Chapter 8: The Chemical Senses Flashcards
What do animals depend on chemical senses to do?
Identify nourishment, poison, or potential mate
What are the five types of basic tastes?
Saltiness, sourness, sweetness, bitterness, and umami
What chemicals taste sour?
Acids
What chemicals taste salty?
Salts
What chemicals taste sweet?
Sugars like fructose, sucrose, and artifical sweetners
What chemicals taste bitter?
Ions like K and Mg, quinine, and caffeine
What do poisonous substances often taste like?
Bitter
When you lick a lollipop, which receptors will be activated?
Sweet
What other sensory modalities contribute to taste?
Temperature, texture, and pain (capsaicin)
What do foliate papillae appear as?
Ridges
What do vallate papillae appear as?
Pimples
What do fungiform papillae appear as?
Mushrooms
What is on the paillae that ranges from 1-hundreds?
Taste buds
What is on each taste bud that ranges from 50-150?
Taste receptor cells
Threshold Concentration
-Just enough exposure of single papilla to selectively detect one taste
-Multiple tastes are detected at higher concentration
What is the taste pore?
Opening to expose taste cell to mouth contents
Where is there connectivity in taste cells?
-Synpase w/ gustatory afferent axons at the basal end of the taste bud
What is the lifespan of a taste cell?
-2 weeks
-Is dependant on connection w/ sensory nerve
Receptor Potential
-Voltage shift (depolarization)-may fire action-potentials
-Voltage-gated Na and voltage-gated Ca channels open
-Transmitter released
What is released when sour and salty?
Serotonin
What is released from sweet, bitter, umami?
ATP
Transduction
Process by which an environmental stimulus causes an electrical response in a sensory receptor
What may salt/sour taste stimuli do in transduction?
-Pass directly through ion channels
What may sour taste stimuli do in transduction?
Binds to and block ion channels
What may bitter/sweet/umami taste stimuli do in transduction?
Bind to G-protein-coupled receptors and activate second messenger to open ion channels
Special Na-selective Channel
-Normally open
-Increased extracellular Na will cause more Na inward current
—>Depolarization is called receptor potential
[Low] salt tastes good, what happens?
Special Na-selective channel
[High] salt tastes bad, what activates?
Activate bitter and sour taste cells
—>repellant
What do protons do?
Causative agents of acidity and sourness
H can bind and block certain K channels which leands to what?
Depolarization
H may activate transient receptor potential (TRP) channels, which leads to what?
Cation current, which causes depolarization
What are the G-protein-coupled taste receptors in bitter, sweet, and umami?
T1R and T2R
How does the second messengers for bitter, sweet, and umami work?
- Open Na Channel leads to depolarization
- Intracelluler Ca opens, ATP-permeable channel opens, ATP releases, activates postsynpatic purinergic receptors
How many types of T2R receptors are there?
25
Can you tell the difference between 2 bitter tastes?
No
What sweet receptors are required?
T1R2 and T1R3
What do the umami receptors do?
Detect amino acids
-T1R1 and T1R3
What cranial nerves are involved in central taste pathways?
-VII Facial: anterior 2/3 of tongue, palate
-IX glossopharyngeal: posterior 1/3 tongue
-X vagus: throat
Where do cranial nerves synapse?
On gustatory nucelus w/in solitary nucleus in medulla
Where do gustaory nucleus axons synapse?
On ventral posterior medial (VPM) nucleus in thalamus
Where do VPM taste axons synapse?
Primary gustatory cortex (mostly ipsilateral to cranial nerves;parietal lobe)
Medulla Function
Swallowing, salivation, gagging, vomitting, digestion, respiration
Hypothalamus
Motivation for eating, control of eating based learned cues
Amygdala
Plasure in eating, control of eating based on learned cues
Ageusia
Loss of taste perception
-lesions in VPM/gustatory cortex
What is the result of localized lesions in the hypothalamus/amygdala?
Chronically overeat/ignore food, alter food preferences
Labeled line hypothesis
Individual taste receptor cells for each stimuli
Population coding
-Large #s of broadly tuned neurons
-Many taste receptor cells may all synpase w/ the same neuron which results in multiple tastes
-Overall pattern leads to taste
-Contribution of smell, temp., and texture of foods
How many smells do we experience?
20,000 smells, but only 20% are pleasant
Pheromones
-Reproductive behavior
-Territorial boundaries
-Identification of individuals
-Signal aggression/submission
What is the role of human pheremones?
-Unclear
-Synchronization of menstrual cycles
-Mother-baby relationship
Olfactory Epithelium
-Small, thin sheet of cells high in nasal cavity
1. Olfactory receptor cells-sites of transduction; neurons; last 4-8 weeks
2. Supporting cells-like glia; produce mucus
3. Basal cells-divide to produce new receptor cells
Mucus coating is replaced every 10 mintues
-Water, mucupolysaccharides, proteins (antibodies, enzymes, odorant binding proteins), salts
-Odorants from sniffing dissolve in the mucus layer before contracting olfactory receptor cells
-Antibodies protect the brain from viruses and bacteria
Do humans have weak smellers compared to many animals?
Yes
What do odorants bind to?
Olfactory receptor cilia on dendrite and activate transduction process
What do olfactory axons in small clusters do?
-Penetrate cribiform plate-thin sheet of bone
-Project to olfactory bulb
Anosmia
Inability to smell
Explain transduction mechanisms of vertebrate olfactory receptor cells
-Odorants bind to ordorant receptor proteins
-Activate Golf
-Increase cAMP
-Open cAMO-gated cation channel
-Influx of Na and Ca
-Open Ca -activated Cl channel
-Cl flows our of the cell
-Depolarization leads to receptor potential
What ways does termination work?
-Diffusion
-Scavenger enzymes in mucus
-Other pathways from cAMP
-Adaptation
Adaptation
Decreased response of receptor to the smell w/in 1 minute
What did Linda Buck and Richard Axel do?
In 1991, discovered more than 1000 odorants receptors in rodents’
-Nobel prize in 2004
How many receptor types does each receptor cell encode for?
1
Does each odorant activates only 1 type of receptor?
No, it activates many
What do olfactory receptor axons project to?
Olfactory bulbs
How large are glomeruli?
50-200 um in diameter
25,000 axons converge on dendrites of 100 what?
Second-order olfactory neurons
What is the orderly map of receptor genes expressed in olfactory epithelium?
Map of odor information
What are the excitatory and inhibitory connections in the mapping of olfactory receptors neurons?
-Glomeruli
-Bulbs
Olfactory population coding
-Combination of neurons firing distinguishes odor
-Humans can discriminate 1 trillion odors
Olfactory maps (sensory maps)
-Orderly arrangement of neurons that correlates w/ certain features of the environment
-“Maps” show neurons activated by specific odors
What is temporal coding in the olfactory system?
-Temporal patterns of spiking in olfactory neurons may encode quality of odors
-Temporal patterns are also clear in spoation odor maps
What is anosmia likely arising from in Covid-19?
Loss of support cell function instead of the neurons themselves
Is sense of smell likely to return in Covid-19 patients?
Yes, but soem experience long-term loss and are called long haulers
