Olfaction Flashcards
What are the two ways that sense of olfaction can be stimulated?
-Orthonasal-inspiration via the nose (Odour)
-Retronasal-via the mouth during consumption(Aroma)
What are the four steps in the olfactory system?
- Odorants bind to receptors.
- Olfactory receptor cells are activated and send electric signals
3.The signals are relayed in glomeruli - The signals are transmitted to higher regions of the brain
During respiration or when air refluxes retronasally, where are voltalies directed?
Into the nasal cavity below the level of the olfactory epithelium.
What is olfactory epithelium a part of?
The mucosa
What is the shape of an olfactory receptor cell?
Long, narrow, and column shaped.
What is the diameter of an olfactory cell?
Less than one micron.
What type of cell is an olfactory cell?
A neuron
what is the lifespan of an olfactory cell?
About one month
How many receptors cells are on either side of the nose?
About 3 million.
what are the steps of the transduction process of the olfactory system?
The signal firstly comes to olfactory bulb, then reaches to piriform cortex(primary cortex), then to orbitofrontal cortex. The secondary process goes to the thalamus.
If stimulus—->action potential—>nerve tract—->sensory cortex, then how do we get different qualities =(submodalities) within a sense?
This is the computational problem of univariance.
what is the step of this univariance?
Odorants–>action potential—>olfactory nerve—->olfactory cortex
How many odour compounds in Strawberry?
11
How many odour compounds in Strawberry?
1000
What is a remarkable ability of the olfactory system?
It can recognize and discriminate a vast array of odors, even at extremely low concentrations.
What system is the olfactory system comparable to in terms of discrimination ability?
A: The immune system.
The immune system.
How is the olfactory system similar to the immune system?
Both can discriminate an immense variety of molecules—odors in the olfactory system and epitopes on antigen molecules in the immune system.
What is specificity coding?
Representation of a specific stimulus by the firing of specifically tuned neurons specialized to just respond to a specific stimulus.
What is population coding?
Representation of a particular object by the pattern of firing of a large number of neurons.
What is population/combinatorial encoding in the olfactory system?
A small number of olfactory receptors (ORs) can interact with and respond to numerous odorants in diverse combinatorial manners.
How do different smells get represented in the olfactory system?
Different patterns of activated glomeruli correspond to distinct smells.
What is an odor threshold?
The lowest concentration of a chemical in the air that people can detect.
What factors influence odor acuity?
The physical and chemical properties of compounds.
Is odour acuity generalized across all odorants?
No, it varies based on the specificity of each compound.
What are two representations of the short-term adaptation?
1.A decrease in responsiveness under conditions of constant stimulation.
2. Resistance to adaptation.
Rapid loss of dour intensity is within?
Decline is more gradual and stabilize at 1-2 mintues.
Who was Paul Broca?
A 19th-century neuroanatomist.
What did Paul Broca say about human and their sense of smell?
He described human as “nonsmellers”.
How does the human olfactory bulb(OB) compared to the other mammals?
It is relatively small.
what does olfactory sensitivity depend on?
The specific odor is detected.
Why do different species have varying olfactory sensitivities?
Different odor receptors are expressed in different species.
Can humans follow outdoor scent trails?
Yes, humans can track scents outdoors.
What behavior do humans exhibit when a scent trail changes direction?
Dog-like casting behavior, zigzagging along the tracking path.
What are the factors of variability in odour sensitivity across population?
Genetic contributions, ageing, enviroment factors, neurological diseases, threshold for dour may also be affected by an interaction of gender and hormonal variation in an individual, thresholds change during pregnancy.
What is anosmia?
Total loss of the sense of smell-very rare
Diagnosis: individual has smell threshold more than two standard deviations above the population mean concentration
What is hyposmia?
Declined ability to detect smells.
What is parosmia?
A change in normal perception of smell(good—>bad)
What is phatosmia?
Presence of smell when it isn’t there.
What is specific anosmia?
Some people with an otherwise normal sense of smell are unable to detect families of similar smelling compounds.
What is the olfactory liking?
Olfactory linking can be substantially different across people, e.g E-2-alkenals present in the herb, which are detected by certain olfactory receptors in some individuals causing a strong, unpleasant
How do olfactory percepts influence beahviour?
They strongly drive approach or avoidance.
What types of smell trigger avoidance behavior?
Smells indicating danger, such as smoke, poison, or rot.
What types of smells trigger approach behavior?
Smells signaling essential resources, such as food, shelter, or a mate for reproduction.
what are the functions of the olfactory system?
- Detection of environmental cues(Olfactory percepts are STRONG drivers of
approach/avoidance behaviour
∎Avoidance - Danger in the environment? Smoke,
Poison, Rot
∎Approach - Something I need in this environment?
Food, Shelter, Mate for reproduction) - Identification(Humans can discriminate more than trillion olfactory stimuli, Humans outperform many species at identifying
certain odours. Macrosmats(excellent smellers) for certain smells. Conspecifics
3.Communication
What did Wallace propose about conspecifics?
Humans can identify male vs. female
humans by smell with 755 accuracy.
What did Mitro propose about conspecifics?
Human can identify younger/middle
aged/older humans by smell. (older individuals are rated to smell better)
Do mammals, including humans, send and receive odor messages?
Yes, mammals communicate through scent signals.
What are some functions of odor-based communication in mammals?
Defense mechanisms, such as warning signals.
How do mammals use scent for territory marking?
They release odors to establish and defend their space.
What emotional information can odors convey?
They can signal stress, fear, or other emotional states.
How are odors involved in sex-related communication?
They indicate fertility, reproductive compatibility, and interest.
Do we or do we not use smell for mate-selection
Yes
What health-related information can be detected through scent?
Odors can signal disease and immune status.
What are pheromones?
Non-volatile chemicals or mixtures released by an organism that trigger specific reactions in members of the same species.
How can pheromones influence emotional state?
They can act as “bringers of excitement.”
What are some types of pheromones?
Alarm pheromones, food trail pheromones, and sex pheromones.
What organ is thought to be involved in pheromone signaling?
The vomeronasal organ (VNO).
Where is the VNO located?
In the anteroinferior portion of the nasal septum, just above the roof of the mouth.
What type of receptor cells are enriched in the VNO?
Pheromone receptor cells.
Why is the VNO considered an anatomical mystery
Although first discovered in humans, many believe we don’t actually have a functional one.
What is the current belief about the human VNO?
It is probably a vestigial organ with a nonoperational sensory function (NHI).
Is there evidence of functional pheromone receptor cells in adult humans?
No, there is no evidence of functional pheromone receptor cells in adult humans.
What have studies identified in the human olfactory mucosa?
Genes that code for potential pheromone receptors
Can olfactory cues influence human behavior?
Yes, but whether it is pheromone-based is still to be discovered.
What is the association between odour and memory?
emotional, autobiographical
memories evoked by an odour, e.g Proust effect
Can we all have vivid images of sensory cues?
Smell and flavour are powerful triggers for vivid memories, but not everyone experiences sensory imagery with the same intensity. Sensory sensitivity is an example of a factor that plays a role in this variability.
What are the three psychophysical measures of olfaction?
Odour detection, intensity differentiation, odour identification and odour naming
