Auditory: Stimulus. Auditory: Receptors. Auditory: Transduction. Auditory: Afferent Signals

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1 Auditory: Stimulus Auditory: Receptors Outer ear Middle ear Inner ear = receptors 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: 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 1

2 Each auditory cortex receives input from both ears BUT primarily from the contralateral ear. Neural signal goes to the primary auditory cortex in the temporal lobe. Auditory: Pathways 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. 2

3 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 Olfactory Transduction 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 LOCK & KEY Chemicals bind to the receptor causing a reaction in the neuron to send a neural signal to the olfactory bulb Each odor has its own pattern of activity 3

4 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 4

5 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 3 afferent sensory nerve relay taste sensations to the brain. Insular cortex = primary taste quality (between the temporal & parietal lobes) Gustatory: Pathways Many secondary areas Gustatory: CNS Areas Limbic system & Frontal Lobe Hypothalamus hunger & satiety Flavor Perception Black bars = normal Gray bars = pinched nose % subjects correctly identify flavored solutions Flavor the overall perception of an oral stimulant Includes taste, smell, texture, temperature, even color & appearance 5

6 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) Sensory neurons enter the spinal cord organized by body region from toe to head, form synapses, & then send axons up the dorsal spinal cord Somatosensory: Pathway 6

7 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 You can not replace CNS neurons but their connections can change with use (experience) For example: each finger is represented in the sensory cortex. Loss of a finger does not result in loss of cortical use - cortical area is taken over by adjacent areas. 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 Perception Pain following injury is often 2 sensations: Sharp immediate pain - myelinated neurons Dull throbbing secondary pain - unmyelinated neurons Speed difference due to myelin on axons! Immediate Sensation Delayed Sensation Overall Perception 7

8 Controlling Pain Sensations & 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. Localized release of endorphins to block the sensation at a precise site Brain output to block pain Pain input to brain 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? 8

9 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 1 st 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 9