Hyoid bone

Generality

The hyoid bone - or simply hyoid - is an unequal and median bone, in the shape of a horseshoe, which is located in the neck, exactly between the chin and the thyroid cartilage of the larynx.

In the hyoid bone it is possible to recognize a central portion, called body, and two extensions on each side, called horns.

Numerous muscles are inserted on the upper surface and on the lower body surface and horns of the hyoid bone.

The muscles that have relations with the hyoid bone play a fundamental role in the movements of the tongue, pharynx and larynx; therefore, the hyoid bone contributes to the mechanisms of chewing, swallowing, phonation and breathing.

What is the hyoid bone?

The hyoid bone, or simpler hyoid, it is the unequal and median bone, in the shape of a horseshoe, which resides in the neck, at the base of the tongue, exactly between the chin and the thyroid cartilage of the larynx .

The hyoid bone is an element of the human skeleton that stands out for its remarkable mobility.

ORIGIN OF THE NAME

The term "hyoid" comes from the Greek word " hioeides " ( ὑοειδής ), whose literal meaning is "ipsilon-shaped". To understand the reason for using the term ioide, it is appropriate to remind readers that the ipsilon, to which the word hioeides refers, is the tiny Greek ipsilon, whose shape resembles a horseshoe or the vowel "u".

Anatomy

The hyoid bone is an irregular bone, in which it is possible to distinguish a central portion, called body, and two lateral bony projections, which take the name of horns .

The hyoid bone has a peculiarity that distinguishes it from all the other bones of the human body: it is the only bone element of the human skeleton that does not articulate with other bones and that is kept in position exclusively by a complex of muscles and ligaments.

BODY

The body has the appearance of a lamina disposed transversally, on which it is possible to identify two faces - the front face and the posterior face - and two margins (or edges) - the upper margin and the lower margin .

The front face is convex and represents the site of insertion of the genioioid, milidioid, styloid, homoioid and ioglossis muscles ;
The back face is the concavity resulting from the convex shape of the front face. Relations with the so-called thyroid membrane ;
The upper margin is rounded and gives insertion to part of the thyroid membrane and to some fibers of the genioglossi muscles;
The inferior margin is, medially, the seat of insertion of the sternoioid muscles and, laterally, the insertion site of the homoioid muscles and of part of the thyroid muscles .

HORNS

The two horns on each side of the body of the hyoid bone are longer than the other.

The long horns of the hyoid bone form the so-called pair of major horns, while the short horns of the hyoid bone make up the so-called pair of minor horns .

The larger horns represent the outermost portion of the hyoid bone. Compared to the body, they are projected in a posterior direction and slightly upwards. Along their course, they tend to thin out, only to grow thicker again at the ends, giving rise to a tubercle (the tubercle of the larger horns ). The so-called lateral thyroid ligament is inserted on the tubercle of the major horns.

On each major horn there is a surface - the upper surface - and two margins (or edges) - the medial margin and the lateral margin .

The upper surface of the larger horns represents the seat of attachment of the ioglossus muscle and of part of the digastric and stylohyoid muscles ;
The medial margin of the larger horns gives insertion to part of the thyroid membrane and to the average constrictor muscle of the pharynx ;
The lateral margin of the major horns gives insertion to the thyroid muscle.

Moving on to the smaller horns, these are two conical eminences, more internal than the larger horns and oriented upwards. They are joined to the body, through fibrous tissue, and to the major horns, through a synovial joint.

An important ligament is found on the apex of the minor horns: the styloid ligament .

LIGAMENTS

In summary, the ligaments that are related to the hyoid bone are: the lateral thyroid ligament and the styloid ligament .

The lateral thyroid ligament is the equal anatomical element, which connects the tubercle of the greater horn of the hyoid bone to the upper horn of the thyroid cartilage .

The styloid ligament, on the other hand, is the equal anatomical element, which joins the apex of each minor horn of the hyoid bone to the styloid process of the temporal bone of the skull .

MUSCLES

By convention, the anatomists distinguish the muscles that find insertion in the hyoid bone in two broad categories: the muscles that find insertion on the upper surfaces of the components of the hyoid bone ( muscles of the upper surface of the hyoid bone ) and the muscles that are inserted on the lower surfaces of the components of the hyoid bone ( muscles of the lower surface of the hyoid bone ).

The first category includes: the average constrictor muscle of the pharynx, the ioglossus muscle, the genioglossus muscle, the intrinsic muscles of the tongue and the so-called suprahyoid muscles (digastric, styloid, genioioid and mylohyoid).

In the second category, on the other hand, belong three of the four subioid muscles : the thyroid muscle, the homoioid muscle and the sternoioid muscle.

Remember that the muscles that form relations with the hyoid bone are all even muscle elements.

vascularization

The inflow to the hyoid bone of oxygen-rich blood depends on the so-called lingual artery .

Even arterial vessel, the lingual artery originates from the external carotid artery and reaches the hyoid bone, where the major horn develops.

The lingual artery is important not only because it provides blood supply to the hyoid bone, but also because it gives rise to a branch - the so-called suprahyoid branch - whose job is to supply the muscles of the upper surface of the hyoid bone with blood.

Functions

The hyoid bone is an anchorage site for muscles that allow tongue, pharynx and larynx movements. Therefore, it plays a fundamental role in the physiological functions performed by the aforementioned anatomical structure, namely: in the mechanisms of mastication, swallowing, phonation and respiration .

MOVEMENTS OF THE IOID BONE DURING THE CONTEMPORARY

During swallowing, the hyoid bone moves upward first, then forward and finally returns to the starting position.

The movement of the hyoid bone depends on the muscles that find insertion on it.

ROLE IN BREATHING

As far as breathing is concerned, the hyoid bone plays a key role in keeping the airways open during night sleep .

Development

The embryonic origin of the hyoid bone features the second pharyngeal arch and the third pharyngeal arch . The minor horns and the upper portion of the body derive from the second pharyngeal arch. The larger horns and the lower portion of the body derive from the third pharyngeal arch.

OSSIFICATION

6 ossification centers contribute to the formation of the hyoid bone : two centers for the body and one center for each horn.

The ossification process of the hyoid bone starts from the larger horns, at the end of fetal development. Shortly afterwards, the ossification of the body begins and, around the 1st-2nd year of life, the ossification of the minor horns begins.

diseases

Numerous clinical studies have shown that the hyoid bone is the protagonist of a very known and widespread nocturnal sleep disorder: the so-called nocturnal obstructive apnea syndrome .

In fact, those who have conducted the aforementioned studies have found that, in many people with the aforementioned syndrome, the hyoid bone occupies a lower position than normal and therefore conditions the mechanism of opening of the airways, during sleep.