Chapter 14 Flashcards
olfaction
The sense of smell.
gustation
The sense of taste.
orthonasal olfaction
Sniffing in and perceiving odors through our nostrils, which occurs when we are smelling something that is in the air.
retronasal olfaction
perceiving odors through the mouth while breathing and chewing; gives us experience of flavor.
odor
The translation of a chemical stimulus into the sensation and odor percept.
odorant
A molecule that is defined by its physiochemical characteristics and that can be translated by the nervous system into the perception of a smell.
olfactory cleft
A narrow space at the back of the nose into which air flows and where the olfactory epithelium is located.
olfactory epithelium
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.
nasal dominance
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.
supporting cell
One of three types of cells in olfactory epithelium; provide metabolic and physical support for the olfactory sensory neurons.
basal cell
One of three types of cells in olfactory epithelium; are the precursor cells to OSNs.
olfactory sensory neuron (OSN)
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.
cilium
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.
odorant receptor (OR)
The region on the cilia of olfactory sensory neurons where odorant molecules bind.
glomerulus
Any of the spherical conglomerates containing the incoming icons of the olfactory sensory neurons. Each OSN converges onto two glomeruli (one medial, one lateral).
olfactory bulb
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.
cribriform plate
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.
anosmia
The total inability to smell, most often resulting from sinus illness or head trauma.
olfactory nerve
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.
ipsilateral
Referring to the same side of the body (or brain).
juxtaglomerular neurons
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.
tufted cells
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.
mitral cells
The deepest layer of neurons in the olfactory bulb. Each mitral cell responds to only a few specific odorants.
granular cells
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.
olfactory tract
The bundle of axons of the mitral and tufted cells within the olfactory bulb that sends odor information to the primary olfactory cortex.
primary olfactory cortex / piriform cortex
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.
amygdala-hippocampal complex
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.
entorhinal cortex
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.
limbic system
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.
trigeminal nerve
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.
shape-pattern theory
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.
vibration theory
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.
specific anosmia
The inability to smell one specific compound amid otherwise normal smell perception.
stereoisomers
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.
binaural rivalry
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.
olfactory white
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.
psychophysics
The science of defining quantitative relationships between physical and psychological (subjective,
perceptual) events.
staircase method
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.
triangle test
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.
tip-of-the-nose phenomenon
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.
G protein-coupled receptor (GPCR)
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.
receptor adaptation
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.
cross-adaptation
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
cognitive habituation
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
odor hedonics
The liking dimension of odor perception, typically measured
by ratings of an odor’s perceived pleasantness, familiarity, and intensity.
learned taste aversion
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.
orbitofrontal cortex (OFC)
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.
main olfactory bulb (MOB)
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.
accessory olfactory bulb (AOB)
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.
vomeronasal organ (VNO)
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.
pheromone
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.
lordosis
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.
releaser pheromone
A pheromone that triggers an immediate behavioral response among conspecifics.
primer pheromone
A pheromone that triggers a physiological (often hormonal) change among conspecifics. This effect usually involves prolonged pheromone exposure.
chemosignal
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.
aromatherapy
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.
