Tongue

INTRODUCTION

The tongue is a muscular organ situated in the floor of the mouth. It is associated with the functions of taste,speech,mastication and deglutition. It has an oral part that lies in the mouth,and a pharyngeal part that lies in the pharynx. The oral and pharyngael parts are separated by a V-shaped sulcus,the sulcus terminalis

     
   Tongue comprises skeletal muscle which is voluntary.These voluntary muscles start behaving as involuntary in any classroom-funny?

   Thanks to the taste buds that the multiple hotels, restaurants, fast food outlets,chat-pakori shops,etc. are flourishing. One need not be too fussy about the taste of the food. Nutritionally, it should be balanced and hygienic.

   "Tongue is barely three inches long, but it can kill a person six feet tall." Tongue appears very mobile, still it cannot be swallowed like food, because tongue is anchored to hyoid bone,mandible,styloid process and soft palate. Four intrinsic and three extrinsic muscles of tongue are supplied by hypoglossal nerve. Only palatoglossus is supplied by vagoaccessory complex. In paralysis of hypoglossal nerve, the tip of tongue if protruded gets deviated to the paralysed side.

EXTERNAL FEATURES

The tongue has:

1. A root,
2. A tip,and
3. A body,which has:

• A curved upper surface or dorsum.
• An inferior surface      

 The dorsum of the tongue,epiglottis and palatine tonsil.

       

          The dorsum is divided into oral and pharyngeal parts. The inferior surface is confined to the oral part only.

    The root is attached to the styloid process and soft palate above, and to mandible and the hyoid bone below. Because of these attachments, we are not able to swallow the tongue itself. In between the two bones, it is related to the geniohyoid and mylohyoid muscles.

    

    The tip of the tongue forms the anterior free end which, at rest, lies behind the upper incisor teeth.

     The dorsum of the tongue is convex in all directions. it divided into: 

• An oral part or anterior two-thirds.
• A pharyngeal part or posterior one-third, 

By a faint V shaped groove, the sulcus terminalis. The two limbs of the 'V' meet at a median pit, named the foramen caecum. they run laterally and forwared up to the palatoglossal arches. The foramen caecum represents the site from which the hhyroid diverticulum grows down in thge embryo. The oral and pharyngeal parts of the tongue differ in their development, topography, structure, and function.

   The oral or papillary part of the tongue is placed on the floor of the mouth. Its margins are free and in contact with the gums and teeth. Just in front of the palatoglossal arch, each margin shows 4 To 5 vertical folds, named the foliate papillae.

   The superior surface of the oral part shows a median furrow and is covered with papillae which make it rough.

   The inferior surface is covered with a smooth mucous membrane, which shows a median fold called the frenulum linguae.

   On either side of the frenulum, there is a prominence produced by the deep lingual veins. More laterally there is a fold called the plica fimbriata that is directed forwared and medially towards the tip of the tongue.

   The pharyngeal or lymphoid part of the tongue lies behind the palatoglossal arches and the sulcus terminalis. Its posterior surafce, sometimes called the base of the tongue, forms the anterior wall of the oropharynx. The mucous membrane has no papillae,but has many lymphoid follicles that collectively constitute the lingual tonsil. Mucous glands are also present.

   The posteriormost part of the tongue is connected to the epiglottis by three-folds of mucous membrane. These are the median glossoepiglottic fold and the right and left lateral glossoepiglottic fold. On either side of the median fold, there is a depression called the vallecula. The lateral folds separate the vallecula from piriform fossa.

The inferior surface of tongue and the floor of the mouth.

   

PAPILLAE OF THE TONGUE

These are projections of mucous membrane or corium which give the anterior two-thirds of the tongue its characteristic roughness. These are of the following three types.

1. vallate or circumvallate papillae- They are large in size 1-2 mm in diameter and are 8-12 in number. They are situated immediately in front of the sulcus terminalis. Each papilla is a cylindrical projection surrounded by a circular sulcus. The walls of the papilla are raised above the surface
2. The fungoform papillae-are numerous near the tip and margins of the tongue, but some of them are also scattered over the dorsum. These are smaller than the vallate papillae. but larger than the filiform papillae. each papilla consists of a narrow pedicle and a large rounded head. They are distinguished by their bright red colour
3. The filiform papillae or conical papillae-cover the presulcal area of the dorsum of the tongue, and give it a characteristic velvety appearance. They are the smallest and most numerous of the lingual papillae. Each iis pointed and covered with keratin; the apex is often split into filamentous processes.
4. foliate papillae-few foliate papillae are also present.

papilla of tongue

MUSCLES OF THE TONGUE

A middle fibrous septum divides the tongue into right and left halves. Each half contains four intrinsic and four extrinsic muscles

Intrinsic Muscles

1. Superior longitudinal.
2. Inferior longitudinal.
3. Transverse.
4. Vertical.

Extrinsic Muscles

1. Genioglossus.
2. Hyoglossus.
3. Styloglossus.
4. Palatoglossus.

    

       The intrinsic muscle occupy the upper part of the tongue, and are attached to the submucous fibrous layer and to the median fibrous septum. They alter the shape of the tongue. The superior longitudinal muscle lies beneath the mucous membrane. It shortens the tongue and makes its dorsum concave.

      The inferior longitudinal muscle is a narrow band lying close to the inferior surface of the tongue betwwen the geniglossus and the hyoglossus. It shortens the tongue and makes its dorsum convex.

      The transverse muscle extends from the median septum to the margins. it makes the tongue narrow and elongated. The vertical muscle is found at the borders of the anterior part of the tongue. It makes the tongue broad and flattened.

      The extrinsic muscles connect the tongue to the mandible via genioglossus; to hyoid bone through hyoglossus; to the styloid process via styloglossus, and the palate via palatoglossus.

