Lecture 6: Chemical Sense Flashcards
Describe the role of chemoreceptors in smell and taste.
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.
Explain how chemicals must be processed for detection by chemoreceptors.
Chemicals must be dissolved in an aqueous solution to be detected by chemoreceptors, which are sensitive to these dissolved substances.
Define the adaptation process of taste receptors.
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.
How does saliva contribute to taste perception?
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.
Define the olfactory epithelium and its location.
The olfactory epithelium is the organ of smell located in the roof of the nasal cavity, covering the superior nasal conchae.
Explain the role of neurotransmitters in taste perception.
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.
What types of cells are found in the olfactory epithelium?
The olfactory epithelium contains olfactory sensory neurons, supporting cells, and olfactory stem cells.
Describe the process of taste receptor activation.
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.
How do olfactory sensory neurons differ from other neurons?
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.
Describe the structure and function of olfactory cilia.
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.
Describe the role of basal epithelial cells in taste perception.
Basal epithelial cells are dynamic stem cells in taste buds that divide every 7–10 days, contributing to the renewal of taste receptor cells.
Explain the process of olfactory adaptation.
Olfactory adaptation is the decreased response to a sustained stimulus, causing individuals to become unable to smell a certain odor after prolonged exposure.
What is the significance of the number of smell genes in humans?
Humans have approximately 400 active ‘smell’ genes in the nose, each encoding a unique receptor protein that responds to one or more odors.
Describe the role of mitral cells in the olfactory pathway.
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.
What is the function of glomeruli in the olfactory system?
Glomeruli are structures where synapses occur between olfactory sensory neurons and mitral cells, with each glomerulus dedicated to a specific type of receptor.
How do odorants activate olfactory sensory neurons?
Dissolved odorants bind to receptor proteins in the membranes of olfactory cilia, cation channels and generating a receptor potential.
Explain the process of smell transduction.
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.
List the five basic taste sensations and their characteristics.
- 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.
How are gustatory signals transmitted to the brain?
Gustatory signals are transmitted to the brain through sensory dendrites coiled around gustatory epithelial cells.
How do impulses from activated mitral cells travel in the brain?
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.
Explain the structure and function of gustatory epithelial cells.
Gustatory epithelial cells are taste receptor cells with microvilli called gustatory hairs that project into taste pores, allowing them to detect taste stimuli.
What is the significance of taste likes and dislikes?
Taste likes and dislikes have homeostatic value, guiding the intake of beneficial substances and warning against potentially harmful ones.
What is required for a substance to be smelled?
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.
Describe the convergence of sensory neurons in the olfactory system.
Axons from sensory neurons with the same type of odorant receptor converge on specific glomeruli, allowing for the integration of olfactory signals.
What happens at the first relay station in the olfactory pathway?
At the first relay station in the olfactory bulb, action potentials are conducted from olfactory sensory neurons to mitral cells.
Describe the role of the limbic system in emotional responses to odors
The limbic system, including the amygdala, is involved in eliciting emotional responses to odors.
Explain the causes of anosmias.
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.
How are olfactory hallucinations typically caused?
Olfactory hallucinations, or phantosmia, are usually caused by temporal lobe epilepsy that involves the olfactory cortex.
Identify the types of papillae on the tongue and their functions.
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.
Where are taste sensations primarily detected?
Taste sensations are primarily detected by chemoreceptors located in the taste buds.
What is the Montreal procedure and its purpose?
The Montreal procedure is a surgical treatment for epilepsy patients aimed at controlling seizures.
Explain the significance of the different thresholds of gustatory cells.
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.
Describe the mechanism of salty taste transduction..
Salty taste is primarily due to the influx of Na+ ions, which directly causes depolarization of gustatory epithelial cells.
How does sour taste transduction occur?
Sour taste is caused by H+ ions acting intracellularly, opening channels that allow other cations to enter, leading to depolarization of the gustatory cells.
Explain the role of G protein gustducin in taste perception.
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.
Describe the relationship between taste and smell.
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.
What other sensory receptors are present in the mouth that affect taste?
The mouth contains thermoreceptors, mechanoreceptors, and nociceptors, which can enhance or detract from the overall taste experience.
How do cranial nerves contribute to taste perception?
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.
Explain the pathway of taste impulses from the tongue to the brain.
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.
Describe the involvement of the hypothalamus and limbic system in taste perception.
The hypothalamus and limbic system are involved in taste perception, influencing emotional responses and preferences related to different tastes.
How do spicy foods affect taste perception?
Spicy foods can excite pain receptors in the mouth, which some individuals may experience as pleasurable, such as the sensation from hot chili peppers.
Describe the role of the amygdala in taste perception.
The amygdala is involved in processing emotional responses to taste, influencing how we perceive and react to different flavors.
Explain the function of the lateral hypothalamus in relation to appetite.
The lateral hypothalamus plays a crucial role in regulating appetite, signaling hunger and the desire to eat.
Define satiety and its significance in taste perception.
Satiety refers to the feeling of fullness and satisfaction after eating, which helps regulate food intake and influences taste perception.
How does taste perception trigger reflexes involved in digestion?
Taste perception can trigger reflexes such as increased saliva secretion and gastric juice production, aiding in the digestive process.
Describe protective reactions that may be initiated by taste perception.
Taste perception can initiate protective reactions like gagging and reflexive vomiting to prevent the ingestion of harmful substances.
Identify common causes of taste disorders.
Common causes of taste disorders include upper respiratory tract infections, head injuries, certain chemicals or medications, and radiation treatment for cancer.
Explain the potential benefit of zinc supplements for taste disorders.
Zinc supplements may help alleviate some cases of radiation-induced taste disorders by supporting the function of taste receptors.
Discuss why taste disorders are less common than smell disorders.
Taste disorders are less common because taste receptors are served by three different nerves, making simultaneous damage to all three less likely.
What is the role of the thalamus cortex in taste perception?
The thalamus cortex is involved in processing sensory information, including taste, and plays a key role in how we perceive flavors.
