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PSYB51 ch.13
Olfaction
Question | Answer |
---|---|
Olfaction | sense of smell |
Gustation | sense of taste |
Odor | general smell sensation of a particular quality. When referring to specific chemical entity, term odorant should be used |
Odorant | specific aromatic chemical |
Olfactory cleft | narrow space @ the back of the nose into which air flows, where the main olfactory epithelium is located |
Olfactory epithelium; secretory mucosa in human nose whose primary function is to detect odorants in the inspired air. | Contains 3 types of cells: olfactory sensory neurons, basal cells, supporting cells. Located on both sides on the upper portion of the nasal cavity and olfactory clefts |
Supporting cells | 1 of the 3 types of cells in the olfactory epithelium. Provides metabolic & physical support for OSNs |
Basal cells | 1 of the 3 types of cells in olfactory epithelium. Precursor cells to olfactory sensory neurons |
Olfactory sensory neurons (OSNs) | main cell of olfactory epithelium. Are small neurons located beneath a watery mucous layer in the epithelium. Cilia on the OSN dendrites contain receptor sites for odorant molecules. |
Cilia | hairlike protrusions on the dendrites of OSNs. The receptor sites for odorant molecules are on the cilia, which are the 1st structures involved in olfactory signal transduction |
Olfactory receptor | region on the cilia of olfactory sensory neurons where odorant molecules bind |
Cribriform plate | bony structure riddled w/tiny holes, @ level of the eyebrows, that separates the nose from the brain. Axons frm the OSNs pass through the tiny holes of the cribriform plate to enter the brain |
Anosmia | total inability to smell, most often resulting from sinus illness or head trauma |
Olfactory (I) nerves | 1st pair of cranial nerves. Axons of the OSNs bundle together after passing through the cribriform plate to form the olfactory nerve |
Olfactory bulb | located just above the nose and where olfactory info. is 1st processed. 2 olfactory bulbs, 1 in each brain hemisphere, corresponding to the right & left nostrils |
Ipsilateral | referring to the same side of the body or brain |
Mitral cells | main projective output neurons in the olfactory bulbs |
Tufted cells | secondary class of output neurons in the olfactory bulbs |
Glomeruli | spherical conglomerates containing the incoming axons of the OSNs. Each OSN converges onto 2 glomeruli (1 medial, 1 lateral) |
Primary olfactory cortex | neural area where olfactory info. is 1st processed, which incl. the amygdala-hippocampal complex & the entorhinal cortex |
Amygdala-hippocampal complex | conjoined regions of the amygdala & hippocampus which are key structures in the limbic system. This complex is critical for the unique emotional & associative properties of olfactory cognition |
Entorhinal cortex | phylogenetically old corticol region that provides the major sensory assoc. input into the hippocampus. Also receives direct projections frm olfactory regions |
Limbic system | contains neural structures: olfactory cortex, amygdala, hippocampus, piriform cortex, & entorhinal cortex. Limbic system is involved in many aspects of emotion & memory. Olfaction is unique b/c of its connection to limbic system |
Trigeminal (V) nerves | cranial nerves which transmit info. abt the ‘feel’ of an odorant (s/a menthol feels cool, cinnamon feels warm), as well as pain and irritation sensations (s/a ammonia feels burning) |
Shape-pattern theory; biochemical theory of how chemical come to be perceived as specific odorants. | diff. scents as a function of odorant-shape to OR-shape fit, activate diff. types of olfactory receptors in the epithelia (pl.). These receptors produce specific firing patterns of neurons in olfactory bulb, which determine particular scent we perceive |
Specific anosmia | inability to smell one specific compound amid otherwise normal smell perception |
Stereoisomers | isomers in which spatial arrangement of the atoms are mirror-image rotations of one another, like a right & left hand. Also called optical isomers. |
Psychophysics | science of defining quantitative relationships b/w physical & psychological (subjective) events. |
Staircase method: psychophysical method of determining the concentration of a stimulus required for detection @ threshold level | stimulus s/a odorant is presented in increasing concentration sequence until detected; then concentration is shifted to decreasing the stimulus until there is no detection. Repeated several times then scores are avg. to determine threshold detection level |
Triangle test; participant given 3 odors to smell of which 2 are the same & 1 is different | required to state which is the odd odor out; order of the odors manipulated easily & test repeated many times to achieve greater accuracy. |
Tip-of-the-nose phenomenon; inability to name an odorant, even if it is very familiar | there is no verbal connection to odor unlike for the tip-of-the-tongue phenomenon to name the odorant and shows the disconnect b/w olfaction and lang. |
G protein-coupled receptors (GPCRs) | class of receptors that are present on the surface of OSNs. All GPCRs are characterized by common structural feature of 7 membrane-spanning alpha-helices |
Receptor adaptation | biochemical phenomenon that occurs after continuous exposure to an odorant, whereby the receptors stop responding to the odorant & the detection ceases |
