Chapter 16: The Chemical Senses Flashcards
What is Anosmia?
A loss of smell which also leads to an inability to sense flavour.
What are three components of the chemical senses?
1: taste - when molecules (usually food) enter the mouth and stimulate the receptors on the tongue
2. Olfaction - when airborne molecules enter the nose and stimulate the receptor neurons in the olfactory Mucosa
3. Flavour - the impression we experience from a combination of taste and olfaction.
Who do chemical senses differ from other senses (visual, audio, cutaneous)?
They differ in that the receptors are exposed to the environment where molecules directly stimulate them. This leaves theme exposed to harmful bacteria and other bad substances. As such chemical receptors go through a cycle of birth, development, and death called neurogensis.
What is the life span of olfactory and taste receptors?
Olfactory receptors cycle every 5-7 weeks.
Taste receptors every 1-2 weeks.
What are the five basic tastes?
Sweet Salty Sour Bitter Umami (meaty/brothy/savory)
What are the different kinds of papillae?
Filiform Papillae - shaped like cones and cover the surface of the tongue
Fungiform Papillae - shaped like mushrooms and found at the tip and sides of the tongue.
Foliate Papillae: Folds on the back and sides of the tongue
Circumvillate Papillae: flat mounds found in a trench located in the back of the tongue.
Describe the characteristics of taste buds.
Taste buds are located in all papilla EXCEPT for filiform.
The tongue has about 10,000 taste buds.
Each taste bud contains 50-100 taste cells with tips that extend into taste pores. Transduction occurs when chemicals contact the receptors at the tips of the taste cells.
Where do neural signals go once they leave the taste cells?
Signals travel from the taste cells along a pathway from four different nerves
- Chorda Tympani nerve (front and side of tongue)
- Glossopharyngeal nerve (from back of the tongue)
- vagus nerve (from mouth and throat)
- Superficial petronasal nerve (soft palate)
From these nerves the signals travel to the nucleus of the solitary tract in the brainstem –> thalamus –> Insula, frontal opervulum cortex, and orbital frontal cortex in the frontal cortex.
Does the taste system use specificity or population coding?
It uses both; the neural system for taste functions quite similarly to colour vision. There is still however, a great deal unconfirmed about neural systems in taste.
What are the differences between types of tasters?
Three types of tasters:
- Non-tasters: have fewer tastebuds, don’t taste PTC
- Tasters: have more taste buds and some specialized receptors for compounds like PTC
- Supertasters: have many more taste buds than tasters, specialized receptors and tend to be extremely sensitive to bitter substances (like PTC).
What does it mean to say that some animals are macrosmatic and some are microsmatic?
Macrosmatic means that the animals have a keen sense of smell that is necessary for survival.
Microsmatic means the sense of smell is less good and not necessary for survival.
For example, humans are microsmatic and rats and dogs are macrosmatic.
Rats have a sense of smell 8-50X better than people, dogs have sense of smell 300-10 000X better.
The difference between micro and macrosmatics is the number of receptors they have.
Humans have ~10 million receptors, dogs have ~1 billion.
What is the olfactory mucosa and its characteristics?
The olfactory mucosa is located at the top of the nasal cavity. Olfactory receptor neurons (ORN) are embedded in the mucosa. An air stream carries odorants up to the mucosa where they contact ORN.
There are ~350 different types of ORN
Where do signals from Olfactory Receptor neurons go?
Signals from the ORN go to the nearby olfactory bulb (specifically the glomeruli) which are then sent to the primary olfactory cortex in the temporal lobe and the amygdala. They then go to the secondary olfactory cortex, the orbitofrontal cortex in the frontal lobe.
How do we recognize odors?
We learn to recognize odors based on repeated exposure to the patterns of firing that odor creates.
What is the Proust Effect?
The Proust effect are odor evoked autobiographical memories
These memories are always autobiographical and usually from the first decade of life.
The Proust effect is likely caused by the fact that the amygdala (emotions and emotional memory) and the hypothalamus (sorting and retrieving memories) are only 2-3 synapse away from the olfactory bulb.
What is flavour?
The interaction of taste and olfaction. Almost all tastes are also influenced by olfaction with the exception of MSG. Food stimulates olfaction systems by reaching the mucosa via the retronasal route.
How are taste and smell merged?
Responses from taste and smell are first combined in the orbital frontal cortex. This area also receives information from the primary somatosensory cortex (touch) and the inferotemporal cortex (visual “what” pathway). Meaning that flavour can be influenced by taste, smell, texture, and visual cues.
How do cognitive factors affect flavour?
Expectations affect flavour
Satiety/hunger influence flavour
memory/emotions influence flavour
