Sternocleidomastoid muscle: anatomy and function


The sternocleidomastoid muscle is a muscle on the surface of the neck that plays an important role in head tilt and neck twisting, among many other things. It extends from the back of the head and attaches to the breastbone and clavicle. The sternocleidomastoid process, often called SCM, is usually quite easy to see. Visually, it looks like a cylindrical strap that sticks out from the side of the neck and tapers towards the ends.

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SCM anatomy

The sternocleidomastoid bone runs diagonally from the back of the ear to the clavicle and sternum.

Unlike other muscles, such as the latissimus dorsi and dorsum majora, the attachment points of the SCM are relatively easy to identify and trace. Unlike the lats, the SCM attaches only to the bones, with only four bones .

A small exception to the simplicity of the SCM insertion pattern is that when the abdomen of the muscle begins to approach the clavicle and sternum, it branches into two 'heads'. Based on this, SCM has two starting points.

So where exactly are these two SCM 'heads' from?

One sticks to the front (that is, the front surface) of the handlebars. The manubrium is the top part of the breastbone. The other head attaches to the top (called the upper part) of the clavicle , near the midline of the body.

The other end of the SCM is inserted over the mastoid, a small bony bump located behind the ear . The mastoid process arises from the temporal bone, which is the part of the skull that forms the temple. You can identify the mastoid process yourself by touching the area behind and slightly below the ear.

Then if you swipe down a bit with your fingers, you can feel a softer area. This is where the SCM attaches to the mastoid bone. Several SCM fibers also insert into the lower part of the occipital bone, which is adjacent to the mastoid process and again forms the lower part of the skull.

The SCM muscle is of interest to anatomists because the unique position it occupies in the neck makes it the key to understanding the location of the neck muscles. On both sides, the SCM diagonally divides the neck muscles into anterior (anterior) and posterior (posterior) triangles, simplifying the examination of the cervical spine.

The sternocleidomastoid muscle is innervated by the accessory nerve.

Sternocleidomastoid function

Some of the neck movements produced by sterocleomastoid cells vary depending on whether one or both SCM muscles are working.

When only one SCM muscle contracts, it tilts the head to the same side (called the ipsilateral side) that the muscle is on. For example, the SCM on the right side of the neck tilts the head to the right.

An SCM can also turn or turn the head in the opposite direction. For example, when you turn or turn your head to the right, your left SCM contracts. In this situation, the SCM also turns the face slightly upward, slightly widening the neck.

When both SCM muscles contract, the result is a neck extension movement that occurs at the first intervertebral joint. The first intervertebral joint is the superior dorsal joint; This is where your head rests on your neck. This extension movement brings the head back.

The contraction of both SCM muscles also flexes your neck, causing the chin to drop in the direction of the sternum. A bilateral SCM contraction pushes your chin forward when your head is level.

The bilateral contraction of the SCM muscles simultaneously also plays a role in the respiratory process. In this case, raise your hand, which is another name for the sternum. It also elevates the area of the clavicles closest to the midline of the body.

The SCM is part of a group of muscles known as the anterolateral neck flexors. Other muscles in the anterolateral flexor group of the neck are the scalene muscles, which are found deeper in the neck than the SCM. The scale muscles are synergistic muscles or accessory muscles of the sternocleidomastoid muscle. They help the SCM to rotate and tilt the head and neck.

Related conditions

SCM is chronically shortened in torticollis. Slope is a condition in which the head is constantly turning to one side. This is often known as neck bias. This can happen in babies during the first positions. Treatment consists of gently stretching the tight SCM muscle to elongate it to its normal shape. Placing a child with torticollis can also help treat this condition.

Any injury or damage to the accessory nerve or cranial nerve XI can cause weakness or paralysis of the SCM. This will cause marked atrophy of the affected SCM and may cause difficulty in turning the head and flexing the neck. Treatment consists of restoring normal nerve function and SCM muscle strengthening exercises.


If you have a weakened SCM muscle, it is important to see your doctor. He or she can do tests to make sure you get an accurate diagnosis and start treatment right away. Working with a physical therapist can be a helpful method of rehabilitation for SCM.

Exercises for SCM may include:

By working to maintain good posture and gently stretching and strengthening your SCM and other neck muscles, you can be sure that you will quickly regain full pain-free function.

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