THE 4 SUPRAHYOID MUSCLES AND THEIR FUNCTIONS - ANATOMY AND PHYSIOLOGY - 2024

The suprahyoid muscles make up a group formed by four muscles located in the anterior region of the neck above the hyoid bone, which, inserted in it, join it to the skull. They are part of a subdivision of the anterior muscle group of the neck, divided topographically by the presence of the hyoid bone to facilitate their study.

Together, this group of muscles participates in the chewing, swallowing and phonetic processes. In addition, together with the infrahyoid muscles, they contribute to the fixation of the hyoid bone, which does not articulate with any other bone.

Suprahyoid muscles

They are located in three planes: a deep plane made up of the geniohyoid muscle, a median plane made up of the mylohyoid muscle, and a superficial plane made up of the digastric and stylohyoid muscles.

Some literatures include the hyoglossus muscle as part of the suprahyoid muscles; however, in most of the bibliographies it is treated as an extrinsic muscle of the tongue, since it does not insert superiorly in any bone structure unlike the rest of the suprahyoid muscles.

Geniohyoid muscle (deep muscle plane)

This muscle, being the deepest of the anterior muscle group and upper subgroup of the neck muscles, must be observed from the oral cavity, where it will be located below the genioglossus muscle.

The geniohyoid muscle is a small, short muscle that is cylindrical in shape. It is located above the digastric muscle and the mylohyoid muscle.

It originates in the lower chin spine of the mandible, also known as the inferior geni process, from where it begins a downward and backward journey, culminating in inserting itself in the middle part of the anterior aspect of the hyoid bone.

It is related to the contralateral geniohyoid medially, below it is related to the superior face of the mylohyoid (also known as the muscle of the mouth) and above it is related to the genioglossus muscle, which separates it from the tongue.

Mylohyoid muscle (median muscle plane)

It is a square-shaped muscle that forms the muscular floor of the mouth. It originates from the internal oblique line of the mandible, from where it runs downward to insert into the hyoid bone and medially in the medial suprahyoid raphe; there he meets his contralateral counterpart.

It is related below and superficially with both bellies of the digastric muscles and, as it is the muscular floor of the mouth, its upper face is directly related to the oral cavity and the geniohyoid muscles.

The mylohyoid muscle participates in the formation of the Pirogoff triangle, made up of the posterior border of the mylohyoid muscle, the intermediate tendon of the digastric muscle, and the hypoglossal nerve. This triangle contains the lingual artery.

Digastric muscle (superficial muscle plane)

It receives this name because it has the characteristic of being one of the few muscles in the human body that has two muscular bellies, one anterior and one posterior, joined by an intermediate tendon.

The posterior belly originates from the mastoid process, from where it runs forward and downward to be followed by an intermediate tendon that crosses the stylohyoid muscle.

Said intermediate tendon is fixed to the hyoid bone by a refractive pulley of fibrous tissue, formed by some musculotendinous fibers coming from the posterior belly of the muscle. At the same time, the intermediate tendon is attached to its counterpart by a set of interlocking fibers called the interdigastric lamina.

It continues with the anterior belly that is directed upwards, forwards and towards the center, to insert into the digastric fossa of the mandible.

It is related through its posterior belly to the sternocleidomastoid muscle and the splenium of the head, which also insert into the mastoid process. Likewise, it is related to the internal jugular vein and the internal carotid and, a little later, to the parotid gland.

The posterior belly of the digastric muscle participates in the formation of the triangle of Beclard, made up of the posterior border of the hyoglossus muscle, the greater horn of the hyoid bone, and the posterior border of the posterior abdomen of the digastric muscle. This triangle contains the hypoglossal nerve and the lingual artery.

The anterior belly is related to its contralateral counterpart, the submandibular gland and the superficial aspect of the mylohyoid muscle.

Stylohyoid muscle (superficial muscle plane)

It is a thin, elongated muscle that originates from the styloid process of the temporal bone and runs downward and forward, ending in a tendon that bifurcates to allow passage of the intermediate tendon of the digastric muscle.

It inserts on the superior border, anterior face, of the body of the hyoid bone and is related to the posterior belly of the digastric muscle on its way. Medially it is related to the styloglossus muscle and the external carotid artery.

Features

The suprahyoid muscles as a whole fulfill the functions of chewing, swallowing and phonetics.

Due to its insertion in the hyoid bone and in different cranial bone structures, its primary movements and those on which it is based for the performance of its functions are the descent of the jaw and the elevation of the hyoid bone.

Some lateral fibers of the mylohyoid muscle also contribute to the lateral movements of the jaw during the chewing process.

The descent of the jaw, which corresponds to the opening of the oral cavity, allows food to enter the cavity to start the digestive process; Likewise, thanks to the descending and lateral movements, the chewing process is allowed, to allow the destruction of the bolus for subsequent swallowing.

In the process of swallowing, the hyoid is raised to assist in the descent of the bolus, pushing it as it returns to its initial position.

The anterior neck muscles use the hyoid bone as an anchor point to contract, thus facilitating the descent of the bolus through the throat and into the esophagus.

References

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2. Neck issues. Anatomy of the submaxillary, sublingual, and minor salivary glands. Recovered from: otorrinoweb.com
3. Latarjet Ruiz Liard. Human Anatomy 4th Edition. Editorial Panamericana. Volume 1. Neck muscles. P. 132-134.
4. Franks H. Netter, MD Atlas of Human Anatomy. 3rd Edition. Editorial Elsevier. Plates 24-25, 27-29, 410.
5. Torsten Liem, Cranial Osteopathy (Second Edition). In: Chapter 12 - The orofacial structures, pterygopalatine ganglion and pharynx. Elsevier, 2004. Pages 437-484