Chapter 14

Question 1

olfaction

Answer 1

The sense of smell.

Question 2

gustation

Answer 2

The sense of taste.

Question 3

orthonasal olfaction

Answer 3

Sniffing in and perceiving odors through our nostrils, which occurs when we are smelling something that is in the air.

Question 4

retronasal olfaction

Answer 4

perceiving odors through the mouth while breathing and chewing; gives us experience of flavor.

Question 5

odor

Answer 5

The translation of a chemical stimulus into the sensation and odor percept.

Question 6

odorant

Answer 6

A molecule that is defined by its physiochemical characteristics and that can be translated by the nervous system into the perception of a smell.

Question 7

olfactory cleft

Answer 7

A narrow space at the back of the nose into which air flows and where the olfactory epithelium is located.

Question 8

olfactory epithelium

Answer 8

A secretory mucous membrane in the nose whose primary function is to detect odorants in inhaled air; contains three types of cells: olfactory sensory neurons, basal cells and supporting cells.

Question 9

nasal dominance

Answer 9

The asymmetry characterizing the intake of air by the two nostrils, which leads to differing sensitivity to odorants between the two nostrils; alternates nostrils throughout the day without predictability.

Question 10

supporting cell

Answer 10

One of three types of cells in olfactory epithelium; provide metabolic and physical support for the olfactory sensory neurons.

Question 11

basal cell

Answer 11

One of three types of cells in olfactory epithelium; are the precursor cells to OSNs.

Question 12

olfactory sensory neuron (OSN)

Answer 12

One of three types of cells in olfactory epithelium (main one); are small neurons located within the mucous layer. The cilia on the OSN dendrites contain receptor sites for odorant molecules.

Question 13

cilium

Answer 13

Any of the hairlike protrusions on the dendrites of OSNs. The receptor sites for odorant molecules are on the cilia, which are the first structures involved in olfactory signal transduction.

Question 14

odorant receptor (OR)

Answer 14

The region on the cilia of olfactory sensory neurons where odorant molecules bind.

Question 15

glomerulus

Answer 15

Any of the spherical conglomerates containing the incoming icons of the olfactory sensory neurons. Each OSN converges onto two glomeruli (one medial, one lateral).

Question 16

olfactory bulb

Answer 16

A blueberry-sized extension of the brain just above the nose, where olfactory info is first processed; there are two, one in each brain hemisphere.

Question 17

cribriform plate

Answer 17

A bony structure riddled with tiny holes that separates the nose from the brain at the level of the eyebrows. The axons from the OSNs pass through the holes of the plate to enter the brain.

Question 18

anosmia

Answer 18

The total inability to smell, most often resulting from sinus illness or head trauma.

Question 19

olfactory nerve

Answer 19

The first cranial nerve. Axons of the OSNs bundle together after passing through cribriform plate to form the olfactory nerve, which conducts impulses from the olfactory epithelium in the nose to the olfactory bulb. Also called cranial nerve I.

Question 20

ipsilateral

Answer 20

Referring to the same side of the body (or brain).

Question 21

juxtaglomerular neurons

Answer 21

The first layer of cells surrounding the glomeruli.
They are a mixture of excitatory and inhibitory cells and respond to a wide range of odorants. The selectivity of neurons to specific odorants increases in a gradient from the surface of the olfactory bulb to the deeper layers.

Question 22

tufted cells

Answer 22

The next layer of cells after the juxtaglomerular neurons. They respond to fewer odorants than the juxtaglomerular neurons, but more than neurons at the deepest layer of cells.

Question 23

mitral cells

Answer 23

The deepest layer of neurons in the olfactory bulb. Each mitral cell responds to only a few specific odorants.

Question 24

granular cells

Answer 24

Like mitral cells, granular cells are at the deepest level of the olfactory bulb. They comprise an extensive network of inhibitory neurons, integrate input from all the earlier projections, and are thought to be the basis of specific odorant identification.

Question 25

olfactory tract

Answer 25

The bundle of axons of the mitral and tufted cells within the olfactory bulb that sends odor information to the primary olfactory cortex.

Question 26

primary olfactory cortex / piriform cortex

Answer 26

The neural area where olfactory information is first processed. It comprises the amygdala, parahippocampal gyrus, and interconnected areas, and it interacts closely with the entorhinal cortex.

Question 27

amygdala-hippocampal complex

Answer 27

The conjoined regions of the amygdala and hippocampus, which are key structures in the limbic system. This complex is critically involved in the unique emotional and associative properties of olfactory cognition.

Question 28

entorhinal cortex

Answer 28

A phylogenetically old cortical region that provides the major sensory association input into the hippocampus. The entorhinal cortex also receives direct projections from olfactory regions.

Question 29

limbic system

Answer 29

The group of neural structures that includes the olfactory cortex, the amygdala, the hippocampus, the piriform cortex, and the entorhinal cortex; is involved in many aspects of emotion and memory. Olfaction is unique among the senses for its direct connection to the limbic system.

Question 30

trigeminal nerve

Answer 30

The fifth cranial nerve, which transmits info about the “feel” of an odorant as well as pain and irritation sensations; also called cranial nerve V.

Question 31

shape-pattern theory

Answer 31

The current dominant biochemical theory for how chemicals come to be perceived as specific odors; contends that different scents—as a function of the fit between odorant shape and OR shape—activate different arrays of olfactory receptors in the olfactory epithelia. These various arrays produce specific firing patterns of neurons in the olfactory bulbs, which then determine the particular scent we perceive.

Question 32

vibration theory

Answer 32

An alternative to shape-pattern theory for describing how olfaction works. Vibration theory proposes that every odorant has a different vibrational frequency and that molecules that produce the same vibrational frequencies will smell the same.

