Taste (Gustation) and Smell (olfaction)

Pheromones

Chemical signal released by 1 member species and sensed by another species to trigger an innate response

• specialized olfactory cells

• important in animals, particularly insects, linked to mating, fighting, communication

Olfaction

Smell

Anatomy of olfaction

1. In nostril there is the olfactory epithelium (olfactory sensory cells)

2. Cribriform plate separates the olfactory epithelium from the brain; it is a bone with little holes that allow olfactory sensory to send projections to the brain

3. Above the cribriform plate is the olfactory bulb (extension of the brain), a bundle of nerves that sends projections through cribriform plate into the olfactory epithelium

Pathway of olfaction

Olfactory bulb → amygdala → piriform cortex → orbitofrontal cortex

5 main tastes

Bitter, salty, sweet, sour, umami (ability to taste glutamate)

• each depends on specific receptor that is localized on the tongue

Taste buds

Concentrated anteriorly (front) on tongue

• contained inside structures called papillae

  • fungiform papillae

  • foliate papillae

  • circumvallate papillae

• in each taste bud are the 5- receptor cells that can detect each taste

Fungiform papillae

Anterior, mushroom shaped structures located on tip and side of the tongue, which contain taste buds

Foliate papillae

Folded structures at the back of the tongue on both sides, which contain taste buds

Circumvallate papillae

Flat mound structures found at the back of the tongue and contain taste buds

Filiform papillae

Do not contain taste buds and exist all over the tongue

• center of the tongue contains only filiform papillae

Labelled lines model

Each taste bud receptor has 5 axon, all which send separate taste information to different parts of the gustatory (taste) cortex

• remain separate to the brain

• All synapse on different parts of the gustatory (taste) cortex

What tastes rely on GPCR receptors?

Sweet, umami, and bitter cells

What tastes rely on ion channels ?

Sour and salty

• bind directly to receptor

• salty binds to salt receptors which detect sodium

• sour binds to sourness receptors that react with hydrogen cations (H+), which closes potassium channels