Lecture 6: Chemical Sense

Question 1

Describe the role of chemoreceptors in smell and taste.

Answer 1

Chemoreceptors are sensory receptors that detect chemical substances, allowing the senses of smell (olfaction) and taste (gustation) to identify whether a substance should be savored or avoided.

Question 2

Explain how chemicals must be processed for detection by chemoreceptors.

Answer 2

Chemicals must be dissolved in an aqueous solution to be detected by chemoreceptors, which are sensitive to these dissolved substances.

Question 3

Define the adaptation process of taste receptors.

Answer 3

Taste receptors adapt within 3–5 seconds, with complete adaptation occurring in 1–5 minutes, meaning that the sensitivity to taste diminishes over time with continuous exposure.

Question 4

How does saliva contribute to taste perception?

Answer 4

Saliva acts as a solvent that dissolves food chemicals, facilitating their diffusion into taste pores and contact with gustatory hairs, which is essential for taste perception.

Question 5

Define the olfactory epithelium and its location.

Answer 5

The olfactory epithelium is the organ of smell located in the roof of the nasal cavity, covering the superior nasal conchae.

Question 6

Explain the role of neurotransmitters in taste perception.

Answer 6

Neurotransmitters released from gustatory epithelial cells bind to the dendrites of sensory neurons, initiating a generator potential that can lead to action potentials, transmitting taste information to the brain.

Question 7

What types of cells are found in the olfactory epithelium?

Answer 7

The olfactory epithelium contains olfactory sensory neurons, supporting cells, and olfactory stem cells.

Question 8

Describe the process of taste receptor activation.

Answer 8

Taste receptor activation begins with the binding of a food chemical (tastant) to the gustatory epithelial cell membrane, leading to depolarization of the cell membrane and the release of neurotransmitters.

Question 9

How do olfactory sensory neurons differ from other neurons?

Answer 9

Olfactory sensory neurons are unusual bipolar neurons with thin apical dendrites that terminate in a knob, and they have stem cells that can regenerate new neurons every 30–60 days.

Question 10

Describe the structure and function of olfactory cilia.

Answer 10

Olfactory cilia are long, largely nonmotile projections that radiate from the knob of olfactory neurons and are covered by mucus, which serves as a solvent for odorants.

Question 11

Describe the role of basal epithelial cells in taste perception.

Answer 11

Basal epithelial cells are dynamic stem cells in taste buds that divide every 7–10 days, contributing to the renewal of taste receptor cells.

Question 12

Explain the process of olfactory adaptation.

Answer 12

Olfactory adaptation is the decreased response to a sustained stimulus, causing individuals to become unable to smell a certain odor after prolonged exposure.

Question 13

What is the significance of the number of smell genes in humans?

Answer 13

Humans have approximately 400 active ‘smell’ genes in the nose, each encoding a unique receptor protein that responds to one or more odors.

Question 14

Describe the role of mitral cells in the olfactory pathway.

Answer 14

Mitral cells are second-order neurons located in the olfactory bulb that receive synaptic input from olfactory sensory neurons and amplify, refine, and relay olfactory signals.

Question 15

What is the function of glomeruli in the olfactory system?

Answer 15

Glomeruli are structures where synapses occur between olfactory sensory neurons and mitral cells, with each glomerulus dedicated to a specific type of receptor.

Question 16

How do odorants activate olfactory sensory neurons?

Answer 16

Dissolved odorants bind to receptor proteins in the membranes of olfactory cilia, cation channels and generating a receptor potential.

Question 17

Explain the process of smell transduction.

Answer 17

Smell transduction involves an odorant binding to a receptor, activating a G protein (Golf), which leads to the synthesis of cAMP, opening Na+ and Ca2+ channels, causing depolarization and impulse transmission.

Question 18

List the five basic taste sensations and their characteristics.

Answer 18

1. Sweet - sugars, saccharin, alcohol, some amino acids; 2. Sour - hydrogen ions in solution; 3. Salty - metal ions, especially sodium chloride; 4. Bitter - alkaloids like quinine and nicotine; 5. Umami - amino acids like glutamate and aspartate.

Question 19

How are gustatory signals transmitted to the brain?

Answer 19

Gustatory signals are transmitted to the brain through sensory dendrites coiled around gustatory epithelial cells.

Question 20

How do impulses from activated mitral cells travel in the brain?

Answer 20

Impulses from activated mitral cells travel via olfactory tracts to the piriform lobe of the olfactory cortex, with some information also sent to the hypothalamus.

Question 21

Explain the structure and function of gustatory epithelial cells.

Answer 21

Gustatory epithelial cells are taste receptor cells with microvilli called gustatory hairs that project into taste pores, allowing them to detect taste stimuli.

Question 22

What is the significance of taste likes and dislikes?

Answer 22

Taste likes and dislikes have homeostatic value, guiding the intake of beneficial substances and warning against potentially harmful ones.

Question 23

What is required for a substance to be smelled?

Answer 23

For a substance to be smelled, it must be volatile, meaning it must be in a gaseous state and able to dissolve in the olfactory epithelium fluid.

Question 24

Describe the convergence of sensory neurons in the olfactory system.

Answer 24

Axons from sensory neurons with the same type of odorant receptor converge on specific glomeruli, allowing for the integration of olfactory signals.

