Secion 0.1.5

Question 1

How do taste and smell work in the body?

Answer 1

Both taste and smell rely on chemoreceptors that generate electrical signals after binding a specific chemical.

Question 2

What additional functions do taste and smell chemoreceptors serve besides detecting flavors and odors?

Answer 2

Taste and smell chemoreceptors can trigger appetite, stimulate the release of digestive juices, and determine whether something is pleasurable or undesirable, acting as a quality control system for ingestion.

Question 3

How does the human sense of smell compare to that of lower animals?

Answer 3

In humans, the sense of smell is not very sensitive compared to lower animals and, therefore, does not greatly influence our behavior

Question 4

Where are the chemoreceptors that sense taste located in the body?

Answer 4

The chemoreceptors that sense taste are located in the tongue, oral cavity, and throat. Most of them are on the tongue, organized into clusters called taste buds.

Question 5

How are taste buds structured, and where are they found?

Answer 5

Taste buds are clusters of nerve endings found on the tongue and in the lining of the mouth. Each taste bud contains about 50 taste receptor cells along with supporting cells. Taste buds have small openings that allow fluids to contact the taste receptors.

Question 6

What distinguishes taste buds from vision or hearing receptors in terms of their lifespan?

Answer 6

Taste buds have a limited lifespan of approximately 10 days, after which they are renewed. This is different from vision or hearing receptors, which do not have a similar renewal process.

Question 7

What happens when a tastant binds to its receptor in a taste bud?

Answer 7

When a tastant binds to its receptor in a taste bud, ion channels create a depolarizing potential. This potential can then initiate an action potential in the nerve endings of afferent neurons.

Question 8

What is a tastant?

Answer 8

Any chemical that stimulates the sensory cells in a taste bud

Question 9

Where do afferent neurons associated with taste buds send their signals first?

Answer 9

Afferent neurons associated with taste buds first send their signals to the brainstem and thalamus.

Question 10

What is the next destination for taste-related signals after the brainstem and thalamus?

Answer 10

After the brainstem and thalamus, taste-related signals proceed to the cortical gustatory area, which is located in the parietal lobe adjacent to the tongue area of the somatosensory cortex.

Question 11

What additional brain regions do some taste-related signals go to from the brainstem?

Answer 11

Some taste-related signals from the brainstem also go to the hypothalamus and limbic systems. This helps in distinguishing between pleasant and unpleasant tastes and can trigger associated behavioral responses.

Question 12

How many primary tastes are there, and what are they?

Answer 12

There are five primary tastes: salty, sour, sweet, bitter, and umami

Question 13

Can taste receptors respond to multiple primary tastes?

Answer 13

Yes, taste receptors are capable of responding to multiple primary tastes, but with varying degrees of sensitivity.

Question 14

What stimulates salty taste cells, and what is their mechanism of action?

Answer 14

Salty taste cells are stimulated by salts such as NaCl. They have specialized Na+ channels that allow direct entry of Na+ ions, leading to cell depolarization.

Question 15

What stimulates sour taste cells, and how does it affect their ion channels?

Answer 15

Sour taste cells are stimulated by acids, and the free H+ ions in acids block K+ channels in these cells. This reduces the outward flow of K+ and can produce depolarization.

Question 16

What stimulates sweet taste cells, and what is the mechanism by which they respond?

Answer 16

Sweet taste cells are stimulated by glucose. Binding of glucose activates a G protein and generates cAMP, which inhibits certain K+ channels, leading to depolarization. Artificial sweeteners also interact with sweet taste cells but contain no calories.

Question 17

What stimulates bitter taste cells, and why is their diversity important?

Answer 17

Bitter taste cells are stimulated by a wide variety of compounds, including alkaloids found in substances like caffeine, nicotine, and toxic plant metabolites. Their diversity is important for detecting potential toxins, as many poisonous compounds taste bitter.

Question 18

What triggers umami taste cells, and what is known about their cellular mechanisms?

Answer 18

Umami taste cells are triggered by amino acids, such as glutamate. While they involve G proteins, the second messenger pathways for umami receptors are relatively unknown. They are associated with sensing protein-rich foods and meaty flavors.

Question 19

Where are the chemoreceptors for smell located?

Answer 19

The chemoreceptors for smell are located in the top of the nasal cavity, specifically in the olfactory mucosa.

Question 20

What does the olfactory mucosa contain besides olfactory receptor cells?