Cross-adaptation; reduction in detection of an odorant following exposure to another odorant | cross-adaptation presumed to occur b/c the 2 odorants share 1 or more olfactory receptors for their transduction, but the order of odorant presentation also plays a role |
Cognitive habituation | after long-term exposure to an odorant, one is no longer able to detect that odorant or has very diminished detection ability (eg. working in bakery rather than stepping in for a few mins.) |
Odor hedonics | liking dimension of odor perception, typically measured w/scales pertaining to an odorant’s perceived pleasantness, familiarity, & intensity. |
Gestation | fetal development during pregnancy. |
Trigeminal system; innervated by trigeminal nerve | enables us to feel gustatory & olfactory experiences s/a burning & cooling |
To be an odorant | (1) must be volatile (eg. float through air) (2) small (approx. less than 5.8 *10 -22) & (3) hydrophobic (repellent to water) |
Nose | primary function of the nose is to warm & humidify air that we breathe, the nose also directs odorants onto the olfactory epithelium |
Function of OSNs | OSN collects odorant molecules via receptors on its dendrites & sends action potentials (APs) to the brain through its axons |
Fractured cribriform plate | slices off olfactory axons & induces anosmia- the total absence of a sense of smell |
Smell recovery after cribriform plate damage | stem cells in olfactory epithelium can form new OSNs; but fractured cribriform plates scar over preventing the new OSN axons frm passing through to the brain & loss of sense of smell for life |
Anosmia | most common way to lose sense of smell is by upper respiratory tract infection (eg. sinus infection); 2nd common is sinonasal disease (polyps) followed by head trauma --- 30% of anosmias caused by head trauma |
How smells are perceived | olfactory info. is transmitted frm the olfactory bulb to the primary olfactory cortex & the amygdala-hippocampal complex of the limbic system in the 1st stage of perceptual-cognitive processing |
sensation in olfaction occurs | when a scent is neurally registered |
perception in olfaction occurs | when we become aware of detecting the scent |
Linda Buck & Richard Axel | showed that the genome contains abt 1000 different olfactory receptor genes. each of which codes for a single type of OR |
Recent biochemical research in olfaction (after shape-pattern theory) suggests | scents are detected by means of combinatorial code. Diff. scents activate diff. ORs in the olfactory epithelia producing specific firing patterns of neurons in olfactory bulb; pattern of electrical activation determines scent we perceive |
how do we process odorant mixtures | synthesis and analysis; most likely process odorants synthetically b/c we perceive mixtures of odors as unitary wholes. Analysis of odor mixtures requires prior training |
olfactory detection thresholds depend on | odorant molecules w/longer or shorter chains (the longer chains are easily detected); gender (women have lower olfactory detection);age (ability to detect odor declines w/age b/c * # of OR that die off continues to rise beyond # that are regenerated |
odor recognition | ability to remember whether or not we've smelled an odor before. Takes as much as 3 times as many odor molecules floating thru the nose to recognize an odor than it does to simply recognize 1; also durability of recognition can last from 30 sec to 10 yrs |
staircase method | odor is presented in ever-increasing concentration increments until the participant reports being able to "smell something" for sev. increments; then odor con. is decreased incrementally until the participants reports no detection |
reversals repeated several times & odorant concentrations @ pt.where reversals occur are avg. to determine the approximate con. needed for that person to detect odorant. concentration can be fine-tuned for precision | |
Staircase methods can be used to | determine detection thresholds across a range of different odors for specific and individualistic testing |
triangle test | participant given 3 odors to smell of which 2 are the same & 1 is diff. participant required to state which is the odd odor out; order of odorants are manipulated & test repeated many times to est. accuracy |
receptor adaptation | the precise length of time for adaptation to occur varies as a function of both the individual & the odorant. also depends on odor concentration & to allow odors to last, dispense odor intermittently (eg. air freshener or IKEA wood smell) |
receptor recycling (receptor adaptation) | odorant binding to an OR causes the OR to be internalized into its cell body where it becomes unbound frm the odorant & is then recycled through the cell & emerges again in # of minutes |
cross-adaptation | exposure to 1 odorant can raise the odor detection threshold for a 2nd completely diff. odorant (eg. perfume store); occurs when odorants rely on similar sets of olfactory receptors |
cognitive habituation involves 3 mechanisms as suggested by Dalton (2002) | 1)ORs that are internalized into their cell bodies during odor adaptation may be more hindered after continuous exposure & take much longer to recycle than they normally would |
2) due to continuous exposure odor molecules may be absorbed in the bloodstream then transported to the ORs via nasal capillaries when we breathe out thru the nose | |
3) cognitive-emotional factors may also be involved |