Class Notes (836,135)
Canada (509,645)
HMB200H1 (140)
Lecture 20

HMB200 2014 Lecture 20.pdf

8 Pages
Unlock Document

Human Biology
John Yeomans

  Lecture  20  :  Brain  Development   Brain  Development  (page  178 -­‐192)   • Visual  cortex  develops  in  response  to  special  signals  (NMDA  receptors  and  glutamate  connections)   • GABA  neurons  are  important  in  development  and  have  diffe rent  pathway  in  reaching  the  cortex   • All  of  these  cells  begins  with  same  nucleus  and  DNA     • All  of  these  cells  come  from  fertilized  egg  cells  (zygote)   • From  Zygote  to  Brain:  1à100  billion  cells.   • Mitosis  and  cell  proliferation   • Daughter  cell  then  has  to  migrate   tissue  where  they  divide,  into  the  tissue  the  can  later  form  connections   • Folding  over  =  gastrolation   à  establishes  position  of  cells   • First  zygote  on  day  0:  forms  compact  cell  mass   • Divides  from  1  cell  to  2  and  so  on   • Quick  divisions  after  fertilization   • This  cell  mass  has  no  special  shape   • This  ball  of  cells  will  fold  over  later  on  =  gastrulation   • This  folding  over  creates  a  line  (longitudinal  axis)   • Establishes  position  of  cells  along  this  axis   • Gastrola  folds  over  to  make  3  layers  of  cells  (day  14 -­‐25)   • Gastrula  eventually  folds  over  to  make  3  layers  of  cells  (day  14 -­‐25)   • First  cells  that  become  brain  and  neural  cells   • Brain  cells  and  neural  cells:  Along  midline  of  dorsal  surface  of  embryo   • Blastula  and  Embryonic  Stem  cells  (7  days).   • Blastula  contains  stem  cells   à  stem  cells  can  be  taken  out  to  make  different  tissues   • Gastrula  to  Ectoderm  and  Neural  Plate  (14 -­‐18  days)     • Formation  of  Neural  Tube  (18 -­‐24  days).   • Formation  of  Brain  (22  days  to  9  months).   • Gene/protein  signals  in  each  cell  must  interact  with  signals  from  other   cells  in  environment.  Development  =   Genesß(interacting  with)àEnvironment.     Embryonic  Stem  Cells     Ø blastula:  thousands  of  cells  ( E7-­‐  embryonic  day  7)   - on  the  inside:  fluid   - outside:  protective  cell  to  cell  that  forms  the  outside  of  the   bastula   - most  cells  are  on  the  inside  à  they  are  embryonic  stem  cells   - Embryonic  stem  cells  are  undifferentiated   –  differentiated  later   on   - Take  these  cells  out  using  pipette,  and  put  onto  petri   dish  to  be  grown   - These  cells  can  be  altered  and  mutated  (DNA  can  be  changed)   - Put  into  test  tube  and  add  extra  DNA  =  transgenic  cell   à  extra  genes   1) Put  cell  into  test  tube   2) Blast  the  test  tube  with  electricity   3) Breaks  surface  membrane   4) DNA  sitting  in  the  bath  outside  can  now  leak  into  the  cell   à  electropouration  àmembrane  is  made  porus   - These  transgenic  cells  can  now  duplicate     - But  mutant  cells  will  have  different  coat  colours   à  make   dark  cells  in  babies  (postnatal)  when  transgentic  cell  is  put   into  blastocyst  (skin  cells  are  dark  from  mutant  stem  cells,   and  white  skin  cells  from  original  cells)   - Mutant  cells  make  dark  cells  as  opposed  to  white   cells   - if  mutant  cells  are  presented  to  the  testes  (dark  skin  around  testes)   à  If  sperm  represents  mutant  cell,  its  bab ies  will  have  mutant  skin   colour  (all  be  black)   Ø after  birth  =  P  (postnatal)   - knockout  mice:  don’t  have  the  gene       - get  the  gene  introduced  to  replace  the  original  DNA   - mutant  DNA  missing  an  essential  piece  (the  knockout)  and  this  mutant  has  to  replace  the  wildtype  DNA   - Homologous  recombination :  get  gene  to  replace  original  gene   - Knockout:  replacing   - Transgenic:  extra  copies     Formation  of  Spinal  Cord   -­‐ Brain  cells  and  neural  cells  are  in  yellow   -­‐ the  brain  and  neural  cells  form  in  the  ectoderm   1) Ectoderm:  outer  layer  that  becomes  the  skin,  brain,  and   eyes   o Outer  layer  of  