Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, I'm going to be talking about the different muscles of the anterior neck. So what I'm going to be doing here is describing the different muscles that we find on the anterior portion of your neck.
And right now we’re looking at the neck anteriorly, and you can see that if we were to remove skin, fats, vessels, and nerves, we would be left with, then, the bones that you see here and some of the muscles.
Now, I'm going to be removing this muscle here known as the platysma to, then, expose the other collection or the entire collection of muscles that will be covered here on this tutorial. We will be covering or talking about the different origins, insertions, innervation, functions associated to all these muscles, these muscles that define the anterior portion of your neck.
Now, the list includes the sternocleidomastoid, the scalene muscles, the infrahyoid muscle group, the suprahyoid muscle group, the longus capitis muscle, the longus colli muscle, and the platysma—the first one that I removed from the image—so quite a lot to cover on this tutorial.
Let’s start off with this one that you see here, highlighted in green. This is known as the sternocleidomastoid muscle. And this muscle is a two-headed muscle of the neck. And you have one on each side of the neck, as you can clearly see on this image.
The muscle lies superficially so that it is both easily visible and palpable, thus every one of us has already seen it or know about it, but now, you know the actual name that we use to describe it in anatomy. You can see and touch the left one when you turn your head to the right and vice versa.
Now, in terms of origins for the sternocleidomastoid muscle, this muscle has two heads: a sternal head and a clavicular head.
Now, the sternal head originates from the manubrium of the sternum, as you can clearly see here from this image, while the clavicular head will originate from the medial one-third of the clavicle, as you can also see from here—so two heads for the sternocleidomastoid muscle.
In terms of the insertion point for this muscle, the insertion is the mastoid process of the temporal bone. And also the superior nuchal line of the occipital bone will serve as insertion point for the sternocleidomastoid.
When it comes to the innervation for this muscle, it is innervated by the accessory nerve or cranial nerve number 11. And you can clearly see here, highlighted in green and piercing through the sternocleidomastoid muscles.
And notice that here, on this image, we’re looking at these structures from a posterior view. From a posterior view, you can see here the pharyngeal muscles and the different blood vessels that you find on the neck.
The sternocleidomastoid muscle is also innervated by direct branches of the cervical plexus.
When it comes to the different functions associated to the sternocleidomastoid muscle, the contraction of one sternocleidomastoid muscle flexes the cervical vertebral column to the same side, what we call ipsilateral flexion, and seen here indicated by this arrow—so when you try to touch your shoulder with your ear—and also rotates the head to the opposite side, known as contralateral rotation.
Now, the contraction of both sternocleidomastoid muscles at the same time leads to what is known to be as dorsal extension or elevation of the head—so looking up into the sky.
In addition, this muscle supports inspiration providing that the head stands still. So we also consider the sternocleidomastoid muscle as an inspiratory breathing muscle.
Now, a few fun facts about the sternocleidomastoid muscle, and these fun facts include that the carotid pulse can be easily felt in the middle third of the front edge of this muscle.
And also important to mention that sensory branches of the cervical plexus merge at the dorsal edge of the muscle at the Erb’s point or punctum nervosum. It can be used as a puncture area for local anesthesia.
Also, a curious fact here, if you remember well, the famous Vulcan nerve pitch from the Star Trek series is done by applying pressure on the point in order to make the enemies collapse. So as you can see, knowing a little bit of anatomy may help you understand what’s going on on your favorite series.
Now, we’re ready to move on to the next group of muscles that you now see on the image. These are known as scalene muscles.
There are three scalene muscles that you need to know: the scalene or the anterior scalene, now seen here written in Latin, the middle scalene, and the posterior scalene. And you can clearly see them here on this image.
So you find here the anterior scalene, the middle scalene just a little bit behind the anterior scalene. And further behind this two, you find, then, the posterior scalene. And in Latin, the word “scalene” means "a ladder." So you can memorize it by picturing them as a ladder between your ribs and vertebrae.
Now, let’s talk about the first one on that list. This is the anterior scalene. In terms of origin points, this muscle is going to originate at the transverse processes of the third to sixth cervical vertebrae. Then it goes all the way to insert at the first rib. And you can clearly see here on this image that the muscle or the two muscles inserting on the first rib.
Next one that we’re going to be talking about is known as the middle scalene. In terms of origin points, the middle scalene starts at the transverse processes of the third to seventh cervical vertebrae. And in terms of insertion point, as you see now on this image that we’re looking at from a lateral left view of this muscle, in terms of insertion point, like the anterior scalene, this muscle will insert at the first rib dorsally from the anterior scalene.
