The Tongue

Overview:
- The tongue is a mass of muscle that is almost completely covered by a mucous membrane.
- It occupies most of the oral cavity and oropharynx.
- It is known for its role in taste, but it also assists with mastication (chewing), deglutition (swallowing), articulation (speech), and oral cleansing.
- Five cranial nerves contribute to the complex innervation of this multifunctional organ.
- The embryologic origins of the tongue first appear at 4 weeks’ gestation:
  - The body of the tongue forms from derivatives of the first branchial arch:
    - This gives rise to two lateral lingual swellings and one median swelling (known as the tuberculum impar):
      - The lateral lingual swellings slowly grow over the tuberculum impar and merge, forming the anterior two thirds of the tongue.
  - Parts of the second, third, and fourth branchial arches give rise to the base of the tongue.
- Occipital somites give rise to myoblasts, which form the intrinsic tongue musculature.

Gross Anatomy:
- From anterior to posterior, the tongue has 3 surfaces:
  - Tip
  - Body
  - Base.
- The tip is the highly mobile, pointed anterior portion of the tongue.
- Posterior to the tip lies the body of the tongue, which has dorsal (superior) and ventral (inferior) surfaces.
- The median sulcus of the tongue separates the body into left and right halves.
- The terminal sulcus, or groove, is a V-shaped furrow that separates the body from the base of the tongue:
  - At the tip of this sulcus is the foramen cecum, a remnant of the proximal thyroglossal duct.
- The base of tongue contains the lingual tonsils, the inferiormost portion of Waldeyer’s ring.

Lingual papillae:
- The surface of the body of the tongue derives its characteristic appearance from the presence of lingual papillae:
  - Which are projections of lamina propria covered with epithelium.
- The four types of lingual papillae are as follows:
  - Vallate (circumvallate)
  - Foliate
  - Filiform
  - Fungiform
- The vallate papillae (circumvallate) are flat, prominent papillae that are surrounded by troughs:
  - In humans, there are 8 to 12 vallate papillae, located directly anterior to the terminal sulcus.
    - The ducts of the lingual glands of von Ebner secrete lingual lipase into the surrounding troughs to begin the process of lipolysis.
- The foliate papillae are small folds of mucosa (short vertical folds) located along the lateral surface of the tongue:
  - They are located on the sides at the back of the tongue, just in front of the palatoglossal arch of the fauces:
    - The foliate papillae appear as a series of red colored, leaf–like ridges of mucosa.
  - There are four or five vertical folds, and their size and shape is variable.
  - They are covered with epithelium, lack keratin and so are softer, and bear many taste buds:
    - Approximately 1000 taste buds.
      - Taste buds, the receptors of the gustatory sense, are scattered over the mucous membrane of their surface.
  - They are usually bilaterally symmetrical.
  - Sometimes they appear small and inconspicuous, and at other times they are prominent.
  - Because their location is a high risk site for oral cancer, and their tendency to occasionally swell, they may be mistaken as tumors or inflammatory disease.
  - Serous glands drain into the folds and clean the taste buds.
  - Lingual tonsils are found immediately behind the foliate papillae and, when hyperplastic, cause a prominence of the papillae.
- The filiform papillae:
  - Are the most numerous of the lingual papillae.
  - They are fine, small, cone-shaped papillae covering most of the dorsum of the tongue.
  - They cover most of the front two-thirds of the tongue’s surface.
  - They appear as very small, conical or cylindrical surface projections, and are arranged in rows which lie parallel to the sulcus terminalis:
    - At the tip of the tongue, these rows become more transverse.
  - They are responsible for giving the tongue its texture and are responsible for the sensation of touch.
  - Unlike the other kinds of papillae, filiform papillae do not contain taste buds.
- The fungiform papillae are mushroom shaped (generally red in color) and are dispersed most densely along the tip and lateral surfaces of the tongue:
  - Humans have approximately 200 to 300 fungiform papillae.
- Each vallate, foliate, and fungiform papilla contains taste buds (250, 1000, and 1600 taste buds, respectively):
  - Each taste bud is innervated by several nerve fibers.
  - In humans, all taste buds can perceive the five different taste qualities:
    - Salt
    - Sweet
    - Bitter
    - Acid
    - Umami.

