L2 - Chemoreception

• What is the ability to detect chemicals called?

  Chemoreception
• What are the two types of chemoreceptors?

  Gustatory and olfactory
• What do gustatory receptors detect?

  Dissolved chemicals at high concentrations
• What do olfactory receptors detect?

  Airborne/dissolved chemicals at low concentrations
• How do chemoreceptors transmit information?

  To the cerebral frontal cortex for processing
• What distinguishes different chemoreceptors?

  Cell types, locations, and transduction mechanisms
• Where is the olfactory epithelium located?

  In the roof of the nasal cavity
• What is the role of olfactory sensory neurons?

  Detect odorants and transmit signals
• What type of neurons are olfactory sensory neurons?

  Bipolar neurons
• How often do olfactory sensory neurons regenerate?

  Approximately every 2 months
• What must odorants be to enter the nose?

  Volatile and soluble in mucus
• What activates olfactory transduction?

  Odorants activating G protein-coupled receptors
• What is the result of cAMP opening cation channels?

  Movement of Na+ and Ca2+ into the cell
• What does the influx of Na+ and Ca2+ cause?

  Depolarization and graded receptor potential
• What triggers an action potential in olfactory receptor cells?

  Voltage-gated Na+ channels
• How many different odorants can olfactory receptor cells detect?

  Over 10,000
• How many genes encode specific receptor proteins for olfactory receptors?

  About 400 genes
• What is the significance of receptor proteins in olfactory receptors?

  They bind discrete components of odorants
• What is a combinatorial code in olfaction?

  Population of receptor cells stimulated by odorants
• What is the olfactory bulb's function?

  Receives input from olfactory cells
• What do olfactory tracts connect to?

  Primary olfactory cortex in the temporal lobe
• What is the role of the limbic system in olfaction?

  Emotional response to odors
• What is olfactory adaptation?

  Rapid decrease in sensitivity to odors
• What is the sensory receptor organ for taste?

  Taste bud
• Where are the majority of taste buds located?

  Within papillae of the tongue
• What do gustatory receptor cells synapse with?

  Afferent neurons projecting to the brain
• How often do basal cells in taste buds replace cells?

  Every ~10 days
• What must tastants do to be detected?

  Dissolve in saliva and enter taste pores
• What are the five primary tastes?

  Sweet, salty, sour, bitter, umami
• What is the most sensitive taste receptor type?

  Bitter receptors
• What type of receptors are involved in salty taste?

  Na+ channels
• What type of receptors are involved in sour taste?

  H+ (proton) channels
• What receptors are involved in sweet, bitter, and umami tastes?

  G protein-coupled receptors
• What happens when gustatory receptors are activated?

  Increase in intracellular [Ca2+] and neurotransmitter release
• What is the role of ion channels in salty and sour taste?

  Allow Na+ or H+ into the cell
• What does gustducin activate in sweet, bitter, and umami taste?

  Phospholipase C to increase IP3
• What is the significance of bitter receptors being the most sensitive?

  To detect potentially harmful substances
• Which cranial nerves are involved in the gustatory pathway?

  Facial, glossopharyngeal, and vagus nerves
• Where do cranial nerves project in the gustatory pathway?

  To the medulla
• What is the role of the thalamus in taste perception?

  Pathway to gustatory cortex for perception