Gustation and Olfaction Flashcards
(30 cards)
Where are olfactory receptor neurons (ORNs) located?
In the olfactory epithelium at the roof of the nasal cavity.
What type of receptors are olfactory receptors?
G-protein coupled receptors (GPCRs)
What is the primary function of the olfactory bulb?
To receive input from ORNs and process it via glomeruli, where signals are passed to mitral and tufted cells.
How do olfactory receptor neurons send their axons to the brain?
They project through the cribriform plate of the ethmoid bone and synapse in the olfactory bulb.
What is the role of glomeruli in the olfactory bulb?
Each glomerulus receives input from ORNs expressing the same receptor type, enabling initial odorant discrimination.
Where do mitral and tufted cells project after the olfactory bulb?
To the olfactory cortex, amygdala, entorhinal cortex, and hypothalamus via the olfactory tract.
Does olfactory processing pass through the thalamus before reaching the cortex?
No, it is unique in that it bypasses the thalamus on the way to the primary olfactory cortex.
Which brain area is considered the primary olfactory cortex?
The piriform cortex
What is the significance of the amygdala and hypothalamus in olfaction?
They link smell to emotions, memory, and autonomic responses, such as hunger or disgust.
What neurotransmitter is primarily used by olfactory sensory neurons?
Glutamate
What happens in anosmia?
Loss of the sense of smell, which may be caused by damage to ORNs, olfactory bulb, or cribriform plate trauma.
How does olfactory transduction occur?
Odorant binds to GPCR → Activates Golf protein → ↑ cAMP → Opens Na⁺/Ca²⁺ channels → Depolarisation
How is olfactory information encoded?
Via a combinatorial code – each odorant activates a unique pattern of receptors, allowing discrimination of many scents.
What cell types in the olfactory bulb modulate signal strength?
Periglomerular cells (lateral inhibition at glomeruli)
Granule cells (inhibit mitral cells via dendrodendritic synapses)
What neurological disease is associated with early olfactory dysfunction?
Parkinson’s disease and Alzheimer’s disease
What are the five primary taste modalities?
Sweet
Sour
Salty
Bitter
Umami (savory)
What types of receptors are used for each taste modality?
Sweet, bitter, umami – GPCRs
Salty, sour – Ion channels
Where are taste receptors primarily located?
In taste buds on the tongue, soft palate, pharynx, and epiglottis
What are the three types of papillae that contain taste buds?
Fungiform (anterior tongue)
Foliate (posterolateral tongue)
Circumvallate (back of tongue)
(Note: Filiform papillae do not contain taste buds.)
Which cranial nerves carry taste information to the brain?
CN VII (Facial) – anterior 2/3 of tongue
CN IX (Glossopharyngeal) – posterior 1/3
CN X (Vagus) – epiglottis and pharynx
Where is the first central relay for taste in the brain?
The nucleus of the solitary tract (NTS) in the medulla oblongata
Describe the central gustatory pathway.
Taste receptors → CN VII, IX, X → Nucleus of the solitary tract → Thalamus (VPM) → Primary gustatory cortex (in insula and frontal operculum)
How does salt taste transduction work?
Na⁺ enters taste receptor cells through ENaC channels, depolarising the cell and triggering neurotransmitter release.
How is sour taste detected?
Through H⁺ ions entering via proton channels or blocking K⁺ channels, leading to depolarisation.
