SENSORY PHYSIOLOGY
              - Campbell 7e reads: C49 pg1045-1049, 1058-63, 1066-74 & fig's 49.8 & 49.12
          - Campbell 8e reads: C50 pg1087-1091, 1099-1105, 1105-1112 & fig's 50.9 & 50.12
                     
                                                                               
   Sensations & Perceptions    
      sensation
- is an awareness of sensory stimuli in brain  
      perception
- meaningful interpretation or conscious understanding of sensory data

             Not unlike the signaling we have seen before...     sensory signaling*          
                                                                                                  
signal transduction hypothesis 
  
5 COMPONENTS of SENSORY PHYSIOLOGY

   1. Sensory Receptors -
            structures that detect changes in external & internal environment   
            modified neurons or epithelial cells that have evolved 
                                                                 to respond to stimuli  (eye, ear, nose, muscles)
 

 

 

 

 

 

 

 

 

 

 

 Classes of Sensory Receptors
     
chemo-receptors:  chemicals sense solutes in solvents, taste, smell
     osmo-receptors:  of hypothalmus which monitors blood osmotic pressure
     photo-receptors:  light - eye, eyespots, infrared receptors of snakes, etc...
     thermo-receptors:  radiant (heat) energy
     phono-receptors sound waves
     electro-receptors:  detect electric currents... electric eels, etc..
     noci-receptors:  pain receptors... naked dendrites of skin (epidermis)
     mechano-receptors:  mechanical forces
- stretching alters membrane permeability
                
(1)   hair cells  (deflection* = depolarization = AP's)
                                 lateral line of fish* ( mechanoreceptor = neuromasts detect water movement - anim)
           
(2)   stretch receptors of muscles
*                           U. Indiana Muscle Stretch reflex animation
           
(3)   equilibrium receptor of inner ear             
animation of Pacinian receptors
           
(4)   receptors of skin (touch, pain, cold, heat)
               

  

 

 

 

 

 

 
     2.  Reception - ability of receptor to absorb energy of a stimulus

     3. Transduction - conversion of stimulus energy into a membrane potential
*, i.e.,
              a Receptor Potential... RP (or generator potential... GP --> fires an AP)...  
                  sort of like an EPSP or IPSP...
                        a change in permeability of a post-synaptic membrane
*
                        often graded = proportional to strength of stimulus
                        may be amplified and/or may be summed
                       
may be strong enough (reaches threshold) to generate action potentials

     4. Transmission - receptor potentials transmitted via AP's to CNS

     5.  Integration - processing of frequency of receptor potentials
 
  

                      sensory information
* is coded as  FREQUENCY  of AP's
                                                                                              


 

 

 

 

 

  

Sensory Adaptation - an attenuation of the stimulus...
 
   a decrease in responsiveness by receptors due to continual stimulation

              a uniformly maintained stimulus of constant intensity is perceived 
                      as progressively weaker with time,   [movie house odor]

                 while a variable intensity stimulus of shorter durations is perceived
                      as a progressivley stronger odor over time

                 Graph of subjective intensity vs. concentration of H2S *

 

 

    for an example of sensory physiology to Muscle Physiology*                                              

 

 

 

 

 

 

 

 

 

 

        SUMMER 2008 Skip the eye sensory material below
An Example of a Sensory Organ...  
         the Human Eye...   
 here's looking at you       &               Visual Neural Pathways

  
  
      structure (parts*) vert eye        fig 50.18*
                                   
How parts of eye work*
         photoreceptors         retina
*       fig 50.23*  
                         rod cells   rhodopsin fig 49.11
*  fig 50.20*
         effect of light on retinal -     
     
     fig 49.12   animation photoisomerization of rhodopsin
*
                 the visual cycle                
fig 49.13 & .14**

   PERCEPTION ...result is visual sensation : 
       
not always what you actually see...
           Some optical illusions
           great optical illusions  shimmer - wheels - wall 

   Practice quiz on parts of the eye by Sumanas, Inc.
 parasympathetic nerve anim  utah.med.fig

 

 

 

 

 

 

 

 

 

 

Some common disorders of vision - correctable by eye glasses
myopia
     
(near-sightedness) 
lens point of focus falls within the vitreous body
so that when light reaches the retina it is out of focus
hyperopia
      (farsightedness)
point of focus falls behind the retina (out of focus) 
astigmatism results from defects in the curvature of the cornea, light rays
don't form a point of focus on the retina = bluriness
night blindness Vit-A deficiency or lack of pigment chromophore... retinal
color blindness lack of trichromatic pigments
glaucoma        result of increased pressure of fluids in the eye, 
produces defects in field of vision & can lead to vision loss

                                                                                                    a pardigmKey Concepts*
            go to Muscle Physiology                                

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   EYE PARTS - a specialized sensory organ capable of light reception 

lens  focuses light on rod & cone cell of retina - cuboidal epithelia
retina  a layer of nerve tissue & millions of light receptor cells (rods/cones)

rod-cone cells

modified neurons -transmits electrical signals of varying light intensity

fovea 

near center of retina, where cone cells give max sharpness of vision
optic nerve retinal cells record light images & transmit to optic nerve, which exits eyeball behind optic disk (blind spot) to the visual centers of brain. 
sclera  tough outer shell of eyeball, made of dense fibrous tissue
cornea  stratified squamous epithelia, main refractory part of eye, 
lets light pass & aids in focusing
vitreous humour  transparent jellylike material, helps eye keep its spheroid shape. 
aqueous humour anterior chamber, filled with a watery fluid
iris & pupil   muscular curtain that opens/closes to regulate amount of 
light entering eye through the pupil (opening of iris into eye)

 

 

 

 

 

                frequency response
     
 

 

 

 

 

 

 

 

 

 

 

 

 

 

Some Optical Illusions - subjective interpretations visual information.

Proximity... Seen as three groups of two asterisks rather than simply six asterisks.

* *    * *    * *

Similarity... Seen as columns of Xs and Os rather than rows of alternating Xs and Os.

X  O  X  O  X  O  X  O  X  O
X  O  X  O  X  O  X  O  X  O
X  O  X  O  X  O  X  O  X  O
X  O  X  O  X  O  X  O  X  O

Good Continuation... Seen as two lines crossing, rather than two bent lines touching,
                              or just a collection of asterisks.                                            

     *        *                    These have crucial significance
      *      *                      for the layout of information
       *   *                         on screens and printed documents.
        *                          
     *   *                         return
  *       *
*          *                       
 

 

 

 

 

 

 

 

 

 

Closure / Good Form... Seen as two overlapping squares rather than one irregular grouping of asterisks.

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