the  body  (blue)   2) Mesoderm  becomes  muscle  cells  (some  internal  tissues)   o The  middle  (in  red)   3) Endoderm:  internal  organs  and  viscera     Formation  of  Early  Brain   -­‐ Folding  over  to  become  the  spinal  cord  from  the  neural   tube   -­‐ By  day  22,  you  will  see  the  neural  tube  in  the  middle   (where  the  original  line  fist  occurred)   -­‐ A  streak  à  groove  à  tube   -­‐ This  tube  extends  to  the  forebrain   -­‐ Brain  plate  folds  over  later     o Once  it  does,  it  causes  rapid  proliferation   -­‐ By  day  24,  the  brain  plate  extends  out  from  the  ectoderm  and  becomes  the  brain   -­‐ Tube  à  bulky  tube  à  brain     o At  the  anterior  end  of  the  neural  tube   -­‐ Happens  because  embryonic  stem  cells  are  dividing  at  a  very  rapid  rate     Brain  Growth   • Neural  plate  above  notocord.   • From  neural  groove  to  tube  (18 -­‐24  d)   • Neural  tube  is  formed  from  the  ectoderm   • Can  now  start  to  see  the  spi nal  cord  along  the  tube   • Brain  is  forming  at  the  anterior  end  of  the  tube   • Brain  development  requires  cells  to  proliferate   • Then  interactions  between  cells  is  then  going  to  cause   expression  of  genes  which  then  makes  lots  of  proteins   • Proteins  then  interact  wit h  signals  to  make  receptors,  release   growth  factors,  etc.   • These  proteins  interact  with  signals  from  other  cells  and  this   causes  the  cells  to  change  =  differentiation     • Process  of  development  involves:  expression  of  genes  of   different  sorts  (can  be  turned  on  or  off  by  interaction  with   proteins,  interactions  with  other  cells)   • This  2  way  conversation  between  proteins  and  genes   and  cells  results  in  a  differentiation  in  different  types   of  cells  to  become  different     • Brain  regions  from  bumps  (25 -­‐100  d).   • Midbrain  in  purple   • Forebrain  in  blue   • As  the  brain  grows,  it  bends   • Bending’s  of  the  brain  define  the  major  divisions  of  the  telencephalon,  etc.   • In  human  brain:  telencephalon  is  especially  large   • On  the  40  day  (E40)   • Hindbrain  has  a  big  lip  in  front  of  it   à  separates  cerebellum  from  the  medulla   • In  front  of  that  is  the  midbrain  (becomes  much  large  by  day  50   –  purple)   • There  is  2  divisions  to  hindbrain,  and  2  divisions  to  the  forebrain       • Going  from  rostral  to  caudal,   we  have  the  telencephalon,  diencephalon  (in  the  forebrain) ,  midbrain,   then  metencephalon  (cerebellum,  medulla/myelencephalon)   • Encephalons:  myel-­‐,  met-­‐,  mes-­‐,  di-­‐,  tel-­‐.   •  By  day  50,  these  parts  become  harder  to  see  (only  in  humans)     • telencephalon  proliferates  so  fast,  producing  so  many  neurons  that  migrate  out  fro m  the  ventricles,   that  these  telencephalon  areas  grow  much  faster   • become  so  large  that  they  cover  the  diencephalon,  and  eventually  the  midbrain     • unique  to  primates  –  exceptionally  rapid  growth  of  cerebral  hemisphere   • By  100  days,  you  can  lateral  features   • Cerebellum  from  hindbrain  rhombic  lip.   • Telencephalon  development,  e.g.  sulci,  connections  and  myelination   (10-­‐36  weeks).     Human  Cortex  Development   -­‐ 10  weeks:  70  days   -­‐ 41  weeks  =  day  of  birth   -­‐ lateral  fissures  can  be  seen  at  15  weeks   -­‐ gyri  and  sulci  can  be  seen  at  24  weeks   -­‐ only  happens  in  animals  with  large  telencephalon   à  ran  out  of  space,   so  there  is  more  and  more  folding  as  the  brain  grows     Making  Neurons  (chap.  23)   • Embryonic  Stem  cells.   • Neural  Stem  cells.   • Glia  or  specific  neuron  types.   • Specific  inducing  factors:  e.g.  Sonic  Hedgehog  (ventralàMotoneurons),  Hormones,  Growth  Factors,  Transcription   Factors.     • Hox  genesàAnt-­‐Post,  Med-­‐Lat  axes.   • Cell-­‐cell  communication.     Life  Cycle  of  Neurons   • Within  neural  tube,  there  are  undifferentiated  dendritic  stem  cells  in  the  wa lls  of  the  central  canal   • Cell  proliferation  near  ventricles.   • single  neurons  start  in  the  wall  of  the  central  canal  of  the  spinal  cord   • new  born  neurons  all  start  at  the  walls  of  the  ventricles   th • in  the  wall  of  the  4  ventricle  (when  you  talk  about  hindbrain)   • the  wall  of  the  3  ventricle  for  diencephalon   • the  walls  of  the  lateral  ventricles  (telencephalon)   • in  this  area,  the  first  cell  divided  are  embryonic  stem  cells  (not  becoming  neurons  until  later)   • Migration  of  daughter  cells  after  birthdate.   • a  single  cell  (made  in  the  wall  of  the  ventricles)  divide  2  times  in  that  wall,  making  daughter  cells   à  one   then  gets  pushed  out,  away  from  the  ventricle  wall   • usually  2  processes,  one  reaching  outwards,  one  reaching  back   à  influence  direction  its  going  to  flow   • once  it  reaches  a  point  in  the  outside  area,  then  you  see  dendrites  and  special  cell  shapes   (pyramidal  cells,  oval  cells,  etc.)  à  these  are  differentiated  neurons  of  different  types   • After  division,  these  embryonic  stem  cells  can  then  migrate  into  different  brain  ar eas   • As  they  migrate  and  reach  brain  areas,  they  then  turn  of  specific  genes   à  can  become  specific  cells   • Differentiation  into  glia  and  neurons.   • Neural  stem  cells  can  go  to  cortex  to  become  different  types  of  glia  and  neurons   • Differentiation  of  neural  stem  c ells  in  the  glia  or  glutamate  neurons,  etc.  occurs  by  a  series  of  steps   • as  they  migrate  outward,  they  express  specific  genes  and  proteins   • they  interact  with  other  cells   • they  become  differentiated  by  these  environmental  interactions     • once  differentiated  cells  are  established,  they  will  make  contacts  with  other  cells  (contacts  can  become   synapses,  or  become  loss  as  a  result  of  competition)   • Process  formation  and  synaptogenesis.   • after  they  make  contact,  and  identify  themselves  as  a  particular  cell  type,  they  f orm  particular  types  of   dendrites,  make  synapses  with  neighboring  cells,  then  send  out  axons  (last  process)   • Selection  of  synapses  and  neurons.       • differentiated  first,  then  form  processes  and  make   contact   • some  cells  stay  on  and  form  neurons,  others  in   competition  will  die  away  (apoptosis  if   programmed)   • other  cells  form  lots  of  new  connections   • Axon  growth  cones,  connections,  and  myelination  by   oligodendroglia.   • once  they  form  a  connection,  they  can  send  out  an   axon   • this  axon  sends  out  a  growth  cone  to  make  cont act   with  distant  brain  areas   à  make  long  pathways   • after  the  process  of  sending  out  an  axon,   oligodendroglia  forms  myelin  around  axons   • myelination  occurs  mainly  after  birth  (last  process  of  all)   à  white  matter  forms  last  in  the  brain   • white  matter  is  from  o ligodendroglia  making   myelin  around  axons  that  already  formed   connections   • Apoptosis  (cell  death)   –  process  of  choosing  successful  cells  and   synapses   • Once  axons  come  out,  they  can  extend  to  other  brain  areas   à   eventually  make  growth  cones,  and  contacts  with  hundreds  of  cells   • Synaptic  contacts  can  becomes  synapses,  but  most  contacts  die  off   (selective)     Cortical  Development   • Spinal  cord  development  occurs  by  migration  inside  the   undifferentiated  substrate     • Cortex,  cerebral  cortex,  cerebellar  cortex  occurs  by   a   different  process   • In  order  to  for  layers  and  columns,  there  have  to   be  special  cells  to  define  where  the  boundaries   of  the  layers  and  columns  are   • In  the  cortex,  the  first  cell  to  come  out  are  radial  glia   cells   • Radial  glia  cells  have  long  scaffold -­‐like   structures     • These  migratin
More Less

Related notes for HMB200H1

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.