The neck serves a number of significant functions, including moving and stabilizing the head. It is the muscles of the neck, including the posterior neck muscles, that are responsible for the function of moving the head, while also giving the neck much of its shape. It may surprise some to know that the neck contains a number of muscles that all help this important conduit in the flexibility department, a task which even modern day science would have a difficult time replicating.
What Are Posterior Neck Muscles?
The neck is filled with a number of important components that all serve vital functions. In addition to muscles and bones, the neck area houses the trachea (or windpipe), the esophagus, arteries and veins, and, of course, many nerves that stimulate all of these components to work in an efficient and coordinated fashion. Of all these neck "components," the muscles are perhaps the easiest to take for granted, with so much of our attention being devoted to tasks like breathing and eating. Fortunately, these muscles, including the posterior neck muscles, can be described in ways that are fairly easy to understand.
About Our Sternocleidomastoid Muscles
Of the many muscles of the neck, the sternocleidomastoid is one of the most important and prominent. The sternocleidomastoid is a long, strap-like muscle that hangs from the back of the ear and runs diagonally toward the front of the neck to connect to the clavicle and sternum. The sternocleidomastoid muscle, or SCM, is important in performing some of the most basic neck movements, such as tilting and rotating the neck. You have two sternocleidomastoid muscles, one on each side of the neck, and they may work synergistically or alone to achieve these significant neck movements.
For example, a contraction of one sternocleidomastoid muscle can tilt your head to that same side. A contraction of this muscle can also rotate your head towards the opposite side or tilt your head upward. It can all get a little confusing. Key things to remember are that the actions of the sternocleidomastoid are driven by the size of the muscle, its points of insertion, the fact that it has two heads, and the fact that you have two of these muscles in your neck. Indeed, the sternocleidomastoid is a prime example of the synergistic action of muscles. This is conveniently demonstrated by the fact that we have two SCMs.
What is the Posterior Triangle of the Neck?
For our purposes, the sternocleidomastoid is important because it helps define what is known as the posterior triangle of the neck. The human body has numerous anatomical regions that scientists and instructors define and delineate to help students (and themselves) visualize muscles quickly and effectively. Learning about muscles by region also helps us understand their functions. The posterior triangle is just such an anatomical area: one that is defined by a number of important anatomical landmarks, including the SCM, and one which contains several muscles and small muscle groups.
The posterior triangle of the neck actually rests on the lateral aspect (the side) of the neck. It is an anatomical area that is very clearly defined by three key anatomical landmarks. The landmarks that define the posterior triangle of the neck are as follows:
- Its anterior boundary is formed by the sternocleidomastoid muscles
- Its inferior boundary is the clavicle (collarbone)
- Its posterior boundary is the trapezius muscle
What About the Trapezius Muscle?
The trapezius muscle is a large muscle of your upper back and shoulders that is involved in a number of important movements such as shrugging and lifting. Much larger than the sternocleidomastoid, the anterior or front part of this muscle forms the posterior (rear or back) border of the posterior triangle. If you were to look at the posterior triangle on an anatomy chart or a cadaver, you would see that several muscles fall within this area.
This is a good way to visualize the posterior neck muscles. The area is covered by a thick layer of connective tissue called fascia, in this case an investing layer of fascia, and the bottom or floor of the posterior triangle is also covered by fascia.
Your posterior neck muscles are those muscles that lie within the posterior triangle of the neck, beneath that investing layer of fascia, although they are not the only inhabitants of this area. In addition to posterior neck muscles called the omohyoid, scalenes, and by other names unfamiliar to most non-physicians, there are also a number of critical blood vessels and nerves. The jugular vein and subclavian vein are two important veins of the neck, while the subclavian artery is an important vessel that can be easily seen because it is apparent between the middle and anterior scalenes.
The accessory nerve, or cranial nerve XI, is a major nerve in this area but not the only significant nerve located in or near the posterior triangle of the neck. The accessory nerve provides enervation and impulses to the sternocleidomastoid muscle. Other major points of interest here are the cervical plexus, brachial plexus, and phrenic nerve. This leads us to the inhabitants of the posterior triangle of the neck that we really care about in this article: the posterior neck muscles.
More Specifics on Posterior Neck Muscles
So what are the posterior neck muscles, specifically? These muscles are the:
- Omohyoid muscle
- Anterior scalene
- Middle scalene
- Posterior scalene
- Levator scapulae muscle
The omohyoid muscle is one of the more significant muscles positioned mostly within the posterior triangle of the neck due to its large size. The inferior belly of the omohyoid runs across the posterior triangle, after which it enters the anterior triangle of the neck, but not before first traveling under the sternocleidomastoid muscle.
What Are Some Posterior Neck Muscle Functions?
With the one significant exception of the omohyoid muscle, our posterior neck muscles are located "on the floor" of the posterior triangle of the neck, These muscles are considered vertebral muscles because vertebral fascia covers them. Posterior neck muscles can also be understood and categorized in terms of their functions. It's helpful to divide the posterior neck muscles into four major groupings: scalenes, the omohyoid, the splenius capitis, and the levator scapulae.
The three scalene muscles are deep within the body relative to their much larger neighbor the sternocleidomastoid muscle, which forms the anterior aspect of the posterior triangle of the neck. The anterior scalene muscle, middle scalene muscle, and posterior scalene muscle lie at increasing levels of depth. They are involved in lifting the ribs and bending the neck.
Specifically, the anterior and middle scalene muscles work to bend the neck to the same side as these muscles and lift the first rib. The posterior scalene muscle bends the neck to that same side and lifts the second rib. Because they are involved in lifting the ribs, they increase the volume in the thoracic cavity and are therefore included among our accessory muscles for respiration.
The omohyoid has a superior and inferior belly, and it is involved in depressing the hyoid bone and the larynx. The hyoid bone is a small bone in the neck that serves as an attachment point for muscles of the mouth and the tongue. Again, the omohyoid does not lie entirely within the posterior triangle of the neck; rather, it merges into the anterior triangle.
Levator Scapulae Muscle
The levator scapulae muscle, as its name implies, elevates the scapula, often working in conjunction with other muscles. It inserts into the scapula (shoulder blade), and like the other posterior neck muscles, there is one on each side. The levator scapulae muscle is also involved in flexing the cervical spine.
There are two splenius muscles: the splenius capitis and the splenius cervicis. The splenius capitis serves an important role in extension of the head and its backward movement. This long muscle arises from the spinous processes of thoracic vertebrae.
Three Things You Probably Didn't Know About Neck Muscles
The varied functions of the posterior neck muscles may come as a surprise to some people. What may also come as a surprise is that the posterior triangle of the neck is really just a snapshot of these muscles. Here are three significant things that most people do not know about the posterior neck muscles:
- The posterior neck muscles are not only involved in tilting and rotating the head, but also in raising the ribs, depressing the hyoid bone, raising the scapula, and flexing and rotating the spine.
- Several of the posterior neck muscles extend far beyond the posterior triangle, including the scalenes and the levator scapulae.
- Several important blood vessels travel through these muscles, including the subclavian artery that passes through two scalene muscles.
The neck is a much more complicated region and structure than it appears. It contains many muscles involved in functions extending beyond obvious motor actions of the head and neck. The posterior neck muscles lie within the posterior triangle of the neck, and these muscles perform many key functions while also providing passage routes for several major arteries, veins and nerves. Understanding the posterior neck muscles is important for clinicians as well as any person experiencing pain or other problems in the head and neck region.