Each taste bud consists of taste receptor, basal cell , and edge cells.
When a taste molecule binds to a taste receptor, the receptor cell depolarizes:
- Causing an influx of Ca++, which results in the release of an unknown neurotransmitter.
- Following depolarization, the afferent neural pathway depends on the location of the taste bud that was stimulated:
  - In the anterior two thirds of the tongue, the chorda tympani branch of the facial nerve (cranial nerve VII) is stimulated.
  - The lingual-tonsillar branch of the glossopharyngeal nerve (cranial nerve IX) relays taste information from the posterior third of the tongue.
Taste fibers from the anterior two thirds of the tongue first travel with the lingual nerve and then are relayed to the chorda tympani nerve:
- This nerve enters the temporal bone from the infratemporal fossa, where it joins the facial nerve and travels to the geniculate ganglion, where its pseudounipolar cell bodies are located.
- From the geniculate ganglion the taste fibers travel in the nervus intermedius to the nucleus of the solitary tract located in the medulla oblongata.
Similarly, taste fibers from the posterior one third of the tongue travel with the lingual-tonsillar nerve to the inferior glossopharyngeal ganglion and then to the nucleus of the solitary tract located in the medulla oblongata.
Second-order neurons then project taste fibers to the parabrachial nucleus of the pons.
The central tegmental tract carries taste sensation from the pons to the thalamus.
The pathway ends in the frontal operculum and insular cortex.

Rodrigo Arrangoiz MS, MD, FACS a head and neck surgeon and is amember of Sociedad Quirúrgica S.C at the America British Cowdray Medical Center.

He is first author on some publications on oral cavity cancer:

Oral Tongue Cancer: Literature Review and Current Management
- https://www.oatext.com/pdf/CRR-2-153.pdf

Understand Cancer: Research and Treatment Oral Cavity Cancer: Literature Review and Current Management.
- https://www.researchgate.net/publication/303366031_Understand_Cancer_Research_and_Treatment_Oral_Cavity_Cancer_Literature_Review_and_Current_Management

Overview:

The tongue is a mass of muscle that is almost completely covered by a mucous membrane.

It occupies most of the oral cavity and oropharynx.

It is known for its role in taste, but it also assists with mastication (chewing), deglutition (swallowing), articulation (speech), and oral cleansing.

Five cranial nerves contribute to the complex innervation of this multifunctional organ.

The embryologic origins of the tongue first appear at 4 weeks’ gestation:

The body of the tongue forms from derivatives of the first branchial arch:

This gives rise to two lateral lingual swellings and one median swelling (known as the tuberculum impar):

The lateral lingual swellings slowly grow over the tuberculum impar and merge, forming the anterior two thirds of the tongue.

Parts of the second, third, and fourth branchial arches give rise to the base of the tongue.

Occipital somites give rise to myoblasts, which form the intrinsic tongue musculature.

Gross Anatomy:

From anterior to posterior, the tongue has 3 surfaces:

Tip

Body

Base.

The tip is the highly mobile, pointed anterior portion of the tongue.

Posterior to the tip lies the body of the tongue, which has dorsal (superior) and ventral (inferior) surfaces.

The median sulcus of the tongue separates the body into left and right halves.

The terminal sulcus, or groove, is a V-shaped furrow that separates the body from the base of the tongue:

At the tip of this sulcus is the foramen cecum, a remnant of the proximal thyroglossal duct.

The base of tongue contains the lingual tonsils, the inferiormost portion of Waldeyer’s ring.

Lingual papillae:

The surface of the body of the tongue derives its characteristic appearance from the presence of lingual papillae:

Which are projections of lamina propria covered with epithelium.

