5b. Olfaction Flashcards
Odourant Dissolution
Odorants dissolve in the mucus film and possibly become associated with oforant binding protein
Olfactory Receptor Length
Long
Send axons through the perforated cribriform plate to synapse in the olfactory bulb.
Olfactory Epithelium
- 3 Cell Types
- Olfactory receptor cells
- Supporting cells
- Basal cells
Odorant Receptor Genes
- Dogs
- Humans
Dogs have 1,000 odourant receptor genes
Humans have 350 odourant receptor genes
Olfactory Epithelium
- Basal Cells
olfactory receptors are renewed every 60 days due to basal cell division
New axons grow into the adult CNS, which is unique
Olfactory Epithelium
- Olfactory Receptor Cell Structure
Cilia cover by the mucus film
Olfactory knob which gives off cilia
Cell body
Axon
Olfactory Receptor
- Structure
G-protein coupled receptor
Golf G protein coupled
Olfactory Receptor
- Cascade
- Activated Golf stimulates adenylyl cyclase to produce cAMP
- cAMP opens cyclic nucleotide gated cation channels in the ciliary membrane
- Influx of Ca2+ and Na+
- Depolarisation and roles of Ca2+
Olfactory Receptor Cells
- Roles of Ca2+
Activates Ca2+ gated Cl- channels
- Olfactory receptor cells actively accumulate Cl- so flow is out of the cell, augmenting depolarisation
Ca2+ binds to calmodulin and decreases the affinity of cyclic nucleotide gated channels for cAMP, allowing channels too close.
- Adaptation
Olfactory Receptor Cells
- Ca2+ Efflux
Ca2+ leaves olfactory receptor cells via:
- Na+:K+:ca2+ exchanger
- Maybe Ca2+ ATPase
Olfactory Bulb
- 2 Cell Types
- Mitral cells
- Tufted cells
Located in medial and lateral glomeruli
Long receptor axons pass through the cribriform plate into the olfactory bulb and synapse with either of these cell types in the medial and lateral glomeruli
Olfactory Bulb
- Output
Mitral and tufted cell axons travel to higher processing centres
Mitral cell axons travel in the lateral olfactory tract
Olfactory Bulb
- Lateral Inhibition Cell Types
- Periglomerular cells
- Granule cells
Olfactory Bulb
- Periglomerular Cells
Make inhibitory connections between glomeruli
Olfactory Bulb
- Granule cells
Make inhibitory connections between basal dendrites of the mitral cells
Olfactory Bulb
- Lateral Inhibition Function
Sharpen mitral cell odour tuning
Olfactory Bulb
- Lateral Inhibition Pathway
Activation fo a mitral cell activates granule or periglomerular cells that synapse with it, which then inhibits surrounding mitral cells, which may have been less effectively stimulated by olfactory fibres
Lateral Olfactory Tract Synapses
- Anterior olfactory nucleus
- Olfactory tubercle
- Pyriform cortex
- Amygdaloid complex
- Entorhinal cortex
Anterior Olfactory Nucleus
Mitral cell axons form synaptic connections with projection neurones in the anterior olfactory nucleus.
These cells send their axons via the anterior com issuere to the contralateral olfactory bulb to stimulate granule cells that will inhibit the contralateral mitral cell population
Olfactory Tubercle
Projects to the medial dorsal nucleus of the thalamus, which projects to the orbitofrontal cortex
Conscious perception of odour
Pyriform Cortex
Projects to other olfactory cortical regions
Amygdaloid Complex
Projects to:
- Hypothalamus = autonomic adjustments
- Reticular formation = Arousal
Entorhinal Cortex
Projects to:
- Hippocampus = motivation and emotion
- Hypothalamus = autonomic adjustments
Odour Selectivity
Increases as the olfactory pathway is ascended
- Lateral inhibition in the olfactory bulb
- Olfactory cortex = relatively un-selective for odours
- Pyriform and amygdala = Slightly more selective for odours
- Orbitofrontal cortex is very selective, where most cells only respond to a single odour type