Last on our list is going to be this muscle here, the posterior scalene. In terms of origin point, it has an origin at the transverse processes of the fifth to seventh cervical vertebrae. It’s, then, going to go all the way, then, to insert not on the first rib but, this time, at the second rib.
Now, in terms of the innervation of the different scalene muscles, we’re going to see that these muscles are going to be innervated by direct branches of the cervical and brachial plexuses.
In terms of the different functions associated to the scalene muscles, the scalene muscles are able to perform elevation of the ribs, as you can see here indicated by this arrow, and therefore, your thorax. For that reason, they are also considered as accessory muscles of inspiration.
When one of the muscles will contract, or what we call the unilateral contraction, this will bend the cervical spine to the side, or what we call a lateral flexion. Then when the two muscles will contract, or what we, then, call the bilateral contraction specifically of the anterior scalene muscle, will cause bending of the cervical spine to the front—what we call ventral flexion, as you can see here, also represented by this arrow.
We are now ready to move on to the next group of muscles that you see now on the screen. Now, these are known as the infrahyoid muscles, and there is a list of four muscles that we need to go over: the sternothyroid, the thyrohyoid, the sternohyoid, and the omohyoid. Now, do not panic. These names are a bit tricky, but they kind of offer you clues on where these muscles are going to be attaching to.
And without further ado, let’s continue on to the first ones on the list, the sternothyroid and the thyrohyoid.
Now, these two muscles form a unit as a thyrohyoid is the continuation of the sternothyroid muscle. In terms of origin points, we’re going to see that the sternothyroid muscle is going to be originating at the dorsal surface of the manubrium of the sternum. And you can clearly see here on this image, the muscle originating from the manubrium of the sternum.
The thyrohyoid is going to, then, originate from the thyroid cartilage, and you can also see here the thyroid cartilage and the origin point for the thyrohyoid.
When it comes from the different insertion points for these muscles, because one is the continuation of the other, the lower one, the sternothyroid muscle, inserts at the thyroid cartilage. The thyrohyoid muscle then runs until the body and also the greater cornu of the hyoid bone. And you can clearly see here the insertion point for the sternothyroid muscle and also the insertion point for the thyrohyoid muscle.
We’re going to move on to the next one on the list that you see now, highlighted in green. This is known as the sternohyoid muscle. And like the name indicates, the origin for this muscle is going to be, then, the sternum or the manubrium of the sternum, and you can clearly see here on this image.
But to be a bit more detailed, the origin point for the sternohyoid muscle is going to be the dorsal surface of the manubrium of the sternum as well as the sternoclavicular joint. Then this muscle will run and insert all the way onto the body of the hyoid bone. And as you can see, this is the most superficial of all infrahyoid muscles.
We’re going to move on to the next muscle on our list, seen here highlighted in green, and as you can see, from all the muscles that we’ve been seeing here, you always find two—one on each side of the neck. Now, this is known as the omohyoid muscle. And it is divided into a superior and inferior belly.
Now, in terms of origin points, for the inferior belly it begins at the superior border of the scapula, and then ascends craniomedially, and merges into an intermediate tendon at the height of the lateral cervical region.
Now, the superior belly originates at the intermediate tendon.
Now, when it comes to the insertion point for the omohyoid, distally, the muscle will attach to, then, the body of the hyoid bone.
We are now ready to talk about the innervation of the infrahyoid muscles. Now, all four infrahyoid muscles are innervated by the deep ansa cervicalis which arises from the cervical plexus. And we see here the ansa cervicalis, highlighted in green.
Now, we’re going to look at the different functions associated to the infrahyoid muscles. And these muscles, in general, will be responsible for positioning of the hyoid bone along with the suprahyoid muscles and also involved in swallowing and movement of the larynx and the hyoid bone—so everything related, all the movements that are related to the points of attachments. So when these muscles contract, they will produce movement and actions or functions associated to these areas of the body.
If we want to be a little bit more specific, all infrahyoid muscles will be causing what is known to be depression of the hyoid bone—so pulling it downward.
There is an exception though: the sternothyroid muscle, because it does not, or this muscle will not insert on the hyoid bone, therefore, it’s not going to be involved in depression of this bone.
Now, the sternothyroid muscle allows depression of the larynx where as the thyrohyoid provides the opposite, or what is known to be as elevation—so when the hyoid bone is fixed.
