L14: Sensory System: Chemical Senses Flashcards
What are the two chemical senses in humans?
Taste (gustation) and smell (olfaction).
What evolutionary advantage do chemical senses provide?
They help detect chemicals in the environment, find food, identify mates, and avoid harmful substances.
What are the five basic tastes?
Sweet, sour, salty, bitter, and umami.
What is umami, and what foods are associated with it?
Umami is a savoury taste associated with foods like mushrooms, soy sauce, and meat.
What type of receptors are involved in detecting chemical senses?
Chemoreceptors.
How does the taste system work to detect stimuli?
Chemicals bind to receptors on taste cells, causing signal transduction, which leads to neural signals sent to the brain.
How are taste buds organised on the tongue?
They are distributed across the tongue, with some areas more sensitive to certain tastes, but all areas can detect all basic tastes.
What is the lifespan of taste receptor cells?
About two weeks, after which they are replaced by basal cells.
What happens when you have a cold, and how does it affect taste?
A blocked nose reduces smell perception, which diminishes the ability to detect flavour since taste and smell combine to create flavour.
What is signal transduction in taste?
The process of converting a chemical signal (taste molecule binding) into an electrical signal (neural message).
How do humans detect salty tastes?
Sodium ions enter taste cells through non-gated channels, causing depolarization.
How do humans detect sour tastes?
Hydrogen ions from acidic substances enter cells and either block potassium channels or depolarize the cell directly.
How are sweet, bitter, and umami tastes detected?
Through G-protein-coupled receptors that trigger intracellular signalling cascades.
What is the role of the brain’s primary gustatory cortex?
It processes taste information for conscious awareness and flavour perception.
How is smell different from taste in terms of receptor cells?
Olfactory receptor cells are neurons and can fire action potentials, while taste receptor cells are not neurons.
Where are olfactory receptors located?
In the olfactory epithelium at the roof of the nasal cavity.
What is population coding in smell?
The process by which the brain decodes patterns of activity from multiple olfactory neurons to identify specific smells.
Why does smell have a strong association with memory and emotion?
Olfactory signals are processed in the limbic system, which is involved in emotions and memory.
What is anosmia?
The loss of the sense of smell, which can occur due to damage to olfactory pathways or the brain.
How do the taste and smell pathways differ in the brain?
The olfactory pathway bypasses the thalamus initially, while the gustatory pathway does not.
How do taste and smell combine to create flavour?
Flavour is the result of both taste and smell information converging in the brain, along with texture and other sensory inputs.
What is the primary purpose of bitterness detection in taste?
To help avoid toxic substances, which are often bitter.
What happens to taste cells if damaged by hot or abrasive food?
They regenerate, as basal cells produce new taste receptor cells every two weeks.
Why do older individuals often experience a decline in their sense of taste?
The rate of taste receptor cell replacement slows down with age.
What are the cranial nerves involved in taste perception?
Facial nerve (cranial nerve VII), glossopharyngeal nerve (cranial nerve IX), and vagus nerve (cranial nerve X).
What is the role of the thalamus in the gustatory pathway?
It serves as a relay station, processing and directing taste signals to the primary gustatory cortex.
How does the brain determine the type of food being consumed?
By integrating signals from different taste receptors and analysing the relative intensity of sweet, sour, salty, bitter, and umami.
What is palatability, and how is it determined?
Palatability refers to how pleasant a food tastes, influenced by individual preferences and taste pathways connecting to the hypothalamus.
How does smell detection work at the cellular level?
Odor molecules bind to specific receptors on olfactory cells, triggering a G-protein-mediated signal transduction pathway that generates action potentials.
What unique feature of olfactory receptor neurons allows them to be replaced?
Unlike most neurons, olfactory receptor neurons regenerate approximately every 30-60 days.
How is smell information processed in the brain?
Olfactory signals travel from the olfactory bulb directly to the olfactory cortex and limbic areas, influencing both recognition and emotional responses.
