auditory: stimulus auditory: receptorswebs.wofford.edu/reidak/psych 150/psy 150 - chapter...
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9/27/2011
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Auditory: Stimulus
440 Hz 1500 Hz• Sound waves vary in amplitude (intensity) and frequency (Hz or cycles per second – tone)
• Humans can detect 20 Hz to 20,000 Hz frequencies at their best (i.e. no environmental damage)
Auditory: Receptors• Outer ear Middle ear Inner ear = receptors
Auditory: Transduction• The tectorial membrane “bounces” on the hair cells in rhythmic fashion to physically open ion channels and produce action potentials in the cochlear nerve
Auditory: Afferent Signals• Receptors in the cochlea are “tuned” to send action potential only for certain frequencies from high (outermost) to low (innermost).
• More receptors/ afferent signals for 500‐5,000 Hz
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Auditory: Pathways
• Each auditory cortex receives input from both ears BUTprimarily from the contralateral ear.
• Neural signal goes to the primary auditory cortex in the temporal lobe.
Auditory: Perception (Left Brain)
• There are specialized brain regions for complex sounds and language. (secondary auditory cortex = language & music)
Green = primary auditory cortex
Brown = language comprehension area
Gold = language production area
Auditory: Perception (Right Brain)
• The same areas of the right hemisphere appear to be specialized to detect all environmental sounds other than language.
Auditory: Summary• Stimulus: 20‐20,000 Hz sound waves• Receptors: Hair cells in the cochlea• Transduction: Physical opening of ion channels in the cochlea by the tectorial membrane
• Afferent Signals: unevenly distributed to allow most signals for range of human speech
• Pathway: contralateral to primary auditory cortex • CNS Areas: Primary in superior temporal lobe; Wernicke’s, Broca’s, and right hemisphere specializations
• Perception: Complex processing of language in the left hemisphere and music in the right hemisphere.
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The chemical senses . . .
• Taste and olfaction are grouped together as “chemical senses” because chemicals are the stimuli that activate both senses.
PHYSICAL STIMULUS:• Taste (gustatory system) stimuli are dissolved chemicals (in solution or saliva)
• Smell (olfactory system) stimuli are typically chemicals suspended in the air
Olfactory Receptors
• Olfactory receptors are found in the back of the nasal cavity. (regenerate)
• Protected by mucous layer
• Olfactory receptors are modified neurons with cilia
OlfactoryTransduction
• Olfactory receptors are similar to the neurotransmitter receptors (both stimuli are chemicals, right?)
• Odorants fit only in certain receptors like a lock & key
LOCK & KEY
Olfactory:Signals
• Chemicals bind tothe receptor causing a reactionin the neuron to send a neural signal to the olfactory bulb
• Each odor has its own pattern of activity
LOCK & KEY
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Olfactory: Pathways & CNS Areas
• What is your perception of odors?
• Olfactory bulb to:• Amygdala –emotional value of stimuli
• Frontal Lobe –memories, moods
Olfactory Perception
• Projections to the limbic system and frontal lobe closely link smell with memories and emotions
• Evolutionary pressure to remember harmful stimuli – strong long‐term memory mechanism
• Olfaction is a powerful component to flavor linked with gustation (taste).
Olfactory: Summary• Stimulus: Chemicals in air from nostrils or mouth• Receptors: Olfactory receptor neurons with lock & key shape binding
• Transduction: Binding activates sending signal• Afferent Signals: Odors produce unique patterns• Pathway: Olfactory bulb Amygdala & Frontal Lobe
• CNS Areas & Perceptions: Amygdala (emotional value), Frontal Lobe (memory association), Orbitofrontal cortex (flavor perception)
Gustatory: Receptors
• Taste buds are found on the surface of the tongue
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Gustatory: Transduction
Chemicals dissolve in saliva and enter the taste bud pits
Chemicals are interact with receptors on the taste receptor cells
Taste cells release neurotransmitters on afferent taste neurons
Gustatory: Pathways
• 3 afferent sensory nerve relay taste sensations to the brain.
