Olfaction

n Airborn molecules

n Olfactory epithelium (or mucosa) – inside at top of nasal cavity (dime sized)

n Olfactory receptor cells (ORN) – 10 million, lives about 5-8 weeks (neurogenesis)

q Each cell – cilia covered with mucus – cilia is where the G-proteins are located/olfactory receptors

q Odors contact the receptors through direct flow or become attached to olfactory binding proteins which carry them across the mucus

n Have 1000 diff olfactory receptors

q Diff number per person

n Abs thresholds vary up to 20 x between people (smokers, gender, working conditions, age), poor diff threshold (5% - 33%).

n Abs and diffn thresh varies on type of odor

q diff controlling concentration reaching nose

n Adaptation - 70% decrease 1 min exposure

q Decay rate of 2.5%/sec

q Can also get cross adaptation

n Anosmia – can’t smell – head trauma, infection, full body paralysis

n Olfactory mucosa – 4 zones

q part. ORN found in 1 zone (many ORN per zone),

q all ORN from one zone go to 1 area of olfactory bulb

n Olfactory bulb – 1K-2K glomeruli, each receiving 5K-10K ORN fibers

q Each glomeruli receives signals from 1 ORN

Olfactory

n 2 pathways

q Thalamus pathway – odor discrimination, mem

q Limbic system – eating, sex, aggression

n Primary olfactory cortex (piriform) – temp lobe

n Secondary olfactory cortex (orbitofrontal) - frontal

Theory of ability to smell

n Problems – odor quality affected by physical and chem prop, elec charge of elements, structure of molecule, 1000 receptors

n Some molecules can smell diff and look sim, others smell sim and look diff chem

n ORNs resp to diff chem – some resp to just a few odorants, some to many (some specificity, many distributed)

n Glomeruli also resp to diff number of odorants – however some more specificity

q Regional sensitivity

Smell theory

n Odor stim mapped onto spatial pattern in glomeruli

n Odotypes – gp of odorants that share sim chem feature – molecule feature, chem gp

q Ex. benzene ring w/ short chain

n By OFC, more specific, also combines w/ taste (bimodal – also see somatosensory and vision)

q Smell, then eat bitter – avoid 81% time by smell, but only 26% after OFC removed

n Infants id mothers w/in 1 week of life

q Can id family members (genetically related)

n Own odor preference

q Wear t-shirt 48 hrs, rate pleasantness of own shirt higher even though id own shirt 25% of time

n Gender id – t-shirts, breath, hand sweat – 80% accuracy

q Women 5-10% better than men

q Can change with menstrual cycle possibly due to estrogen levels (Exaltolide)

n Id some moods through smell – happy, fear and can change person’s mood (make more happy) w/ exposure to human odors

n Pheromones – vomeronasal organs, located on either side of septum

q Thought to be vestigial in humans until recently

n McClintock effect – menstrual synchrony

q From armpit gland

q Swab lip of donor woman on part. 3x/week, see sim cycles in 3-5 mo.

n Male odors – length and timing of menstrual cycle

q Irregular cycles – 14 weeks, cycles more normal

n Applicants for job rated lower by men if wearing scent, higher for women

n Improve performance on tasks, gamble more

n Odors & memory - problems recognizing odors (can improve w/ training, however can be strong link to mem, part if em laden – episodic odors

q Can also link w/ stressful and pleasant events

n Illness – detect diseases