ORDOR

chemical stimulus => smell sensation

odorant

• molecule defined by physiochemical characteristics
  • translated into nervous system => perception of smell

To be smelled, ordorants must be:

1. violate (able to float the air)
2. small
3. hydrophobic

human olfactory apparatus

• primarly purpose => to filter, warm, and humidity air we breathe
• small ridges, olfactory cleft, and olfactory epithelium

human olfactory apparatus

olfactory cleft

• narrow space at back of nose where air flows
• where main olfactory epithelium is

human olfactory apparatus

olfactory epithelium

• secretory mucous membrane
• detects odorants in inhaled air

3 types of cells in Olfactory epithelium

1. supporting cells
2. basal cells
3. olfactory sensory neurons (OSNs)

Olfactory epithelium Cells

Supporting cells

• provides metabolic and physical support to OLF sensory neurons

Olfactory epithelium

Basal Cells

• cells before olfactory sensory neurons (precursor)

Olfactory epithelium

Olfactory sensory neurons (OSNs)

• main cell type in OLF Epi
• small neurons under watery mucous layer in epith

Cillium / cilia

• hair-like protrusions on dentrites of OSNs
• receptor side for ordorant molecules
• first structures with olfactory signal transduction

olfactory receptor (OR)

• region on cilia where odorant molecules bind
• 7-8 odor molecules bind to receptor => start action potential
• 40 nerve impulses = reported smell

olfactory graph?

slide 19

cribriform plate

• boney structure with holes // @ level of eyebrows // separates nose from brain
• where axons from OSNs pass through (holes) => brain

anosmia

• can't smell from sinus illness or head trauma
  • hard blow to front of head => crib form fractures => slice off olfactory neurons
• can cause lost of taste too

olfactory nerves

• first pair of cranial nerves
• axons bundle together after passing cribiform
  • forms olfactory nerve

olfactory bulb

• small, round extension of brain
  • where olfactory information is first processed
• 2 olfactory bulbs => one in each brain hemisphere
  • connections are ipsilateral (same side)

glomeruli

• spherical conglomerates with incoming axons of OSNs
  • 1 OSN => 2 glomeruli (1 medial, 1 lateral)
  • activity patterns => what type of order
• Surrounded by layers of cells
  • juxtaglomerular neurons, tufted cells, mitral cells, granule cells

juxtaglomerular neurons

• first layer cells surrounding the glomeruli
• mix of excitatory + inhibitory cells (responds to order)

tufted cells

• after juxt neuron layers
• respond to fewer odorants than juxt
  • more than deepest layer of cells

mitral cells

• deppest layer of neurons in OLF bulb
• respond to few specific odorants

granule cells

• deepest layer of neurons
• extensive network of inhibitory neurons
  • takes input from other layers + basis of identifying ordors

primary olfactory cortext

• neural area where olfactory information is first processed
  • amygdala, parahippocampus gyrus, interconnected areas, and entorhinal cortex

Entorhinal cortext

• a phylogenetically old cortical region that provides major sensory input from hippocampus
• receives direct projections from olfactory regions

Limbic system

• group of neural structures
  • olfactory cortex, amygdala, hippocampus, piriform cortex, entorhinal cortex
• emotion + memory
• olfaction = direct and intimate connection to system
  • strong emotion associations

Pseudogens

• humans has 60%-70%
• different % for every person
• evolutionary trade-off between vision + olfaction

The feel of scent and nerves

• odorants can stimulate somatosensory system (polymodial nocieceptors)
  • touch, pain, temperature receptors
• sensations mediated by trigeminal nerve (cranial nerve 5)
• WIP

Theories of olfactory perception

Shape-pattern theory

• dominant theory of how chemicals are perceived as specific orders
• different function of scents => different odorant shape => activate different olfactory receptors
  • in olfactory epithelium
  • specific firing patterns of neurons

Theories of olfactory perception

Vibration theory

• every perceived smell = different vibrational frequency
  • same vibrational frequency = same smell

Specific anosmia

• inability to smell one specific compound but have normal smell perception
  • 20-40& people with androstenone anosmia (armpit sweat+pigs)
  • smells "sweet-musky-floral" scent
  • sensitivity can be increased w/ training

Stereoisomes

• mirror-image rotations of molecules
  • same atoms => different smells
  • D-Carvone (cloves) => L carvone (mint)

Odors and Patterns

• we can detect the patterni of activity across receptors
• intentist of odorant => changes rwaht reptors are activqated
  
  • weak smells = not same as strong smells
• Specific time order of activation of OR receptors

odor mixtures

• we smell mixtures NOT pure odorants

odor mixtures

Analysis

• auditory mixtures example
  • high notes + low note played together = can each individual note

odor mixtures

synthesis

• color mixtures example
  • mixing red and green => yellow result but can't see green or red anymore
• Most of olfaction

Binary rivarly

• competition between the two nostrils for ordor perceptions
  • one scent at a time, not a combination of 2 scents

olfactory white

• the olfactory equivalent of "white nose" or the color white
• at least 30 odorants of equal intensity (can not tell one mixture from another)

Durability

• recognition of smells is durable even after several days, months, or years

staircase method

• method for determining the concentration of a stimulus required for detection at a threshold level
  • stim. presented in increasing concentrations until detected

triangle test

• participant given 3 odors to smell (2 same, 1 differnt)
• order of 3 varies and tested several times => increase accuracy

tip-of-the-nose phenomemon

• the inability to name an odorant even of VERY similar

receptor adaptation

• biochemical phenomenon after continuous exposure to an odorant
  • receptors stop responding to the odorant + detection decreases

cross adaptation

• reduction in detection after an odorant
  • following exposure to another odorant
  • b/c share one or more olfactory receptors for transduction

cognitive habituation

• the psychological process where after long-term exposure to an odorant => no longer able to detect odorant / diminished detection ability
  • going out of town + noticing how your house smells

Three mechanisms of olfactory

1. olfactory receptors internalized in cell bodies => hinder after continuous exposure (take longer to recycle)
2. OD molecules may bye absorbed into bloodstream => cause adaptation to continue
3. cognitive emotional factors

attention and conscious perception

• we cannot smell when we are asleep
• attention increases our ability to detect odors
• attention is cut off during sleep + attention to respond to odors

odor hedonics

• odor perception measured with scales to odorant pleasantness, familiarity, and intensity

taste aversion

avoidance of a novel flavor after it has been paired with gastric illness (stomach ache)

chemosignal

• any chemicals emitted by humans that are detected by olfactory system and has same effects on mood, behavior, hormonal status, and/or sexual arousal of other humans

McClintock effect

• 1 woman on period => triggers other women around her to start theirs

primer pheromone

• triggers a physiological (hormonal) change among conspecifics
  • prolonged pheromone exposure

releaser pherome

• triggers an immediate behavioral respond among conspecifics

Pheromone

• chemical emitted by one member of a species that triggers a physiological or behavioral response in another member of the same species
  • chemical communication (does not need to have smell)

Other parts of the nose // sub-division of olfactory system

• vomeronasal organ (VNO)
  • at base of nasal cavity, detects large and/or aqueous molecules // chem. sensing organ
• accessory olfactory bulb (AOB)
  • behind MOB // receives input from vomeronasal organ
• Main olfactory bulb (MOB)
  • olfactory bulb //

orbitofrontal cortex

• olfaction is processed here
• cortical area for assigning affective value (hedonic judgement)
• help explain increased emotionality of smells