Sternocleidohyoid muscle: what it is, characteristics and how it works

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 muscles that contract voluntarily (skeletal). According to other authors, smooth or involuntary and cardiac muscles would also enter into this system.

In any case (and despite the 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 enable the functionality of the systems internal. We are not just talking about picking up 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, the musculature allows us to transmit emotions, show disagreement, joy and even speak and manifest ourselves as a species. From movement to speech, through blood pumping and stability in airspace, to conceive of life without musculature today would be an impossible task. So stay with us

we tell you everything about an extremely unique muscle: the sternocleidohyoid.

• Related article: "Muscular system: what it is, parts and functions"

What are muscles?

Before diving into the particularities of this muscle, it is convenient to establish the bases that surround the subject. A muscle could be defined as a contractile organ that determines the shape and contour of our body and that, in addition, has cells capable of elongating 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 the skeleton its shape and allow movement.
• Smooth muscle tissue: it is involuntary. These muscles take longer to contract than skeletal muscles, but can remain in this position for longer.
• Cardiac muscle tissue: Found in the heart. Its contractions, rhythmic and strong, expel blood from this organ while it beats.

We have a minimum of 650 muscles that make up our body, all of them volunteers (skeletal). If we start counting cardiac and smooth muscle, this number easily rises to 840 total muscles. Of course, we move in figures that are not inconsiderable.

What is the sternocleidohyoid muscle?

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

This muscle is characterized by having a tapered 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 from 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 middle side 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 with the breastbone).

2. inserts

Its anatomical course is "up" and towards the center to the lower edge of the hyoid bone.. To do this, it is inserted on the upper face of the posterior edge of the clavicle, on the posterior face of sternoclavicular ligament, in the lateral half of the sternal manubrium and in the first cartilage sack, bag. It should be noted that its trajectory towards the hyoid bone is not completely straight, since the Adam's apple is interposed between the lower insertion point and the aforementioned bone.

• You may be interested in: "Neuromuscular junction: the bridge between neuron and muscle"

3. innervation

Its innervation comes from the hypoglossal loop, the junction of fibers from the C1-C2-C3 roots of the cervical plexus. This nerve structure mainly controls the motor functions of the neck. The contraction of the sternocleidohyoid muscle, through the nerve signals of this plexus, causes the descent of the hyoid bone. (in which it is inserted in its posterior section).

4. Relations

As we have said before, the sternocleidohyoid muscle is part of the infrahyoid muscle group, located below the hyoid bone. These muscles attach to the bone and cause its descent through contractions, which is essential for phonation and swallowing., among other things. Some of the muscles that are related to the one that attracts us here are the following:

• Homohyoid muscle: A digastric muscle that acts as a depressor of the hyoid bone and as a tensor of the median cervical fascia.
• Sternothyroid muscle: It has a ribbon shape, just 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 human tissues, requires blood flow so your cells can get oxygen and nutrients, among other things. This is done by the lingual artery and the superior thyroid.

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

Functions of the sternocleidohyoid muscle

The anterior part of the neck contains a series of vital structures for the development and survival of the human species.. The muscles involved (among which is the sternocleidohyoid) are responsible for performing head movements and neck, but they also play essential functions in processes such as facilitating swallowing and phonation (speech in the being human).

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

Above them sits the neck fat, an important absorber of mechanical damage that could seriously compromise the speech, respiratory and swallowing apparatus. Lastly, the skin of the neck is located on top of this fat, the first barrier that prevents the entry of pathogens.

The role of the sternocleidohyoid in swallowing

As a final note, we are going to 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 airways, preventing food from getting into the wrong places.. After food has passed from the pharynx into the esophagus, the sternocleidohyoid muscle helps to reopen the esophagus. laryngeal cavity (by lowering the hyoid and larynx), thus allowing airflow back into the lungs. Without a structure as small and simple as this muscle, the breathing and swallowing process in humans would surely be much more difficult.

Summary

Spaces like this show that even the smallest muscle and even the least bone “relevant” play essential roles in the physiology and maintenance of the human body throughout weather. Thanks to the sternocleidohideo muscle (along with others) the lowering of the hyoid bone is produced, an essential process for swallowing, sound production and breathing, among other things.

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