Question 25

What happens at the first relay station in the olfactory pathway?

Answer 25

At the first relay station in the olfactory bulb, action potentials are conducted from olfactory sensory neurons to mitral cells.

Question 26

Describe the role of the limbic system in emotional responses to odors

Answer 26

The limbic system, including the amygdala, is involved in eliciting emotional responses to odors.

Question 27

Explain the causes of anosmias.

Answer 27

Anosmias, or olfactory disorders, often result from head injuries that tear olfactory nerves, aftereffects of nasal cavity inflammation, or neurological disorders such as Parkinson’s disease.

Question 28

How are olfactory hallucinations typically caused?

Answer 28

Olfactory hallucinations, or phantosmia, are usually caused by temporal lobe epilepsy that involves the olfactory cortex.

Question 29

Identify the types of papillae on the tongue and their functions.

Answer 29

Fungiform papillae house most taste buds and are scattered across the tongue; foliate papillae are located on the side walls of the tongue; vallate papillae are the largest taste buds forming a 'V' at the back of the tongue.

Question 30

Where are taste sensations primarily detected?

Answer 30

Taste sensations are primarily detected by chemoreceptors located in the taste buds.

Question 31

What is the Montreal procedure and its purpose?

Answer 31

The Montreal procedure is a surgical treatment for epilepsy patients aimed at controlling seizures.

Question 32

Explain the significance of the different thresholds of gustatory cells.

Answer 32

Different gustatory cells have varying thresholds for activation, with bitter receptors being the most sensitive, allowing for a range of taste perceptions based on the concentration of tastants.

Question 33

Describe the mechanism of salty taste transduction..

Answer 33

Salty taste is primarily due to the influx of Na+ ions, which directly causes depolarization of gustatory epithelial cells.

Question 34

How does sour taste transduction occur?

Answer 34

Sour taste is caused by H+ ions acting intracellularly, opening channels that allow other cations to enter, leading to depolarization of the gustatory cells.

Question 35

Explain the role of G protein gustducin in taste perception.

Answer 35

Unique receptors for sweet, bitter, and umami tastes are coupled to the G protein gustducin, which, when activated, causes the release of stored Ca2+ that opens cation channels, resulting in depolarization and neurotransmitter release.

Question 36

Describe the relationship between taste and smell.

Answer 36

Taste is significantly influenced by smell, with approximately 80% of taste perception being attributed to olfactory input; when the nose is blocked, foods often taste bland.

Question 37

What other sensory receptors are present in the mouth that affect taste?

Answer 37

The mouth contains thermoreceptors, mechanoreceptors, and nociceptors, which can enhance or detract from the overall taste experience.

Question 38

How do cranial nerves contribute to taste perception?

Answer 38

Two main cranial nerve pairs, the facial nerve (VII) and glossopharyngeal nerve (IX), carry taste impulses from the tongue to the brain, while the vagus nerve (X) transmits taste information from the epiglottis and lower pharynx.

Question 39

Explain the pathway of taste impulses from the tongue to the brain.

Answer 39

Taste impulses from the tongue travel through cranial nerves to the solitary nucleus of the medulla, then to the thalamus, and finally to the gustatory cortex located in the insula.

Question 40

Describe the involvement of the hypothalamus and limbic system in taste perception.

Answer 40

The hypothalamus and limbic system are involved in taste perception, influencing emotional responses and preferences related to different tastes.

Question 41

How do spicy foods affect taste perception?

Answer 41

Spicy foods can excite pain receptors in the mouth, which some individuals may experience as pleasurable, such as the sensation from hot chili peppers.

Question 42

Describe the role of the amygdala in taste perception.

Answer 42

The amygdala is involved in processing emotional responses to taste, influencing how we perceive and react to different flavors.

Question 43

Explain the function of the lateral hypothalamus in relation to appetite.

Answer 43

The lateral hypothalamus plays a crucial role in regulating appetite, signaling hunger and the desire to eat.

Question 44

Define satiety and its significance in taste perception.

Answer 44

Satiety refers to the feeling of fullness and satisfaction after eating, which helps regulate food intake and influences taste perception.

Question 45

How does taste perception trigger reflexes involved in digestion?

Answer 45

Taste perception can trigger reflexes such as increased saliva secretion and gastric juice production, aiding in the digestive process.

Question 46

Describe protective reactions that may be initiated by taste perception.

Answer 46

Taste perception can initiate protective reactions like gagging and reflexive vomiting to prevent the ingestion of harmful substances.

Question 47

Identify common causes of taste disorders.

Answer 47

Common causes of taste disorders include upper respiratory tract infections, head injuries, certain chemicals or medications, and radiation treatment for cancer.

Question 48

Explain the potential benefit of zinc supplements for taste disorders.

Answer 48

Zinc supplements may help alleviate some cases of radiation-induced taste disorders by supporting the function of taste receptors.

Question 49

Discuss why taste disorders are less common than smell disorders.

Answer 49

Taste disorders are less common because taste receptors are served by three different nerves, making simultaneous damage to all three less likely.

Question 50

What is the role of the thalamus cortex in taste perception?

Answer 50

The thalamus cortex is involved in processing sensory information, including taste, and plays a key role in how we perceive flavors.