Nervous System: Sensory Systems:

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Nervous System: Sensory Systems:
2011-01-29 19:12:00
Nervous System Sensory Systems

Nervous System: Sensory Systems
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  1. Generalizations of Sensory Systems
    • Sense organ or specialized receptors allow for transduction (conversion of some form of environmental signal to neural signal)
    • Pathway to cortex through spinal nerves or cranial nerves
  2. Modality of Sensory Encoding
    • Type of stimulus
    • Determined by types of neurons activated
  3. Location of Sensory Encoding
    • Where the stimulus is located on the body or in the environment
    • Usually determined by location of neurons that are activated by stimulus
  4. Intensity if Sensory Encoding
    Usually determined by number of activated neurons or frequency of action potentials
  5. Duration of Sensory Encoding
    • Phasic receptors: activated by change in stimulus (when stimulus begins AND ends), adapt quickly
    • Tonic receptors: respond as long as stimulus is present
  6. Types of Receptors by Stimulus Modality
    • Thermoreceptors (hot and cold)
    • Photoreceptors (light)
    • Nociceptors (pain)
    • Chemoreceptors (chemicals)
    • Mechanoreceptors (vibration, touch, pressure, and stretch)
  7. Type of Receptors by Stimulus Origin
    • Exteroreceptors (stimulus outside body)
    • Interoreceptors (stimulus in internal organs)
    • Proprioceptors (position of the body)
  8. Distribution of Receptors
    • General (receptors located throughout the body)
    • Special (receptors in special sense organ)
  9. Receptive Fields
    Each sensory neuron responds to a very specific stimulus like somatosensory, olfactory, gustatory, visual, and auditory neurons
  10. Size of Receptive Fields
    • Bigger dendritic field = bigger receptive field
    • Bigger receptive field + fewer sensory neurons = decreased ability to determine location of stimulus
  11. Mechanism of Transduction
    • Touch stimuli deform skin and underlying sensory endings
    • Stretch in the sensory endings causes Na+ channels to open, depolarization and action potential generation
  12. Taste Transduction
    • A different mechanism for each type of taste (sour, salty, sweet, bitter and umami)
    • Sour and salty tastants can enter cell and depolarize it
    • Sweet, bitter, and umami have separate receptors on taste cells
  13. Transduction of Odorants
    Odorant binds to its receptor, leads to depolarization
  14. Projections of Olfactory Bulb
    Note that olfactory system is the ONLY sensory system in which all input doesn't go through thalamus
  15. Neuronal Responses to Light
    • Photoreceptors release Glu in dark which inhibits bipolar cells thus no activation of ganglion cells
    • Photoreceptors stop releasing Glu in light. Bipolar and ganglion cells are active
  16. Spacial Discrimination in Ganglion Cells
    Ganglion cells receiving input from rods have larger receptive fields (= poor spatial discrimination)
  17. Visual Pathway
    • Some ganglion cells decussate in optic chiasm
    • Synapse in thalamus, then go to occipital lobe
  18. Cortical Processing
    • Processing simple to complex
    • V1 cell active with light in certain location
    • IT call only active when viewing specific face