Ch. 14 Flashcards
olfaction
the sense of smell; for molecules floating in the air
gustation
the sense of taste; for molecules that enter our mouth
trigeminal system
enables us to feel gustatory and olfactory experiences, like burning and cooling
two routes through which we perceive odors
orthonasal olfaction and retronasal olfaction
orthonasal olfaction
sniffing in and perceiving odors through our nostrils, which occurs when we are smelling something that is in the air; molecules travel through the nostrils, up the nose, and onto the olfactory epithelium
retronasal olfaction
perceiving odors through the mouth while breathing and chewing; this is what gives us the experience of flavor; exhale molecules in the mouth and they travel up from the back of the mouth into the upper nasal cavity and onto the olfactory epithelium
odor
the translation of a chemical stimulus into the sensation of an odor percept
odorant
a specific molecule defined by its physicochemical characteristics that can be translated by the central nervous system into the perception of an odor
volatile
a molecule that is buoyant in air and therefore can be inhaled
- odorants are volatile molecules
primary function of the nose
to filter, warm, and humidify the air that carries oxygen to our lungs
- human olfactory system is “tacked on” to an organ that serves another purpose
turbinates
curled bony protrusions inside the nasal cavity; these small ridges 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
olfactory cleft
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
olfactory epithelium
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), it contains three types of cells: sustentacular cells, basal cells, and olfactory sensory neurons
pathway of odorants through the nose
The inside of the nose has small ridges called turbinates that add turbulence to the incoming air, causing a small puff of each breath to rise upward, pass through a narrow space called the olfactory cleft, and settle on a yellowish patch of mucous membrane called the olfactory epithelium
nasal dominance
the asymmetry characterizing the intake of air by the two nostrils, which leads to differing sensitivity to odorants between the two nostrils; differs throughout the day, but there is no predictability for when the nostrils alternate
three types of cells in the olfactory epithelium
sustentacular cell, basal cell, olfactory sensory neuron (OSN)
sustentacular cell
one of the three types of cells in the olfactory epithelium; provide metabolic and physical support for the olfactory sensory neurons
basal cell
one of the three types of cells in the olfactory epithelium; the precursor cells to olfactory sensory neurons
olfactory sensory neuron (OSN)
one of the three cell types— the main one— in the olfactory epithelium; small neurons located within a mucous layer in the epithelium; cilia on these neurons’ dendrites contain receptor sites for odorant molecules
cilium
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; the cilia protrude into the mucus covering the olfactory epithelium
odorant receptor (OR)
the region in the cilia of olfactory sensory neurons where odorant molecules bind
glomerulus
any of the spherical conglomerates containing the incoming axons of the olfactory sensory neurons; each OSN converges onto two glomeruli (one medial, one lateral)
“one to one to one” rule of olfactory sensory physiology
Each OSN expresses only one type of OR, and all OSNs expressing the same type of OR project to the same type of glomerulus
G protein-coupled receptor (GPCR)
any of a class of receptors that are present on the cilia of olfactory sensory neurons; all 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
- odorant receptors
when an odorant binds to the receptor on the cilium…
it transmits a signal through the membrane to a G protein (guanine-nucleotide binding protein) in the cilium interior; this interaction between an odorant and its receptor stimulates the G protein and initiates a cascade of biochemical events, ultimately producing an action potential that is transmitted along the axons of the OSN to the olfactory bulb
olfactory bulb
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
to initiate an action potential…
about 7 or 8 odorant molecules must bind to a receptor
takes about __ nerve impulses for a smell sensation to be registered by the olfactory bulb
40
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 olfactory sensory neurons (OSNs) pass through these holes to enter the brain
anosmia
the total inability to smell, most often resulting from sinus or viral illness
orbitofrontal cortex (OFC)
the part of the frontal lobe of the cortex that lies behind the bone (orbit) containing the eyes; responsible for the conscious experience of olfaction, as well as the integration of pleasure and displeasure from food; also involved in many other functions and is critical for assigning affective value to stimuli (determining hedonic meaning)
hippocampus
a region of the brain involved in spatial mapping, associative learning and memory, and processing olfactory information
olfactory nerve
the first cranial nerve; the axons of the olfactory sensory neurons bundle together after passing through the cribriform plate to form the olfactory nerve, which conducts impulses from the olfactory epithelium in the nose to the olfactory bulb
olfaction is ________
ipsilateral
- The right olfactory bulb gets information from the right nostril and the left olfactory bulb gets information from the left nostril
ipsilateral
referring to the same side of the body (or brain)
from OR to the brain
- All neurons expressing a particular OR type send their axons to the same glomerulus pair (consisting of one medial and one lateral glomerulus) in the olfactory bulb
- The distinct pattern of OR activation for a specific odorant is then translated into a specific pattern of spatial activity across the glomeruli
- The specific pattern of glomerular activity is then interpreted by the brain as indicating a specific odor
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
- these cells respond to much wider range of odorants than the next layer of neurons, tufted cells
tufted cells
the next layer of cells after the juxtaglomerular neurons; respond to fewer odorants than the juxtaglomerular neurons, but more than neurons at the deepest layer of cells, mitral cells
mitral cells
the deepest layer of neurons in the olfactory bulb; each cell responds to only a few specific odorants
granular cells
at the deepest level of the olfactory bulb; 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
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
- axons of the mitral and tufted cells of each bulb combine to form this tract
piriform cortex (primary olfactory cortex)
the neural area where olfactory information is first processed; 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 to the hippocampus; also receives direct projections from olfactory regions
limbic system
a group of neural structures that includes the primary olfactory cortex (piriform cortex) and the entorhinal cortex; involved in many aspects of emotion and memory
- processes olfactory information
subtle difference between sensation and perception in olfaction
- Sensation → occurs when an odor is neurally registered
- Perception → occurs when we become aware of detecting a scent
the number of particular receptors people express can modulate their liking for an odor
Having more receptors leads to a more intense smell and strong scents in general tend to be perceived as less pleasant than the same scents at a lower intensity
