Gustation and Olfaction

Anosmia

loss of sense of smell

The stimulus for olfaction is

a volatile substance (a rapidly vaporising substance releasing air borne molecules)

The stimulus for taste is

water soluble substances (molecules entering the mouth in solid or liquid form)

Flavour

A perceptual experience produced by a combination of taste (gustation), olfaction and other sensations.

Taste

the sensation that occurs when molecules enter the mouth in a solid or liquid form and stimulate receptors on the tongue

Sweetness

associated with substances that have nutritive or caloric value

Salty

indicates the presence of sodium

Bitterness

associated with substances that are potentially harmful

Papillae

rough, bumpy elevations on surface of tongue containing several hundreds of taste buds with each taste bud containing 50-100 taste receptor cells

Filiform Papillae

Shaped like cones and cover entire surface of tongue. Contain no taste buds. Only papillae present on central area of tongue's surface.

Fungiform Papillae

Mushroom-shaped structures containing taste buds and located on the sides and tip of the tongue.

Foliate Papillae

Series of folds with taste buds located on lateral aspects of posterior tongue

Circumvallate Papillae

Large papillae with taste buds shaped like flat mounds in a trench; located at back of the tongue

Primary Taste Area

Located in insula

Gustation

the sensation of taste

Taste Pore

An opening in the taste bud through which the tips of taste cells protrude. When chemical enter here they stimulate the taste cells resulting in trasnduction.

Taste Receptor Cell

Cell located in taste buds that causes the transduction of chemical to electrical energy when chemicals contact receptors sites at the tip of this cell.

Taste Bud

Structure located within papillae on tongue that contains taste cells. About 10,000 located over tongue.

Where are taste cell receptor sites located?

On the membrane of taste cells.

What do different types of taste cell receptor sites respond to?

Different chemicals.

What happens when chemicals contact taste cell receptor sites?

They open ion channels and cause transduction by affecting ion flow across the membrane of the cell.

Lifespan of Olfactory Receptor Cells

5-7 weeks

Olfactory Bulb

Brain structure(s) located above the nasal cavity beneath the frontal lobes. Contain neural circuits responsible for first level of processing of olfactory information. Receives information directly from the the olfactory receptor cells.

Olfactory Mucosa

Membrane lining superior region of nasal cavity, below the olfactory bulb. Contains olfactory receptor neurons.

Olfactory receptor neurons

Sensory receptor cells in olfactory mucosa that transduce chemical signals from odorants into neural impulses that travel to the brain.

How many types of olfactory receptor neurons do humans have?

350-400

The perception of a particular odorant's smell is related to:

A specific pattern of firing across different types of olfactory receptor neurons - similar to trichromatic coding for colour vision

Odorant Recognition Profile

The pattern of olfactory activation for an odorant, indicating which olfactory receptor neurons are activated by the odorant

Macrosmatic

Having a keen sense of smell; usually important to an animal's survival.

Microsmatic

Having a weaker sense of smell. Usually occurs in animals like humans, in which the sense of smell is not crucial for survival.

What is Phenylthiocarbamide (PTC)?

A bitter substance used to detect the ability to taste it.

What determines the ability to taste PTC?

The ability to taste the bitterness of PTC is determined by the presence or absence of the PTC receptor, which is genetically inherited

Do mice typically have the PTC receptor?

Mice typically lack the PTC receptor.

Recognition threshold

For smell, the concentration at which the quality of an odor can be recognized.

Piriform cortex

an area of medial temporal cortex adjacent to the amygdala that receives direct olfactory input - considered to be primary olfactory area

Orbitofrontal Cortex

Area of the frontal lobe acting as a convergence zone for sensory information including olfactory processing - considered to be secondary olfactory area

Retronasal route

The opening from the oral cavity, through the nasal pharynx, into the nasal cavity. One route that volatile substances reach the olfactory mucosa.

Orthonasal route

The route by which volatile substances enter the front of the nose to stimulate the olfactory receptors.

Hyposmia

partially impaired sense of smell