Olfaction and Gustation Flashcards
Classification of odours
No real official classification, but it’s notable that different compounds associated with different scent characteristics can be sensed at different levels
Broad mechanism of olfaction/smell
Breath in, air swirls around the nasal cavities; turbulence delivers airborne particles/compounds to olfactory organs
Olfactory epithelium
Up at the top of the nose
2-3 cm squared
Nerves go all the way through to the cribriform plate then through to the olfactory bulb
Cribriform plate
Bone structure with tiny hairs (??)
Inhaled air route
Orthonasal
Back of the oral cavity
Retronasal route
Bone components of the Turbinates
*** I’m a bit lost icl
Alternate name for concha (3 of them)
Something to do with humidifying air?? -> create turbulence?
Olfactory receptors
Modified neurons with multiple cilia
Exposed tip of each receptor cells is called a knob
Knob is the base for up to 20 cilia
CIlia are within the mucous
Large surface area for molecule detection
Mucous
Mucous is secreted by Bowmans gland
Compounds reaching the olfactory organs must diffuse into the mucous -> must be water soluble + lipid soluble. More soluble, stronger smell
Receptors - one chemical or many?
300-400 receptor proteins in humans
Like other sensory receptor cells, olfactory receptor neurons are sensitive to a subset of chemical stimuli that define a “tuning curve”. Depending on the particular olfactory receptor molecules they contain, some olfactory receptor neurons exhibit marked selectivity to particular chemical stimuli whereas others are activated by a number of different odorant molecules
Transduction
Dissolved compounds interact with receptors (usually GPCRs) called odorant binding proteins. This leads to an action potential being sent to the olfactory cortex
Sensitivity
Only 4 molecules needed to activate a receptor
One afferent fibre may not be enough to raise your conscious awareness to a smell
Olfaction is conducted via a convergent pathway
Also have central inhibition of action potentials, adaptation to a persistent smell
Convergent pathway
Multiple receptors converge in a glomeruli that signals to the mitral cells
Pathway of transmission
Axons -> olfactory bulb -> olfactory tract -> olfactory cortex -> hypothalamus -> limbic system
Discrimination
We can detect subtle differences
2000 – 4000 different chemical stimuli
Receptor populations with distinct sensitivities.
CNS translates each smell in accordance with a pattern of activity
Ageing
Receptors are replaced regularly
Basal cells proliferate and differentiate into new receptors
The number of receptors declines with age
Receptors become insensitive
Application of knowledge - COVID
Ansonia was reported in up to 80% of COVID-19 patients infected with the early strains of the virus
Gustation
Taste receptors (gustatory receptors) on the superficial surface of the tongue
Present on the pharnyx and larynx in children, not in adults due to degeneration
Specialised epithelial cells
On average over 3000 taste buds
Different shape formations in different areas of the tongue
Superior surface - Lingual papillae
Filiform papillae (thread like)
Fungiform papillae (mushroom like)
Circumvillate papillae (rounded)
Filiform papillae
Friction no taste buds
Fungiform papillae
5 taste buds each
Circumvillate papillae
~100 taste buds each
V formation at the back of the tongue
Taste buds
Each taste bud has approximately 40 receptors called Gustatory cells
Found recessed into epithelium
Have slender microvilli (taste hairs) which project through a taste pore.
“lifespan” of a taste bud
10 days
