Human Anatomy - Kotsan I. Y. 2009

Splanchnology
Digestive System
Tongue

The human Tongue (lingua) is composed of Striated Muscle tissue covered by a mucous membrane. It performs A wide variety of Functions, taking part in chewing, swallowing, and speech articulation. In addition, it serves as an ORGAN OF TASTE and Touch. In infants, the tongue plays an essential role in suckling milk.

Two PARTS OF THE tongue are distinguished: the anterior, free portion, or body of the tongue (corpus linguae), and the posterior part, the ROOT of the tongue (radix linguae). The body of the tongue terminates anteriorly in a rounded apex, or tip of the tongue (apex linguae). Posteriorly, the body is separated from the root by the terminal sulcus (sulcus terminalis). The terminal sulcus consists of two halves that converge along the median plane of the tongue at an obtuse angle pointing forward. The upper surface, or dorsum of the tongue (dorsum linguae), is free, convex, and considerably longer than the lower surface. The Inferior surface of the tongue (facies inferior linguae) is free only in its anterior part. The boundary between the upper and lower surfaces on each side is the margin of the tongue (margo linguae).

The mucous membrane of the inferior surface of the tongue is thin, delicate, and translucent, forming folds due to its mobile attachment to the underlying Muscles. Along the median line on the underside runs a fold of the mucous membrane known as the frenulum of the tongue (frenulum linguae), which is clearly visible when the tip of the tongue is raised. On either side of the frenulum, on the floor of the Oral Cavity, lies a small, rounded elevation called the sublingual caruncle (caruncula sublingualis), which serves as the opening for the ducts of the submandibular and sublingual Salivary Glands. Extending laterally and posteriorly from the sublingual caruncle is the sublingual fold (plica sublingualis), upon which the minor sublingual ducts open. Parallel to the margins of the tongue and converging slightly forward are the fimbriated folds (plicae fimbriatae).

On the upper surface of the tongue, running longitudinally, is the median sulcus of the tongue (sulcus medianus linguae), which divides the body into right and left halves. The mucous membrane of the dorsum of the tongue is thick and opaque throughout its length, firmly adherent to the muscles, and covered anteriorly to the terminal sulcus with small projections known as lingual papillae (papillae linguales). The human lingual papillae vary in size and shape and contain Blood Vessels and nerve endings that transmit gustatory and general sensation. Each papilla represents an outgrown projection of Connective Tissue covered, like the rest of the mucous membrane, by stratified squamous non-keratinized epithelium. Based on their shape, several types of papillae are distinguished.

Filiform and conical papillae (papillae filiformes et papillae conicae) are the most numerous and smallest of all the papillae, distributed across the entire surface of the dorsum of the tongue anterior to the terminal sulcus. They contain specialized nerve endings that perceive pain and touch. Furthermore, filiform and conical papillae perform a mechanical function by preventing food from sliding off the dorsum of the tongue. These papillae contain no taste buds for perceiving gustatory sensations.

Fungiform papillae (papillae fungiformes) are also scattered across the entire surface of the dorsum of the tongue, though the majority are localized mainly on the apex and margins. Fungiform papillae are significantly fewer in number (ranging from 150 to 200) than the filiform ones, but they are larger and easily visible to the naked eye. In appearance, fungiform papillae resemble mushrooms, with a stem (base) attached to the dorsum of the tongue and a cap (an expanded, rounded apex) directed into the oral cavity. Fungiform papillae contain taste buds that detect gustatory stimuli.

Vallate (circumvallate) papillae (papillae vallatae) are the largest of all. Ranging in number from 8 to 12, they are situated anterior to the terminal sulcus and the foramen caecum in a line resembling the Roman numeral V (five). The diameter of a single such papilla is 2–3 mm. In the center of the papilla is an elevation containing taste buds, surrounded by a circular wall separated from the central part by a deep, narrow circular furrow.

Foliate papillae (papillae foliatae) are located on the lateral margins of the tongue. They consist of 5–8 parallel, flat, vertical plates (leaves) separated by furrows and arranged one behind the other. Foliate papillae vary in size (ranging from 2–5 mm in length) and are better developed in the posterior part of the tongue margins. These papillae contain numerous taste buds which, similar to those in fungiform and vallate papillae, act as receptors for the gustatory analyzer (perceiving taste sensations).

The mucous membrane of the root of the tongue lacks papillae; its surface is uneven due to the subepithelial accumulation of numerous Cytology/cytology/61.html">Lymphatic follicles of varying sizes. Collectively, this complex of follicles in the mucous membrane of the root of the tongue is termed the lingual tonsil (tonsilla lingualis).

The Muscles of the tongue (mm. linguae) are paired and composed of striated muscle tissue.

The longitudinal fibrous septum of the tongue (septum linguae) divides the organ into two symmetrical halves, separating the muscles of one side from the other. This septum is situated vertically in the median plane. Its upper margin, without reaching the mucous membrane of the dorsum, corresponds to the median sulcus of the tongue.

The muscles of the tongue are divided into two groups:

1) skeletal muscles of the tongue, which originate from the bones, soft palate, and Pharynx, and insert into the substance of the tongue. They provide mobility within the Oral Cavity and maintain muscle tone;

2) intrinsic muscles of the tongue, which make up its body. They originate and insert entirely within the tongue and alter its shape upon contraction. The intrinsic muscles consist of fibers running in three directions—longitudinal, transverse, and vertical—which interlace with one another and with the skeletal muscles.

All muscles of the tongue are innervated by fibers of the XII pair of Cranial Nerves.

Skeletal muscles of the tongue.

1. Styloglossus muscle (m. styloglossus) originates from the styloid process of the Temporal bone and fans out into the substance of the lateral and inferior parts of the tongue. Function: pulls the tongue backward and upward.

2. Hyoglossus muscle (m. hyoglossus) originates from the body and greater cornu of the Hyoid bone, extends forward and upward, and inserts into the substance of the tongue near its margins. Function: pulls the root of the tongue backward and downward.

3. Genioglossus muscle (m. genioglossus) originates from the mental spine of the Mandible, fans out among the other lingual muscles, and inserts into the substance of the tongue along its entire length. Function: pulls the tongue forward and downward.

Intrinsic muscles of the tongue.

1. Superior longitudinal muscle (m. longitudinalis superior) is located in the upper Regions of the tongue, directly beneath the mucous membrane. It originates in the substance of the root of the tongue, with some fascicles arising from the anterior surface of the epiglottis and the lesser cornua of the hyoid bone. It inserts into the aponeurosis of the tongue's apex. Function: shortens the tongue, elevates the apex, and, upon unilateral contraction, deviates it to the side.

2. Inferior longitudinal muscle (m. longitudinalis inferior) is situated in the lower regions of the tongue. It originates in the region of the tongue root and inserts into its apex. Function: shortens the tongue, depresses the apex, and, upon unilateral contraction, deviates it to the side.

3. Transverse muscle of the tongue (m. transversus linguae) consists of fiber fascicles running transversely from the lingual septum in both directions toward the margins. Function: narrows and elongates the tongue.

4. Vertical muscle of the tongue (m. verticalis linguae) consists of short muscle fascicles arranged in the Free part of the tongue between the mucous membrane of the dorsum and the inferior surface. Function: contraction of this muscle flattens and broadens the tongue.