taste

• Taste

  • Function of taste buds in the mouth
  • Sense of smell strongly contributes to taste perception
• Taste Buds


  • Sense organ for taste
  • 50 - 70 μm
  • 4 Types of Cells: Basal cells, Sustentacular cells (Type 1 & 2), Gustatory receptor cells (Type 3)
  • Types 1, 2 & 3 have microvilli that project to taste pore
  • Each is innervated by 50 nerve fibers
  • Each nerve fiber receives input from 5 taste buds
  • Basal cells arise from epithelial cells
  • Half life of 10 days
  • Also located in mucosa of epiglottis, palate & pharynx
  • Walls of fungiform & vallate papillae of tongue
  • 5 taste buds per fungiform; 100 taste buds per vallate
  • Filliform papillae have no taste buds
  • 10,000 taste buds
• Parts of the tongue

  • Fungiform papilla
  • Body of the tongue
  • Filiform
  • Circumvallate papilla
  • Lingual tonsils
  • Palatine tonsils
  • Root of the tongue
  • Epiglottis
• Circumvallate papilla


  • Taste buds where chemicals would enter
• Taste Pathways

  1. Anterior 2/3 of tongue travel via chorda tympani of CN VII (facial nerve)

  2. Posterior 1/3 of tongue travel to brainstem via CN IX (glossopharyngeal nerve)

  3. Other areas via CN X (vagus nerve)

  4. Unite at medulla to enter Nucleus of Tractus Solitarus in the medulla oblongata

  5. Synapse to 2nd order neurons & decussate to join the medial lemniscus

  6. Terminally ends at the cutaneous sensation for face located at the foot of post central gyrus near the area that subserves touch and pressure to the oral area
• Taste Pathways

  1. Taste buds to the first order neuron to the second order neuron

  2. Vagus, Glossopharyngeal, and Facial nerve converge at the Tractus solitarius: nucleus that subserves the taste fibers from the tongue, then will go to the thalamus, then will end at the foot of post-central gyrus (taste area)

  3. Decussate at the medial lemniscus, go up to the thalamus, then to the taste area in the opercula of insula region
• Basic Taste Modalities

  • Sweet (tip of tongue, sucrose)
  • Sour (along the edges, hydrochloric acid)
  • Salty (dorsum anteriorly, sodium chloride)
  • Bitter (back of tongue, quinine)
  • Umami (everywhere, monosodium glutamate)
• Substances Evoking Primary Tastes

  • Two major types of receptors: ligand-gated channel (ionotropic) and G-protein coupled receptor (GPCR) (metabotropic)
  • Salt and sour triggered by activation of ligand-gated
  • Sour, bitter, umami, sweet triggered by activation of G-protein
• Sour

  Acids, H+ ions stimulate the receptors, H+ ions may also bind to and block a K+-sensitive channel, decrease in K+ permeability → membrane depolarization
• Salty

  Na+ enters into salt receptor → membrane depolarizes → receptor potential generated
• Sweet


  Organic substances present in food
• Bitter


  Morphine, nicotine, caffeine & urea, inorganic salts: Mg+, NH4+ (Ammonia) & Ca++
• Taste Thresholds


  • Minimum concentration at which a substance can be perceived (by taste)
  • relatively crude as smell
  • a 30% change in concentration to detect difference
  • the lower the threshold, the more you can easily taste it
  • bitter substances have the lowest threshold
  • some toxic substances have a bitter taste at very low concentrations, preventing accidental ingestion (serves as a warning)
• Hydrochloric acid (sour) threshold → 100 μmol/L
• Sodium chloride (salt) threshold → 2000 μmol/L
• Strychnine hydrochloride (bitter) threshold → 1.6 μmol/L
• Glucose (sweet) threshold → 80000 μmol/L
• Sucrose (sweet) threshold → 10000 μmol/L
• Saccharin (sweet) threshold → 23 μmol/L
• Receptor Stimulation

  • Chemoreceptors act on exposed microvilli
  • Sour: H+ blocking apical K+ channels
  • Salty: Na+ enters
  • Sweet: G protein & adenylyl cyclase, Decreased K+ conductance
  • Bitter: G protein & phospholipase C, trigger Ca++ release from ER
• Ebner's Glands


  • Secrete mucus
  • Found around vallate papillae
  • Concentrating & transport of taste-producing molecule