trigeminal nerve
the fifth cranial nerve; transmits information about the “feel” of an odorant as well as pain and irritation sensations
- E.g., mint feels cool, cinnamon feels warm, ammonia feels burning
- Responds to stimuli in and around the mouth, nose, and eyes
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
- Odorant molecules have different shapes and olfactory receptors have different shapes, and an odorant will be detected by a specific OR to the extent that the odorant’s molecules fit into that OR
- Scents are detected by means of a combinatorial code, where one odorant may bind to several different receptors and one receptor may bind several different odorants to varying degrees
vibration theory
proposes that every odorant has a different vibrational frequency and that molecules that produce the same vibrational frequencies will smell the same
- strongest alternative to shape-pattern theory
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
- Although they contain all the same atoms, they can smell completely different
- According to shape-pattern theory, this difference arises because the rotated molecules do not fit the same receptors
- Vibration theory cannot explain why stereoisomers smell different because their vibrations should be the same
a molecule may have features that stimulate several different receptors
- detect odors by the pattern of activity across different receptor types
- the perception of different odors is due to complex factors that include different OR firing patterns and firing of the same receptors at different speeds and/or in different sequences
binaral 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
- supports the idea of odor perception as analytical
ten perceptual categories of odorants
fragrant, woody/resinous, chemical, fruity (not lemon), lemony, sickening/sour, minty, sweet, nutty, and sickening/sulfurous
- supports the idea of odor perception as analytical
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
ability to detect an odorant can be manipulated by experience
- Through repeated testing sensitivity to androstenone (the steroidal musk compound for which many people have a specific anosmia) can be induced in about half of the people who are initially unable to detect it
- Increased sensitivity to some common odorants can be induced through repeated exposure to these chemicals
- Smell training has been shown to improve anyone’s olfactory abilities
- Not definitely known how these enhancements take place, but cognition, neuroplasticity, and gene expression all appear to be involved
- detection influenced by attention
need up to __ times as many odorant molecules to recognize an odor as we do to simply detect its presence
3
staircase method
a psychophysical method for determining the concentration of a stimulus required for detection at the threshold level; a stimulus 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
- method of limits
triangle test
a test in which a participant is given three odorants to smell, of which two are the same and one is different; participant is required to state which is the odd odor out; typically, the order in which the three odorants are given 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
individual differences in olfaction
- how many and which OR genes are expressed in our olfactory epithelia
- genetic variability
- sex and age
receptor recycling
an odorant binding to an OR causes the OR to be internalized into its cell body, where it becomes unbound from the odorant and is then recycled through the cell and emerges again in a number of minutes if that same odorant doesn’t block it
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
- the ORs retreat into the cell body and are no longer physically available to respond to scent molecules
- precise length of time required for adaptation varies as a function of both the individual and the odorant
- magnitude of adaptation affected by odor intensity
cross-adaptation
the reduction in detection of one odorant following exposure to a prior odorant; presumed to occur because the components of the 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 long-term 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
we often perceive pleasant odors as being more ________ than unpleasant odors
familiar
intensity and odor liking
- inverted U-function
- depends on the odorant
- A rose scent may be evaluated as more positive with increasing intensity up to a point, then the function reverses and as the scent becomes stronger, it is judged to be more disagreeable
- A fishy odor may be acceptable at low concentrations, but as intensity increases, its perception becomes steadily more negative
great deal of evidence points to odor hedonics being…
almost exclusively learned (nurture, rather than nature)
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
- original association made to an odor is etched into the brain and produces a unique neural signation in the amygdala-hippocampal complex
neuroanatomy supports the proposition that our olfactory system is especially prepared to learn affective significance of odors
- The amygdala, which synapses directly with the olfactory nerve, is critical for emotional associative learning and emotional memory
- Amygdala-hippocampal complex is critically important for the cognitive and emotional aspects of olfaction
- Orbitofrontal cortex (OFC) is where we consciously experience and perceive odors and is also the neural locus for assigning affective value in general (hedonic responses)
- Right OFC in particular plays an important role in conscious olfactory perception
in some vertebrates that rely on smell for survival, the olfactory system consists of two subdivisions
main olfactory bulb (MOB) and accessory olfactory bulb (AOB)
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)
accessory olfactory bulb (AOB)
a neural structure found in nonhuman animals that is smaller than the main olfactory bulb and located behind it; receives input from the vomeronasal organ
- attached to the back of the MOB
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; it evolved to detect chemicals that cannot be processed by ORs, such as large and/or aqueous molecules, the types of molecules that constitute pheromones
- in order for the AOB to be activated, the VNO needs to be engaged
- primary function is to detect pheromones
pheromone
a chemical emitted by one member of a species that triggers a physiological or behavioral response in another member of the same species; signals for chemical communication and may or may not have any smell
many uses of pheromones in chemical communication
- Identify territory
- Initiate alarm or defense reactions
- Communication about reproductive behavior
two types of pheromones that have two kinds of effects
primer pheromone and releaser pheromone
primer pheromone
a pheromone that triggers a physiological (often hormonal) change among conspecifics; this effect usually involves prolonged pheromone exposure
- slow and produce a physiological change in the recipient over time
releaser pheromone
a pheromone that triggers an immediate behavioral response among conspecifics
- fast and always produce behavioral responses
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, hormones, and/or sexual arousal of other humans
- Since the existence of human pheromones is highly unlikely, a more impartial way to discuss human chemical communication is to use the term chemosignal
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