The four types of lingual papillae are as follows:

Vallate (circumvallate)

Foliate

Filiform

Fungiform

The vallate papillae (circumvallate) are flat, prominent papillae that are surrounded by troughs:

In humans, there are 8 to 12 vallate papillae, located directly anterior to the terminal sulcus.

The ducts of the lingual glands of von Ebner secrete lingual lipase into the surrounding troughs to begin the process of lipolysis.

The foliate papillae are small folds of mucosa (short vertical folds) located along the lateral surface of the tongue:

They are located on the sides at the back of the tongue, just in front of the palatoglossal arch of the fauces:

The foliate papillae appear as a series of red colored, leaf–like ridges of mucosa.

There are four or five vertical folds, and their size and shape is variable.

They are covered with epithelium, lack keratin and so are softer, and bear many taste buds:

Approximately 1000 taste buds.

Taste buds, the receptors of the gustatory sense, are scattered over the mucous membrane of their surface.

They are usually bilaterally symmetrical.

Sometimes they appear small and inconspicuous, and at other times they are prominent.

Because their location is a high risk site for oral cancer, and their tendency to occasionally swell, they may be mistaken as tumors or inflammatory disease.

Serous glands drain into the folds and clean the taste buds.

Lingual tonsils are found immediately behind the foliate papillae and, when hyperplastic, cause a prominence of the papillae.

The filiform papillae:

Are the most numerous of the lingual papillae.

They are fine, small, cone-shaped papillae covering most of the dorsum of the tongue.

They cover most of the front two-thirds of the tongue’s surface.

They appear as very small, conical or cylindrical surface projections, and are arranged in rows which lie parallel to the sulcus terminalis:

At the tip of the tongue, these rows become more transverse.

They are responsible for giving the tongue its texture and are responsible for the sensation of touch.

Unlike the other kinds of papillae, filiform papillae do not contain taste buds.

The fungiform papillae are mushroom shaped (generally red in color) and are dispersed most densely along the tip and lateral surfaces of the tongue:

Humans have approximately 200 to 300 fungiform papillae.

Each vallate, foliate, and fungiform papilla contains taste buds (250, 1000, and 1600 taste buds, respectively):

Each taste bud is innervated by several nerve fibers.

In humans, all taste buds can perceive the five different taste qualities:

Salt

Sweet

Bitter

Acid

Umami.

Each taste bud consists of taste receptor, basal cell , and edge cells.

When a taste molecule binds to a taste receptor, the receptor cell depolarizes:

Causing an influx of Ca++, which results in the release of an unknown neurotransmitter.

Following depolarization, the afferent neural pathway depends on the location of the taste bud that was stimulated:

In the anterior two thirds of the tongue, the chorda tympani branch of the facial nerve (cranial nerve VII) is stimulated.

The lingual-tonsillar branch of the glossopharyngeal nerve (cranial nerve IX) relays taste information from the posterior third of the tongue.

Taste fibers from the anterior two thirds of the tongue first travel with the lingual nerve and then are relayed to the chorda tympani nerve:

This nerve enters the temporal bone from the infratemporal fossa, where it joins the facial nerve and travels to the geniculate ganglion, where its pseudounipolar cell bodies are located.

From the geniculate ganglion the taste fibers travel in the nervus intermedius to the nucleus of the solitary tract located in the medulla oblongata.

Similarly, taste fibers from the posterior one third of the tongue travel with the lingual-tonsillar nerve to the inferior glossopharyngeal ganglion and then to the nucleus of the solitary tract located in the medulla oblongata.

Second-order neurons then project taste fibers to the parabrachial nucleus of the pons.

The central tegmental tract carries taste sensation from the pons to the thalamus.

The pathway ends in the frontal operculum and insular cortex.

Rodrigo Arrangoiz MS, MD, FACS a head and neck surgeon and is amember of Sociedad Quirúrgica S.C at the America British Cowdray Medical Center.

He is first author on some publications on oral cavity cancer:

Oral Tongue Cancer: Literature Review and Current Management

https://www.oatext.com/pdf/CRR-2-153.pdf