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Chemical senses
Taste
Smell
Trigeminal system
Taste
Interaction between substances and taste buds in the tongue and oral cavity
Different taste distinction
sweet
sour
salty
bitter
umami
Why can we differentiate different tasty things (like marchmallow and fruit)
More specific taste distinctions are possible because food activates olfactory system via retronasal olfaction
smell
Perceived by olfactory receptors in the olfactory mucosa in the upper portion of the nasal cavity
We can distinguish millions-billions of different odours
Olfactory stimuli are volatile substance
Odorants enter the body - then contact with olfactory receptors
Trigeminal system
Its receptors are located on fibers of the trigeminal nerve of the nasal and oral mucosa
Trigeminal stimuli evoke sensations such as irritation, burning, freshness and tingling
Many substances that activate this system activates olfaction
Tast buds location
located on the mucosa of the tongue (and elsewhere in the oral cavity)
are found in the papillae of the tongue:
fungiform papillae
foliate papillae
circumvallate papillae
(filiform papillae) – not involved in taste; only in somatosensory perception of tongue
Taste pathway
taste buds → CN VII, IX & X) → ventral posterior medial nucleus of thalamus → primary gustatory cortex in insula and parietal cortex
vomeronasal organ
plays a role in the effect of pheromones
olfactrory receptor neurons
situated in roof portion of the nasal cavity
the receptors are located in their cilia
surrounded by supporting cells and can regenerate from stem cells
olfactory cell hairs have the receptors for odorants
Olfactory receptors
human approximately 400 different types of olfactory receptors
high variability across individuals in number and type of receptors
each individual has a different olfactory receptor repertoire
each receptor responds to physical-chemical characteristics of odors
each olfactory receptor neuron (ORN) carries only one type of receptor
each ORN can be activated by different substances
each substance can activate different types of ORN
nearly infinite combinations possible
we can distinguish billions of odors
Macroscopic structures of olfaction
axons of the ORN pass through the cribriform plate of the ethmoid bone and reach the olfactory bulb. First synapse is in the olfactory bulb. All ORNs carrying the same receptor converge to the same structure within the olfactory bulb - glomerulum - in the mucosa they were distributed at random
Orthonasal olfaction
odor enter nose - mucosa - perceived
Retronasal olfaction
perceive odours inside our body
food in our mouth
air enter nasal cavity from mouth
if sense of ssmell is lost - finer tastes cannot be perceived
smell functions
Warning: microbial threats (disgust), non-microbial threats (fear)
Nutrition: detection, expectancy violation, intake regulation, breastfeeding
Social/communication: reproduction (incest avoidance, fitness evaluation in potential partners), emotional contagion
olfactory dysfunction
up to 20% of the population suffer from olfactory dysfunction
Quantitative dysfunction:
anosmis: complete loss of olfactory function
hyposmia: partial loss
Qualitative dysfunction
parosmia: odours are perceived differently than they are supposed to
phantosmia: perception of smells in the absence of an odour source
olfactory dysfunction causes
Diseases of the nose or the nasal mucosa (sinusite, allergies, cold)
Neurological diseases: TBI, alzheimer and Parkinson (pre diagnosis), congenital anosmia
Unknown
Age
Covid effect on olfactory capacity
up to 60% reduction in olfactory abilities
Factors that influence olfaction
age, sex, education level, smoking, alcohol, BMI, blood pressure, TBI parkinson, dementia
Taste functions
Warning (bitterness = alkoids, poison, but adults have learn to like it)
Nutrition: sweet = carbs, umami = proteins
Homeostasis: electrolytes (salty and acid)
Trigeminal functions
warning and nutrition