Question 33

specific anosmia

Answer 33

The inability to smell one specific compound amid otherwise normal smell perception.

Question 34

stereoisomers

Answer 34

Isomers (molecules that can exist in different structural forms) in which the spatial arrangements of the atoms are mirror-image rotations of one another, like a right and left hand.

Question 35

binaural rivalry

Answer 35

Competition between the two nostrils for odor perception.
When a different scent is presented
to each nostril simultaneously, we perceive each scent to be alternating back and forth with the other, and not a blend of the two scents.

Question 36

olfactory white

Answer 36

The olfactory equivalent of white noise or the color white.
When at least 30 odorants of equal intensity that span olfactory physiochemical and psychological (perceptual) space are mixed, they produce a resultant odor perception that is the same as that of every other mixture of 30 odorants meeting the same span and equivalent intensity criteria, even though the various mixtures do not share any common odorants.

Question 37

psychophysics

Answer 37

The science of defining quantitative relationships between physical and psychological (subjective,
perceptual) events.

Question 38

staircase method

Answer 38

A psychophysical method for determining the concentration of a stimulus required for detection at the threshold level; a method of limits. A stimulus (e.g., odorant) is presented in an ascending concentration sequence until detection is indicated, and then the concentration is shifted to a descending sequence until the response changes to “no detection.” This ascending and descending sequence is typically repeated several times, and the concentrations at which reversals occur are averaged to determine the threshold detection level of that odorant for a given individual.

Question 39

triangle test

Answer 39

A test in which a participant is given three odorants to smell, of which two are the same and one is different. The participant is required to state which is the odd odor out. Typically, the order in which the three odorants are given (e.g., same, same, different; different, same, same; same, different, same) is manipulated and the test is repeated several times for greater accuracy.

Question 40

tip-of-the-nose phenomenon

Answer 40

The inability to name an odor, even though it is very familiar. Contrary to the tip-of- the-tongue phenomenon, one has no lexical access to the name of the odor, such as first letter, rhyme, number of syllables, and so on, when in the tip-of- the-nose state. This is an example of how language and olfactory perception are deeply disconnected.

Question 41

G protein-coupled receptor (GPCR)

Answer 41

Any of the class of receptors that are present on the surface of olfactory sensory neurons. All GPCRs are characterized by a common structural feature of seven membrane-spanning helices.

Question 42

receptor adaptation

Answer 42

The biochemical phenomenon that occurs after continual exposure to an odorant, whereby receptors are no longer available to respond to the odorant and detection ceases.

Question 43

cross-adaptation

Answer 43

The reduction in detection of one odorant following
exposure to a prior odorant. Cross-adaptation is presumed to occur because the components of the odors (or odorants) in question share one or more olfactory receptors for their transduction, but the order in which odorants are presented also plays a role

Question 44

cognitive habituation

Answer 44

The psychological process by which, after longterm exposure to an odor, one no longer has the ability to detect that odor or has very diminished detection ability

Question 45

odor hedonics

Answer 45

The liking dimension of odor perception, typically measured

by ratings of an odor’s perceived pleasantness, familiarity, and intensity.

Question 46

learned taste aversion

Answer 46

The avoidance of a novel flavor after it has been paired with gastric illness. The smell, not the taste, of the substance is key for the learned aversion response in humans.

Question 47

orbitofrontal cortex (OFC)

Answer 47

The part of the frontal lobe of the cortex that lies
behind the bone (orbit) containing the eyes. The OFC is responsible for the conscious experience of olfaction, as well as the integration of pleasure and displeasure from food. The OFC is also involved in many other functions, and it is critical for assigning affective value to stimuli—in other words, determining hedonic meaning. It is also referred to as the secondary olfactory cortex and the secondary taste cortex.

Question 48

main olfactory bulb (MOB)

Answer 48

The rounded extension of the brain just above the nose that is the first region of the brain where smells are processed. In humans we refer simply to olfactory bulb(s); in nonhuman animals with accessory olfactory bulbs, we distinguish between main and accessory.

Question 49

accessory olfactory bulb (AOB)

Answer 49

A neural structure found in nonhuman animals that is smaller than the main olfactory bulb and located behind it and that receives input from the vomeronasal organ.

Question 50

vomeronasal organ (VNO)

Answer 50

Found in nonhuman animals, it is a chemical-sensing organ at the base of the nasal cavity with a curved tubular shape. The VNO evolved to detect chemicals that cannot be processed by ORs, such as large and/or aqueous molecules, the types of molecules that constitute pheromones. Also called Jacobson’s organ.

Question 51

pheromone

Answer 51

A chemical emitted by one member of a species that triggers a physiological or behavioral response
in another member of the same species. Pheromones are signals for chemical communication and may or may not have any smell.

Question 52

lordosis

Answer 52

The position that females of some species (e.g., pigs and rats) need to assume in order to be impregnated. It involves the downward curving of the spinal column and exposure of the genitals.

Question 53

releaser pheromone

Answer 53

A pheromone that triggers an immediate behavioral response among conspecifics.

Question 54

primer pheromone

Answer 54

A pheromone that triggers a physiological (often hormonal) change among conspecifics. This effect usually involves prolonged pheromone exposure.

Question 55

chemosignal

Answer 55

Any of various chemicals emitted by humans that are detected by the olfactory system and that may have some effect on the mood, behavior, hormonal status, and/ or sexual arousal of other humans.

Question 56

aromatherapy

Answer 56

The manipulation of odors to influence mood, performance, and well-being as well as the physiological correlates of emotion such as heart rate, blood pressure, and sleep.