SENSORY  PHYSIOLOGY  

Physiology  Unit  2  

Sensory  System  

•  Sensory  informa4on  – Conscious  sensa4ons  – Unconscious  sensa4ons  

•  Sensory  processing  – Transferring  s4mulus  energy  into  a  graded  poten4al  (receptor  poten4al)  

– Then  to  an  ac4on  poten4al  in  an  afferent  neuron  •  Pa>ern  of  ac4on  poten4als  is  the  code  that  provides  informa4on  on  the  s4mulus  

General  Classes  of  Receptors  

•  Mechanoreceptors  •  Thermoreceptors  •  Photoreceptors  •  Chemoreceptors  •  Nociceptors  

Sensory  Receptors  •  Specialized  endings  of  

sensory  neurons  •  Separate  cells  that  signal  

the  afferent  neurons  by  releasing  chemical  messengers  

•  The  energy  or  chemical  that  ac4vates  a  sensory  receptor  is  a  s"mulus  

•  The  process  by  which  a  s4mulus  is  transformed  into  an  electrical  response  is  sensory  transduc"on  

Receptor  Poten4al  

•  Sensory  transduc4on  involves  the  opening/closing  of  ion  channels  

Graded  Poten4al  to  Ac4on  Poten4al  

•  The  ini4al  ion  movement  generates  local  current  that  flows  a  short  distance  along  the  axon  to    a  region  where  the  membrane  has  voltage-­‐gated  ion  channels  an  an  AP  can  be  generated  

•  Usually  the  first              Node  of  Ranvier  

Primary  Sensory  Coding  

•  Conver4ng  s4mulus  energy  that  conveys  relevant  sensory  informa4on  to  the  CNS  is  coding  –  Type  of  energy  it  represents  (modality)  

–  Intensity  –  Loca4on  of  the  body  affected  

Sensory Unit

Sensory  Modality  

•  Modali4es  – Temperature,  taste,  sound,  touch  

•  Submodali4es  of  sensa4on    – Submodality  of  temperature:  hot/cold  – Submodali4es  of  taste:  sweet,  bi>er,  salty,  sour,  umame  

– Submodality  of  sound:  pitch,  volume  

S4mulus  Intensity  

S4mulus  Dura4on  •  Rapid  adapta4on  

–  Phasic  receptors  –  Signal  change  –  Rapid  fading  of  sensa4on  –  “on”  and  “off”  response  

•  Slow  adapta4on  –  Tonic  receptors  –  Signal  slow  changes  or  

prolonged  events  –  Joint,  muscle  receptors  for  

maintaining  posture  

 

Sensory  Pathways  

•  A  Sensory  Pathway  – A  bundle  of  parallel,  3  neuron  chains  that  run  together  

– Also  called  ascending  pathways  – Non-­‐specific  – Specific  

– Most  sensory  pathways  convey  informa4on  from  a  single  type  of  sensa4on  (mechanoreceptors,  thermoreceptors,  etc.)  

Specific  Ascending  Pathways  

•  Sensory  pathways  ascend  to    1.  Brainstem  (RAS)    2.  Thalamus    3.  Final  neurons  in  the  pathway  terminate  in  the  

specific  sensory  area  of  the  cortex  

•  Excep1on:  olfactory  neurons  branch  to  the  limbic  system  rather  than  the  thalamus  

Soma4c  Sensa4on  •  Sensa4ons  from    

–  Skin  –  Muscles    –  Bones    –  Tendons  –  Joints  

•  Sensa4ons  of    –  Touch  –  Pressure    –  Body  posi4on  –  Temperature  –  Pain  

Somatosensory  System  Pathways  Spinothalamic  Pathway  

•  1st  neuron  travels  into  the  spinal  cord  

•  2nd  neuron  decusates  in  the  spinal  cord  and  up  to  the  thalamus    

•  3rd  neuron  travels  to  the  somatosensory  cortex  

•  Processes    •  Pain  •  Temperature  

DecusaBon  in  the  spinal  cord  

Somatosensory  System  Pathways  Dorsal  Column  Pathway  

•  1st  neuron  passes  into  the  spinal  cord  and  up  to  the  brainstem  where  it  decusates  

•  2nd  neuron  travels  to  the  thalamus  

•  3rd  neuron  travels  to  the  somatosensory  cortex  

•  Processes  •  Fine  touch  •  Vibra4on    •  Propriocep4on  

DecusaBon  in  the  brainstem  

Distribu4on  of  Peripheral  S4muli  

Special  Sense:  Vision  

•  Op4cal  component  – Focuses  visual  image  on  the  receptor  cells  

•  Neural  component  – Transforms  the  visual  image  to  a  pa>ern  of  graded  and  ac4on  poten4als  

Light  

•  The  receptors  of  the  eye  are  only  sensi4ve  to  a  small  por4on  of  the  electromagne4c  spectrum  

•  The  visible  spectrum  is  between  400-­‐750  nm  

•  Different  wavelengths  of  light  are  perceived  as  different  colors  

Color  Vision  

The  Op4cs  of  Vision  

•  Refrac4ng  light  is  how  our  eyes  focus  on  objects  

•  The  cornea  and  the  lens  refract  light  to  focus  it  in  the  re4na  

•  Adjustments  for  distance  is  made  by  changes  the  shape  of  the  lens.  This  is  accommoda"on  

Accommoda4on  

Photoreceptor  Cells  •  Outer  segment  made  of  

stacked  layers  of  membrane  (discs).    

•  The  discs  hold  the  photopigments  which  absorb  light  

•  Photopigments  are  membrane  bound  proteins  called  opsins  which  surround  and  bind  a  molecule  called  re"nol  •  Re4nol  is  a  deriva4ve  of  

vitamin  A  

Photoreceptor  Cells  

•  There  are  4  unique  photopigments  in  the  re4na  •  Rods  have  the  photopigment  rhodopsin  

•  The  others  are  found  in  the  3  types  cones  

Phototransduc4on  

Neural  Pathway  of  Vision  

•  Pathway:    – Op4c  Nerve  (C.N.  II)    – Op4c  chiasm  

•  SCN  

– Op4c  tract    – Thalamus    – Visual  cortex  

Suprachiasma4c  nucleus  (SCN)  controls  circadian  rhythms  

Special  Sense  -­‐  Hearing  

Sound  Transmission  

Organ  of  Cor4  

Sensory Hair Cells

Neural  Pathway  for  Hearing  

•  Pathway:    – Sensory  hair  cells  – Cochlear  branch  of  ves4bulocochlear  nerve            (C.N.  VII,  Auditory  Nerve)    

– Brainstem    – Thalamus    – Auditory  cortex  

Ves4bular  System  

•  Ves4bular  apparatus  – Semicircular  canals  

– Utricle  – Saccule  

Semicircular  Canals  Rota4onal  Movement  

Utricle  and  Sacule  •  The  macula  provides  info  on  changes  in  head  posi4on  rela4ve  to:  –  Force  of  gravity  –  Linear  accelera4on  

•  Ves4bular  informa4on  is  used  for:  –  Control  eye  movements  –  Reflexes  to  maintain  posture  

–  Conscious  awareness  of  ourselves  in  “space”  

Gusta4on  

Olfac4on