Chapter 14- Olfaction

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. This is what gives us the experience of flavor.

Question 5

Odor

Answer 5

The translation of a chemical stimulus into the sensation of an order percept. For example, “The cake has a chocolate odor.”

Question 6

Odorant

Answer 6

A specific molecule defined by its physicochemical characteristics that can be translated by the central nervous system into the perception of an odor. For example, “The odorant methyl salicylate has the odor of wintergreen mint.”

Question 7

Volatile

Answer 7

A molecule that is buoyant in air and therefore can be inhaled. Odorants are volatile molecules.

Question 8

Turbinates

Answer 8

Curled protrusions inside the nasal cavity. The small ridges of the turbinates create turbulence to incoming air, causing a small puff of each inhalation to rise and pass through the olfactory cleft facilitating the ability to detect odorants.

Question 9

Olfactory Cleft

Answer 9

A narrow space at the back of the nose into which air flows and where the olfactory epithelium is located. It can vary in size.

Question 10

Olfactory Epithelium

Answer 10

A mucous membrane in the nose whose primary function is to detect odorants in inhaled air. Located on both sides of the upper portion of the nasal cavity (the olfactory clefts), the olfactory epithelium contains three types of cells: sustentacular cells, basal cells, and olfactory sensory neurons.

Question 11

Nasal Dominance

Answer 11

The asymmetry characterizing the intake of air by the two nostrils, which leads to differing sensitivity to odorants between the two nostrils. Nasal dominance alternates nostrils throughout the day, but there is no predictability for when the nostrils alternate.

Question 12

Sustentacular or Supporting Cell

Answer 12

One of the three types of cells in the olfactory epithelium. They provide metabolic and physical support for the olfactory sensory neurons. Also called stem cells.

Question 13

Basal Cell or Stem Cell

Answer 13

One of the three types of cells in the olfactory epithelium. They are the precursor cells to olfactory sensory neurons.

Question 14

Olfactory Sensory Neuron (OSN)

Answer 14

One of the three cell types- the main one- in the olfactory epithelium. OSNs are small neurons located within a mucous layer in the epithelium. Cilia on the OSN dendrites contain receptor sites for odorant molecules.

Question 15

Cilium

Answer 15

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

Question 16

Odorant Receptor (OR)

Answer 16

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

Question 17

Glomerulus

Answer 17

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

Question 18

G Protein-Coupled Receptor (GPCR)

Answer 18

Any of a class of receptors that are present on the cilia of olfactory sensory neurons. All GPCRs are characterized by a common structural feature of seven membrane-spanning helices. Binding of a substrate molecule to the receptor transmits a signal across the membrane to a G protein, which then initiates a cascade of biochemical events.

Question 19

Olfactory Bulb

Answer 19

A blueberry-sized extension of the forebrain just above the nose, where olfactory information is first processed. There are two olfactory bulbs, one in each brain hemisphere, corresponding to the right and left nostrils.

Question 20

Cribriform Plate

Answer 20

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

Question 21

Anosmia

Answer 21

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

Question 22

Orbitofrontal Cortex (OFC)

Answer 22

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 i also referred to as the secondary olfactory cortex and the secondary taste cortex.

Question 23

Hippocampus

Answer 23

A region of the brain involved in spatial mapping, associative learning and memory, and processing olfactory information. It is adjacent to the amygdala, which processes emotion.

Question 24

Olfactory Nerve

Answer 24

The first cranial nerve. The axons of the olfactory sensory neurons bundle together after pressing through the cribriform plate to form the olfactory nerve, which conducts impulses form the olfactory epithelium in the nose to the olfactory bulb. Also called cranial nerve I.

Question 25

Ipsilateral

Answer 25

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

Question 26

Juxtaglomerular Neurons

Answer 26

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 deepest layers.

Question 27

Tufted Cells

Answer 27

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 28

Mitral Cells

Answer 28

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

Question 29

Granular Cells

Answer 29

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

Question 30

Olfactory Tract

Answer 30

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

Question 31

Piriform Cortex (The Primary Olfactory Cortex)

Answer 31

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 32

Amygdala-Hippocampal Complex

Answer 32

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 33

Entorhinal Cortex

Answer 33

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

Question 34

Limbic System

Answer 34

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

Question 35

Trigeminal Nerve

Answer 35

The fifth cranial nerve. It transmits information about the “feel” of an odorant (e.g., mint feels cool, cinnamon feels warm), as well as pain and irritation sensations (e.g., ammonia feels burning). Also called cranial nerve V.

Question 36

Shape-Pattern Theory

Answer 36

The current dominant biochemical theory for how chemicals come to be perceived as specific odors. Shape-pattern theory 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 37

Vibration Theory

Answer 37

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

Question 38

Specific Anosmia

Answer 38

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

Question 39

Stereoisomers

Answer 39

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 40

Binaral Rivalry

Answer 40

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 41

Olfactory White

Answer 41

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 42

Psychophysics

Answer 42

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

Question 43

Staircase Method

Answer 43

A psychophysical method for determining the concentration of a stimulus required for detection at the threshold level. The staircase method is an example of 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. Also called reverse staircase method.

Question 44

Triangle Test

Answer 44

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 45

Tip-of-the-Nose Phenomenon

Answer 45

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 46

Receptor Adaptation

Answer 46

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 47

Cross-Adaptation

Answer 47

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

Question 48

Cognitive Habituation

Answer 48

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

Question 49

Odor Hedonics

Answer 49

The liking dimension of odor perception, typically measured by ratings of an odor’s perceived pleasantness, familiarity, and intensity.

Question 50

Learned Taste Aversion

Answer 50

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

Question 51

Main Olfactory Bulb (MOB)

Answer 51

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 52

Accessory Olfactory Bulb (AOB)

Answer 52

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

Question 53

Vomeronasal Organ (VNO)

Answer 53

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 54

Pheromone

Answer 54

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 55

Primer Pheromone

Answer 55

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

Question 56

Releaser Pheromone

Answer 56

A pheromone that triggers an immediate behavioral response among conspecifics.

Question 57

Chemosignal

Answer 57

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

Question 58

Aromatherapy

Answer 58

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.