Taste perception

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Taste is one of the traditional five senses and refers to the ability to detect of flavor of foodstuffs. In humans and many other vertebrate animals, the sense of taste partners with olfaction (also called the sense of smell), in the brain's perception of flavor. Flavor is based on chemical composition of the item tasted.

Taste is a sensory function of the central nervous system. The receptor cells for taste in humans are found studded on the surface of the tongue, and in the back of the throat (pharynx). Three different cranial nerves carry impulses from the tastebuds.

Role of the nervous system

Main article: Gustatory system

Smell helps you taste. In humans, the sense of taste is transduced by gustatory hairs, taste buds and is conveyed via three of the twelve cranial nerves. The facial nerve carries taste sensations from the anterior two thirds of the tongue (excluding the circumvallate papillae, see lingual papilla) and soft palate, the glossopharyngeal nerve carries taste sensations from the posterior one third of the tongue (including the circumvallate papillae) while a branch of the vagus nerve carries some taste sensations from the back of the oral cavity (i.e. pharynx and epiglottis). Information from these cranial nerves is processed by the gustatory system. Impulses generated by the gustatory taste hairs on the superior surface of the tongue, travel from the tongue to either the facial or glossopharengeal cranial nerves. They move to the medulla oblongata, to the thalamus, ending up in the gustatorial area of the cortex of the parietal lobe of the cerebrum.

It is important to note that the axons from these cranial nerves ascend in the spinal cord without crossing over. These fibers terminate in the amygdala, hypothalamus, and ventral posterior medial nucleus of the thalamus, which then projects to the somatosensory cortex within the brain. Thus, a lesion of the rostral nucleus solitarius, tractus solitarius, or solitariothalamic tract results in loss of taste from the ipsilesional, the same side as the lesion, half of the tongue.

Basic classification of tastes

Main article: Basic taste

As a general rule, taste is a holistic assessment of the interaction of the fundamental taste systems of sweetness, sourness, bitterness, saltiness, and umami (savouriness). Location of the stimulus on the tongue is not important, despite the common misperception of a "taste map" of sensitivity to different tastes thought to correspond to specific areas of the tongue [1]. The "mouth map" is a myth, generally attributed to the mis-translation of a German text, and perpetuated in North American schools since the early twentieth century . In reality, the separate populations of taste buds, sensing each of the basic tastes, are distributed across the tongue, though not entirely equally; for instance, the front of the mouth is biased toward sweetness and the rear toward bitterness. The brain also plays a part in the tongue's sensory distribution. If, for instance, half of the tongue is blocked from sending information to the brain, rather than any diminishment, people will instead report that a doubling of psychological perception has occurred for each taste, and no loss to any one.

New evidence is emerging that supports the inclusion of a sixth taste category for free fatty acids, the chemical components of dietary fat. A taste receptor mechanism for free fatty acids has been identified [2], an animal model for the detection of free fatty acids is being characterized [3], and studies of human detection of free fatty acids are beginning[4].

Factors affecting taste perception

Many factors affect taste perception, including:

• Aging
• Hormonal influences
• Genetic variations - See Phenylthiocarbamide
• Oral temperature
• Drugs and chemicals
• CNS Tumours (esp. Temporal lobe lesions)

It is also important to consider that flavor is the overall, total sensation induced during mastication (e.g. taste, touch, pain and smell). Smell (olfactory stimulation) plays a major role in flavor perception.

Disorders of taste

• ageusia (complete loss)
• hypogeusia (partial loss)
• parageusia (unpleasant taste)
• dysgeusia (inaccurate taste)

Developmental aspects of gustation

Everyone knows that children have different tastes than adults.

Main article: Developmental aspects of gustation

References

de:Geschmackssinn es:Gusto fr:Goût he:טעם pt:Paladar sv:Smak