Chapter 14-olfaction Flashcards
Odor
The translation of a chemical stimulus into a smell sensation
Odorant
A molecule that is defined by its physiochemical characteristics, which are capable of being translated by the nervous system into the perception of smell; physical thing you smell
In order to be smelled, odorants must b
Volatile, small, hydrophobic
Human olfactory apparatus contains
Olfactory clefts and olfactory epithelium
Olfactory cleft
Narrow space at the back of the nose into which air flows
Olfactory epithelium
Mucous membrane in the human nose whose primary function is to detect odorants
Primary function of the nose
Breathe; filter, warm and humidify air that you breathe
Odor receptors sites are located where
On the cilia of olfactory sensory neurons where odorant molecules bind
Odor receptors are what kind of receptors
Chemoreceptors; receptive sites bind with molecules
Mitral cells receive projections from how many and what type of receptors
About 200, same type of receptor; convergent, lose spatial information
How many different receptor types are ther
About 1000, respond to distinct chemical molecules or parts of molecules
How many molecules are needed to activate odor receptors
7-8
Humans have how many receptors
6 million
Olfactory pathway
Olfactory bulb, Piriform cortex, entorhinal cortex, limbic system, orbitofrontal
Olfactory bulb
Olfactory info first processed here, 1 in each hemisphere that corresponds ipsilaterally to each nostril
Primary olfactory cortex also known as
Piriform cortex
Entorhinal cortex
Old, sensory association area, connect to the limbic system
Limbic system
Emotion (fear) and memory, base survival learning
Orbitofrontal cortex
Conscious perception and hedonics (liking)
Shape pattern theory
Dominant biochemical theory for how chemicals come to be perceived as specific odors. Contends that different scents-as a function of odorant-shape to OR shape fit-activate different arrays of olfactory receptors in the olfactory epithelium. Population coding
Population coding
Part of shape pattern theory; the various arrays produce specific firing patterns of neurons in the olfactory bulb, which then determine the scent we perceive
Shape of odor molecule
Physical molecule
Pattern of odor molecule
Which scent of odor receptor and to what degree, combination processing
Chemical aromas
Smell odors that are not physically present; activate odor receptors, smell is an epiphenomenon (not directly representing physical world)
How does population coding work
Odorants have different physical shapes that matter the most, and different colors (content) that also matter; receptors are selective to the shape and content of odorants
Stereoisomers
Similar chemical compound but a different shape; result in different perceptual states-shape matters
Odorant and receptor table: a given odorant will excite several receptors due to what
Its chemical composition
Odorant and receptor table: a given receptor will respond to several odors, but the ___ of activity represents the composition of any given odor
Pattern
Intensity
Certain receptors are more sensitive to aspects; can influence which receptors are active, due to relative amounts of different components of the odorant
Because we rarely smell pure odorants, we smell mixtures; how do we process the components
Analysis and synthesis
Analysis
Separate into parts
Synthesis
Combine into a new whole
Binaral rivalry
Competition between the two nostrils for odor perception; when a differen scent is presented to each nostril, we experience one scent at a time, not a combination of the two scents together
What we smell can affect what we
See
Adaptation
Sense of smell is a change detector; allows for responses to new smells and/or important information
Bottom up receptor adaptation
Receptors stop responding to the odorant and detection stops; firing rate
Top down influence of adaptation
Conscious thought can influence time course of adaptation
Negative bias of smell makes it
Stronger for longer, more important
Positive bias to a smell makes it
Decrease over time more than the neutral smell
Odor hedonics
The liking dimension of odor perception, typically measured with scales pertaining to an odorants perceive pleasantness, familiarity and intensity
Familiarity of smells
We like odors that we have smelled before
Intensity of smells
Good smells: neutral for less intense smells, unpleasant for very intense
Bad smells: dislike increases the more intense the smell gets
Hedonic responds are most likely from nurture
Odor preferences of infants vary from adults, cross cultural data supports associative learning
2 aspects to support nature of hedonics
Pain response to irritating odors and variability in receptor types and amounts
Sniffing sticks
Pre-determined set of odorant sin distinct performance for discrimination
Triangle test
Participant is given 3 odors to smell, two are the same and 1 is different; identity the odd odor; used for detection and discrimination
