Topic 16: The Chemical Senses Flashcards
Taste
the chemical sense that occurs when molecules – often associated with food – enter the mouth in solid or liquid form and stimulate receptors on the tongue
Olfaction
the sense of smell
usually results from stimulation of receptors in the olfactory muscosa
Flavor
the perception that occurs from the combination of taste and olfaction
Neurogenesis
the cycle of birth, development, and death of a neuron
this process occurs for the receptors for olfaction and taste
Papillae
ridges and valleys on the tongue, some of which contain taste buds
there are four types of papillae: filiform, fungiform, foliate, and circumvallate
Taste Buds
a structure located within papillae on the tongue that contains the taste cells
Taste Cells
cell located in taste buds that causes the transduction of chemical to electrical energy when chemical contact receptor sites or channels located at the tip of this cell
Taste Pore
an opening in the taste bud through which the tips of taste cells protrude
when chemicals enter a taste pore, they stimulate the taste cells and result in transduction
Nucleus of the Solitary Tract
the nucleus in the brain stem that receives signals from the tongue, the mouth, and the larynx transmitted by the chorda tympani, glossopharyngeal, and vagus nerves
Insula
an area in the frontal lobe of the cortex that receives signals from the taste system and is also involved in the affective component of the perception of pain
Frontal Operculum
an area in the frontal lobe of the cortex that receives signals from the taste system
Across-Fiber Pattern
the pattern of nerve firing that a stimulus causes across a number of neurons
also referred to as distributed coding
Amiloride
a substance that blocks the flow of sodium into taste receptors
Microsmatic
having a weak sense if smell
this usually occurs in animals, such as humans, in which the sense of smell is not crucial for survival
Macrosmatic
having a keen sense of smell
usually important to an animal’s survival
Detection Threshold
for olfaction the detection threshold is the lowest concentration at which an odorant can be detected
Forced-Choice Method
method in which two choices are given, and the subject has to pick one
for example, a subject is presented with a weak odorant on one trial, and no odorant on another trial, and has to pick the trial on which the odorant was present
Sustentacular Cells
cells that provide metabolic and structural support to the olfactory sensory neurons
Alzheimer’s Disease
serious loss of memory and other cognitive functions that is often preceded by mild cognitive impairment (MCI)
Mild Cognitive Impairment
cognitive impairments that extend beyond those associated with normal aging, but which often do not interfere with activities of daily living
often is a precursor to more serious conditions such as Alzheimer’s disease
Odor Objects
the source of an odor, such as coffee, bacon, a rose, or car exhaust
Olfactory Mucosa
the region inside the nose that contains the receptors for the sense of smell
Olfactory Bulb
the structure that receives signals directly from the olfactory receptors
the olfactory bulb contain glomeruli, which receive these signals from the receptors
Olfactory Receptor Neurons (ORNs)
sensory neurons located in the olfactory mucosa that contain the olfactory receptors
Olfactory Receptors
a protein strong that responds to odor stimuli
Calcium Imaging
a method of measuring receptor activity by using fluorescence to measure the concentration of calcium inside the receptor
this technique has been used to measure the activation of olfactory receptor neurons
Recognition Profile
the pattern of olfactory activation for an odorant, indicating which ORNs are activated by the odorant
Glomeruli
small structures in the olfactory bulb that receive signals from similar olfactory receptor neurons
one function of each glomerulus is to collect information about a small group of odorants
Chemotropic Maps
the pattern of activation in the olfactory system in which chemicals with different properties create a “map” of activation based on these properties
for example, there is evidence that chemicals are mapped in the olfactory bulb based on carbon-chain length
also called odor map
Piriform Cortex (PC)
an area under the temporal lobe that receives signals from glomeruli in the olfactory bulb
also called the primary olfactory area
Orbitofrontal Cortex
an area in the frontal lobe, near the eyes, that receives signals originating in the olfactory bulb
also called the primary olfactory area
Orbitofrontal Cortex
an area in the frontal lobe, near the eyes, that receives signals originating in the olfactory receptors
also known as the secondary olfactory cortex
Amygdala
a subcortical structure that is involved in emotional responding and in processing olfactory signals
Proust Effect
the elicitation of memories through taste and olfaction
named for Marcel Proust, who described how the taste and smell of a tea-soaked madeleine cake unlocked childhood memories
Odor-Evoked Autobiographical Memories
memories about events from a person’s life that are elicited by odors
Retro-nasal Route
the opening from the oral cavity, through the nasal pharynx, into the nasal cavity
this route is the basis for the way smell combines with taste to create flavor
Nasal Pharynx
a passageway that connects the mouth cavity and the nasal cavity
Oral Capture
the condition in which sensations from both olfaction and taste are perceived as being located in the mouth
Bimodal Neurons
a neuron that responds to stimuli associated with more than one sense
Sensory-Specific Satiety
the effect on perception of the odor associated with food eaten to satiety (the state of being satiated or “full”)
for example, after eating bananas until satiety, the pleasantness rating for vanilla decreased slightly (but was still positive), but rating for banana odor decreased much more and became negative
What is gustation?
flavor is a combination of smell and taste, but may also include texture and other sensory aspects
difficult to identify food without olfaction
not a “far” sense; gustation is the most intimate sense
adapted to test whether food with edible, spoiled, or poisionous
What is the taste stimuli: salty?
in-/organic salts
cation is most important (e.g., Na+ in NaCl)
What is the taste stimuli: sour?
in/organic acids that release H+ ions in solution
not all acids are sour
What is the taste stimuli: sweet?
complex organic molecules: sugar, aspartame
What is the taste stimuli: bitter?
varied: alkaloids; some nitrogen-containing molecules; some related to but having different molecular arrangement than sweet molecules
What is the taste stimuli: umami?
brothy, meaty, or savory
salts of glutamic acid
found in protein-rich foods, Parmesan cheese, tomatoes, mushrooms, and Marmite yeast extract
glutamic acid + Na+ –> monosodium glutamate (MSG)
What are the receptors of gustation?
tongue is covered with 4 kinds of bumps called papillae
we have up to 10,000 buds
each bud has several taste cells (receptors)
microvilli of receptor cells project out of taste pore
taste buds wear out and are replaced every 7-10 days; less frequently replaced after age 45
Where are taste buds found on?
fungiform: mushroom-shaped; on tip and sides
foliate: folds along sides of tongue
circumvallate: flat mounds surrounded by a trench; on back of tongue
also found on soft palate
What is transduction in gustation?
sodium penetrates membrane of receptor, depolarizing it
sour substances contain H+ which blocks ion channels
other substances may form bonds with molecules in the membrane, causing chemical changes within the cell
What is labeled-line (specificity coding)?
different taste stimuli activate specific fibers; firing rate represents intensity
each nerve fiber is “labeled” as corresponding to a particular taste sensation
activity in a few fiber types is all that’s needed to code stimuli
however, many substances elicit more than one taste (e.g. sodium saccharine shifts from sweet to bitter with increased concentration)
What is across-fiber pattern (population coding)?
there are no specialized receptors for each taste; taste quality signaled by pattern of activity across many fibers
each fibers type responds to a variety of substances, but seems to be tuned to respond best to one type of taste
