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Lecture 10

HMB200 2014 Lecture 10.pdf
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Department
Human Biology
Course
HMB200H1
Professor
John Yeomans
Semester
Winter

Description
  Lecture  10:  Taste  and  Smell   Taste  Pathways   - begin  at  the  tip  of  the  tongue   - taste  buds  at  the  side  of  the  tongue  –  taste   receptors   - at  the  tip  of  the  tongue  is  cranial  nerve  7  (facial   nerve)   - provides  information  from  touch  and   taste  buds,  and  which  tastants  soak  into   the  taste  buds  by  way  of  saliva   - mainly  water  borne  signals  coming  from   the  taste  buds   - the  back  of  the  tongue  and  throat:  cranial  nerve  9   - the  Glossopharyngeal  nerve   - glossal  =  tongue   - pharynx  =  throat   - carries  food  and  chemical  signals  from   the   tongue  to  the  throat  to  the  stomach   - visceral  information  that  continues  down   to  the  GI  tract   - salivation  is  parasympathetic  –  controlled  by  CN   VII  and  IX   - work  together  to  dissolve  chemicals  into   taste  buds   th - sensory  and  motor  components  of  the  7   and  9  cranial  nerve  work  together   - this  information  goes  from  the  taste  buds  into  the   hindbrain   - within  the  hindbrain  is  the   Solitary   Nucleus  (a  visceral  nucleus)  à  processes   all  of  this  visceral  information   - the  Solitary  Nucleus  is  separate  from  all  of   these  sensory  systems  for  touch  and   hearing   - trigeminal  nerve  goes  to  the  trigeminal  nucleus  à   map  of  the  tactile  world  in  the  trigeminal  space   - synaptotopic  map:  from  the  spinal  cord  coming  up   to  provide  information  of  the  body   - spinal  cord  touch  information  and  trigeminal:   provide  information  about  the  outside  of  the  body   - visual  retinotopic  map:  coming  from  the  eyes   - visceral  information’s  are  separate   –  own  little  chain  of  nuclei  that  are  out  in  the  middle  of  the  hindbrain  =  solitary   (separate  from  all  other  sensory  nuclei’s)   • solitary  nuclei  and  tract  carries  information   to  the  thalamus  and  hypothalamus,  then  the  taste  cortex   • solitary  nucleus  has  2/3  of  the  bottom  represented  by  information  from  the  vagus  nerve  (from  thorax  and   abdomen)  à  information  coming  from  throughout  the  body  up  into  the  ventral  2/3s  of  the  solitary  nucleus   • the  solitary  nucleus  has  a  somatotopic  map  of  the  viscera  ( of  the  inside  of  the  body)  à  from  tip  of  the   tongue  to  the  anus   • visceral  information  for  swallowing  and  responding  controls  visceral  reflexes  like  swallowing  and  salivation  and  GI   tract  juices   - all  work  together  to  allow  tastings  to  be  disso lved  and  to  go  into  the  taste  buds,  and  allow  chemicals  to  be   broken  up  by  the  GI  tract  (which  can  then  be  used  for  energy)   - this  information  then  goes  for  conscious  perceptions  to  the  taste  cortex  by  way  of  relaying  in  thalamus   - primary  taste  cortex  influence  the  insula  and  influences  visceral  sensations  and  emotions   • also  other  visceral  information  coming  by  way  of   hormonal  signals   - can  be  the  release  of  chemicals  from  the  gastric  tract   - ghrelin  from  fat  cells  =  leptin   - insulin  and  glucagon  from  the  pancreas         - these  hormonal  signals  from  the  GI  tract  also  influence  the  hypothalamus     - in  addition  to  neural  signals  going  to  the  solitary  nucleus,  there   are  also  hormonal  signals  that  go  to  the   hypothalamus   • once  you  get  to  the  solitary  nucleus,  it  sends  information  up  the  brainstem     - goes  especially  to  the  hypothalamus   –  controls  feeding  and  drinking   - has  descending  pathway  that  controls  visceral  reflexes  (e x.  Salivation,  gastric  release)   - important  pathway  for  visceral  reflexes  going  down  and  for  visceral  processing  going  up  to  the   hypothalamus  (controls  pituitary  and  motivated  visceral  responses)   - after  going  to  hypothalamus  and  thalamus,  it  relays  up  to  the   cortex  à  only  a  small  part  of  the  cortex:   primary  taste  area  of  the  cortex  processes  this  information   - the  taste  zone  of  the  cortex:  bottom  of  the  somatosensory  cortex   - primary  taste  cortex  is  much  smaller   –  coming  from  the  thalamus  to  this  taste  zone   - then  connects  to  an  area  inside  the  Lateral   Sylvian  Fissure   - island  of  cortex  inside  the  Sylvian  Fissure:  Insula   - if  you  pull  the  temporal  and  parietal  lobe  away,  you  can   see  this  island  of  cortical  tissue   à  insular   cortex   - insula:  receives  taste  information  and  influences  visceral  feelings  and  emotions   à  also  