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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
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Modality of Sensory Encoding
- Type of stimulus
- Determined by types of neurons activated
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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
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Intensity if Sensory Encoding
Usually determined by number of activated neurons or frequency of action potentials
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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
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Types of Receptors by Stimulus Modality
- Thermoreceptors (hot and cold)
- Photoreceptors (light)
- Nociceptors (pain)
- Chemoreceptors (chemicals)
- Mechanoreceptors (vibration, touch, pressure, and stretch)
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Type of Receptors by Stimulus Origin
- Exteroreceptors (stimulus outside body)
- Interoreceptors (stimulus in internal organs)
- Proprioceptors (position of the body)
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Distribution of Receptors
- General (receptors located throughout the body)
- Special (receptors in special sense organ)
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Receptive Fields
Each sensory neuron responds to a very specific stimulus like somatosensory, olfactory, gustatory, visual, and auditory neurons
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Size of Receptive Fields
- Bigger dendritic field = bigger receptive field
- Bigger receptive field + fewer sensory neurons = decreased ability to determine location of stimulus
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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
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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
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Transduction of Odorants
Odorant binds to its receptor, leads to depolarization
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Projections of Olfactory Bulb
Note that olfactory system is the ONLY sensory system in which all input doesn't go through thalamus
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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
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Spacial Discrimination in Ganglion Cells
Ganglion cells receiving input from rods have larger receptive fields (= poor spatial discrimination)
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Visual Pathway
- Some ganglion cells decussate in optic chiasm
- Synapse in thalamus, then go to occipital lobe
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Cortical Processing
- Processing simple to complex
- V1 cell active with light in certain location
- IT call only active when viewing specific face
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