Exam 2 Gustation and Olfaction Flashcards
•Taste and smell include positive and negative chemotaxis.
What are their definitions?
–Positive chemotaxis is used to find nutrients or locate a mate, for example.
–Negative chemotaxis helps us avoid noxious agents such as rotten smells and food.
Our nervous system codes for chemicals in our environment by using a mixture of ______ and _______.
Labeled Line
Population Coding
What is: Each chemical is a preferred stimulus which has its own receptor and circuit
Labeled line
What is: Receptors and circuits are not ultimately selective. Instead the nervous system analyzes all of the chemical responses coming in and compares them in order to pinpoint what the chemical stimulus might be.
Population Coding (Pattern Coding)
•Most of what we perceive as taste actually comes from our sense of ______. Taste buds identify only five flavors. Our nose does the rest by identifying “odor molecules” from food.
Smell
Taste buds identify only five flavors. Our nose does the rest by identifying “odor molecules” from food.
What are the three types of papillae and where are they located?
- Circumvallate (pimples), posterior 1/3 of the tongue.
- Foliate (ridges) posterior and lateral surface of the tongue.
- Fungiform (mushrooms), top and sides of the tongue.
What are the three taste cell types?
–Receptor cells, are modified epithelial cells, 50-150 per taste bud.
– Supporting cells develop into receptor cells.
– Basal cells develop into supporting cells.
How often does a taste receptor cell turnover?
•Receptor cells turnover every 1 to 2 weeks.
–These are among the shortest-lived cells in the body.
–Basal cells become supporting cells become receptor cells.
What does saliva act as?
What does taste receptors act as?
- Saliva= filter, saliva mixes with food and goes to pore, this is where the taste receptors are
- Taste= transducer, because the taste molecules are changing the mV
Explain innervation of taste cells
1) Afferent nerves enter the buds and end on the receptor cells.
2) Nerves are separated from the cell by synaptic clefts (chemical synapse).
3) One nerve fiber may innervate several receptors.
4) One receptor may be innervated by several nerves.
5) Taste nerves continually remodel synapses on a new receptor cell.
6) Receptors need innervation to stay healthy otherwise they will degenerate.
What nerves are taste buds innervated by?
Taste buds are innervated by cranial nerves VII (facial), IX (glossopharyngeal), X (vagus).
Where are the first, second and third synapses located in central gustatory connections
The first synapse is in the taste bud.
The second synapse is in the medulla.
The third synapse is in the thalamus.
The signal ends up in the primary gustatory cortex.
Other pathways exist.
The gustatory pathway is distinctive in that most of its fibers are uncrossed.
What are the five types of taste sensations?
–salty (NaCl)
–sour (acids)
–bitter (quinine, toxic plants)
–sweet (stereochemical configuration of glucose)
–umami (glutamate)
- One receptor cell can respond to ____ than one basic category of taste, but it has a preferred taste at threshold levels.
- Most of the tongue is sensitive to____ basic tastes. Certain regions are more sensitive to specific basic tastes than other regions.
- Afferent fibers show _____ firing patterns in response to _____ substances.
- Receptor potentials of taste receptor cells are _____, changing (either depolarizing or hyperpolarizing) by an appropriate chemical.
–The frequency of action potentials ______ with the quantity of taste molecules.
1) More
2) All
3) Different, Different
4) Graded
5) Increases
What coding type for:
The greater the amount of tastant, the faster the firing rate of afferent fibers (the more AP)
-In picture what is it showing?
Intensity Coding
-In this picture it is showing us that fiber one is specific for NaCl, each fiber has a preferential stimulus
What type of coding:
Each taste cell responds differently to four tastants
-for a different types of tastants each fiber can have a different type of firing
Pattern Coding
Explain the Mechanism of taste transduction
Mechanism of Taste Transduction
A Second messenger can start an AP by either two routes:
1) Ion channel
2) Opening of CA2+
- if there is more stimulus there will be more firing
When you release the serotinin (neurotransmitter) you get an AP
What type of coding;
•The responses of four taste cells to four different tastants are combined in the brain to determine the final taste.
–The height of the bars is an indication of the number of action potentials in the gustatory afferent axon.
Population Coding
Explain the different taste transduction for Salt and Sour
Different methods of producing AP depending on taste
What type of cell are olfactory receptor cells?
Neuronal! taste are just epithelial cells
•The sense of smell is carried by olfactory receptors in the olfactory epithelium, lying deep within the nasal cavity just below the cribriform plate.
The olfactory receptor cells is the:
The Receptor cillia is the:
encoder
transducer
Explain Olfactory Trandsduction
–The odorant molecule is absorbed into the mucus layer.
–The molecule contacts the cilia of receptor cells.
–The molecule binds to receptor sites.
–G-proteins are stimulated.
–Adenylyl cyclase is activated. (enzyme)
–Cyclic AMP is formed. (second messenger)
–cAMP binds to a specific cation channel (Na+).
–Cation channels open and Ca2+ influx occurs.
–This opens calcium-activated chloride channels.
–The membrane depolarizes generating a receptor potential.
–Receptor potentials are graded depending on odorant concentration.
–Strong odorants may suppress this activity.
–Following activation there may be post-excitatory inhibition.
–Transduction ends.
- The odorants diffuse away.
- Scavenger enzymes in the mucus break down odorants.
- cAMP in the receptor cell may activate other signaling pathways that end the transduction process.
