PRAXIS Tongue Anatomy & Physiology

The tongue serves as the primary organ of taste, participates in mastication (chewing), and aids in the process of swallowing (deglutition).

The tongue is involved in the formulation of speech sounds and is responsible for modifying the resonant characteristics of the vocal tract.

The two primary parts of the tongue are the blade and the root.

The blade is the visible part of the tongue.

The root of the tongue is below the blade and cannot be easily seen.

The blade of the tongue is divided into a tip, blade, front, and back.

The tip of the tongue will rest against the anterior teeth, the blade will rest against the alveolar ridge, the front will rest against the hard palate, and the back will rest against the velum (soft palate).

The longitudinal median sulcus is a furrow that runs lengthwise down the center of the tongue.

The longitudinal median sulcus intersects with the sulcus terminalis approximately two-thirds of the way down the length of the dorsum of the tongue from its tip.

The foramen cecum is a small pit located at the point where the longitudinal median sulcus intersects the sulcus terminalis.

The three slips of tissue are the median and lateral glossoepiglottic folds.

The small depressions are called valleculae.

The presence of papillae all over the surface of the tongue anterior to the sulcus terminalis gives it a rough appearance.

The four types of papillae are filiform, fungiform, simple, and vallate.

The papillae house the taste buds, which are the essential organs for the sense of taste.

The posterior one-third of the tongue is smoother in appearance compared to the anterior portion.

In the posterior one-third of the tongue, several mucous glands and lymphoid tissue known as the lingual tonsil are found.

The lingual frenulum is a vertically oriented slip of mucous membrane that extends from the inferior surface of the tongue to the floor of the oral cavity.

The lingual frenulum is located on the under-surface of the tongue, towards the anterior portion.

In some cases, a person may have a lingual frenulum (the membrane connecting the tongue to the floor of the mouth) that is too short, limiting the mobility of the tongue and affecting speech articulation.

The mucous membrane on the outer surface of the tongue is continuous with the covering of all other structures in the oral cavity. On the inferior surface of the tongue, the mucous membrane is relatively thin.

The mucous membrane in the region posterior to the sulcus terminalis is thick, loose, and freely movable.

The mucous membrane anterior to the sulcus terminalis is thin and closely adheres to the underlying muscle tissue.

The corium is a dense and somewhat felt-like connective tissue layer that can be thought of as the "skeleton" of the tongue. It provides structure and support to the tongue.

The tongue contains intrinsic muscles, which are entirely housed within the tongue, and extrinsic muscles, which originate outside the tongue but attach to it.

The tongue has relatively little skeletal support. Instead, it relies on its ability to change shape and position without reducing its volume.

The tongue's ability to change shape and position without diminishing its volume is referred to as a muscular hydrostat.

A muscular hydrostat is a structure, such as the tongue, composed of muscle tissue that can change its shape and position without changing its volume, similar to a fluid-filled structure.

Eight muscles, consisting of four intrinsic muscles and four extrinsic muscles, rely on the leverage provided by the corium of the tongue.

The muscles of the tongue, aided by the corium, play off each other to effect the various movements the tongue is capable of making.

The tongue's hydrostatic property allows it to preserve its volume. When one area of the tongue undergoes inward displacement, another area experiences outward displacement, maintaining the overall volume of the tongue.

The tongue, with its hydrostatic property, can perform a wide range of movements, including bulging, centralizing, curling, flattening, grooving, lateralizing, pointing, protruding, retracting, and moving from side to side, among others.

The four intrinsic muscles of the tongue are the inferior longitudinal, superior longitudinal, transverse, and vertical muscles.

The intrinsic muscles are considered paired due to the presence of a vertically oriented cavity within the tongue called the fibrous midline septum.

The fibers of the superior longitudinal muscles are primarily confined to the mid-region of the tongue, while the inferior longitudinal muscles can be found more laterally. Both muscles have fibers that course along the length of the tongue.

The transverse muscle has fibers arranged in the transverse plane, while the vertical muscle has fibers arranged in the vertical plane.

The intrinsic muscles of the tongue are primarily responsible for refined tongue movements and postures, such as elongating, flattening, narrowing, and shortening.

The two halves of the interior of the tongue receive independent neural innervation and blood supply.

In cases of unilateral paralysis, where one half of the tongue is affected, the unaffected half will still function properly.

A clinical sign of unilateral paralysis of the tongue is the deviation of the tongue to the paralyzed side when the patient is asked to stick out their tongue.

When one side of the tongue is paralyzed, the unaffected muscles on the other side will overbalance and mechanically turn the tongue toward the side of least resistance, which is the paralyzed side.

The four extrinsic muscles responsible for gross posturing of the tongue are the genioglossus, styloglossus, palatoglossus, and hyoglossus.

