The Chemical Senses - Taste and Smell

What are the five basic tastes and their associated chemicals?

Sweet: glucose, fructose, sucrose; Bitter: Mg2+ and K+; Sour: HCl; Salty: NaCl; Umami: glutamate, monosodium, MSG.

What is a tastant?

Taste stimuli that activates taste receptor cells.

How does taste transduction occur?

Tastants convert into a nerve impulse by passing through ion channels (salty, sour), blocking ion channels (sour), or binding to G-protein coupled receptors (bitter, sweet, umami).

Describe the taste pathway.

CN7 (facial), CN9 (glossopharyngeal), and CN10 (vagus) carry gustatory axons to the gustatory nucleus in the medulla, which synapse at the VPM of the thalamus and finally to the primary gustatory cortex on the insula.

What is olfactory transduction?

Odorants bind to receptor proteins, stimulating G-proteins, which open Ca2+ activated Cl- channels after depolarization, causing current flow and membrane depolarization.

What is an odorant?

The chemical that causes the sense of smell.

What are the basic organs of smell?

The olfactory epithelium and olfactory receptor cells (neurons) are involved in the sense of smell.

How do olfactory receptor neurons function?

They regularly replace neurons and their axons terminate in glomeruli, sending signals to the olfactory cortex through the olfactory tract.

What are pheromones?

Chemicals released by the body that mark territories, identify individuals, and indicate aggression or stress.

What occurs when a tastant activates a receptor cell?

The receptor cell's membrane potential changes, typically depolarizing, leading to the opening of voltage-gated Ca+ channels and creating action potentials.