What is the significance of the limbic system in olfaction?
It connects smells to emotions and memories, explaining why certain smells can trigger vivid recollections or emotional responses.
What is the difference between the olfactory and gustatory pathways?
Olfactory signals bypass the thalamus initially, whereas gustatory signals pass through the thalamus before reaching the cortex.
Why do smells become less noticeable after prolonged exposure?
Due to sensory adaptation, where olfactory receptors reduce their response over time when continuously exposed to the same stimulus.
How do G-protein-coupled receptors contribute to taste and smell?
They mediate signal transduction by triggering intracellular pathways in response to binding with specific chemicals.
What is agnosia, and how does it relate to taste and smell?
Agnosia is the inability to recognize certain sensory inputs; in taste or smell, it can result from brain damage impairing perception pathways.
Why is the idea of a ‘taste map’ on the tongue incorrect?
All areas of the tongue can detect all basic tastes; sensitivity varies, but regions are not exclusively dedicated to one taste.
What types of chemicals are typically detected by sour taste receptors?
Hydrogen ions (H+) from acidic substances.
How do olfactory receptors detect a wide range of odours?
Each receptor can bind multiple odour molecules, and the brain decodes the pattern of activity from different receptors to identify specific smells.
How does signal transduction differ between taste and smell?
Taste cells use neurotransmitter-like signals to activate nearby neurons, while olfactory cells generate action potentials directly as they are neurons themselves.
What is signal transduction in sensory systems?
The process of converting a stimulus (e.g., chemical, light, sound) into an electrical signal that the nervous system can process.
What are the two major receptor families involved in taste detection?
T1 (Taste 1) receptors for sweet and umami, and T2 (Taste 2) receptors for bitter.
How do hydrogen ions (H+) contribute to the sensation of sour taste?
They either block potassium channels to prevent repolarization or enter cells directly to cause depolarization.
How is saltiness detected in food?
By sodium ions (Na+) entering taste cells through non-gated ion channels, leading to depolarization.
What role do basal cells play in the gustatory system?
They produce new taste receptor cells, enabling continuous renewal of taste detection.
What experimental techniques helped identify taste receptor genes?
Genetic modification in mice, such as gene knockouts, to observe changes in taste detection.
What happens when there is a mutation in a taste receptor gene?
It can impair the ability to detect certain tastes, such as sweet or bitter.
What is the primary role of the cranial nerves in taste?
To transmit taste signals from the tongue and oral cavity to the brain.
What is the function of the ventral posterior medial (VPM) nucleus of the thalamus in taste perception?
It processes taste signals before relaying them to the primary gustatory cortex.
How do texture and other sensations contribute to flavour?
They combine with taste and smell information to create the overall perception of flavour.
What is population coding in olfaction?
A method where the brain interprets patterns of activity from multiple olfactory receptors to identify specific smells.
Why is the sense of smell more evolutionarily ancient than taste?
It bypasses the thalamus and connects directly to primitive brain regions like the limbic system.
How does the brain differentiate between sweet and umami tastes?
By using different combinations of T1 receptor subunits specific to each taste.
What is the difference between primary and secondary neurons in sensory pathways?
Primary neurons detect stimuli and synapse onto secondary neurons, which relay signals to higher brain centres.
What is a ‘glomerulus’ in the olfactory bulb?
A structure where axons of olfactory receptor neurons with the same receptor type converge.
What is the role of the primary olfactory cortex?
To process raw smell signals and identify specific odours.
Why is the adaptation of smell important?
It prevents overstimulation from constant exposure to the same odour, allowing focus on new smells.
How can memories and emotions be triggered by smells?
Smells are processed in the limbic system, which governs emotion and memory, creating strong associations.
What is the evolutionary advantage of combining taste and smell?
It enhances the ability to evaluate food for nutritional value or potential danger.
What is the significance of olfactory receptor diversity?
Thousands of receptor types allow humans to detect a wide range of odours through combinatorial coding.
