Exam 4 Flashcards
Taste=
sensations evoked by solutions that contact the tongue and roof of the mouth
○ Salt, sweet, bitter, sour, umami
Flavor=
combination of retronasal olfaction and true taste
Retronasal olfaction=
what comes from your mouth out of your nose; perceiving odors through the mouth while breathing and chewing, giving us the experience of flavor
Be sure to know that modifying the level of tastants (e.g. sugar) or volatile chemicals can modify your perception of flavor
-Tastants (such as sugar, salt, acids, etc.) modify the direct taste perception, while volatile chemicals (smells) contribute to the aroma and flavor experience.
-Altering the concentration of tastants or volatile compounds can drastically change how we perceive the flavor of food.
-Our sense of taste and smell work together to create the overall perception of flavor, and even small changes in one aspect of this can lead to a very different experience of the food or drink.
Taste bud=
a globular cluster of cells that has the function of creating neural signals conveyed to the brain by the taste nerves (in papillae)
Papillae
structures that house the taste buds
Taste receptor cell (taste bud cell)
a cell within the taste bud that contains sites on its apical projections (microvilli) that can interact with taste stimuli
Sites with 2 major categories:
-interacting with charged particles (e.g. sodium and hydrogen ions)
-G protein-coupled receptors that interact with sweet and bitter stimuli
What are the types of papillae?
Filiform papillae
Fungiform papillae
Foliate papillae
Circumvallate papillae
Filiform papillae:
=small structures on the tongue that provide most of its bumpy appearance
□ Have no taste function
□ In other animals, they have a different shape and function to help the animal drink (e.g. lapping up water)
Fungiform papillae:
=mushroom-shaped papillae located on the edge of the tongue
□ Concentrated on the tip of the tongue
□ Elevated in people who are super taster
□ Multiple taste buds in each
Foliate papillae:
= folds of tissue that contains taste buds
□ Located in the rear of the tongue, on the edges
Fold on the side
What is the tongue map?
Edwin Boring plotted somewhat smoothed curves that seemed to show a picture of how the classic taste qualities varied across tongue locations based on Hanig’s data of tastant thresholds
What is portrayed on the internet and what is the reality of the tongue map?
Enshrined in texts
It is bogus; It doesn’t exist
○ Taste thresholds only vary slightly across the tongue
□ ○ The original paper (in German) was translated as sensitivity not relative sensitivity
□ ○ Thresholds only reflect the lowest detectable taste concentrations; they don’t predict taste intensities
What are the types of taste buds?
Type I, II, III, IV
Type I cells
® Responds to salt & cell maintenance
® No synapse & release ATP
® Selective ion channel
® Though to function in maintenance of the cell; Glial-like cell
® Epithelium sodium channel (ENac) is the primary detector of salts
® Sodium enters via the ENac channel, depolarizing the cell
These receptors don’t have typical synapses. They secrete ATP which activates taste axons
Type II cells
® Classical taste receptors
® Respond to sweet, bitter, or umami taste
® No synapse & releases ATP
® Express G-Coupled Protein Receptors (GCPR)
◊ Different ones for different tastes
® More complex stimulus => more complex receptor
® When a tastant binds to a taste receptor. The inside portion of the receptor triggers a cascade of molecular events.
® Cause increase in Calcium and then release ATP
These receptors don’t have synapses. They secrete ATP which activates taste axons.
Type III cells
® Also called presynaptic cells (because they do have synapses)
® Release serotonin at the synapse
® Mediate sour taste
® Sour comes in as Hydrogen, the more Hydrogen ions there are the more sour it is
® Hydrogen selective channel
® Another way it gets into the cell, the undissociated acid can enter and then dissociate
-Depolarizes, increasing calcium
Type IV cells
® No tastant, develops the other cells
® Develop into Type I, II, III cells
® No transduction
® Not in the diagram
® Basal cells
Presumably undifferentiated cells that will give rise to new taste bud cells
Why don’t we lose our taste as we get older?
