  the  action  potential  propagate  in  one  direction   •signal  propagates  because  action  potential  in  one  area  of  axon  depolarizes   neighboring  region   –neighboring  region  surpasses  threshold  and  has  own  action  potential   + •activation  of  K  and  inactivation  of  Na+  channels  during  refractory  period   prohibits  regression   –action  potential  too  short  to  excite  area  that  was  just  excited   •speed  of  propagation  increases  with  axon  diameter   –less  resistance;  depolarization  can  spread  further   –narrow  axon  cm/sec,  wide  m/sec;  e.g.,  squid  giant  axon   •speed  of  propagation  increases  with  “insulation”  by  glial  cells     •2  kinds  of  glial  cells  provide  a  myelin  sheath  around  axons:  electrical  insulation   –wrap  axons  in  multiple  layers  of  cell  membrane   –no  leakage  to  dampen  effect  with  distance   –oligodendrocytes  in  CNS   –Schwann  cells  in  PNS   •insulation  allows  depolarization  to  propagate  farther/faster   –20  µm  vertebrate  axon  conductions  faster  than  1000  µm  squid  axon   •voltage  gated  Na  channels  limited  to  gaps  in  myelin  sheath:  nodes  of  Ranvier   –depolarization  jumps  from  node  to  node       **Info  passes  in  chemical  form  from  1  neuron  to  another**   •most  cases,  action  potentials  not  transmitted  across  a  synapse  (connection   between  2  cells)   •Electrical  synapses  less  common  in  vertebrates   •Chemical  synapses  most  common   –neurotransmitter:  pre-­‐synaptic  chemical  released  by  neuron   •presynaptic  axon  terminal:  neurotransmitter  packaged  into  synaptic  vesicles   –depolarization  of  terminal  results  in  vesicles  fusing  with  membrane   –neurotransmitter  released  into  synaptic  cleft  (space  between  presynaptic   &  postsynaptic  cells)   •postsynaptic  membrane  has  ligand-­gated  ion  channels  that  bind   neurotransmitter   –binding  results  in  change  in  the  postsynaptic  membrane  potential   –excitatory  postsynaptic  potentials:  depolarize  membrane  (a  little)   –inhibitory  postsynaptic  potentials:  hyperpolarize  membrane  (a  little)     **#  and  type  of  synapses  determines  the  response**   •postsynaptic  potentials  graded  rather  than  all-­or-­nothing   –don’t  exceed  threshold,  then  they  fade   –but,  multiple  excitatory  potentials  can  add  up   •temporal  summation:  series  of  potentials  from  same  synapse   •spatial  summation:  potentials  from  different  synapse  on  cell   –inhibitory  potentials  can  cancel  out  excitatory  potentials   •every  synapse  contributes  to  whether  or  not  the  postsynaptic  neuron  produces  an   action  potential       Lecture  33     **Networks  of  neurons  vary  in  complexity  among  animals**       •the  different  taxa  have  variously  developed  nervous  systems   –reflects  both  evolutionary  history  and  life-­‐style   •cnidarians:  diffuse  nerve  net   •more  complex  animals:  nerves  of  multiple  neurons   –central  nervous  system  (CNS):  brain  +  nerve  cord(s)  running  body  length   •“protostomes”  have  ventral  nerve  cords   •deuterostomes  have  a  dorsal  nerve  cord   •more  derived  animals  concentrate  more  nervous  system  into  the  brain:   cephalization   –esp.  sensory  and  interneurons   –peripheral  nervous  system  (PNS):  ganglia  (cell  bodies)  and  nerves   outside  CNS     Vertebrate  CNS   •brain:  is  where  all  stimulus  and  voluntary  (and  involuntary)  behavior  is  processed   •spinal  cord:  carries  impulses  to  &  from  brain   –mediates  reflexes:  involuntary  movement   •both  made  of  gray  matter  (non-­‐myelin)  and  white  matter  (myelin)   –brain,  gray  on  outside   –spinal  cord,  white  on  outside   •both  derived  from  “hollow  dorsal  nerve  cord,”  like  other  chordates   –central  canal  of  spinal  cord   –ventricles  of  the  brain   –both  filled  with  cerebrospinal  fluid:  filtered  from  blood   •diffusion  of  resources  and  waste   •cushion   •glial  cells  create  tight  blood-­brain  barrier         Role  of  Glia  in  the  CNS▯     •glia  present  in  the  vertebrate  brain  and  spinal  cord  nourish,  support,  and   regulate  the  functioning  of  neurons.   •radial  glia:  embryonic  glia  that  form  tracks  along  which  newly  formed  neurons   migrate  from  the  neural  tube,  the  structure  that  gives  rise  to  the  CNS   •  astrocytes:  facilitate  information  transfer  at  synapses  and  sometimes  release   neurotransmitters;  initiates  formation  of  the  blood-­‐brain  barrier  during  embryonic   development   •radial  glia  and  astrocytes:  can  act  as  stem  cells,  generating  new  neurons  in  glia   •oligodendrocytes:  myelinate  axons  in  the  CNS   •  schwann  cells:  myelinate  axons  in  the  PNS   •  microglia:  immune  cells  that  protect  against  pathogens   •ependymal  cells:  line  ventricles  and  promote  circulation  of  cerebrospinal  fluid       **PNS  carries  info  from  CNS**     •cranial  nerves:  connect  brain  with  head   •spinal  nerves:  connect  spinal  cord  to  rest  of  body   •afferent  neurons:  bring  information  to  the  CNS     –sensory   •efferent  neurons:  carry  information  from  CNS    –motor  system:  skeletal  muscles;  voluntary  (&   reflexes)   •respond  to  external  stimuli    –autonomic  nervous  system:  smooth  &  cardiac   muscle,  glands,  etc;  involuntary   •sympathetic  division:  arousal,  “fight  or  flight”   •parasympathetic  division:  calming,  “rest  and  digest”   •enteric  division:  digestion     Functions   •during  embryogenesis,  the  brain  increases  in  complexity;  begins  as  3  bulges  of   neural  tube    –each  embryonic  region  develops  into  specific  adult   structures   •hindbrain  &  midbrain     –brainstem  =  midbrain  +  pons  +  medulla   •homeostasis,  coordination  of  movement,  sharing  information  among  other  brain   centers  and  PNS   •attention,  alertness,  motivation    –cerebellum:  coordinates  movement,  hand-­‐eye   coordination       •forebrain     –diencephalon:  thalamus  +  hypothalamus  +  epithalamus   •functions  in  homeostasis,  coordinating  sensory  information,  circadian  rhythms     –cerebrum:  center  for  learning,  emotion,  memory,  perception   •about  80%  of  brain   •outer  cortex  of  gray  matter   •left  &  right  hemispheres;  receive  information  from  opposite  sites   •connected  by  corpus  callosum       Sleep  &  Emotions   •Sleep  and  arousal  are  controlled  in  part  by  the  reticular  formation,  a  diffuse   network  of  neurons  in  the  core  of  the  brain  stem.     •Reticular  formation  filters  incoming  information  and  determines  what  reaches   the  cerebellum.   •The  more  information  the  cerebrum  receives,  the  more  alert  and  aware  the  person   is   •  Pons  and  medulla  also  regulate  sleep   •biological  clock,  regulates  sleep  cycles,  coordinated  by  a  group  of  neurons  in  the   hypothalamus  and  melatonin  from  the  pineal  gland    Limbic  system  borders  the  brainstem,  responsible  for  emotions,  includes   amygdala,  hippocampus,  and  thalamus       •cortex  has  4  lobes:  frontal,  parietal,  occipital,  temporal     –each  specialized  to  process  different  information   •sensory  information  received  from  thalamus     –received  in  primary  sensory  areas     –e.g.,  visual  to  occipital  lobe     –then  to  association  areas  to  make  sense  of  sensory  info.     –then  to  frontal  association  area  to  be  acted  on   •different  functions  localized  in  different  places     –even  the  individual  parts  of  language  map  to  different  areas     –Broca’s  area:  controls  muscles  in  the  face,  active  during  speech  generation     –Wernicke’s  area:  active  when  speech  is  heard,  facilitates  comprehension  of   speech   •lateralization:  two  hemisphere’s  not  identical  in  function     –e.g.,  left  does  math,  logic,  language     –e.g.,  right  recognizes  spatial  patterns,  non-­‐verbal  thinking       •three  processes  determine  structure  of  the  nervous  system  during  embryonic   development     1.gene  expression,  signal  transduction,  etc.  establish  structures     2.huge  neuron  die-­‐off     1.those  that  aren’t  in  the  right  places  die  off  (determined  by  access  to  growth   factors)   2.50%  of  neurons  are  lost   3.synapse  reconfiguration       1.each  neuron  initially  forms  more  synapses  than  it  needs     2.gets  rid  of  the  extras  (more  than  50%)   •learning  and  memory  based  upon  neural  plasticity  after  embryonic  development     –synaptic  connections  get  weaker  or  stronger     –memories  formed  by  rearranging  connections  in  the  hippocampus   •short-­term  memories:  store  stimuli  for  a  short  time,  see  if  they  are  important   •long-­term  memories:  rearrangements  in  the  cerebral  cortex   •long-­term  potentiation;  example  of  how  synaptic  connections  changed   –frequent  excitation  of  a  synapse  can  make  the  postsynaptic  neuron  more   sensitive  to  the  presynaptic  neuron   •neural  stem  cells  in  brain:  new  neurons  play  an  essential  role  in  learning  and   memory,  recruited  as  needed      


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