Olfaction

olfactory epithelium

olfactory epithelium

contains supporting cells, basal cells, and olfactory sensory neurons

olfactory sensory neuron (OSN)

cilia protruding into mucus covering olfactory epithelium

olfactory receptors (OR)

interact with odorants producing an action potential

~1000 different genes in humans, 300-400 are active, each gene codes for a single one

olfactory nerve

cranial nerve I

thin axon, slow signals

anosmia

complete loss of smell due to lesions in olfactory nerve

parosmia

partial loss of smell due to lesions in olfactory nerve

olfactory bulb

contains glomeruli, has chemotopogtaphic organization

ipsilateral projections

direct projections to entorhinal cortex and amygdala-hippocampal complex

glomeruli

spherical structure olfactory sensory neurons synapse to

contain tufted and mitral cells

juxtaglomerular neurons

first layer of glomeruli

respond to many odorants

tufted cells

second layer of cells in glomeruli

respond to few odorants

mitral cells

deepest layer of glomeruli

responds to very few odorants

granular cells

deepest level of olfactory bulb

network on inhibitory neurons, integrant input

basis of specific odorant identification

trigeminal nerve

odorants can stimulate somatosensory system which is mediated by ____ __________

multisensory perception, odorants can sometimes be felt and/or tasted

shape pattern theory

match between shapes of odorants and odour receptors

lock & key

with only 300-400 receptors, many odours can be identified through odorants interacting with many receptors

odour mixtures

identified through mostly synthesis (combination) and analysis (breaking down into components) if trained

detection thresholds

based on length of carbon chains

based on sex (women vary throughout menstrual cycle)

durability

our recognition of smell can last for days, months, or years.

identification

tip of the nose phenomenon

difficult to attach labels to smells

G protein coupled receptor (GPCR)

odors bind to receptors which indirectly open Na+ channels

with continuous stimulation they bury themselves inside cells

receptor adaptation

continuous stimulation

GPCRs bury themselves inside cells

cross adaptation

reduced detection of odor after exposure to odors that stimulate the sole olfactory receptor

cognitive habituation

long term exposure to an odorant creates a diminished ability to detect it

long term receptor adaptation

may be caused by odorants being absorbed into blood stream

odor hedonics

liking dimensions of odor

tendency to like familiar odours (nuture)

intensity influences as well