Taste and Taste Transduction

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Questions and Answers

What should you do when you receive candy from your neighbor?

Taste it immediately without exchanging.

Look at the wrapper before eating.

Open it and exchange without telling the flavor. (correct)

Smell it before tasting.

What is the primary function of gustatory epithelial cells?

To produce saliva for taste.

To provide structural support for taste buds.

To regenerate damaged taste buds.

To send taste signals to the brain. (correct)

What happens to the taste perception if you do not un-pinch your nose while tasting?

Only sweet sensations are detected.

Taste is enhanced significantly.

Taste perception remains unchanged.

Flavors become indistinguishable. (correct)

How often do basal epithelial cells divide?

Every 7-10 days. Signup and view all the answers

Which of the following is NOT a type of gustatory epithelial cell?

Cell that produces acetylcholine. Signup and view all the answers

What type of projections do gustatory epithelial cells have?

Microvilli. Signup and view all the answers

What sensory organs are primarily involved in tasting flavors?

Tongue and taste buds. Signup and view all the answers

What is the approximate number of taste buds located on the tongue?

About 10,000. Signup and view all the answers

What type of neurons are found in the olfactory epithelium?

Bipolar neurons Signup and view all the answers

What is the role of the mucous layer covering the olfactory cilia?

To act as a solvent for odorants Signup and view all the answers

How frequently do olfactory neurons regenerate?

Every 30–60 days Signup and view all the answers

What is the primary function of olfactory stem cells in the olfactory epithelium?

To form new olfactory neurons Signup and view all the answers

How many unique receptor proteins do humans have related to smell?

Approximately 400 Signup and view all the answers

What phenomenon describes the constant influx of Ca2+ leading to a reduced ability to smell over time?

Olfactory adaptation Signup and view all the answers

Which structure serves as the second-order neuron in the olfactory pathway?

Mitral cells Signup and view all the answers

What type of coding helps form olfactory maps in the brain?

Population coding Signup and view all the answers

Which lobe processes and interprets smell signals in humans?

Piriform lobe Signup and view all the answers

What is the synapse site called where axons from neurons with the same receptor type converge?

Glomeruli Signup and view all the answers

Which emotion-related brain structures receive some olfactory information?

Hypothalamus and amygdala Signup and view all the answers

How does the brain collectively identify different scents?

Through the combination of odorants and activated glomeruli Signup and view all the answers

What can result in anosmia?

Head injuries that damage olfactory nerves Signup and view all the answers

Which type of hallucination is primarily related to the sense of smell?

Olfactory hallucinations Signup and view all the answers

What primarily encodes the strength of odors in the olfactory system?

The frequency and pattern of action potentials Signup and view all the answers

What condition must be met for a substance to be smelled?

It must be volatile and in gaseous state. Signup and view all the answers

Which of the following correctly defines the role of cAMP in olfactory transduction?

It acts as a second messenger in the signaling pathway. Signup and view all the answers

What triggers the activation of olfactory sensory neurons?

Odorant binding to receptor proteins in the nasal passage. Signup and view all the answers

What is the first step in the olfactory transduction biochemical pathway?

Odorant binds to its receptor. Signup and view all the answers

The TRPA1 receptor is primarily associated with which of the following?

Responding to temperature and irritants. Signup and view all the answers

Which type of amino acids are primarily associated with the umami taste sensation?

Glutamate and aspartate Signup and view all the answers

What is the primary mechanism by which salt-sensitive taste cells are depolarized?

Direct entry of Na+ through Na+-selective channels Signup and view all the answers

Which cranial nerve is responsible for carrying taste impulses from the anterior two-thirds of the tongue?

Facial nerve (VII) Signup and view all the answers

What type of receptors are primarily involved in the bitterness taste sensation?

T2R receptors Signup and view all the answers

What role does the limbic system play in gustatory processing?

Determining taste appreciation and feeding regulation Signup and view all the answers

What sensory experience primarily enhances the sensation of taste?

Olfactory (smell) sensations Signup and view all the answers

Which of the following conditions is NOT a common cause of taste disorders?

Obesity Signup and view all the answers

How long does it typically take for the complete adaptation of taste sensations to occur?

1-5 minutes Signup and view all the answers

What compound primarily causes the perception of sour taste?

Hydrogen ions Signup and view all the answers

What is the role of the neurotransmitter ATP in taste transduction?

Helps to initiate action potentials in sensory neurons Signup and view all the answers

Which taste sensation is most sensitive, requiring lower concentration of its specific tastant for activation?

Bitter Signup and view all the answers

Which type of taste receptor genes are necessary for sweet taste detection?

T1R2 and T1R3 Signup and view all the answers

What is a potential sixth taste that has been suggested based on recent findings?

Fatty acid taste from long-chain fatty acids Signup and view all the answers

Which statement is true about the physiological requirements for tasting a substance?

The substance must be dissolved in saliva. Signup and view all the answers

Study Notes

Taste

Taste buds are located on the tongue and other oral structures like the soft palate, cheeks, pharynx, epiglottis.
Taste buds are composed of gustatory and basal epithelial cells.
Gustatory epithelial cells are taste receptor cells that have microvilli called gustatory hairs that project into taste pores, bathed in saliva.
Sensory dendrites coiled around gustatory epithelial cells send taste signals to the brain.
Three types of gustatory epithelial cells are: one releases serotonin, others lack synaptic vesicles, but one releases ATP as a neurotransmitter.
Basal epithelial cells are dynamic stem cells that divide every 7-10 days.
The five basic taste sensations are: sweet, sour, salty, bitter, umami.
For a chemical to be tasted, it must dissolve in saliva, diffuse into the taste pore, and contact gustatory hairs.