Respiratory epithelium replaces the olfactory epithelium when damaged through old age
Are taste receptors only in the mouth?
No
-Extraoral taste receptors
-Gut taste receptors
What is the function of taste receptors in the gut?
These receptors ‘taste’ the luminal content and transmit signals that regulate nutrient transporter expression and nutrient uptake
Also regulates the release of gut hormones and neurotransmitters involved in the regulation of energy and glucose homeostasis
Is spicy a tastant?
No
What is capsaicin?
= it is a receptor that produces the burn associated with chili peppers
-it stimulates TRPV1 receptors associated with the trigeminal system (i.e. not the gustatory system)
-it also responds to heat
What sensory system regulates spicy? What is the receptor?
Trigeminal system
-TRPV1 receptor
What cranial nerves receive taste afferent projects from the tongue ->?
Cranial Nerve VII (Facial)
Cranial Nerve IX (Glossopharyngeal)
Cranial Nerve X (vagus)
-each for different parts of the tongue and then project to the Medulla
What is the taste processing pathway in the brain?
Medulla -> Thalamus -> Insular Cortex -> Orbitofrontal Cortex
What is the function of the Insular Cortex in the taste processing pathway?
Another name for the Gustatory cortex
§ Very important in the processing of tastants
Your brain allowing you to perceive which of the basic tastes
What is the function of the Orbitofrontal Cortex in the taste processing pathway?
Multimodal region (temperature, touch, smell)
Odor=
olfactory sensation (i.e. smell of strawberry)
Odorant=
chemical compounds (78 volatile chemicals that contribute to the smell of strawberries)
-the chemicals that trigger odor
Glomeruli (glomerulus)=
cluster/ball of axons
* Humans have two, one for the left and one for the right
* Two glomeruli per receptor per olfactory bulb
What are some features of olfactory stimuli that make them unusual and difficult to study?
- Even though an odor can be made up of 10s to 100s of odorants they are usually perceived as a single entity (i.e. smell of coffeeO
- Olfactory stimuli are spatially and temporally variable = not consistent from one moment to another even if you stayed in the same location
- Even at different intensity levels the same odor can be perceived = (ex: you still perceive the smell of coffee if you put your nose right next to your coffee cup or walk by the store brewing coffee)
- The stimulus can remain long after the sender has left (ex: dog’s bark (auditory) vs urine (olfactory) left on a tree
Orthonasal olfaction=
odorants enter your nose and onto your olfactory epithelium (‘smelling strawberries’)
-Into nose
-Smell
Retronasal olfaction=
odorants travel from the back of our mouth into our upper nasal cavity and onto the olfactory epithelium (‘strawberry flavor’)
-Into mouth and out through your nose
-Taste
What are the 4 types of olfactory bulb neurons?
Juxtaglomerular neurons
Mitral and Tufted neurons
Granule neurons
Juxtaglomerular neurons=
excitatory and inhibitatory neurons that surround the glomerulus
○ Nearby cells
○ These neurons help shape the neural representation of the odorant
○ Get feedback from the brain and modify the signal
Mitral and Tufted neurons
○ synapse in the glomerulus and send their axons to higher brain regions (i.e. projection neurons)
-To the olfactory cortex (multiple regions)
Granule neurons
=Deepest layer of the olfactory bulb is an extensive network of inhibitory neurons that account for the second layer or inhibition within the bulb
○ Inhibit mitral and tufted cells
-Get feedback from the brain and modify the signal
What are the 3 types of cells in the olfactory epithelium?
Supporting cells
Basal cells
Olfactory sensory neurons
Supporting cells
§ Non-neural cells that provide metabolic and physical support for the epithelium
§ Supporting neurons
Basal cells
§ Function- stem cells become supporting cells and Olfactory sensory neurons
§ Provides some ability to recover the epithelium
Olfactory sensory neurons
§ Function- Transduce
§ Sensory neurons
Ratio of receptors to glomeruli in the mouse and that is differs in humans?
