Sensory Physiology Ch. 10 Flashcards
Sensing the environment
Receptors are tuned to specific stimuli (modalities)
Chemoreceptor
Mechanoreceptor
Photoreceptor
Thermoreceptor
Nociceptor
Proprioceptor
Function of Sensory System
1.Signal detection
2.Discrimination of some aspects of the sensory input
Estimation
What must be estimated from the input: of Sensory System
- Qualitative features: modality: what is stimulus?
- Quantitative features: intensity
- Temporal features: duration or frequency
- Spatial location: where
Sensory estimation
Depends on:
Specific receptor cell activity
Specific processing area in the brain
Sender and receiver!
Sensory coding
Receptor cell sends type of stimulus
Remember: Kind of receptor activated + brain processing determine perception
Receptor cell sends intensity of stimulus
frequency of APs
Receptor cell sends location of stimulus
receptive field
Receptive Field
Area of skin that, when stimulated, changes the firing rate of a neuron
Size of area depends on density of receptors in that region of skin
The more receptors, the smaller the field, the larger the brain area for processing.
Sensory Acuity
Ability to detect details
A small receptive field = greater tactile acuity – sharpness of the sensation
Two-point discrimination threshold
Receptive fields can be determined by measuring at what distance a person can perceive two separate points of touch.
Measurement of tactile acuity.
Generator potential or receptor potential
Equivalent to EPSPs
Produced in response to strong enough stimulus
Generates action potential if it reaches threshold
Sensory physiology
A signal from a specific sensory cell is sent to a specific processing center in brain.
Because of specific anatomical connection, signal indicates sensory modality and location of the stimulus.
Stimulus intensity is indicated by the frequency of APs.
Input-Output Relations
Receptor response is proportional to logarithm of the stimulus intensity (semi-log).
Meaning: high-intensity end of scale becomes compressed Extending dynamic range of detection.
Sunlight is 109 times more intense than moonlight!
Human auditory system capable of detection sound intensity differing 12 orders of magnitude!
Range fractionation:
different cells with different but overlapping sensitivities, extending dynamic range
Function of sensory adaptation?
Extending dynamic range of detection, allowing detection of weak and strong stimuli.
Phasic response:
Firing activity only when stimulus strength changes (on/off)
Tonic response:
Firing activity continues for the duration of the stimulus
Lateral Inhibition
Can occur with a group of adjacent receptor cells, such as found in the eye.
Neighboring cells may be connected with each other by inhibitory synapses.
Result: Enhanced Contrast
Sensory Pathways
Convey the type and location of sensory stimulus.
Type of stimulus: because of type of receptor activated.
Location: because brain has a map of location of each receptor.
Sensory Pathways
Olfactory pathways from the nose project directly to the cortex
All other pathways pass through the thalamus before they project to their relevant cortical area
Sensory Processing
Somatosensory cortex: somatic senses
Sensory association areas (integration of all sensory input)
Visual cortex
Auditory cortex
Olfactory cortex
Somatosensory Processing
Somatic Senses: somesthetic (“body feelings”) sensations:
touch, pressure, heat, cold, pain, from surface of the body
This information is “projected” to the somatosensory cortex in mammals.
Somatotopic order in human primary sensory cortex
More brain area means more information processing and relatively more important.
Sensory Physiology: Big Picture
Stimulus energy is “converted” to action potential energy.
Same response for all different stimuli.
Signals are interpreted as sight, sound, taste, depending on which sensory cells send the signal and which tissue in CNS receives it!
Note, modality is not coded for by AP!
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