1. What is the tongue?
The tongue is a highly sensitive muscular organ that lies in the oral cavity and is concerned with mastication, deglutition or swallowing, speech, and taste.
The tongue is developed in the endodermal floor of the pharynx by two rudiments. An anterior rudiment and a posterior rudiment. Sulcus Terminalis mark the union of these rudiments.
The functions of the tongue are listed below :
4. Parts of Tongue:
The superior surface of the body is called the dorsal surface or dorsum. The inferior surface of the body is called the ventral surface. The dorsum has two parts and is called anterior 2/3rd and posterior 1/3rd. The anterior 2/3rd is called the oral part or the buccal part and the posterior 1/3rd is called the pharyngeal part or lymphoid part. These two parts differ developmentally, topographically, in appearance, structurally, histologically, functionally, and in nerve and blood supply.
The posterior 1/3rd of the tongue forms the anterior wall of the pharynx so it is known as the pharyngeal part and contains so many lymphoid tissues that it is also known as lymphoid part.
The anterior and posterior part is separated by a “V” Shaped groove called Sulcus Terminalis. There is a depression in the center of the separation and the depression is called foramen caecum.
5. Mucosal Folds:
There are three mucous folds. They are frenulum linguae or Lingual Frenum and glossoepiglottic folds(One median and two lateral). Frenulum linguae is the vertical folds of mucous membrane connecting the tongue to the floor of the mouth. It separates the opening of the sum-mandibular duct.
Glossoepiglottic Folds: There are one median and two lateral folds. These are folds of the mucous membrane between the dorsum of the tongue and the anterior surface of the epiglottis. Between them, there is depression is called vallecula.
6. Nerve Supply.
Anterior 2/3rd by lingual nerve and chorda tympani branch of the facial nerve. The Posterior 1/3rd is supplied by the glossopharyngeal nerve for sensory and hypoglossal for the motor.
7. Blood Supply.
The tongue receives blood supply from the lingual artery on the floor of the mouth and there is also a secondary blood supply from the tonsillar branch of the facial artery and ascending pharyngeal artery.
8. Lymphatic Drainage.
Lymphatic Drainage is divided into four sets:
- Apical Sets.
- Central Sets.
- Basal Sets.
- Marginal Sets.
Apical Sets:- From the tip drain into the submental lymph node and suprahyoid lymph node.
Central Sets- Lymph vessels from the upper part drain into the upper deep cervical lymph node.
Basal Sets:- From the posterior end/part drain into the lower deep cervical lymph node.
Marginal Sets:- Lymph vessels from the lateral border drain to the submandibular grooves of the lymph node.
9. Muscles of Tongue.
All the muscles of the tongue are skeletal muscles. There is a midline fibrous septum that divides it into two equal halves i.e right and left halves. Each half contains two sets of muscles, an intrinsic and extrinsic set. Extrinsic sets are those that take origin from sources outside the tongue and are inserted into the corresponding sides. Intrinsic muscles are confined to the tongue and both the origin and insertion are within the tongue.
9.1. Extrinsic Muscles.
There are five sets of extrinsic muscles present on each side. Extrinsic muscles are as follows:
Origin is from the superior genial tubercle of the mandible. The action of this muscle is the protraction of the tongue. This muscle is called as safety muscle of the tongue because when this muscle gets paralyzed the tongue will roll back and closes the laryngeal opening which results in suffocation.
Origin is from the upper part of the body of hyoid bone and greater cornu. It is a depressor muscle that pulls the tongue toward the floor of the mouth.
The lower part of the hyoid bone is called chondroglossus. This muscle originates from the lower part hyoid bone and lesser horn or cornu.
Originates from the apical part of the styloid process of the temporal bone. It acts as the retractor of the tongue. It helps to withdraw the tongue and also helps raise the posterior part.
Originates from the inferior surface of the palatine aponeurosis. It acts as the elevator i.e it helps to raise the tongue.
9.2. Intrinsic Muscles.
There are three sets of intrinsic muscles called longitudinal, vertical, and transverse sets. Intrinsic muscles are arranged in three planes at the right angle to each other.
It contains superior longitudinal and inferior longitudinal muscles. These muscles extend from the tip to the base of the tongue. The vertical lingual muscles are placed between two longitudinal muscles mainly at the tip and the lateral walls.
It originates from the midline fibrous septum and then runs toward the lateral wall.
It lies between two longitudinal muscles. It helps in altering the shape and deviation of the tip of the tongue to one side.
9.3. Nerve Supply of Muscles.
All muscles except palatoglossus are supplied by the hypoglossal nerve which is the 12th cranial nerve. Whereas the palatoglossus is supplied by the cranial part of the accessory nerve i.e the 11th cranial nerve.
9.4. Blood Supply of Muscles.
When the hypoglossal nerve is paralyzed then the corresponding half of the tongue undergoes atrophy.