Mouse- 1:2
Humans- 11:1
Pathway from volatile odorants in the air to the olfactory cortex
- Sniffing (or breathing through your nose) brings volatile chemicals (i.e., odorants) into your nasal cavity
+filters, warms, and humidifies the air that carry oxygen to our lungs - Inside the nose are small cartilaginous ridges (turbinates) which direct the air flow and increase the surface area for the epithelium (allowing more sensory neurons to come into contact with odorants)
- On the turbinates, is olfactory epithelium (for smelling) and respiratory epithelium (for breathing)
○ Respiratory epithelium replaces the olfactory epithelium when damaged through old age - Volatile odorants enter the nasal cavity where they come in contact with olfactory sensory neurons
○ Olfactory receptors are on the cilia and it is what comes into contact with odors - Cilia at the end of the dendrite protrudes into the air space (same for humans)
- Cilia express olfactory receptors that transduce chemicals into neural signals
- Olfactory receptors are G-coupled protein receptors
- Each sensory neuron expresses only a single olfactory receptor (assumed to be true in humans
- The expressed olfactory receptor determines what odorants the olfactory sensory neuron responds to
- Axons from sensory neurons that express the same receptor converge to form glomeruli (cluster of axons) in the olfactory bulb
- Human olfactory bulb is assumed to be organized the same way, EXCEPT humans have 5500 glomeruli but only 400n receptors (11:1 ratio)
- Olfactory bulb: first area of olfactory processing (part of the brain)
○ Cranial nerve I
○ 4 different cell types within this bulb: Juxtaglomerular neurons, Mitral and Tufted neurons, Granule neurons - Goes from the bulb to the cortex
○ Bypasses the thalamus
(Processed by the Juxtaglomerular and Granule neurons and Sent by the Mitral and Tufted neurons)
○ Not a single region, goes to multiple regions (9)
§ Need multiple regions doing different jobs in order to process it fast
How are odorants transduced?
- Odorant binds to the olfactory receptor (through sniffing)
○ Nose also helps with respiration, warming/humifiying/filtering
○ Turbinates direct airflow - Triggers a secondary messenger cascade
- Increases calcium levels within the neuron
○ Eventually triggers neurotransmitter (glutamate) release to stimulate postsynaptic neuron
Where are the receptors located?
In the olfactory epithelium
Lack of one-to-one specificity with odors-
olfactory receptors lack one-to-one specificity with odorants. Odorant can activate multiple receptors and a single receptor can be activated by multiple odorants
Shape pattern theory=
odorants have different ‘shapes’ and an odorant will be detected by a specific receptor to the extent that the odorant fits into the binding pocket of the receptor
Combinatorial code
=currently it is thought that the pattern of receptor/glomerular activation determines the scent we perceive
○ Responds in a different pattern => different perception
○ However, patterns aren’t stable across concentration
○ Yet, we still usually (but not always) perceive the same smell
Theory of Primacy:
the earliest activated glomeruli encode the identity of the odor
Types of olfactory disorders
Hyposmia
Anosmia
Parosmia
Phantosmia
Hyposmia
=reduced ability to detect odors
Anosmia
=complete inability to detect odors (~1.4% of the US population)
Parosmia
= change in the normal perception of odors
Phantosmia
=sensation of an odor that isn’t there
-similar to phantom limb
Receptor adaptation
= olfactory sensory neuron adapts with previous exposure to the stimulus
○ Also known as olfactory fatigue
-Short term adaptation
-Receptor internalization
Short term adaptation
Happens quickly and lasts only a short amount of time.
The exact mechanism is not clear but it involves the secondary messenger cacscade
Receptor internalization
mechanism common to all GCPRs (class of receptors including olfactory receptors). Odorant binding can cause the receptor to be internalized into the cell = it is not physically available and lasts several minutes
Cross Adaptation
= when exposure to one odor can cause reduced sensitivity to a different odor; presumably occurs when the odors bind to the same receptors
Cognitive Habituation
= when our brain habituates to a smell you live with, causing a reduced response
