Physiology of Gustation Taste Sensation Notes

Taste Sensation Gustation

Taste and smell sensations are considered to be visceral sensations, as they are associated with gastrointestinal functions. The flavor of any food is due to the combination of both taste and smell.

Thus, in common cold, the taste of the food is lost as there is a loss of smell sensation. In this chapter, only taste sensation is discussed. The taste sensation is due to the stimulation of chemoreceptors present in the taste buds.

Read And Learn More: Oral Physiology Notes

Taste Sensation Gustation Functional Anatomy

The receptors of taste sensation are the taste buds.

• In infants, there are about 10,000 taste receptors. As age advances, the number of taste receptors diminishes. These taste receptors are situated on and near the tongue.
• The tongue is a muscular organ present in the mouth.
  • The dorsal surface of the tongue, also called the dorsum of the tongue, is covered by stratified squamous epithelium.
  • At the junction of the anterior two-thirds and posterior one-third of the Tongue, lies a V-shaped line called ‘sulcus terminals’.
  • All over the dorsum of the tongue, numerous small elevations called ‘papillae’ are present. There are four types of papillae:

1. 1. 1. Filiform papillae
      2. Fungiform papillae
      3. Vallate papillae
      4. Foliate papillae

• Taste buds are present all over the papillae, except the filiform papillae. Each taste bud is an oval-shaped structure. Each taste bud has between 50 and 100 taste cells.
• Taste receptors from the anterior two-thirds of the tongue are innervated by chorda tympani nerve, and those of the posterior one-third of the tongue are supplied by the glossopharyngeal nerve.
• General sensations (touch, temperature, pain) are carried by the Trigeminal nerve from all parts of the tongue.

Mechanism Of Taste Sensation

1. The mechanism of taste sensation has the following steps: Dissolution of the substance to be tasted in saliva to stimulate the taste receptors.
2. Binding of the taste chemical to a protein receptor molecule situated on the outer surface of the taste receptor cell.
3. Opening of the ion channels, which allows positively charged ions to enter and depolarize the receptor cell
4. Depolarization causes the opening of voltage-gated calcium channels and Calcium enters the receptor cell.
5. Release of neurotransmitter (serotonin) from the receptor cells which stimulates the afferent neurons

Gustatory Sense

Basic Modalities Of Taste Sensation

In humans, there are five primary modalities of taste sensations:

• Salt
• Sour
• Bitter
• Sweet
• Umami

Although sensitivity differs in different areas of the tongue, all taste sensations are perceived by most of the areas of the tongue.

Salt: A sour sensation is brought about when sodium in the food enters the taste receptor by opening of the epithelial sodium channel (each).

Sour: A sour sensation can be brought about, when

1. 1. Hydrogen ions enter the receptor through emacs
   2. Hydrogen ions bind and block the potassium-sensitive channels
   3. Hyperpolarisation of activated cyclic nucleotide-gated cation channel (HCN)

Bitter: A bitter sensation is brought about when stimulants bind to and block Potassium-selective channels.

Sweet: The substances that taste sweet are detected by two types of GPCR (G protein-coupled receptor), T1R2 and T1R3. They act through cAMP and IP3 metabolism.

Umami: This sensation is due to the activation of the mglur4 channel, in the taste Receptor. The taste of monosodium glutamate (MSG/Ajinomoto salts) gives rise to this taste.

Taste Sensation Pathway

Significance Of Taste

• Plays an important role in food intake.
• Taste sensations help animals to avoid poisonous food, which is usually bitter.

Taste Sensation Clinical Considerations

Ageusia: Absence of the sense of taste

Hypogeusia: Diminished taste sensitivity

Dysgeusia: Disturbed sense of taste

Taste blindness: Some people are taste blind for certain substances, especially for different types of thiourea compounds.

Gustatory Sense

Taste Sensation Gustation Synopsis

• Taste and smell sensations are considered to be visceral sensations, as they are associated with gastrointestinal functions.
• The taste sensation is due to the stimulation of chemoreceptors present in the taste buds.
• The receptors of taste sensations are the taste buds.
• The tongue is a muscular organ present in the mouth.
• The dorsal surface of the tongue, also called the dorsum of the tongue, is covered by stratified squamous epithelium.
• All over the dorsum of the tongue, numerous small elevations called papillae are present.
• There are four types of papillae, i.e. filiform papillae, fungiform papillae, vallate papillae, and foliate papillae.
• Taste buds are present all over the papillae, except the filiform papillae.
• In humans, there are five primary modalities of taste sensations: Salt, sour, bitter, sweet, and umami.