connects   with  emotional  processing   o vagus  nerve:  a  long  nerve  that  ends  up  in  the  medulla  by  way  of  cranial  nerve  10   - wanders  from  intestines  and  liver  and  stomach  and  goes  into  the  solitary  nucleus   - important  for  controlling  the  viscera  by  way  of  parasympathetic  output   - 90%  of  the  fibers  of  the  vagus  nerve  are  sensory   –  mainly  a  visceral  sensory  information,  but   includes   motor  outputs  that  control  the  GI  tract     Taste  Sensations   - fast  sensations  that  are  immediately  stimulating  the  tongue   - ionotropic  receptors  that  respond  to  salt  and  sour   - Salt:  Na+  ions  enter   - Sodium  ions  are  dissolved  in  water  (NaCl)   - Salt  ions  enter  taste  buds   - Presence  of  salt  ions  produces  a  sensation  of  saltiness   - Very  fast,  happens  by  qu ick  ionotropic  entering  of  sodium  ions  and  depolarization  of  the  taste  buds   - Sour:  H+  ions  block  K+  channels   - Very  fast  sensation  of  sour   - H+  ions  separates,  and  hydrogen   acids  (sour  taste)  results  in  the  release  of  hydrogen  ions   in  fluids   - These  hydrogen  ions  then  block  potassium  channels  =  excitation   - Blocking  k+  channels  =  depolarization   - Sweet:  sugars  activate  G-­‐protein  coupled  receptors,  T1R2/T1R3  dimers   - Complex  sensation  –  taste  a  little  longer   - Produce  the  taste  by  way  of  the  sweet  receptors   à  have  sugars  broken  down  into  simple  sugars   - This  then  activates  the  GPCR  sweet  receptors   à  produces  a  slower,  but  still  quick  sensation  of  sweet   - Bitter:  many  G-­‐coupled  receptors  for  proteins  –  T2R  family   - Complex  sensation  –  taste  a  little  longer   - Mediated  by  GPCR  by  a  wh ole  variety  of  T2R  proteins   - Lots  of  genes  that  respond  to  lots  of  complex  proteins   - Why  produce  a  unpleasant  sensation  of  bitter?  Most  poisons  are  proteins   à  bigger  receptors  signal  for   poisons   - Complicated  receptors  for  complicated  polypeptides     - Tells  you  to  spit  it  out   - Umami:  glutamate  receptors  for  “good  taste”,  G -­‐coupled  –  T1R/T1R3  dimers   - Complex  sensation  –  taste  longer   - Glutamate  activates  this  receptor   - Glutamate  receptors  respond  to  a  single  amino  acid     - When  broken  down,  it  will  activate  special  dimers   (TR1,  TR2,  etc.  à  dimerized  proteins  that  responds  to   glutamate  to  produce  a  positive  sensation  of  taste)   - (MSG):  Glutamate  is  bad  for  you   à  too  much  glutamate  =  activation  of  NMDA  receptors  =  activation  of  too   many  NMDA  receptors  =   too  much  calcium  gets  in  =  too  much  calcium  in  brain  cells  =  process  of  killing   cells  (calcium  mediated  cell  death)   - Saliva  important  for  dissolving  tastants       - Cranial  nerves  VII  and  IX:  sensation  and  salivation     Taste  Buds  in  Tongue   - taste  buds  are  not  on  the  surface  of  the  skin  of  the  tongue,  instead  they  are  down   in  the  cracks  near  the  taste  buds   - these  channels  are  designed  so  that  water  borne  molecules  can  reach  them  –   water  borne  molecules  that  you  bring  into  your  mouth,  have  to  be  dissolved  and   broken  down  à  complex  sugars  broken  down  by  amylase   - these  complex  molecules  can  then  reach  the  taste  buds,  but  only  if  they’re   dissolved  and  broken  down   - these  are  then  carried  by  saliva  and  water  in  your  mouth  into  the  taste  buds  (but   still  do  not  get  straight  in)  à  receptors  are  buried  deep  in  the  taste  buds   - they  have  to  get  into  the  pore,  carried  through  the  microvilli,  and  contact   receptors  in  the  nerve  fiber  terminals   - requires  water  borne  salivation  and  liquid  dissolving  molecules   - all  of  these  sensations  requires  a  series  of  chemical  p rocesses  in  saliva  that  then   allow  these  simpler  molecules  to  reach  the  taste  buds  and  get  the  effect   - carried  in  by  way  of  cranial  nerve  7  and  9,   within  the  solitary  nucleus  and   thalamus  à  different  neurons  that  respond  to  these  different  taste  sensations     Olfaction   - many  G-­‐coupled  receptors  in  olfactory  epithelium  respond  to  airborne  odorants   - receptors  are  located  at  the  top  of  the  nasal  cavity   - respond  to  air  borne  odours   - rats  have  2  organs:     1) accessory  olfactory  system  (Vomeronasal  Organ  –  responds  to  water  borne  molecules)     2) 2  system  is  at  the  back  of  the  nasal  cavity   –  for  olfactory   epithelium   - when  we  sniff,  these  odour  roots  can  be  sniffed  up  into  these   spaces   o air  borne  odourants  get  wafted  up  into  the  cavity  (pulled   into  th
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