ex. 26 [olfaction and taste]

• receptors for taste and smell are classifies as chemoreceptors because they respond to chemicals in solution
• pseudostratified ciliated columnar epithelium a.k.a. olfactory epithelium is the organ of smell, occupying the roof lining of nasal cavity
• three cell types in olfactory epithelium

  • olfactory sensory neurons: specialized receptor cells; bipolar w/ nonmotile cilia
  • supporting cells: columnar cell surrounding and supporting olfactory sensory neurons; bulk of epithelium
  • stem cells: located near basal surface of epithelium, form new sensory neurons
• filaments of olfactory nerve penetrate cribriform foramina and synapse in olfactory bulbs
• taste buds contain specific receptors for sense of taste
• most taste buds are located in papillae on the dorsal surface of tongue and some are found on soft palate, epiglottis, pharynx, and inner surface of cheek
• taste buds located in side walls of large vallate papillae (v-shape in posterior tongue surface), side wall of foliate papillae and fungiform scattered everywhere
• each taste bud consists of

  • gustatory epithelial cells: taste receptors; have long microvilli called gustatory hairs that project through taste pore
  • basal epithelial cells: precursor cells that divide to replace gustatory epithelial cells
• when gustatory hairs contact food molecules dissolved in saliva, gustatory epithelial cells depolarize. afferent neurons innervating taste buds are

  • facial nerve (7): anterior 2/3
  • glossopharyngeal (9): posterior 1/3
  • vagus (10): few fibers from pharyngeal region
• sweet receptors: sugars, saccharine, some lead salts, some amino acids
• sour: hydrogen ions
• salty: influx of Na ions
• umami: a savory taste that is produced by the amino acid glutamate
• bitter: alkaloids
• nasal

  A) glomeruli

  B) olfactory stem cell

  C) olfactory sensory neuron

  D) supporting cell

  E) olfactory epithelium

  F) supporting cell

  G) olfactory sensory neuron

  H) olfactory cilia

  
• supporting cells: surround and support olfactory sensory neurons, forming a bulk of the olfactory epithelium
• olfactory adaption: how smells are less noticeable after some time spent smelling it
• tongue

  A) foliate papillae

  B) fungiform papillae

  C) vallate papilla

  D) gustatory hair

  E) taste pore

  F) gustatory epithelial cell

  G) basal epithelial cell