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PSYB51 ch.13

Olfaction

QuestionAnswer
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
Created by: Ugly.Beauty
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