Dominic Stone
The tongue is a muscular organ situated in the oral cavity, with its main functions including taste, swallowing, and speech. The muscles of the tongue can be divided into two groups: the intrinsic muscles, which comprise the core of the tongue and are placed within it, and the extrinsic muscles, which are outside the tongue but are functionally associated with it and help it perform its function. The four extrinsic muscles are the genioglossus, hyoglossus, styloglossus, and palatoglossus muscles. All the extrinsic muscles of the tongue are innervated by the hypoglossal nerve (CN XII), except for the palatoglossus muscle, which is supplied by the vagus nerve (CN X).
| Characteristics | Values |
|---|---|
| Innervating Nerve | Hypoglossal nerve (CN XII) |
| Innervating Nerve (exception) | Palatoglossus muscle is innervated by the vagus nerve (CN X) |
| Function | Alter the position of the tongue |
| Function (exception) | Palatoglossus elevates the posterior portion of the tongue |
| Number of muscles | 4 pairs of extrinsic muscles |
| Muscle Names | Genioglossus, Hyoglossus, Styloglossus, Palatoglossus |
| Muscle Origin | Genioglossus arises from mandibular symphysis; Hyoglossus arises from the hyoid; Styloglossus originates at styloid process and temporal bone; Palatoglossus arises from the palatine aponeurosis |
| Muscle Insertion | Genioglossus inserts into the body of the hyoid/full length of tongue; Hyoglossus inserts into the side of the tongue; Styloglossus inserts into the side of the tongue; Palatoglossus inserts across the tongue |
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What You'll Learn
Genioglossus muscle
The genioglossus is one of four pairs of extrinsic tongue muscles, along with the hyoglossus, styloglossus, and palatoglossus. These muscles are responsible for altering the position of the tongue. The genioglossus muscle is innervated by the hypoglossal nerve (CN XII), as are all tongue muscles except for the palatoglossus, which is supplied by the vagus nerve (CN X).
The genioglossus is a thick, fan-shaped muscle that constitutes the bulk of the tongue. It originates from the mandibular symphysis and inserts into the body of the hyoid bone and the full length of the tongue. This muscle is responsible for protruding, depressing, and drawing the tip of the tongue back and down. Bilateral contraction of the genioglossus depresses and protrudes the tongue, while unilateral contraction deviates the tongue to the contralateral side. The left and right genioglossus muscles protrude the tongue anteriorly out of the mouth and deviate it towards the opposite side. When acting together, these muscles protrude the tongue directly forward and depress the centre of the tongue at its back.
The genioglossus muscle plays a crucial role in stabilising and enlarging the upper portion of the respiratory tract, specifically the section most vulnerable to collapse. This muscle's ability to influence the size and position of the airway is particularly important in preventing obstructive sleep apnea. Additionally, the genioglossus muscle is electrically involved in generating maximal sniff nasal inspiratory and expiratory pressures.
The canine genioglossus muscle has been classified into horizontal and oblique compartments. Histologically, the anterior section of the genioglossus muscle contains a significant amount of type 2 fibres, while the posterior portion does not exhibit a large presence of these fibres. The specific fibres present in each portion of the muscle determine its function. The genioglossus muscle is susceptible to the negative effects of pathologies, such as constant hypoxia during sleep, which can alter muscle metabolism and lead to functional muscle weakness.
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Hyoglossus muscle
The hyoglossus muscle is one of the four extrinsic muscles of the tongue. It is a thin, quadrilateral skeletal muscle that originates from the hyoid bone and inserts into the side of the tongue. The hyoid bone is located in the floor of the oral cavity. The hyoglossus muscle is innervated by the hypoglossal nerve (CN XII), also known as the twelfth cranial nerve.
The hypoglossal nerve originates from the posterior portion of the medulla oblongata and exits the skull through the hypoglossal canal in the posterior fossa. It then descends between the sternocleidomastoid muscle and the external carotid artery before turning horizontally towards the greater cornu of the hyoid bone. The hypoglossal nerve innervates all the intrinsic muscles of the tongue, as well as the extrinsic muscles of the tongue, except for the palatoglossus muscle.
The hyoglossus muscle depresses and retracts the tongue, and it also makes the dorsum more convex. The fibres of the hyoglossus muscle pass almost vertically upward from the hyoid bone to enter the side of the tongue, inserting between the styloglossus and the inferior longitudinal muscle of the tongue. The glossopharyngeal nerve (CN IX), the stylohyoid ligament, and the lingual artery and lingual vein are all medial or deep to the hyoglossus muscle. The lingual vein passes medial to the hyoglossus, while the lingual artery passes deep to it.
The hyoglossus muscle receives its blood supply mainly from the lingual artery, which is the third branch of the external carotid artery. The lingual artery gives rise to four main branches, including the sublingual artery, which supplies the hyoglossus muscle. Additionally, the hyoglossus muscle receives blood supply from the facial artery, specifically the submental branch. The lymphatic drainage of the hyoglossus muscle is through the deep cervical group of lymph nodes.
