Tongue Muscles: The Power Behind Speech And Taste

The human tongue is a muscular structure that plays a crucial role in various functions, including speech, eating, and swallowing. The tongue's complex movements are made possible by the coordination of two main groups of muscles: the intrinsic and extrinsic muscles. The intrinsic muscles, comprising four pairs, originate and insert within the tongue and are responsible for altering its shape. On the other hand, the four extrinsic muscles originate from bone and extend to the tongue, allowing for changes in its position. These muscles work together to enable the tongue's flexibility and adaptability during various activities, such as speaking, tasting, and swallowing.

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Intrinsic and extrinsic muscles

The tongue is composed of eight muscles, divided into two main groups: the intrinsic and extrinsic muscles. The intrinsic muscles are responsible for altering the shape of the tongue, while the extrinsic muscles change the tongue's position.

Intrinsic Muscles

The four intrinsic muscles are located within the tongue and are not attached to any bone. They are named based on the direction in which they travel: superior longitudinal, inferior longitudinal, transverse, and vertical muscles. These muscles affect the tongue's shape and size, enabling functions such as tongue rolling, speech, eating, and swallowing. For example, the superior longitudinal muscle shortens and curls the tongue upward, while the inferior longitudinal muscle shortens and curls it downward. The vertical muscle flattens the tongue, and the transverse muscle lengthens and narrows it.

Extrinsic Muscles

The four extrinsic muscles originate from structures outside the tongue, such as bones, and insert into it. They are responsible for altering the tongue's position, allowing for movements like protrusion, retraction, and side-to-side motion. The genioglossus muscle, also known as the tongue's "safety muscle," enables the tongue to protrude or stick out. The hyoglossus muscle, along with the chondroglossus, contributes to tongue retraction and depression. The styloglossus muscle elevates and retracts the tongue, and the palatoglossus muscle elevates the posterior portion of the tongue during swallowing.

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The genioglossus muscle

The genioglossus is a large, thick extrinsic muscle that contributes significantly to the shape of the tongue. It arises from the mandibular symphysis and inserts onto the body of the hyoid bone and the entire length of the tongue. The genioglossus is innervated by the hypoglossal nerve, as are all muscles of the tongue except for the palatoglossus. The left and right genioglossus muscles work together to protrude the tongue (anteriorly, out of the mouth) and deviate it towards the opposite side. When acting in tandem, the muscles protrude the tongue directly forward and depress the centre of the tongue at its back.

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Tongue shape and size alteration

The tongue is a muscular organ that consists of two groups of muscles: the extrinsic and intrinsic muscles. The intrinsic muscles are responsible for changing the shape of the tongue, while the extrinsic muscles are responsible for moving the tongue in different directions.

The Intrinsic Muscles

The intrinsic muscles are not attached to any bone. There are four paired intrinsic muscles: the superior longitudinal, inferior longitudinal, transverse, and vertical muscles. These muscles alter the shape of the tongue by lengthening and shortening it, curling and uncurling its apex and edges, and flattening and rounding its surface. For example, the superior longitudinal muscles shorten the tongue and dorsiflex its tip, while the inferior longitudinal muscles provide ventroflexion and allow for the retroflexion of the tongue's base. The transverse muscles help to narrow the tongue, and the vertical muscles flatten it. These muscles play a crucial role in speech, eating, and swallowing.

The Extrinsic Muscles

The extrinsic muscles originate from structures outside the tongue and insert into it. They are anchored to bone. The four extrinsic muscles are the genioglossus, hyoglossus, styloglossus, and palatoglossus. The genioglossus protrudes the tongue and is known as the "'safety muscle' as it is the only muscle that propels the tongue forward. The hyoglossus depresses and retracts the tongue. The styloglossus retracts and elevates the tongue, creating a trough for swallowing. The palatoglossus elevates the posterior portion of the tongue, facilitating swallowing and closing off the oral cavity from the oropharynx.

Tongue movements

The tongue is a muscular structure that plays a crucial role in various functions, including speech, eating, and swallowing. Tongue movements are made possible by the complex coordination of multiple muscles, which can be broadly classified into two groups: intrinsic and extrinsic muscles.

Intrinsic Muscles

The intrinsic muscles of the tongue originate and insert within the tongue itself, with no attachments to bone. There are four paired intrinsic muscles: the superior longitudinal, inferior longitudinal, transverse, and vertical muscles. These muscles are responsible for altering the shape of the tongue by lengthening, shortening, curling, and flattening it. For example, the superior longitudinal muscle shortens and curls the tongue upward, while the inferior longitudinal muscle works in conjunction with the styloglossus muscle to shorten and curl the tongue downward. The vertical muscle, located in the middle of the tongue, flattens it, while the transverse muscle divides the tongue, attaching to the mucous membranes along its sides and lengthening and narrowing it. These shape changes are essential for tongue rolling and facilitating speech, swallowing, and eating.

Extrinsic Muscles

In contrast, the extrinsic muscles of the tongue originate from structures outside the tongue and insert onto it. There are four extrinsic muscles: the genioglossus, hyoglossus, styloglossus, and palatoglossus. These muscles alter the tongue's position, allowing for protrusion, retraction, and side-to-side movements. The genioglossus muscle, also known as the tongue's "safety muscle," arises from the mandible and is responsible for protruding the tongue forward. The hyoglossus muscle, located in the floor of the oral cavity, retracts and depresses the tongue. The styloglossus muscle, a thin, paired muscle, retracts and elevates the tongue by drawing its sides up. Lastly, the palatoglossus muscle depresses the soft palate, moves the palatoglossal fold towards the midline, and elevates the back of the tongue during swallowing.

Innervation and Blood Supply

The intrinsic and extrinsic muscles of the tongue are innervated primarily by the hypoglossal nerve (CN XII), with the exception of the palatoglossus muscle, which is innervated by the vagus nerve (CN X). The tongue receives its blood supply mainly from the lingual artery, a branch of the external carotid artery. The lingual artery passes deep to the hyoglossus muscle and supplies the anterior tongue, while its branch, the sublingual artery, supplies the floor of the mouth and provides blood to the genioglossus muscle. The deep lingual artery, a termination of the lingual artery, supplies the apex of the tongue.

The role of the hypoglossal nerve

The hypoglossal nerve is the twelfth cranial nerve, also known as CN XII. It is a somatic efferent nerve that innervates the tongue musculature. The nerve originates from the medulla and travels caudally and dorsally to the tongue.

The hypoglossal nerve provides motor innervation to all the intrinsic and extrinsic muscles of the tongue, except for the palatoglossus muscle, which is supplied by the vagus nerve. The muscular branch of the hypoglossal nerve controls most tongue actions, including protruding, retracting, depressing, and changing the tongue's shape.

Damage to the hypoglossal nerve can cause paralysis, fasciculations, and atrophy of the tongue muscles. When the nerve is injured, the tongue may deviate to one side when protruded, due to the genioglossus muscle receiving signals from only one side. The nerve can be damaged at the hypoglossal nucleus, above it (supranuclear), or at the motor axons (infranuclear). Supranuclear lesions can cause the tongue to protrude away from the nerve, resulting in slow and spastic tongue movements.

The hypoglossal nerve is also involved in controlling tongue movements required for speech and swallowing. It interacts with the reticular formation, aiding in the control of reflexive and automatic motions, as well as speech and articulation. In addition, mild stimulation of the hypoglossal nerve can be used to treat obstructive sleep apnea (OSA) by pulling the tongue forward and improving airflow.

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