olfaction and taste

What are the five taste categories?

Sweet, bitter, salty, sour, and umami.

How do taste categories relate to nutritional requirements?

Bitter may signal toxicity, salty helps regulate electrolytes, and others correspond to different dietary needs.

Where are taste buds located?

Papillae of the tongue:

fungiform, foliate, and circumvallate.

What cranial nerves innervate taste buds?

The chorda tympani and glossopharyngeal nerves (cranial nerves VII, IX, and X)

Which taste receptor types are ionotropic?

salty and sour

Which taste receptor types are G-protein coupled (metabotropic)?

Sweet, bitter, and umami

What type of receptors are used for salty taste?

Epithelial sodium channels (ENaC) in Type I cells.

What receptors mediate sweet taste?

T1R2 and T1R3 receptors in Type II cells.

Which receptor is responsible for umami taste?

T1R1 and T1R3 (metabotropic dimer) in Type II cells.

What type of receptor detects bitter taste?

T2R receptors (monomeric metabotropic) in Type II cells.

What is the receptor for sour taste?

Otopetrin1 (proton-permeable) in Type III cells.

Through which brain structures does taste information travel?

From cranial nerves → nucleus of the solitary tract (brainstem) → thalamus → gustatory cortex.

What are odorants?

Volatile compounds detected as odors via the olfactory system.

What are the two routes for odor detection?

Orthonasal (through the nose) and retronasal (from the throat to the nose).

What type of receptors are olfactory receptors?

G-protein coupled receptors.

How do olfactory receptors activate neurons?

Odorants bind to receptors, triggering cAMP, leading to Ca²⁺ influx, Cl⁻ efflux, and neuron depolarization.

How many functional olfactory receptor genes exist in humans?

391 genes.

How is odor discrimination achieved?

Different combinations of olfactory receptors encode different odorants.

Where do olfactory sensory neurons project?

To two specific glomeruli in the olfactory bulb.

What is the first relay station for olfactory signals?

The olfactory bulb.

How is olfactory information transmitted to the brain?

Via the lateral olfactory tract to the olfactory cortex (bypassing the thalamus).

What is anosmia?

Loss of the sense of smell.

What are common causes of anosmia?

Respiratory infections, toxic substance exposure, certain medications, and neurodegenerative diseases.

How does the olfactory system regenerate neurons?

Supporting sustentacular cells and basal cells (globose and horizontal) replace damaged olfactory sensory neurons.

How does COVID-19 cause anosmia?

It infects supporting sustentacular cells in the olfactory epithelium, leading to sensory neuron death.

Why is olfactory function recoverable after COVID-19?

Basal cells regenerate new olfactory sensory neurons.

What is the process of olfactory sensory neuron regeneration via supporting cells in the olfactory epithelium

1. supporting sustentacular cells will divide

2. forming immature sensory neurons

3. these will develop into mature sensory neurons

4. if the sustentacular cells are damaged then the vertical basal cells will divide into globose basal cells which will then divide again into sustentacular cells