Answer 20

The olfactory mucosa contains olfactory receptor cells, supporting cells that secrete mucus, and basal cells, which are the precursors for new olfactory receptor cells

Question 21

What is the lifespan of basal cells in the olfactory mucosa?

Answer 21

Basal cells in the olfactory mucosa have a lifespan of approximately two months.

Question 22

What is formed by the axons of olfactory receptor cells?

Answer 22

The axons of olfactory receptor cells form the olfactory nerve.

Question 23

What happens when chemicals, or odourants, come into contact with the olfactory receptor cells?

Answer 23

Odourants dissolve in the mucous layer and interact with cilia on the olfactory receptor cells.

Question 24

What is the role of G proteins and cAMP in the olfaction process?

Answer 24

Binding of an odourant activates G proteins, which mobilize the second messenger cAMP. This, in turn, opens Na+ channels, initiating a depolarizing receptor potential and subsequent action potential in the afferent fiber.

Question 25

How many olfactory receptors are there in the human nose, and how are they categorized?

Answer 25

There are five million olfactory receptors in the human nose, which can be divided into over a thousand different types.

Question 26

Why is the diversity of olfactory receptors significant?

Answer 26

The diversity of olfactory receptors allows different odourants to activate several receptors, creating distinct and complex smells.

Question 27

Approximately how many distinct smells can the cortex identify?

Answer 27

The cortex can identify over 10,000 distinct smells.

Question 28

Describe the process of olfaction

Answer 28

Olfaction: The Sense of Smell

1. Odourant Detection:
   Chemicals known as odourants dissolve in the mucous layer of the nasal cavity.
2. Interaction with Olfactory Receptor Cells:
   These odourants interact with cilia, small hair-like structures, on the olfactory receptor cells.
3. Activation of G Proteins:
   Binding of odourants activates G proteins within the olfactory receptor cells.
4. Mobilization of cAMP:
   G proteins trigger the production of the second messenger cAMP (cyclic adenosine monophosphate).
5. Opening of Na+ Channels:
   cAMP leads to the opening of Na+ (sodium) channels in the olfactory receptor cells.
6. Receptor Potential and Action Potential:
   The opening of Na+ channels initiates a depolarizing receptor potential.
   This depolarization results in the generation of an action potential in the afferent nerve fiber.

Question 29

What are some general properties of efferent neurons?

Answer 29

Efferent neurons typically have oval cell bodies with multiple dendrites and a single long axon that forms a neuronal junction with the effector. Only two neurotransmitters, acetylcholine and norepinephrine, are used.

Question 30

What is the autonomic nervous system, and how does it relate to the peripheral nervous system?

Answer 30

The autonomic nervous system is the involuntary branch of the peripheral nervous system. It regulates functions such as heart rate, digestion, and breathing.

Question 31

What is the somatic nervous system, and how does it differ from the autonomic nervous system?

Answer 31

The somatic nervous system is the voluntary branch of the peripheral nervous system. It controls voluntary muscle movements and sensory perception.

Question 32

Describe, in general, how taste buds function.

Answer 32

Taste buds are clusters of specialized cells located on the tongue and in the lining of the mouth. They contain taste receptor cells that detect different flavors. When you consume food, molecules from the food dissolve in saliva and interact with taste receptor cells. These cells generate electrical signals (receptor potentials) in response to specific chemicals, leading to the perception of taste.

Question 33

Discriminate between the different tastes and describe how this is possible.

Answer 33

There are five primary tastes: salty, sour, sweet, bitter, and umami. Taste discrimination is possible because taste receptor cells are capable of responding to each of these primary tastes, but they vary in sensitivity. For example, salty taste cells are stimulated by salts, while sweet taste cells respond to sugars. Bitter taste cells are triggered by various compounds, often associated with toxicity. The brain processes the combination of signals from these cells to create distinct taste perceptions.

Question 34

Describe the olfactory mucosa and how “smells” are converted into electrical signals.

Answer 34

The olfactory mucosa is a small patch of skin located in the nasal cavity’s ceiling. It contains olfactory receptor cells, supporting cells, and basal cells. When you smell something, odor molecules interact with olfactory receptor cells. This interaction triggers receptor cells to generate electrical signals. These electrical signals are then transmitted to the olfactory nerve and sent to the brain, specifically the olfactory cortex, where they are processed and interpreted as smells.