Physiology of Olfaction and Gustation Dr. Pierce Flashcards
What occurs at the apical domain of taste cells, what does it contain?
- Location of chemosensory transduction
- Contains:
- microvilli
- tastant receptors
- voltage gated ion channels
- TRP receptors
What occurs in the basolateral domain aand what is in it?
- Location of NT release
- Serotonin and ATP
What is the pathway for salt or sour flavors?
- Tastant binds to ion channel allowing H ions or Na in
- Depolarization opens the voltage gated calcium channels and triggers NT release
- Serotonin is released
What is the pathway for Sweet, Umami or Bitter flavors?
- Ligand binds receptor GPCR on apical domain
- Umami is mGlu4 specifically
- Depolarization opens voltage gated ca channels which allows for NT release
- ATP is the NT relased
What are Olfactory cells?
Bipolar neurons that release Glu as their NT we have roughly 350 olfactory receptors but can detect 12 million odors
How can we detect millions of smells with only hundreds of receptors?
Different combinations of odorant receptors act like a signature for a particular odor
How does Sensory transduction in ORN’s work?
- Odorants diffuse into nasal mucosa binds olfactory cilia receptor proteins activates the cell
- OR’s are GPCR called Golf receptors
- Uses cAMP
- opens CNGC allowing Na and Ca to influx into the ccell
- Depolarization occurs
- Ca gated chloride channels open providing remainder of depolarization to generate receptor potential to chieve action potential
How do the olfactory receptor neurons adapt to smells?
- Receptor potential is reduced when cAMP concentration drops due to enzymes breaking it down
- Recovery depends on binding of Ca to Calmodulin which reduces affinity for channel to cAMP
- Odorant receptor can become phosphorylated which modifies sensitivity to odorants
Why do bitter tastants have high affinity with their receptors?
- Bitter is innately associtated with poisons and toxic foods
- GPCR’s bind the ligand with high affinity so it only takes low concentration of the bitter taste to avoid eating/drinking large amounts of a potential toxin
what is the physiological significance of sweet, salty, umami and sour tastants?
- Sweets: signals presence of carbs -energy
- Salty: govern intake of Na and other salts for water balance and bp
- Umami: reflects protein content
- Sour: presence of dietary acids
- generally aversive as we can throw acid base balance and spoiled foods are often acidic
Why does gustatory sensitivity decline?
- # taste buds decrease with age
- Shrink in size
- >60 yo
- mouth produces less saliva
- medications disease smoking pollutants and toxins
Why does olfactory sensitivity decline?
- Decreased mucus production
- fibers and receptors of ORN’s decrease with age
- >70 yo
- medications disease smoking pollutants and toxins
When and how does sensitivity to gustatory and olfactory develop?
- In utero
- Fetus tastes amniotic fluid which reflects the mothers diet and external environment
How can sweet tastes help newborns?
- Small amounts of sweet solutions can be placed on the tongue of a newborn to calm them
- decrease HR and calmness within minutes
- Used for minor painful procedures
- Response to sweet solution is similar to a response of pleasurable stimulation
- ONLY works via oral cavity- direct stomach loading doesn’t give same response
How does the analgesic effect of sweet solutions work?
- General brainarousal can be suppressed leading to distraction from procedure
- Reward effect of sweet flavors blunts stress promoting calmness
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Anti-nociceptive action:
- Sweet taste induced beta endorphin release activates endogenous opoid system
Describe the layout of olfactory processing.
- Begins with olfactory receptors
- one olfactory neuron expresses same odorant on all of its cilia
- one neuron converges onto one glomerulus
- similar odorant receptors converge onto same glomerulus
- Glomeruli send info up to Mitral/Tufted cell which then goes to brain via olfactory nerve
