Human tongue and the sense of Taste

 The receptors for taste, called taste buds, are situated chiefly in the tongue, but they are also located in the roof of the mouth and near the pharynx. They are able to detect four basic tastes: salty, sweet, bitter, and sour. The tongue also can detect a sensation called “umami” from taste receptors sensitive to amino acids. Generally, the taste buds close to the tip of the tongue are sensitive to sweet tastes, whereas those in the back of the tongue are sensitive to bitter tastes. 

The taste buds on top and on the side of the tongue are sensitive to salty and sour tastes. At the base of each taste bud there is a nerve that sends the sensations to the brain. The sense of taste functions in coordination with the sense of smell. The number of taste buds varies substantially from individual to individual, but greater numbers increase sensitivity. Women, in general, have a greater number of taste buds than men. As in the case of colour blindness, some people are insensitive to some tastes.

HUMAN TONGUE STRUCTURE

The human tongue has three distinct divisions, namely, the apex, the body and the root. You can view the parts by having a side view of this extremely flexible muscular organ. The surface is divisible into anterior and posterior.

Human Tongue and its Parts

Below is the brief description of the major tongue parts:

1. The Tip or Apex

The tip or apex of the tongue accounts for one-third of the anterior surface of tongue. It is highly movable and rests against the incisor teeth in the mouth cavity. The taste buds for “sweet” are present on this part.

The tip also plays its role in the production of labiodental and alveolar sounds.

The Body or Main Part

The anterior two-thirds of the tongue form its body. The presence of lingual papillae on the upper side makes the surface rough. A layer of mucosa, on the other hand, keeps it moist.

It is this part of the tongue where the tongue taste buds for salt, bitter and sour taste are present.

The Root or Base

The root is that part of the tongue which attaches it to the bottom or floor of the mouth cavity. It appears between the mandible and the hyoid bone. The primary job of the hyoid bone is to provide anchorage to the tongue.

The dorsal portion of the root lies in the oropharynx. What is oropharynx? It is the part of the pharynx lying between the soft palate and epiglottis.

Occupying most of the oral cavity and oropharynx, your tongue is a mass of muscles. The specific arrangement of muscle fibres allows it to move freely in any direction inside the mouth cavity to performs several different tasks, including eating, swallowing, speaking, licking, sucking, oral cleansing, and catching pray, etc.

You can distinguish between three tongue parts, the tip, the body and the base. The tip is highly mobile, anterior portion. Posterior to it lies the body which has ventral and dorsal surfaces. Next comes the base which attaches tongue to the floor of mouth.

The major aspects of tongue anatomy are being explained below:

Lingual Papillae on the Surface

Where does the tongue get its characteristic appearance? The lingual papillae on the surface of the organ are small bumps which contain taste buds. These projections of lamina propria are covered with tongue epithelium.

Filiform, foliate, vallate and fungiform are the four different types of papillae found on the surface. Different papillae contain different number of taste buds. For example, a vallate papilla may contain 250 taste buds, while the number of taste buds may reach 1600 in the fungiform papilla.

A taste receptor, edge and basal cells are found in each taste bud. Meanwhile, several nerve fibers innervate each taste bud.

Tongue Muscles

The musculature of tongue consists of four extrinsic and four intrinsic muscles. A fibrous septum separates the tongue muscles on each side. The intrinsic muscles originate from within the tongue body while extrinsic muscles have their origin outside the tongue body.

Both types of muscles work in coordination to create various tongue movements. However, they have their individual roles as well. For example, the extrinsic muscles change the position of tongue while the intrinsic muscles alter its shape.

5. Tongue Nerve Supply and Vasculature

The arterial blood supply for tongue comes from the external carotid artery. It branches off to join lingual artery which has three main branches, namely, the dorsal, the deep and the sublingual arteries. The branches of lingual artery supply blood to different parts of the tongue.

Turning to tongue nerve supply, the hypoglossal nerve provides most innervation for all the tongue muscles.

6. Tongue Surface

What are the tongue bumps? As you can observe in the tongue pictures, the human tongue has got a rough texture. It is because of the presence of tiny bumps, the tongue papillae, all over the dorsal surface of the tongue that make it look so rough.

Tongue Surface

The surfaces of the tongue papillae, on the other hand, contain thousands of taste buds. The taste buds are actually a collection of the nerve-like cells. Nerves develop a connection between taste buds and the brain.

The upper most layer of tissue on the human tongue is that of mucosa. The mucosa keeps it moist. It also makes the tongue a bit slippery to touch.

Tongue Function

You spend so much money in making the food delicious. How do you taste deliciousness of the food? You owe this faculty to your tongue. In addition to detecting taste, the human tongue also performs several other important functions.

For example, the tongue function also involves the mastication of food, catching prey, licking, sucking and swallowing. Do you know any other interesting tongue function? The list of the some of the important tongue functions is given below:

Tongue – Tool to Taste Food

The ability of tongue to taste food is because of the presence of taste buds on its surface. According to traditional belief, different parts of the tongue sense only a specific taste.

The modern research rejects this belief. It suggests that different parts of tongue detect a specific taste more easily (and strongly) but they can detect other tastes as well. However, each receptor cell is sensitive to a particular taste only.

Different types of receptor cells help distinguish between various sorts of differently tasting substances, such as sweet, sour, bitter, spicy and salty. On the tip, you will find taste buds for sensing sweet.

Sections of the tongue as tool to taste food

Behind the apex and along the sides, there are receptors for tasting bitter, sour and salty things.

Dorsum – the upper surface of the tongue – contains lots of lingual papillae. The papillae house the taste buds and the taste receptors. These receptors assist in the sensation of taste of different types of dietary components which come into contact with them.

The taste receptors are of five main types – sweet taste receptors, bitter taste receptors, salty taste receptors, sour taste receptors and umami taste receptors.

The umami taste receptors help you detect the taste of amino acids in the food.

Human Tongue’s Role in Mastication & Chewing

After the food enters the mouth cavity, two processes start and go side by side, grinding and mastication. During grinding, teeth break down the large food particles into smaller ones.

Thus, there is easy mixing of these particles with saliva to form bolus. Mastication involves the mixing of finely ground food with saliva. That is why you also call the process as chewing.

Tongue facilitates the process of mastication and chewing. Particularly, it helps in the positioning of food between the teeth. Secondly, as the food turns around, it is mixed with saliva.

The masticatory muscles provide the enormous strength of jaw closure. It is in large part due to the pinnated arrangement of fibres in the masseter. The masseter is the masticatory muscle of the posterior cheek.

Removal of Hard and Ill-Tasting Substances

How do you take hard and unwanted substances out that accidently enter the mouth with food? Tongue has also a role in separating, sorting out and removing unsuitable particles that may accidently come with the food, such as bones and the ill-tasting soft or hard substances.

Swallowing Food

The masticated food forms a rounded mass, the bolus, with the help of tongue. The task of this fantastic muscular organ does not end here. Its next duty is to expel the bolus into oesophagus at the back of the mouth cavity. The food bolus then moves through the oesophagus with the help of peristaltic contractions and enters the stomach.