TONGUE

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TONGUE
Is a mass of skeletal muscle covered by mucous membrane, situated in the floor of the mouth. It is mobile and located partly in the oral cavity and partly in the oropharynx. It is associated with the function of taste, speech, mastication and deglutition. The superior surface of the tongue is covered by stratified squamous epithelium with numerous papillae containing nerve ending of sense of taste sometimes called taste buds. 

The papilla (lingua papilla) includes:
• Fungiform papillae:- are mushroom – shaped and appear as pink or red spots. They are scattered among the filiform papillae but are most numerous at the apex and sides of the tongue.
• Filiform papillae:- they are the smallest but most numerous papillae. They are located on the anterior 2/3 of the tongue. They contain keratin, which stiffens them and gives the tongue its whitish appearance.
• Foliate papillae:- are located on the lateral aspect of the posterior tongue. They are poorly developed in human.
• Vallate papillae:- are arranged in a V-shaped row at the back of the tongue (toward the base) they are the largest and most easily seen.
 
The fungiform, circumvallate and foliate papillae house taste buds, but those on the foliate papillae function in taste primarily in infancy.

The four basic taste sensations are:
  Sweetness – apex (tip)
  Saltiness – lateral margins
  Sourness and bitterness – posterior part.

Muscles of the tongue
The tongue has both intrinsic and extrinsic skeletal muscle fibers.

➡️ The intrinsic muscles are confined in the tongue and are not attached to bones. Their muscle fibers, run in several different planes, allow the tongue to change its shape (but not its position), becoming thicker, thinner, longer, or shorter as needed for speech and swallowing.

➡️ The extrinsic muscles extend to the tongue from their points of origin on bones of the skull or the soft palate. The extrinsic muscles alter the tongue’s position. They protrude it, retract it and move it from side to side.  A fold of mucosa (lingual frenulum) secures the tongue to the floor of the mouth and limits posterior movement of the tongue.

The extrinsic muscles are:
1. Genioglossus – protrude the tongue, and also depress it
2. Hyoglossus – depresses and retracts the tongue
3. Styloglossus – retracts (and elevates) tongue 
4. Palatoglossus – elevates posterior part of the tongue

Blood supply
The main arterial supply to the tongue is by the lingual branch of the external carotid artery. It is drained by the lingual vein which joins the internal jugular vein.

Nerve supply
  ➡️ Hypoglossal nerve which is sensory to the skeletal muscle
  ➡️ Lingual nerves (branch of mandibular nerve)
 ➡️  Glossopharyngeal and facial nerve for taste.
The tongue also receives parasympathetic supply that is secremotor through the lingual nerve.

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