 

Intrinsic muscles of Tongue

Intrinsic muscles of Tongue

Extrinsic muscles of Tongue

Muscle of tongue

Extrinsic muscle of tongue

1. Muscle- Palatoglossus

• Origin- Oral surface of palatine aponeurosis
• Insertion- Descends in the palatoglossal arch to the side od tongue at the junction of oral and pharyngeal parts
• Action- Pulls up the root of tongue

    2.   Muscle- Hyoglossus

• Origin- whole length of greater cornua and lateral part of hyoid bone
• Insertion- Side of tongue betwwen styloglossus and inferior longitudinal muscle of tongue
• Action- Depresses Tongue, Makes dorsum convex.

    3.   Muscle-Styloglossus

• Origin- Tip and part of anterior surface of styloid process
• Insertion- Into the side of tongue
• Action- pulls tongue upwards and backwards

    4.   Muscle-Genioglossus(Fan shaped bulky muscle)

• Origin- Upper genial tubercle of mandible
• Insertion- Upper fibers into the tip of tongue. Middle fibres into the dorsum. Lower fibres into the hyoid bone
• Action- Retracts the tongue.Depresses the tongue.Pulls the posterior part of tongue.It is life saving muscle

ARTERIAL SUPPLY OF TONGUE

It is derived from the tortuous lingual artery a branch of the external carotid artery. The root thye tongue is also supplied by the tonsillar a branch of facial artery, and ascending pharyngeal barnch of external carotid.

VENOUS DRAINAGE

The arrangement of the vena comitantes/veins of the tongue is variable. Two venae comitantes accompany the lingual artery, and one vena comitantes accompanies the hypoglossal nerve. The deep lingual vein is the largest and principle vein of the tongue. It is visible on the inferior surface of the tongue. It runs backwards and cross the genioglossus and the hyoglossus below the hypoglossal nerve.

       

       These veins unite at the posterior border of the hyoglossus to form the lingual vein which ends in the internal jugular vein

lYMPHATIC DRAINAGE

1. The tip of the tongue drains bilaterally to the submental nodes.
2. The anterior two-thirds of the tongue drain unilaterally to the submandibular nodes.
3. The posterior one-thirds of the tongue drains bilaterally to the jugulo-omohyoid nodes.
4. The posterior most part of the tongue drains bilaterally into the upper deep cervical lymph nodes.

Lymphatic drainage of tongue

NERVE SUPPLY

Motor Nerves

                               All the intrinsic and extrinsic muscles except the palatoglossus, are supplied by the hypoglossal nerve, The palatoglossus is supplied by the cranial root of the accessory nerve through the pharyngeal plexus.

Sensory nerves 

                      The lingual nerves is the nerve of genral sensation and the chorda tympani is the nerve of taste for the anterior two-thirds of the except vallate papillae.

           

             The glossopharyngeal nerve is the nerve for both genral sensation and taste for the posterior one-third of the tongue including the circumvallate papillae. The posterior most part of the tongue is supplied by the vagus nerve through the internal laryngeal branch.

Nerve supply- Sensory

• Anterior two-thirds-lingual
• posterior one-third-Glossopharyngeal
• posterior most part or vallecula- Internal laryngael branch of vagus

Nerve supply- Taste

• Anterior two-thirds- Chorda tympani except vallate papillae
• Posterior one-third- Glossopharyngeal including the vallate papillae
• Posterior most part or vallecula- Internal laryngeal branch of vagus

Nerve supply of tongue

HISTOLOGY

1. The bulk of the tongue is made up of striated muscles.
2. The mucous membrane consists os a layer of connective tissue lined by stratified squamous epithelium. On the oral part of the dorsum, it is thin ,forms papillae, and is adherent to the muscles. On the pharyngeal part of the dorsum, it is very rich in lymphoid follicles. On the inferior surface, it is thin and smooth. Numerous glands, both mucous and serous lie deep to the mucous membrane.
3. taste buds are most numerous on the sides of the vallate papillae, and on the walls of the surrounding sulci. taste buds are numerous over the foliate papillae and over the posterior one -thirds of tongue; and sparsely distributed on the fungiform papillae,the soft palate,the epiglottis and the pharynx. there are no taste buds on the mid-dorsal region of the oral part of the tongue.

DEVELOPMENT OF TONGUE

1. Epithelium

• Anterior two-thirds: From two lingual swellings and one tuberculum impar, which arise from the first branchial arch. The tuberculum impar soon disappears.therfor, it is supplied by lingual nerve and chorda tympani
• Posterior one-third: From the third arch Therefore,it is supplied by the glossopharyngeal nerve.
• posterior most part from the fourth arch. This is therefore supplied by the vagus nerve.

   2. Muscles

• The muscles develop fromn the occipital myotomes which are supplied by the hypoglossal nerve 

   3.  Connective Tissue

• The connective tissue develops from the local mesenchyme

TASTE PATHWAY

• The taste from anterior two-thirds of tongue except from vallate papillae is carried by chorda tympani branch of facial till the geniculate ganglion. The central processes go to tractus solitarius in the medulla.
• Taste from posterior one-third of tongue including the vallate papillae is carried by cranial nerve 9 th till the inferior ganglion. The central processe also reach the tractus solitarius 
• Taste from posterior most part of tongue and epiglottis travels through vagus nerve till the inferior ganglion of vagus. These central processes also also reach tractus solitarius.
• After a relay in tractus solitarius, the solitariothalamic tract is formed which becomes a part of trigeminal lemniscus and reaches posteroventromedial nucleus of thalamus of the opposite side. Another relay here takes them to lowest part of postcentral gyrus, which is the area for taste.

                                      Taste pathway