Term Paper on the Human Tongue | Vocal Organs | Biology

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Term Paper on the Human Tongue

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Term Paper # 1. Introduction of the Human Tongue:

It is a muscular and mobile organ. It is concerned with swallowing, speech and taste.

Situation:

Oral cavity and anterior wall of oropharynx.

Shape:

Inverted shoe shaped.

Development:

1. Muscles – occipital myotomes.

2. Mucous membrane of anterior 2/3 – Lingual swellings and tuberculum impar.

3. Mucous membrane of posterior 1/3 – Hypobronchial eminence.

Parts:

1. Tip- Contacts the incisor teeth.

2. Base (root)- Directs towards oropharynx.

3. Dorsal surface-Convex in appearance.

4. Ventral surface- Directed towards floor of mouth.

5. Borders- Two lateral borders right and left.

Dorsal Surface:

Anterior:

Oral portion is freely mobile. This is horizontal at rest.

Posterior:

Pharyngeal portion is more fixed and vertical. This has papillae and sensory nerve supply.

Sulcus Terminalis:

A ‘V’ shaped groove separates anterior 2/3 of dorsum from posterior 1/3.

Foramen Caecum:

Behind the apex of the sulcus there is a small depression called foramen caecum, this marks the site of origin of thyroid diverticulum.

Mucous Membrane:

This differs on the two regions of dorsum of the tongue – oral part and posterior 1/3. The oral part has small projections of lamina propria creating papillae which increase surface area of mucosa for taste receptors.

Papillae:

It is of four types (Mucous Membrane of Anterior 2/3 of Tongue):

1. Vallate Papillae:

These are 10 to 12 in number and present infront of sulcus terminalis in a single row, largest 2-4 mm in diameter. Papilla has a central circular elevation surrounded by a groove and a narrow wall. Taste buds are situated in the walls of groove.

2. Fungiform Papillae:

Bright red, flat dots of about 1 mm in diameter, along the edges, dorsum and tip of tongue.

These contain taste buds.

3. Filiform Papillae:

They are conical projections on dorsal surface, arranged in ‘V’ shaped rows parallel to sulcus.

Apex of these papillae is keratinised.

No taste buds are found.

Giving velvety appearance of tongue.

4. Foliate Papillae:

They form transverse mucosal folds on the lateral aspect of the tongue.

Taste Buds:

They are found on and around the papilla in large numbers, present on mucous membrane of pharyngeal part of tongue, undersurface of soft palate and back of epiglottis.

Features of Dorsal Surface of Posterior 1/3 of Tongue:

i. Taste buds and papillae are absent.

ii. Collection of lymphoid tissue under mucous membrane called lingual tonsils – makes the surface humpy.

iii. Lingual tonsil with faucial tubal and pharyngeal tonsils makes the lymphoid ring of Waldeyer.

iv. Mucous membrane reflected on epiglottis as median glosso epiglottic fold and lateral glosso- epiglottic folds between these folds on each side there is a depression called Vallecula.

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Term Paper # 2. Muscles of the Human Tongue:

Tongue is divided into two symmetrical halves by a median fibrous septum.

Each half contains muscles arranged in two groups:

I. Extrinsic Muscles:

These alter the position of tongue and are paired:

1. Hyoglossus (Chondro glossus)

2. Styloglossus

3. Genioglossus

4. Palatoglossus

All extrinsic muscles take origin from outside the tongue.

They change the position of the tongue and all are supplied by branches of hypoglossal nerve except palatoglossus – which is supplied by vago-accessory complex, i.e., through pharyngeal plexus of nerves.

II. Intrinsic Muscles:

Alter the shape of the tongue.

Form a large part of muscle mass of the tongue.

Attached to the septum and mucous membrane.

Named according to the direction of their fibres:

a. Superior longitudinal muscle

b. Inferior longitudinal muscle

c. Transverse lingual muscle

d. Vertical muscle.

Action:

Longitudinal Muscle:

a. Turn the tip upwards (superior fibres)

b. Turn the tip downwards (inferior fibres)

c. These reduce the length of the tongue during contraction.

Transversalis:

This produces narrowing and lengthening of the tongue.

Verticalis:

This flattens and broadens the tongue.

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Term Paper # 3. Nerve Supply and Blood Supply of the Human Tongue:

1. Motor Supply:

All extrinsic and intrinsic muscles of the tongue are supplied by hypoglossal nerve (XII) except palatoglossus supplied via pharyngeal plexus of nerves.

2. Sensory Supply:

(a) Anterior 2/3 – lingual nerve branch of mandibular division. This is sensory for general sensations (V₃).

Chordo Tympani:

This is a branch of VII and carries taste sensation from anterior 2/3 of tongue accompanies lingual nerve.

(b) Posterior 1/3 – glossopharyngeal – both sensory and carries taste sensation.

Also carries sensation and taste from circumvallate papillae.

Root of tongue near vallecula is supplied by internal laryngeal branch of Xth cranial nerve.

3. Sympathetic:

Plexus around lingual artery.

Blood Supply of Tongue:

A. Arterial Supply:

1. Lingual artery and its branches.

2. Facial artery – Ascending palatine and tonsillar branches.

3. Ascending pharyngeal artery.

B. Venous Drainage:

1. Superficial Veins of Tongue:

Drains inferior surface and tip – accompanies XIIth nerve joins with deep lingual and sublingual veins which ends in internal jugular vein.

2. Deep Veins:

Drains dorsum of tongue and follows lingual artery and ends in internal jugular vein.

Lymphatic Drainage of Tongue:

Divided into:

1. Apical vessels drain into submental lymph nodes → jugulo omohyoid lymph nodes.

2. Marginal vessels drain into submandibular, jugulo omohyoid and jugulo digastric group of lymph nodes.

3. Central vessels go to jugulo omohyoid and jugulo digastric lymph nodes.

4. Basal or dorsal vessels go to retropharyngeal, jugulo digastric and jugulo omohyoid lymph nodes.

All lymph of tongue ultimately enters the jugulo omohyoid nodes, hence known as lingual nodes.

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Term Paper # 4. Applied Anatomy of the Human Tongue:

1. Agenesis of tongue- Aglossia.

2. Bifid tongue- Tip of tongue is divided.

3. Microglossia- Small tongue.

4. Macroglossia- Large tongue.

5. Ankyloglossia or tongue tie- Short frenulum linguae.

6. Hemiglossia- One-half of tongue is developed.

7. Lingual thyroid- Present around foramen caecum.

8. Fissured tongue- Deep furrows present.

9. Infections of tongue- Glossitis, e.g., Tuberculosis, syphilis and pyogenic infection.

10. Ulcers of tongue: Due to destruction of mucous membrane may be dental ulcer.

Syphilitic ulcer present in midline

Tubercular ulcer

Malignant ulcer – CA.

11. Agueusia- Loss of taste or reduced sensation.

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