chapter 16 part 2 Flashcards
what does it mean for an animal to be macrosmatic?
it means that they have a keen sense of smell that is necessary to survival
what does it means for an animal to be microsmatic?
it means they have a less keen sense of smell that is not crucial to survival
how do we measure the detection threshold for odors?
yes no procedure:
- ps presented with odors and blanks
- indicated yes or no to whether they can detect them
forced choice:
- two trials are given, one with odorant and one without
- ps indicate which smells the strongest
- theshold: concentration that results in a correct response on 75 percent of trials
what is the difference between the sense of smell in human and rats? humans and dogs?
rats are 8 to 50 times more sensitive to odors than us
dogs are 300 to 10,000 times more sensitive to odors than us
the difference lies in the number of receptors (not the sensitivity of individual receptors)
- dogs have one billion receptors and humans have ten million
how good are humans at detecting odors?
we can discriminate more than one trillion different odors
- but find it difficult to identify odors
- tend only to be successful half the time
why is the perceptual experience of smelling something difficult to map onto the physical attributes of odorants
- there isn’t a specific language for odor quality
- some molecules that have a similar structure smell different, and some molecules that have a different structure smell different
olfactory mucosa
area at the top of the nasal cavity just below the olfactory bulb which contains olfactory receptor neurons. these neurons contain olfactory receptors
odorants are carried along the mucosa so that they can come into contact with these neurons
how many olfactory receptors do humans have?
350 types of receptors - each have a protein that crosses the membrane seven times
what are the two stages of olfactory processing that happen when we perceive odors
- analyzing: takes place at the beginning of the olfactory system in the olfactory mucosa and olfactory bulb. the olfactory system analyzes the different chemical components of odors and transforms these components into neural activity at specific places in the olfactory bulb
- synthesizing - takes place in the olfactory cortex and beyond. the olfactory system synthesizes information about chemical components received from the olfactory bulb into representations of odor objects
where does the olfactory bulb send its signals
to the primary olfactory (piriform) cortex in the temporal lobe and amygdala (plays a role in emotional reactions to odors)
then to the secondary olfactory (orbitofrontal) cortex in the frontal lobe
rennaker experiment
used multiple electrodes to measure neural responding in the piriform cortex, and found that isoamyl acetate causes activation across the cortex
how are odors represented
- odorant molecules come off the odor object
- a chemotopic map is activated in the olfactory bulb
- scattered activation in the piriform cortex
- after learning piriform cortex forms a patter for the odor object
wilson experiment
study that provides support for the idea that learning plays and important role in perceiving odors
- measured response of neurons in the rats piriform to two odorants
1. a mixture: isoamyl acetate and peppermint
2. a compound: isoamyl acetate alone
with enough exposure, the piriform cortex could discriminate between the mixture and the compound
recent measures of human odor sensitivity
humans are more sensitive to many odors than a wide range of animals, including mice, monkeys, rabbits, and seals
anosmia
no sense of smell
what is a possible explanation for why COVID-19 causes people to lose their sense of smell
covid molecules attach to an enzyme called ACE2 that is found in the intestines, lungs, arteries, heart, and nose. In the nose, it is found on the surface of sustentacular cells, which provide metabolic and structural support to the olfactory sensory neurons
because of this, it has been proposed that COVID-19 causes loss of smell by attacking the supporting cells of sensory neurons
sustentacular cells
cells which provide metabolic and structural support to the olfactory sensory neurons
what is the difference between loss of smell ins Alzheimer’s and in COVID
loss of olfaction in Alzheimer’s patients begins occurring decades before the occurrence of clinical symptoms such as memory loss and difficulties in reasoning
attack on the olfactory system also tends to be more widespread than in COVID19
differences between the visual system and the olfactory system
there are 400 different types of olfactory receptors, each sensitve to a different group of odorants, compared to only four types of visual pgments
olfactory bulb
the structure that receives signals directly from the olfactory receptors - the olfactory bulb contains glomeruli, which receive these signals from receptors
calcium imaging to measure receptor response to odorants
when an olfactory receptor responds, the concentration of calcium ions increases inside the receptor. calcium imaging measures this increase by soaking the neurons in a chemical that causes them to fluoresce when exposed to ultraviolet light - increasing Ca++ decreases the glow
measuring decrease in fluorescence indicates how strongly the neuron is activated
odorant recognition profile
the pattern of olfactory activation for an odorant, indicating which ORNs (olfactory receptor neurons) are activated by the odorant
can use the profiles to see that each odorant causes a different pattern of firing across ORNs
glomeruli
small structures in the olfactory bulb that receive signals from similar olfactory receptor neurons. one function of each glomerulus is to collect information about a small group of odorants
chemotopic maps/odor/odotopic maps
the pattern of activation in the olfactory system in which chemicals with different properties create a “map” of activation based on these properties
ex. evidence suggests that chemicals are mapped in the olfactory bulb based on carbon chain length
what happens to the chemotopic map in the piriform cortex
it disappears and gets replaced with widespread activation/overlap
how are odor objects represented in the piriform cortex?
similar to how memories are formed
- the cortex learns to link together the scattered activations that occur for a particular object - eventually the cortex is able to remember the pattern of activation and forms neural connections between the scattered areas of activation
odor objects become formed when experience with an odor causes neurons in the piriform cortex to become linked
proust effect
the elicitation of memories through taste and olfaction
odor evoked autobiographical memories
proust effect
- memories about events from a person’s life that are elicited by odors
associated with strong emotions and feelings of being brought back in time
amygdala is involved
retronasal route
the opening from the oral cavity, through the nasal pharnyx (connects the mouth cavity and the nasal cavity), into the nasal cavity. This route is the basis for the way smell combines with taste to create flavor
retronasal route
the opening from the oral cavity, through the nasal pharnyx (connects the mouth cavity and the nasal cavity), into the nasal cavity. This route is the basis for the way smell combines with taste to create flavor
oral capture
the condition in which sensations from both olfaction and taste are perceived as being located in the moth
bimodal neurons
neurons that respond to more than one sense - often respond to similar qualities
orbitofrontal cortex contains many of these types of neurons
bimodal neurons
neurons that respond to more than one sense - often respond to similar qualities
orbitofrontal cortex contains many of these types of neurons
sensory specific satiety
the effect on perception of the odor associated with food eaten to satiety - pleasantness rating of the smell of whatever food we have just eaten will go down after we are full
what does the finding that orbitofrontal cortex activity is related to the pleasantness of an odor or flavor suggest?
that the orbitofrontal cortex is involved in determining the reward value of foods
multimodal interactions
interactions that involve more than one sense
correspondences
refer to how a property of a chemical sense is associated with properties of other senses:
- odors and tastes can be associated with different pitches and instruments
- odors can be associated with different colors
- odors can be associated with different textures