• Insular cortex = primary taste quality (between the temporal & parietal lobes)
Gustatory: CNS Areas
• Many secondary areas
Limbic system & Frontal LobeHypothalamus – hunger & satiety
Flavor Perception
• Flavor ‐ the overall perception of an oral stimulant
• Includes taste, smell, texture, temperature, even color & appearance
Black bars = normal Gray bars = pinched nose
% subjects correctly identify flavored solutions
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Gustatory: Summary• Stimulus: Chemicals in saliva or solutions• Receptors: Taste receptor cells in taste buds• Transduction: Different for each taste category• Afferent Pathway: 3 nerves from oral cavity to the NST of the brainstem
• CNS Areas & Perceptions: Insular cortex (primary taste categories), Amygdala (cravings and aversions), Frontal Lobe (memory association), Hypothalamus (hunger & satiety) Orbitofrontal cortex (flavor perception)
Somatosensory: Stimuli & Receptors
Somatosensory: Transduction
• Mechanoreceptors (Meisners, Merkel, Ruffini, Pacinian, and Hair cells): physical movement opens ion channels to depolarize the neuron and send action potentials to the brain
• Bare or Free Nerve endings: detect increases or decreases in temperature and chemicals released in response to tissue damage (like histamines)
Somatosensory: Pathway• Sensory neurons enter the spinal cord organized by body region from toe to head, form synapses, & then send axons up the dorsal spinal cord
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Somatosensory: Pathway• Temperature and Pain pathway comes into the spinal cord, crosses over, then goes up through the anterolateral pathway
• Special destination: anterior cingulate gyrus (pain perception)
Plasticity in the CNS
Loss of a finger does not result in loss of cortical use - cortical area is taken over by adjacent areas.
• You can not replace CNS neurons but their connections can change with use (experience)
• For example: each finger is represented in the sensory cortex.
Temperature & Pain
• Free nerve endings are specialized to detect:– changes in temperature
• Cold fibers respond only to decreasing temp.• Warm fibers respond only to increasing temp.
– extreme stimuli• Pressure (cuts) or temperature (burns)
– chemical signals from tissue damage• Histamines, capsaicin, etc.
• Pain following injury is often 2 sensations:• Sharp immediate pain• Dull throbbing secondary pain• Speed difference due to myelin on axons!
Pain Perception
- unmyelinated neurons- myelinated neurons
Immediate Sensation Delayed Sensation Overall Perception
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Controlling PainSensations & Perceptions
• Pain perception can be modified!• Reduction of the sensation through the :
Natural Pain Management System
• Efferent signal from the brain to the spinal cord at pain sensation level.
Pain input to brain
Brain output to block pain
• Localized release of endorphins to block the sensation at a precise site
Somatosensory: Summary• Stimulus: mechanical, thermal, and chemical• Receptors: Mechanoreceptors & Free nerve endings• Transduction: Physical movement, change in temp., or chemicals released by tissue damage
• Afferent Pathway: Dorsal column pathway for touch, anterolateral pathway for temp and pain
• CNS Areas & Perceptions: Postcentral gyrus is the primary somatosensory cortex (touch organized by body part); anterior cingulate gyrus (pain)
• Gate control theory is natural pain management
Psychophysics
• Psychophysics is the study of the our perceptions (behavior) to physical stimuli
• The first field of experimental psychology!• Two types of thresholds:
– Absolute: can you detect a stimulus or not?– Difference: can you detect a change in a stimulus?
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Signal Detection Theory
• The sensory system must deal with interference and noise to detect appropriate stimuli
• There are four possible outcomes when trying to detect stimuli: hits, misses, false alarms, and correct rejections
Difference Thresholds
• Usually our perception of stimuli does not exactly match changes in the actual stimulus
• Weber’s law provided an equation to quantify (& predict) changes in perceptions based on changes in stimuli
• 1800s – 1st quantification of brain activity!
Sensory Adaptation
• Decrease in perception due to a constant stimulus• Bottom‐up adaptation at the level of the receptor:
–Olfactory and Gustatory Systems• Top‐down adaptation at the level of the thalamus:
–Auditory & Somatosensory Systems
• Allows us to focus are relevant stimuli and ignore unimportant stimuli
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