Tongue
TONGUE- Muscular organ concerned with taste,speech,mastication and deglutition.
Situation: Oral cavity and anterior wall of oropharynx.
The Tongue has a root, a tip (apex) and a body.
- Body has an upper surface (dorsum) and an inferior surface.
- The dorsum is divided into oral and pharyngeal parts by a V-shaped, the sulcus terminalis. The two limbs of ‘V’ meet at a median pit, known as foramen caecum.
- The oral and pharyngeal part differ in their development, topography, structure and function.
- Thus tongue has three parts:
- Oral or papillary part
- Pharyngeal or lymphoid part
- Posterior most part
DEVELOPMENT:
- Starts to develop near the end of the fourth week of intrauterine life.
Epithelium of tongue:
- Anterior 2/3 from 2 lingual swellings and one tuberculum impar, i.e., from first branchial arch supplied by lingual nerve (post-trematic) and chorda tympani (pre-trematic)
- Posterior 1/3 from the cranial half of the hypobranchial eminence, i.e., from the third arch supplied by glossopharyngeal nerve
- Posterior most part from the fourth arch supplied by vagus nerve.
Muscles of tongue:
- Muscles develop from the occipital myotomes which are supplied by hypoglossal nerve.
- Palatoglossus muscle does not develop from occipital myotomes.
- Connective tissue develops from local mesenchyme.
|
PART OF TONGUE |
EMBRYO PART FROM WHICH DERIVED |
SENSORY (General sensation) |
TASTE |
MOTOR |
|
Epithelium over Ant. 2/3rd |
Ist |
Lingual nerve(Mandibular branch of Vth Cranial nerve) |
Chorda tympanibranch of facial nerve(VII) |
– |
|
Epithelium over Post. 1/3rd |
IIIrd
|
Glossopharyngeal Nerve |
Glossopharyngeal nerve |
– |
|
Epithelium over Posterior most |
IVth |
Sup. Laryngeal branch of Xth C.N |
Sup. Laryngeal nerve |
– |
|
Muscles |
Occipital myotomes except Palatoglossal muscle |
– |
– |
Hypoglossal nerve (XII)except Palatoglossal nerve |
SURFACES OF TONGUE:
Ventral surface
- The thin strip of tissue that runs vertically from the floor of the mouth to the undersurface of the tongue is called the lingual frenulum. It tends to limit the movement of the tongue.
- On either side of frenulum there is a prominence produced by deep lingual veins, more laterally there is a fold called plica fimbriata.
1. Glands of Blandin-Nuhn
- Anterior lingual glands (also called apical glands) are deeply placed seromucous glands that are located near the tip of the tongue on each side of the frenulum linguae.
- They are found on the under surface of the apex of the tongue, and are covered by a bundle of muscular fibers derived from the Styloglossus and Longitudinalis inferior.
- They are between 12 to 25 mm. in length, and approximately 8 mm. wide, and each opens by three or four ducts on the under surface of the tongue’s apex.
2. Glands of Von-Ebner
- They are serous salivary glands.
- Located adjacent to the moats surrounding the circumvallate and foliate papillae.
- Von Ebner’s glands secrete lingual lipase.
- This secretion flushes material from the moat to enable the taste buds to respond rapidly to changing stimuli.
- Von Ebner’s glands are innervated by cranial nerve IX, the glossopharyngeal nerve.
3. Gland of Weber
- They lie along the lateral border of the tongue
- These glands are pure mucous secreting glands.
- These open into the crypts of the lingual tonsils on the posterior tongue dorsum.
- Abscess formed due to accumulation of pus and fluids in this gland is called Peritonsillar Abscess
Pharyngeal Part
- Lies behind the palatoglossal arches.
- Forms the anterior wall of the oropharynx.
- Devoid of papillae.
- Underlying lymphoid nodules embedded in the submucosa collectively called as lingual tonsils.
Papillae Of Tongue:
1. Filiform papillae
- Minute, conical, cylindrical projections which cover most of the presulcul dorsal area.
- Increase the friction between the tongue and food.
- They bear many secondary papillae which are more pointed than those of vallate and fungiform papillae and covered with keratin.
- No taste buds are found.
2. Fungiform Papillae
- Located mainly on the lingual margin.
- Differ from filiform because are larger, rounded and deep red in colour.
- Bears one or more taste buds on its apical surface.
- These are mushroom shaped, more numerous near tip & margins of tongue but some of them scattered over the dorsum.
3. Foliate Papillae
- Red leaf-like mucosal ridg
- Bilaterally at the sides of the tongue near sulcus terminalis.
- Bear numerous taste buds.
4. Circumvallate Papillae
- Large cylindrical structures
- 8 to 12 in number
- Form a ‘V’ shaped row in front of sulcus terminalis on the dorsal surface at base of the tongue.
- The entire structure is covered with squamous epithelium, in both sulcal walls & taste buds around.
Taste Buds:
- Present in relation to cirumvallate papillae, fungiform papillae and foliate papillae.
- Also present on the soft palate, the epiglottis, the palatoglossal arches, and the posterior wall of the oropharynx.
- They are modified columnar elongated cells which act as receptors.
- They have darkly-stained’ elongated central nuclei.
- The superficial part of these cells is provided with short hairs (hairlets or microvilli).
- These hairlets project into the taste pore.
- The base of the taste cells is surrounded by sensory nerve fibres, carry the impulses of taste sensation to the brain.
- Supporting cells in taste buds : They are elongated columnar cells with dark cytoplasm but lightly-stained nuclei.
- They form the outer wall of the taste bud. They have long microvilli that extend from their surfaces into the taste pore.
- Basal cells are present at the base of the taste bud. They act as stem cells for renewal of taste cells and supporting cells.
- Gustatory receptors detect four main types of taste sensation:
- Sweet: tip
- Sour: middle
- Salty: anterolateral
- Bitter: base
- However recent evidence indicates that all areas of tongue are responsive to all taste stimuli.
- Muscles of tongue develop from the occipital myotomes.
- Palatoglossus muscle does not develop from occipital myotomes.
- Anterior 2/3 of tongue develops from 2 lingual swellings and one tuberculum impar, i.e., from first branchial arch supplied by lingual nerve (post-trematic) and chorda tympani (pre-trematic).
- Posterior 1/3 of tongue develops from the cranial half of the Hypobranchial eminence, i.e., from the third arch supplied by glossopharyngeal nerve.
- Fungiform Papillae near tip & margins of tongue.
- Foliate Papillae form transverse mucosal folds on the lateral aspect of tongue.
- No taste buds are found in Filiform papillae.
- Referred otalgia from base of tongue or oropharynx is carried by Cranial nerve IX (Glossopharyngeal nerve).
- Most common site of carcinoma tongue is middle of lateral border or the ventral aspect of the tongue followed by tip and dorsum.
|
PART OF TONGUE |
EMBRYO PART FROM WHICH DERIVED |
SENSORY (General sensation) |
TASTE |
MOTOR |
|
Epithelium over Ant. 2/3rd |
Ist |
Lingual nerve (Mandibular branch of Vth Cranial nerve) |
Chorda tympani branch of facial nerve(VII) |
– |
|
Epithelium over Post. 1/3rd |
IIIrd
|
Glossopharyngeal Nerve |
Glossopharyngeal nerve |
– |
|
Epithelium over Posterior most |
IVth |
Sup. Laryngeal branch of Xth C.N |
Sup. Laryngeal nerve |
– |
|
Muscles |
Occipital myotomes except Palatoglossal muscle |
– |
– |
Hypoglossal nerve (XII) except Palatoglossal nerve |