The palatoglossus muscle functions as both a muscle of the tongue and a muscle of the velum.

The extrinsic muscles of the tongue are named with the term "-glossus" (referring to the tongue) as the second half of their name. The first half of the name refers to the other structure to which the muscle is attached. For example, "genio-" refers to the chin or inside of the mandible, "stylo-" refers to the styloid process, and "palato-" and "hyo-" refer to the palatal and hyoid bone, respectively.

The anterior and posterior muscle fibers of the genioglossus contribute to the bulk of the tongue tissue. They play a role in shaping and positioning the tongue.

The genioglossus is the largest and strongest of all the tongue muscles.

The styloglossus muscle acts as an antagonist to the genioglossus, meaning its action is opposite to that of the genioglossus.

The palatoglossus muscle has three functions: (a) pulling the velum down, (b) elevating the posterior portion of the tongue, or (c) performing both actions. The specific action depends on whether the tongue or the velum is anchored or if both structures are free to move.

The hydrostatic interplay between the intrinsic and extrinsic muscles enables intricate posturing and maneuvering of the tongue.

The superior longitudinal muscle elevates the tongue tip, while the inferior longitudinal muscle performs the opposite function. The transverse muscle narrows the tongue.

Tongue protrusion is primarily accomplished by the contraction of the posterior fibers of the genioglossus muscle. However, for effective protrusion, the superior longitudinal, inferior longitudinal, and vertical muscles assist by pointing the tongue tip and narrowing the tongue body.

Retraction of the tongue is primarily achieved by the anterior fibers of the genioglossus muscle. The superior and inferior longitudinal muscles help shorten the tongue during retraction, while the hyoglossus muscle depresses the sides of the tongue.

To retract the tongue fully into the pharynx, the styloglossus muscle would be contracted.

Contraction of the superior and inferior longitudinal muscles allows for movement of the tongue from side to side. Simultaneous contraction of these muscles on the right will turn the tongue tip to the right, while contraction on the left will turn the tongue tip to the left.

The genioglossus muscle, located in the medial portion of the tongue, and the hyoglossus muscle, which acts on the lateral edges of the tongue, are responsible for the depression of the body of the tongue.

Contraction of the palatoglossus muscle is necessary to elevate the posterior part of the tongue.

The transverse muscle assists the palatoglossus by bunching up the back of the tongue, contributing to its elevation.

To create a longitudinal groove along the middle of the tongue, you would need to contract the geniohyoid and vertical muscles.

Contracting only a part of the geniohyoid muscle would create a shallow groove on the tongue.

Contraction of the entire geniohyoid muscle would create a deep groove on the tongue.

Relaxation of the lateral edges of the tongue is achieved by contracting the posterior fibers of the genioglossus muscle, as well as the superior longitudinal and transverse muscles.

These intricate muscle actions highlight the tongue's capacity for refined movement and posturing, requiring coordination between the intrinsic and extrinsic tongue muscles.

The temporomandibular joint (TMJ) is the joint formed by the articulation between the mandible and the temporal bone of the skull.

The mandible is the lower jawbone and is illustrated in Figure 10-4. It is one of the bones of the skull and has been described in detail in previous sections.

The temporomandibular joint (TMJ) is formed by the articulation of the condylar process of the mandible with the mandibular fossa of the temporal bone.

The mandibular condyle is separated from the mandibular fossa by the articular meniscus.

The articulating surfaces of the condyle and mandibular fossa are covered by a fibrocartilage. This is different from typical joint architecture where hyaline cartilage is usually present.

The TMJ is classified as a ginglymoarthrodial joint, which allows for hinge-like movement with limited gliding.

The condyle is held in place by the temporomandibular (or lateral), sphenomandibular, and stylomandibular ligaments.

The TMJ allows for movement in three dimensions: vertically (opening and closing), anteroposteriorly (protruding and retracting), and transversely (from side to side). These movements occur during activities such as chewing and speaking.

TMJ dysfunction syndrome can severely restrict one's ability to utilize the mandible for chewing or speech purposes.

Symptoms of TMJ dysfunction syndrome may include facial pain and spasm, reduced mandibular movement, and noises in the joint.

Treatment for TMJ dysfunction may include surgery or the use of an orthodontic prosthesis to reduce teeth grinding.

The primary movements of the mandible are elevation (closing the mouth) and depression (opening the mouth).

The mandibular elevator muscles include the masseter, medial pterygoid, and temporalis.

The masseter is the most powerful muscle of mastication.

The temporalis muscle is quicker in its action and is responsible for snapping movements.

The medial pterygoid and masseter muscles are referred to as the mandibular sling muscles because they suspend the mandible in place along with the mandibular ligaments.

The mandibular depressor muscles include the digastricus, mylohyoid, geniohyoid, and lateral pterygoid.