Musculature of the Tongue
The musculature of the tongue is divided into two halves by the septum of the tongue (septum linguae), a sheet of connective tissue at the mid-line.The position of this septum can be seen from the superior surface of the tongue as the median sulcus (sulcus medianus linguae).Two groups of tongue muscles can be identified by their course, namely those that originate from parts of the skeleton and end in the tongue and those that have their origin and ending in the tongue itself. The first group are known as extrinsic (originating outside the tongue), while the muscles entirely within the tongue are referred to as intrinsic.
Extrinsic muscles (which may also be known as skeletal muscles of the tongue) originate from the mandible, the hyoid bone, and the styloid process (Fig 6-51). The fiber bundles of these muscles run into the tongue, are arranged in the three planes in the body of the tongue, and merge into the intrinsic musculature. The internal muscles are mainly responsible for changing the shape of the tongue (deformability) as they interact antagonistically and force the antagonists to relax.
Extrinsic muscles of the tongue
- The genioglossus muscle (musculus genioglos-sus) originates as a paired muscle at the mental spine and fans out to both the apex and the base of the tongue.This muscle draws the base of the tongue forward with its lower fibers, while the other fibers draw the tongue to the floor of the mouth.
- The hyoglossus muscle (musculus hyoglossus) originates as a thin plate of muscle from the greater horn of the hyoid bone and from parts of the adjacent body of the hyoid. Its parallel fibers lie along the outer side of the genioglossus muscle, and it is able to draw the tongue downward and backward with the hyoid bone fixed.
- The styloglossus muscle (musculus styloglossus) radiates from the styloid process of the temporal bone over the lateral margin of the tongue to the apex. The muscle is able to draw back the apex and even the whole of the tongue. Because this muscle is also paired, one-sided activity can produce side-to-side movement of the tongue.
Intrinsic muscles of the tongue
Transverse muscle (musculus transversus linguae) originates from both sides of the septum and extends to the mucosa of the margin and dorsum of the tongue. The posterior fibers are also joined to the muscles of the gullet.
Vertical muscle (musculus verticalis linguae) arises with its fibers perpendicular to the transverse muscles, while the fibers of the inferior and superior longitudinal muscles (M longitudinalis inferior and superior) run from front to back and thus perpendicular to the genioglossus and hyo-glossus muscles.
When the longitudinal muscles and transverse muscles of the tongue are contracted, the vertical muscles are relaxed and the tongue becomes short and high. If the longitudinal muscles and the vertical muscles are stretched as the transverse muscles relax, the tongue becomes short and low.
The interaction of all the muscles produces the complex tongue movements during speech. The extremely active deformability of the tongue also means that all areas of the oral cavity and vestibule can be reached, which ensures self-cleaning of the dentition. Even in resting phases, with the mouth closed, the tongue exerts gentle, constant pressure on the rows of teeth, which have to be kept in equilibrium by pressure from the lips and cheeks. This equilibrium of muscle tone helps to create and maintain the correct jaw shape.
During chewing, the tongue turns the food over on the rough pressure and fricative field of the palate while mixing saliva in with the food. The food particles dissolved in saliva are pressed into the taste papillae, which is how the taste stimuli are sensed. In addition, the tongue continually pushes the food between the teeth on the working side and checks the food for inedible fragments (eg, fishbones, bone splinters).
The swallowing process involves bringing the mandible into a stable position by habitual intercuspation. The hyoid and floor of the mouth are raised so that the tongue is able to push the food over the palate into the gullet. This is done by the movable soft palate falling downward, allowing the food to be guided backward toward the esophagus.