Taste Buds and the Sense of Taste

Overview of Taste

• Taste, also known as gustation, is a chemical sense.
• Sensations arise from interactions of molecules with taste receptors (taste buds).
• Molecules need to be dissolved in saliva to bind to taste buds.

Basic Tastes

• There are five basic tastes:
  • Sweet
  • Salty
  • Sour
  • Bitter
  • Umami (savory or meaty flavor).
• A combined taste sensation arises from these primary tastes, olfactory (smell), and tactile (touch) sensations.

Role of Smell

• Olfaction (smell) is more sensitive than gustation.
• Affects taste perception, especially noticeable during a cold or allergies.

Location and Structure of Taste Buds

• Located on the tongue, soft palate, pharynx, and epiglottis.
• Each taste bud consists of:
  • Supporting Cells: Provide structural support, maintain chemical environment, capable of division.
  • Gustatory Receptor Cells: Detect tastes, lifespan of about 10 days.
  • Basal Cells: Stem cells, develop into supporting cells and then gustatory receptor cells.
• Microvilli: Hairlike structures on gustatory receptor cells that project through a taste pore.

Taste Transduction

• Tastants: Food molecules that stimulate gustatory receptors.
• Process:
  • Tastants dissolve in saliva and bind to receptors on microvilli.
  • Receptors undergo structural change, opening ion channels.
  • Specific ions (e.g., sodium, hydrogen) cause depolarization.
  • Sweet, bitter, umami use receptors linked to G proteins activating secondary messengers.

Neural Pathway

• Three cranial nerves involved:
  • Facial Nerve (Cranial Nerve 7): Anterior 2/3 of the tongue.
  • Glossopharyngeal Nerve: Posterior 1/3 of the tongue.
  • Vagus Nerve (Cranial Nerve 10): Throat and epiglottis.
• Pathway:
  • Nerve impulses travel to the gustatory nucleus in the medulla.
  • Axons project to the limbic system, hypothalamus, thalamus.
  • Those projecting to the thalamus and primary gustatory area give conscious taste sensation.