Olfaction

1
Olfaction

• pair of olfactory organs
• location- nasal cavity above superior turbinate
• two layers
• 1. olfactory epithelium
• olfactory receptors, supporting cells and basal
  cells
• 2. lamina propria
• olfactory glands - form a thick , pigmented mucus
• 2 of inhaled air reaches organ
• water-soluble and lipid soluble materials diffuse
  into the mucus before can stimulate olfactory
  receptors

2
Olfactory Receptors

• highly modified neurons in roof of nasal cavity
  with up to 20 cilia that extend into surrounding
  mucus
• cells are modified neurons - olfactory reception
  occurs on the surfaces of olfactory cilia or
  hairs
• dissolved chemicals interact with receptors
  called odorant finding proteins on membrane
  surface
• odorants
• small organic molecules
• strongest are highly soluble in lipids and in
  water
• open sodium channels in membrane which begins
  depolarization
• 10 - 20 million olfactory receptors

3
Olfaction

• discrimination
• can make subtle distinction among 2000 - 4000
  chemicals
• at least 50 primary smells are known
• adapt quickly
• aging
• high turnover of olfactory receptors but have
  neuronal replacement
• elderly have difficulty detecting odors in low
  concentrations

4
Taste or Gustation

• taste receptors
• over superior surface of tongue
• portions of pharynx and larynx
• with specialized cells form taste buds
• have about 3000 taste buds
• tongue papillae
• filiform papillae - no taste buds
• fungiform papillae - each contains 5 taste buds,
  tip and sides of tongue
• circumvallate papillae - form a V on back of
  tongue
• contain 250 taste buds each

5
Taste Receptors

• each taste bud contains about 40 to 60 slender
  receptors called gustatory cells and many
  supporting cells
• taste buds are recessed into surrounding
  epithelium
• each gustatory cell extends slender microvilli
  called taste hairs into the surrounding fluids
  thru the taste pore
• gustatory cells survive for only about 7-10 days
  and then replaced by mitosis

6
Gustatory Discrimination

• dissolved chemicals contacting taste hairs bind
  to receptor proteins
• taste sensations
• A. Sweet - organic compounds, especially sugars
• B. Salt - electrolytes like sodium and potassium
• C. Sour - acids in foods such as citrus fruits
• D. Bitter - in spoiled foods and alkaloids such
  as nicotine, caffeine, quinine and morphine
• E. Umami - amino acids such as aspartic and
  glutamic acids
• beef and chicken broth
• F. Water