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Styloglossus muscle
The styloglossus muscle is a bilaterally paired extrinsic muscle of the tongue. It is the smallest and shortest of the three styloid muscles. The muscle originates at the styloid process of the temporal bone and inserts into the side of the tongue. The styloglossus muscle elevates and retracts the tongue, drawing up the sides of the tongue to create a trough for swallowing.
The styloglossus muscle is innervated by the hypoglossal nerve (CN XII), along with the other extrinsic muscles of the tongue, except for the palatoglossus muscle, which is innervated by the vagus nerve (CN X). The hypoglossal nerve allows the styloglossus muscle to carry out its functions of altering tongue position, affecting the tongue's shape and size, and guiding speech, eating, and swallowing.
The styloglossus muscle coordinates with the other extrinsic muscles of the tongue, including the hyoglossus muscle, the genioglossus muscle, and the palatoglossus muscle, to produce the various movements of the tongue. The styloglossus muscle acts bilaterally, with both muscles contracting simultaneously to aid in retracting the tongue. The external and internal fibres of the styloglossus muscle also fuse with parts of the superior pharyngeal constrictor muscle and the palatoglossus muscle, respectively.
The bundles of the styloglossus muscle run bilaterally and meet at the midline of the tongue's floor, forming an arch. The posterior bundles split into approximately 10 smaller bundles of fibres that enter the tongue. These smaller bundles course between the inferior longitudinal intrinsic muscles of the tongue and the genioglossus muscle and ultimately insert into the lingual septum.
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Palatoglossus muscle
The palatoglossus muscle is an extrinsic muscle of the tongue. It is also associated with the soft palate and is therefore innervated by the vagus nerve (CN X). The muscle has its origin from the inferior surface of the palatine aponeurosis of the soft palate and gets inserted into the posterolateral surface of the tongue. The palatoglossus muscle elevates the posterior portion of the tongue. It also draws the soft palate inferiorly, thereby narrowing the diameter of the oropharyngeal isthmus. This action plays a significant role during swallowing by propelling the food bolus towards the oesophagus and preventing retrograde food flow.
The palatoglossus muscle is the only tongue muscle derived from the fourth branchial arch. All the other muscles of the tongue are derived from the occipital myotomes. This is why all the other tongue muscles receive innervation from the twelfth cranial nerve (hypoglossal nerve) except the palatoglossus muscle. The palatoglossus muscle is innervated by the tenth cranial nerve (vagus nerve). The vagus nerve gives off branches that form the pharyngeal plexus, and it is these branches that innervate the palatoglossus muscle.
The palatoglossus muscle is also referred to as the musculus palatoglossus. It is among the four extrinsic muscles of the tongue and the paired muscles of the soft palate. The right and left palatoglossus muscles create ridges in the lateral pharyngeal wall, referred to as the palatoglossal arches (anterior faucial pillars). These pillars separate the oral cavity and the oropharynx. The palatoglossus muscle functions as an antagonist to the levator veli palatini muscle.
The palatoglossus muscle is involved in speech. During the pronunciation of vowels such as “u,” constriction of a larger area of the oropharyngeal isthmus is necessary. This is significantly affected by the activity of the palatoglossus muscle. The muscle also has a role in preventing the spill of saliva from the vestibule into the oropharynx by maintaining the palatoglossal arch.
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Innervation and embryology
The tongue is a muscular organ situated in the oral cavity, with important roles in taste, swallowing, and speech. The tongue is made up of both intrinsic and extrinsic muscles. The former are entirely within the tongue, with no external attachments, and they alter the shape of the tongue. The latter are outside the tongue but are functionally associated with it, helping it perform its function by altering its position.
The four extrinsic muscles are the styloglossus, hyoglossus, genioglossus, and palatoglossus muscles. The first three muscles are innervated by the hypoglossal nerve (CN XII), while the fourth is innervated by the vagus nerve (CN X). The hypoglossal nerve travels superficially to the hyoglossus muscle. Damage to the hypoglossal nerve results in ipsilateral deviation of the tongue, i.e. damage to the left hypoglossal nerve will cause deviation of the tongue to the left side.
The embryological development of the tongue begins in the fourth week of life from the median tongue bud or tuberculum impar (arising from the 1st pharyngeal arch). In the fifth week, paired lateral lingual swellings begin to grow and cover the median tongue bud, fusing to form the anterior two-thirds of the tongue. The line of fusion is demarcated by the median sulcus. Around the lingual swellings, the cells degenerate to form a sulcus, freeing the tongue from the floor of the mouth except in the midline where an attachment remains (midline lingual frenulum).
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Frequently asked questions
The extrinsic tongue muscles are a group of four paired muscles that are outside the tongue but are functionally associated with it and help it perform its function. They are the genioglossus, hyoglossus, styloglossus, and palatoglossus muscles.
The extrinsic tongue muscles alter the position of the tongue. They produce movements of the tongue that the intrinsic muscles cannot, such as protrusion, retraction/retrusion, depression, and elevation of the tongue.
All the extrinsic tongue muscles are innervated by the hypoglossal nerve (CN XII), except for the palatoglossus muscle, which is innervated by the vagus nerve (CN X).
Damage to the hypoglossal nerve can lead to weakness and atrophy of the ipsilateral tongue, causing it to deviate towards the side of the lesion or injury.
