Taste Sensation Introduction Taste is the ability to

Taste Sensation

Introduction • Taste is the ability to respond to dissolved molecules and ions. • The sense of taste is also called Gustation. • The substance which stimulate taste is called Tastants • Tongue is the sense organ that detects taste and the sensory structure that detects taste stimuli are Taste Buds.

Tongue Anatomy (Taste Related ) • The tongue is covered with 4 types of projections called papillae v. Sharp or Filiform papillae : no taste buds v. Fungifiorm papillae : rounded with taste buds v. Circumvallate papillae : large papillae with taste buds v Foliate papillae

Vallate (Circumvallate) Papillae • About 12 very large circular Vallate papillae form an inverted V-shaped row at the back of the tongue. • Each of these papillae contains approximately 100 -300 taste buds.

Vallate Papillae

Fungiform Papillae • The Fungiform (mushroom like) papillae are mushroom shaped elevations scattered over the entire surface of the tongue. • They contain about 5 taste buds each.

Fungiform or Foliate Papillae

Filiform Papillae • Filiform papillae cover the entire surface of the tongue. • They are pointed, threadlike structures that contain tactile receptors but no taste buds. • They increase friction between the tongue and the food, making it easier for the tongue to move food into the oral cavity.

Filiform Papillae

Foliate Papillae • The foliate (leaflike) papillae are located in small trenches on the lateral margins of the tongue, but most of their taste buds degenerate in early childhood.

Taste Buds • More than 10, 000 or so taste buds are found on the tongue, also located on Soft palate, Cheeks, throat and lips! • Taste buds are found in papillae of the tongue mucosa. A single taste bud contains 50 -100 taste cells representing all 5 taste sensations

Cont… • Each taste receptor (chemoreceptor) cell is connected, through a synapse, to a sensory neuron leading back to the brain. • Each taste bud is made up of many (between 50 -150) receptor cells. Receptor cells live for only 1 to 2 weeks and then are replaced by new receptor cells • Each receptor in a taste bud responds best to one of the basic tastes. A receptor can respond to the other tastes, but it responds strongest to a particular taste.

Taste Buds

Primary sensation of taste • The identities of the specific chemical that excite different taste receptors are not all known. Even so psychological and neurological studies have identified at least 13 possible chemical receptors in the taste cell. • For the practical analysis of taste these receptors have been grouped into five general categories called primary sensations of taste. • They are Sour, Salty, Sweet, Bitter and Umami

Cont… § Sweet Sugars, saccharin, alcohol, and some amino acids are plentiful near the tip of the tongue. § Salt Metal ions are abundant in the tip and upper portion of the tongue. § Sour Hydrogen ions occur along the lateral edges of the tongue. § Bitter Alkaloids such as quinine and nicotine are at the back of the tongue. § Umami Elicited by the amino acid glutamate ( Protein )

Taste Pathway • The stimulus energy of taste is converted into a nerve impulse by: v. Na+ influx in salty tastes v. H+ in sour tastes (by directly entering the cell, by opening cation channels, or by blockade of K+ channels) v. Gustducin in sweet and bitter tastes

Taste Pathway • Cranial Nerves VII , IX and CN X carry impulses from taste buds to the solitary nucleus of the medulla. These impulses then travel to the thalamus, and from there fibers branch to the Gustatory cortex (taste) Hypothalamus and limbic system (appreciation of taste)

Experiment q Objective • To test the ability to identify familiar taste with eye closed q Equipment • Solution of 5% sucrose, 1% acetic acid, 5% Na. Cl and 0. 5% quinine sulphat.

How to prepare the solutions • sweet solution Mix 2 teaspoons (~ 8 gr) of sugar in 1 glass (~250 ml) of water. • Salt Solution Mix 3 teaspoons (~15 gr) of salt in 1 glass (~250 ml) of water. • Sour Solution It usually takes 5 -10 teaspoons of lemon juice per glass to get the solution to have the same “taste intensity” as your salt solution • Bitter solution Mix 2 teaspoons (~114 mgr caffeine) of instant coffee in 1 glass (~250 ml) of water

Procedure • To test the sense of taste use strong solution of sugar (for sweet), common salt (for salt), weak solution of citric acid (for sour), and quinine (for bitter). Four vials of solutions are placed on the table with labels. Dry the tongue with paper towel and apply the different solutions with applicator stick/glass rod to the tip, sides and back of the tongue as following

Cont… • Inform the volunteer that you will be testing different tastes and asking him/her to rate where the taste feels stronger. • Ask the volunteer to rinse his/her mouth with a sip of water, occlude both his/her nostrils and stick his/her tongue out. • Dip a clean cotton swap into the first solution and place it on the tip of the volunteer’s tongue.

Cont… • Soak the cotton swab well to get a big drop and allow a few seconds for the tastant to reach the taste buds. • Dip the cotton swab into the same solution again and touch the left side. • Repeat for the right side and the back of the tongue, each time dipping the cotton swab in the solution again. • Ask the volunteer to rate the strength of each taste (on a scale from 1 -4, four being the strongest of all) • Repeat for all solutions

Cont… • The patient is asked to keep the tongue protruded while applying one solution at a time. After each taste mouth must be rinsed. • The different taste is written on the paper

Taste adaptation Complete adaptation of a taste can occur in 1 -5 minutes if continuous stimulation.

Taste Aversion • The taste projections to the hypothalamus and limbic system account for the strong association between taste and emotions. • Sweet foods evoke reactions of pleasure, while bitter foods can evoke reactions of disgust

Do you know ? Why do the elders like to take in food with strong flavour? It’s too salty!

Because …. • When you were a baby, you had taste buds, not only on your tongue, but on the sides and roof of your mouth. This means you were very sensitive to different foods. • As you grew, the taste buds began to disappear from the sides and roof of your mouth, leaving taste buds mostly on your tongue. • As you get older, your taste buds will become even less sensitive, so you will be more likely to eat foods that you thought were too strong as a child.

Remember q Spicy’ is not a taste. It is the sensation of pain in the tongue resulting from the destruction of taste buds by the ‘hot’ food like chilly. It is spicy!

Also Note q Taste is influence by olfactory sensation and nasal congestion affect your taste. q Tongue can detect other stimuli rather than taste like temperature and Texture. q In general, girls have more taste buds than boys. q. Flavor is a complex mixture of sensory input composed of taste (Gustation), smell (olfaction) and the tactile sensation of food as it is being munched. q The receptors for alkaloids evolved to be the most sensitive in order to allow humans to detect plant poisons before they are eaten.

Taste Disorders q Ageusia (complete loss of taste) q Dysgeusia (persistent abnormal taste)

What causes taste disorders? q Upper respiratory and middle ear infections q Radiation therapy for cancers of the head and neck q Exposure to certain chemicals, such as insecticides and some medications, including some common antibiotics and antihistamines q Head injury q Some surgeries to the ear, nose, and throat (e. g. , third molar—wisdom tooth—extraction and middle ear surgery) q Poor oral hygiene and dental problems