GUSTATION: SENSE OF TASTE - Human Anatomy and Physiology B. Pharma 1st Semester

GUSTATION: SENSE OF TASTE

Objectives

At the end of this lecture, student will be able to

• Describe the anatomy of taste bud and papillae

• Explain the physiology of gustation and gustatory pathway

Content

• Anatomy of taste bud and papillae

• Physiology of gustation and gustatory pathway

GUSTATION: SENSE OF TASTE

• Taste or gustation like olfaction, is a chemical sense

Five primary tastes can be distinguished:

• Sour, sweet, bitter, salty, and umami

• Umami taste, recently reported by japanese scientists, is described as “meaty” or “savory”

Anatomy of Taste Buds and Papillae

• Receptors for sensations of taste, located in the taste buds

• Taste bud - an oval body consisting of three kinds of epithelial cells

a) Supporting cells

b) Gustatory receptor cells

c) Basal cells

• Supporting cells surround about 50 gustatory receptor cells

• A single, long microvillus, called a gustatory hair

Projects from each gustatory receptor cell to the external surface

• Through the taste pore (opening in the taste bud)

• Basal cells, stem cells found at the periphery of the taste bud

• Produce supporting cells, develop into gustatory receptor cells

• Gustatory receptor cells synapse with dendrites of the first-order neurons

• Form the first part of the gustatory pathway

Papillae

• Taste buds are found in elevation on the tongue, Papillae

• Provide a rough texture to the upper surface of the tongue

• Three types of papillae contain taste buds

a) Vallate (circumvallate) papillae

b) Fungiform papillae

c) Foliate papillae

Circular vallate (circumvallate) papillae

• About 10-12, form an inverted V-shaped row at the back of the tongue

• Each of these papillae houses 100–300 taste buds

Fungiform papillae

• Mushroom-shaped elevations scattered over the entire surface of the tongue

• Contain about five taste buds each

Foliate papillae

• Located in small trenches on the lateral margins of the tongue

• Most of their taste buds degenerate in early childhood

Physiology of Gustation

Chemicals that stimulate gustatory receptor cells are known as tastants, Tastant is dissolved in saliva

â

Contact with the plasma membrane of the gustatory hairs (sites of taste transduction)

                                 â Receptor potential

Exocytosis of synaptic vesicles from the gustatory receptor cell

â

Neurotransmitter release

â

Nerve impulses in the first-order sensory neurons

The receptor potential arises differently for different tastants

• Sodium ions (Na+) in a salty food enter gustatory receptor cells

• Via Na+ channels in the plasma membrane

• Accumulation of Na+ inside cause depolarization

• Leads to release of Neurotransmitter

Tastants, responsible for stimulating sweet, bitter, and umami tastes

• Bind to receptors on the plasma membrane that are linked to G proteins

• Activate second messengers

• Depolarization; release of neurotransmitter

The Gustatory Pathway

• Gustatory receptor cells trigger nerve impulses in cranial nerves VII (facial), IX (glossopharyngeal) and X (Vagus)

• Taste signals then pass to the medulla oblongata, thalamus, and cerebral cortex (parietal lobe)

Summary

• Gustation is a chemical sense

• Five primary tastes - Sour, sweet, bitter, salty, and umami

• Receptors for sensations of taste are located in the taste buds

• Tastants binds to receptors; generates potential; release of neurotransmitter; initiates nerve impulse

• Taste signals pass to the medulla oblongata, thalamus, and cerebral cortex (parietal lobe)