Taste Transduction

Taste stimuli (tastants) can pass directly through ion channels, bind to and block ion channels, or bind to G-protein-coupled receptors and activate second messengers to open ion channels.
Tastant binding depolarizes the cell membrane of the gustatory epithelial cell, causing the release of a neurotransmitter.
The neurotransmitter binds to the dendrite of a sensory neuron and initiates a generator potential that leads to action potentials.

Salt Taste Transduction

Salt-sensitive taste cells are depolarized by Na+.
Sodium ions influx directly causes depolarization through Na+-selective channels.
Amiloride can block Na+ channels.

Sour Taste Transduction

Sour-sensitive taste cells are depolarized by protons.
Protons enter intracellularly by opening channels that allow other cations to enter.

Bitter Taste Transduction

Bitter-sensitive taste cells are depolarized by unique families of taste receptor genes (T1R and T2R).
These receptors are bound to the specific G-protein gustducin.
Activation causes the release of stored Ca2+ that opens cation channels, leading to depolarization and release of neurotransmitter ATP.

Sweet Taste Transduction

Sweet-sensitive taste cells are depolarized by unique families of taste receptor genes (T1R2 and T1R3 receptors).
Both T1R2 and T1R3 receptors are required to activate sweet taste.
Activation of these receptors causes the release of stored Ca2+ that opens cation channels, leading to depolarization and release of neurotransmitter ATP.

Umami Taste Transduction

Umami-sensitive taste cells are depolarized by unique families of taste receptor genes (T1R1 and T1R3 receptors).
Both T1R1 and T1R3 receptors are required to activate umami taste.
Activation of these receptors causes the release of stored Ca2+ that opens cation channels, leading to depolarization and release of neurotransmitter ATP.

Transmission of Gustatory Information

Two major cranial nerve pairs carry taste impulses to the brain: the facial nerve and the glossopharyngeal nerve.
The facial nerve (VII) carries impulses from the anterior two-thirds of the tongue.
The glossopharyngeal (IX) nerve carries impulses from the posterior one-third and pharynx.
The vagus nerve (X) transmits impulses from the epiglottis and lower pharynx.
Nerve fibers synapse in the solitary nucleus of the medulla.
Information then travels to the thalamus and then to the gustatory cortex in the insula.
The hypothalamus and limbic system are involved in determining appreciation of taste and regulating feeding and digestion physiology.

Influence of Other Sensations on Taste

Taste is 80% smell.
The mouth also contains thermoreceptors, mechanoreceptors, and nociceptors.
Temperature and texture enhance or detract from taste.
Spicy hot foods can excite pain receptors in the mouth, adding to gustatory experience.

Olfactory Receptors

The olfactory epithelium is the organ of smell located in the roof of the nasal cavity.
It covers the superior nasal conchae and contains olfactory sensory neurons.
Olfactory sensory neurons are bipolar neurons with radiating olfactory cilia.
Supporting cells surround and cushion olfactory receptor cells.
Olfactory stem cells are located at the base of the epithelium.

Olfactory Transduction

In order to smell a substance, it must be volatile and must dissolve in olfactory epithelium fluid.
Odorants bind to receptor proteins in the olfactory cilium membranes.
Binding opens cation channels, generating a receptor potential.
At threshold, an action potential is conducted to the first relay station in the olfactory bulb.

Olfactory Transduction: Biochemical Pathway

Odorant binds to its receptor.
Receptor activates the G protein (Golf).
G protein activates the enzyme adenylate cyclase.
Adenylate cyclase converts ATP to the 2nd messenger cyclic AMP (cAMP).
cAMP opens cyclic AMP-gated cation channels, causing depolarization.

Transmission of Olfactory Information

Filaments of olfactory nerves synapse with mitral cells in the olfactory bulb.
Mitral cells are second-order neurons that form the olfactory tract.
Synapse occurs in structures called glomeruli.
Axons from neurons with the same receptor type converge on a given type of glomerulus.
The mitral cells amplify, refine, and relay signals.
Impulses from activated mitral cells travel via olfactory tracts to the piriform lobe of the olfactory cortex.
Some information is sent to the frontal lobe; some passes through the thalamus first, where smell is consciously interpreted and identified.
Some information sent to the hypothalamus, amygdala, and other regions of the limbic system (through the thalamus) elicits emotional responses to odors.
Smell is a relatively fast-adapting sense, due to constant Ca2+ influx that saturates receptors.

Processing of Odor Information

The olfactory cortex and frontal lobe work together to help determine precise scent identities based on the combination of odorants received and olfactory glomeruli activated.
Population coding of olfactory association neurons can form olfactory maps.

Clinical Connection: Sense of Smell

Anosmias are olfactory disorders that are most often caused by head injuries, aftereffects of nasal cavity inflammation, neurological disorders such as Parkinson's disease, and Covid-19.
Olfactory hallucinations are usually caused by temporal lobe epilepsy that involves the olfactory cortex.
Some people have olfactory auras prior to epileptic seizures.

Clinical Connection: Sense of Taste

Taste disorders are less common than disorders of smell.
Causes of taste disorders include upper respiratory tract infections, head injuries, chemicals or medications, and head and neck radiation for cancer treatment.
Zinc supplements may help with radiation-induced taste disorders.

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Description

Explore the fascinating world of taste in this quiz that covers the anatomy of taste buds, the types of gustatory cells, and the process of taste transduction. Learn about the five basic taste sensations and how taste signals are transmitted to the brain. Challenge your knowledge of these crucial aspects of human physiology.