Chapter 14 - Smell 2/3 Flashcards
The Feeling Sesnation of Odors
- 3rd chemosensory system detects chemical irratants (vinegar, chilli)
- has polymodal nociceptive neurons with free nerve endings inthe oral and nasal chambers
- the axons make up the trigeminal nerve (cranial)
- chemicals act directly on ion channels on nerve endings to depolarize
- AP transmitted through brainstem to somatosensory processing
Olfactory Psychophysics
Detection - How much of an order do we need to sense it – absolute threshold
Discrimination – differentiating between multiple odors
Recognition – noticing that you’ve been exposed to it before – not identifying
Identification – smell odor and name it
Psychophysical methods for detection
Staircase method – odorant presented in increasing/decrease concentration increments untill they detect - find detection threshold
Magnitude estimation task – subjects sniff concentrations and assigns numerical value of intensity
- measures suprathreshold (how intense varies with concentration)
Triangle Test - subject sniffs 3 odors, two are the same one is different - discrimination
**Problems – adaptation (you’ll learn the smell and sensitivity decreases), difficult to control,
Factors that affect detection threshold
Gender:
- Females > males
- females sense during menstral cycle
- females have larger olfactory bulbs with more neurons and cilia
Age:
- decrease in OSN numbers
- activation of orbitofrontal cortex, piriform cortex and amygdala by familiar ordors in young and old subjects
- gets slower to replenish OSN while they are dying off
Experiences
- people initially anosmic can become sensitive after repeated exposure
Attention
- more of our brain can detect more odors when we focus on smelling
- distractions reduce ability to dtect
Factors that temporarliy affect detection thresholds
Alchol
- light use increases olfactory sensitify, heavy impairs it
Mairjuana
- may stimulus appeite by increasing smell sensitivity
- prescribed during chemotherapy
Odor discrimination vs recognition
- healthy people can discriminate many odors and proffesionalls much more
- HARDER to RECOGNIZE odors than to discriminate
Study:
- odorants are long lasting
Identification of odors and language disconnection
- identifying is harder than recognizing
- tip of the nose - sniff something with no visual cues and you cant find the words to describe
Olfaction and language are disconnected
- not relayed through thalamus (process lang)
- processing in different hemipheres
- piriform cortex isint connected to languge
Factors that affect odor idenitification
Age
- Elementary school is in the middle – 20-40 is much better – after decreases
- kids don’t have enough experience – language to assign to odors, older – losing olfactory
- Consequence for older people
Sex:
- White bar – females were much better at identification
Genetics
- Mutations that bind to different odors or perhaps don’t bind at all
- If you have odor receptor then you smell from asparagus pee – genetic difference
How Genes affect smell
- humans have pseudogenes - (proteins coded for dont get made) - environment determines
- many functional genes or genes among different people
- different people express different functional receptors
=- more copies = more sensitive (can affect liking foods)
Olfactory Adaption 1
- Reduced awarenss of odors after prolonged exposure
- temporary - reduction in the detection threshold and reduced responses to suprathreshold intensities
Short term - receptor adaptation
- receptors are internalized and reycled, can be undone quickly
Depends on
- person, intensity, length of exposure, cogntitive emotional factors
Cross adaptation - the reduction in the detecrion of an oderatnt following exposure to another odorant - 2 odorants sharing one or more ORs
Adaptation 2
Long term - due to processing of olfatory system
- cognitive habitual - psychological process after long term exposure to odor no longer has ability to detect it (recovery takes weeks)
Mechanisms
- OR internalization with slowed recycling to plasma membrane
- odorants might be absorbed into blood stream after exposre - constantly stimulating OR
- Cognitive-emotional factors may be involved
Abnormalities deficits of olfactory function - anosmias
Anosmia - total loss of smell sensation
* Can arise from genetic condition (rare), sinus and viral infections, nasal polyps, head trauma
- Hyposmia - reduced smell perception
- Can result from (i) infection/ inflammation (ii) traumatic injury (iii) toxin exposure
- Specific anosmia à loss of smell for a particular odor
- Genetic loss of specific odorant receptor?
- Parosmia à distortions in odor quality
- Phantosmia à odor perception in the absence of airborne odourants
- Cacosmia à olfactory hallucination of aversive smell
Consequences of anosmia and marker for disease
- Loss of appetite and loss of flavour – less enjoyable food
- Change in emotions becasuse of limbic system – depression
- Lose danger system – gasses to smell, expired food
- Relationships – communication between organisms with intimacy
Impaired smell is one of the earliest and most common symptoms of alzhiemers and parkinsons
The Shape pattern
States that odorant molecules have different shapes and olfactory receptors (ORs) have different shapes
* An odourant will be detected by a specific OR to the extent that the odourant’s molecules fit into that OR
* Odour creates a unique spatial-temporal pattern of activity in the glomeruli
combinatorial coding
* Odour intensity changes which receptors are
activated and therefore our perception
- binding at a different degree of intensity with can effect perception, higher concentration = higher perception
Responses of individual glomeruli of the fruit fly
Activation in response to different molecules
Shape patern theory- if each glomerlus is receiving info from osn that express a receptor when those receptors are activated they are going to send an input to 1 glomerlius and then it will be activate
