Sternocleidohyoid muscle: what is it, characteristics and how does it work?

These are the characteristics of the sternocleidohyoid muscle, one of those located in the neck.

The human body has more than 650 total muscles, which together comprise 40-50% of the weight of a healthy adult individual.

Although the muscular system has been extensively studied on multiple occasions, it is necessary to emphasize that some researchers only include in this apparatus the muscles that contract voluntarily (skeletal). According to other authors, the smooth or involuntary musculature and the cardiac musculature would also fall within this system.

In any case (and in spite of organizational disagreements), the function of the musculature is clear and concise: to allow the movement and permanence of the human being in a three-dimensional space and to make possible the functionality of the internal systems. We are not just talking about grasping an object or pumping blood: did you know that, for example, a human being requires the action of 12 facial muscles to smile?

Beyond running and jogging, musculature allows us to convey emotions, show disagreement, show joy, and even speak and express ourselves as a species. From movement to speech, from pumping Blood to stability in an airspace, conceiving life without muscles today would be an impossible task. Stay with us as we tell you all about we tell you all about an extremely unique muscle: the sternocleidohyoid muscle..

What are muscles?

Before we dive into the particularities of this muscle, it is convenient to establish the basics surrounding the subject. A muscle could be defined as a contractile organ that determines the shape and contour of our body and also has cells capable of elongating along its axis of contraction. along its axis of contraction.

There are 3 types of muscle tissue, which in turn give rise to 3 major muscle variants. These are the following:

• Skeletal (striated) muscle tissue: voluntary and striated muscles. They are attached to the bones, so they give shape to the skeleton and allow movement.
• Smooth muscle tissue: is involuntary. These muscles take longer to contract than skeletal muscles, but can remain in this position longer.
• Cardiac muscle tissue: found in the heart. Its contractions, rhythmic and strong, expel blood from this organ as it beats.

We have a minimum of 650 muscles making up our body, all of them voluntary (skeletal).all of them voluntary (skeletal). If we start counting the smooth and cardiac musculature, this figure easily rises to 840 muscles in total. Of course, we are moving in not inconsiderable numbers.

What is the sternocleidohyoid muscle?

The muscle that concerns us today belongs to the skeletal group, that is to say, to the voluntary striated muscles of the muscular apparatus. It is the most superficial of the muscles of the infrahyoid region (below the hyoid bone). (below the hyoid bone, located in the anterior part of the neck and below the tongue), whose joint function is to flex the head and allow the movement of the larynx during speech, among other things.

This muscle is characterized by a ribbed shape that is distributed on both sides of the neck, about 20 millimeters wide and fleshy in nature. We dissect each of its particularities in the following lines.

1. Origin

The sternocleidohyoid muscle originates with a tendon that inserts into 4 different structures.. These are the posterior border of the clavicle (connecting bone of the sternum with the shoulder blade), the posterior aspect of the sternoclavicular ligament, the lateral half of the manubrium of the sternum (bone of the central and front part of the thorax) and the first costal cartilage (which joins the first ribs to the sternum).

2. Insertions

Its anatomical path is "upwards" and towards the center to the lower edge of the hyoid bone.. For this, it inserts on the superior face of the posterior border of the clavicle, on the posterior face of the sternoclavicular ligament, on the lateral half of the sternal manubrium and on the first costal cartilage. It should be noted that its trajectory towards the hyoid bone is not completely straight, since the Adam's apple interposes itself between the inferior insertion point and the aforementioned bone.

3. Innervation

Its innervation comes from the hypoglossal loop, the junction of fibers coming from the C1-C2-C3 roots of the cervical plexus. This nerve structure mainly controls the motor functions of the neck. Contraction of the sternocleidohyoid muscle, by means of nerve signals from this plexus, causes the hyoid bone to descend (into which it inserts in its posterior section).

4. Relations

As mentioned above, the sternocleidohyoid muscle is part of the infrahyoid muscle group, located below the hyoid bone. These muscles fix the bone and cause its descent by contractions, which is essential for phonation and swallowing, among other things.among other things. Some of the muscles that are related to the one we are concerned with here are the following:

• Homohyoid muscle: a digastric muscle that acts as a depressor of the hyoid bone and as a tensor of the middle cervical aponeurosis.
• Sternothyroid muscle: has a ribbon-like shape, like the sternocleidohyoid. Its main function is to lower the larynx.
• Thyrohyoid muscle: short and quadrilateral, this muscle also favors the lowering of the hyoid bone with its contraction.

5. Blood supply

The sternocleidohyoid muscle, like all tissues of the human being, requires a blood flow for its contraction, requires a blood supply so that its cells can obtain oxygen and nutrients, among other things.. This is taken care of by the lingual artery and the superior thyroid artery.

Before the lingual artery enters the tongue tissue (its final destination), it gives off a hyoid branch that follows the upper edge of the hyoid bone. Thus, it gives off a series of branches that nourish the aforementioned muscles.

Functions of the sternocleidohyoid muscle

The anterior part of the neck contains a number of structures vital to the development and survival of the human species. The muscles involved (including the sternocleidohyoid) are responsible for head and neck movements, but also play essential roles in processes such as the facilitation of swallowing and phonation (human speech).

In addition to producing the lowering of the hyoid bone when contracting, the infrahyoid muscles act as protectors of the trachea, esophagus, the vascularization of the area and the thyroid glands (which produce the hormone to produce the hormone to produce the thyroid hormone to produce the hormone to produce the thyroid hormone).(which produce parathyroid hormone, which modulates the amount of circulating calcium).

Above them sits the neck fat, an important absorber of mechanical damage that could seriously compromise the phonatory, respiratory and swallowing apparatus. Finally, above this fat is the skin of the neck, the first barrier that prevents the entry of pathogens.

The role of the sternocleidohyoid in swallowing

As a final note, let us explore the mechanism by which the sternocleidohyoid facilitates swallowing in our species.

The suprahyoid muscles elevate the hyoid bone (and consequently the larynx) with their contraction, an activity produced in the act of swallowing. This action closes the air passages, which prevents food from entering the wrong places.. Once the food has passed from the pharynx into the esophagus, the sternocleidohyoid muscle helps to reopen the laryngeal cavity (by lowering the hyoid and larynx), thus allowing airflow back into the lungs. Without such a small and simple structure as this muscle, the breathing and swallowing process in humans would surely be much more difficult.

Summary

Spaces like this one highlight that even the smallest muscle and the least "relevant" bone play essential roles in the physiology and maintenance of the human body over time. Thanks to the sternocleidohyoid muscle (along with others) the lowering of the hyoid bone occurs, a process essential for swallowing, sound production and breathing, among other things.

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