The omohyoid has an additional function due to its structure. Remember that it has the intermediate tendon that we looked at, and this tendon is attached to the carotid sheet which contains the internal jugular vein, the common carotid artery, vagus nerve, and lymph nodes. And by pulling this sheet, it prevents the big, thin jugular vein from collapsing and maintains a low pressure in the internal jugular vein. This way, it increases the blood return from the head to the superior vena cava.
Now, we’re ready to move on to the next set of muscles. They are known as, then, the suprahyoid muscles. The suprahyoid muscles are four muscles running from the mandible to the hyoid bone. And together with surrounding tissues, they form the floor of the mouth.
The list of the suprahyoid muscles include the digastric, the mylohyoid, the geniohyoid, and the stylohyoid muscle.
Now, we’re going to start off with this one that you see here, highlighted in green. This is known as the digastric muscle. And it consists of two parts, so Latin for two bellies, “digastric,” which are then separated by this intermediate tendon that you see here.
Now, in terms of the origin points for this muscle, the anterior belly will originate from the digastric fossa of the mandible, and then the posterior belly will originate from the mastoid notch of the temporal bone.
When it comes to the insertion point for the digastric, together, they will insert, these two bellies will insert at that intermediate tendon. So this is what we consider the insertion point for this muscle.
We’re now ready to move on to the next one on the list. This is known as the mylohyoid muscle. And in terms of origin point, this muscle is originating at the mylohyoid line of the mandible.
The muscle fibers run to a median tendon known as the mylohyoid raphe, where both parts of the muscle meet. The mylohyoid raphe continues its course and inserts on the body of the hyoid. And you can clearly see here on this image, the mylohyoid raphe and then the insertion point which will, then, be the body of the hyoid bone.
We’re now looking at this nerve that you see here, highlighted in green. And this is, then, the innervation for the mylohyoid muscle. This is the mandibular nerve. The muscles are supplied or innervated by the mylohyoid nerve from the mandibular nerve, which is one of the three branches of the trigeminal nerve or cranial nerve number 5.
So an important point to make is that the mylohyoid and the anterior belly of the digastric muscle are, then, innervated by the mylohyoid nerve.
Next on our list is going to be this muscle that you see here, highlighted in green, the geniohyoid muscle. And in terms of the origin point for this muscle, it’s going to originate from the mental spines of the mandible at the inner surface of the mandible.
The muscle is going to insert distally to the body of the hyoid bone. And you can clearly also see here the muscle inserting on the body of the hyoid bone.
When it comes to the innervation of the geniohyoid muscle, it is important to mention that this muscle is going to be innervated by branches of the cervical plexus—as you see here, highlighted in green on this image—also by the hypoglossal nerve, which is seen highlighted in green, cranial nerve number 12.
We’re now ready to move on to the next muscle that you see here, the stylohyoid muscle, which then will originate from the styloid process of the temporal bone.
This muscle is going to insert to, then, the body of the hyoid bone. And its distal part, the muscle divides into two tendons. And you can clearly see here the muscle dividing into two tendons.
A word about the innervation of the stylohyoid muscle, this nerve that you see here, highlighted in green, this is known as the facial nerve, and this is going to innervate the stylohyoid muscle.
An important point to make here is that the stylohyoid muscle and the posterior belly of the digastric muscle are innervated by, then, the facial nerve.
We’re now going to look at the different functions associated to the suprahyoid muscles. The suprahyoid muscles form the floor of the mouth and play an important role in chewing, swallowing, and speech. Together with the infrahyoid muscles, they are responsible for positioning of the hyoid bone.
But if we go into a little bit more detail on the functions of the suprahyoid muscles, the digastric and stylohyoid allow elevation of the hyoid bone during swallowing and also help keep the mouth open.
The geniohyoid muscle moves the hyoid bone forward and supports opening and lateral movement of the mandible.
The main function of the mylohyoid muscle is the elevation of the floor of the mouth, but it can also assist the jaw opening and chewing movements.
We are now ready to move on to other two muscles that we’re going to be discussing on this tutorial on anterior neck. These are known as—the one seen here—the longus capitis on the left side, and the one on the right image is the longus colli. They are found deep in the neck in front of the spine and allow us to bend our heads when nodding.
Take a closer look here at the longus capitis muscle. When it comes to its origin, this muscle originates at the anterior tubercles of the transverse processes of the third to sixth cervical vertebrae. Then, it goes to insert at the basilar part of the occipital bone.
We take a look now at the longus colli muscle. When it comes to its origin, this muscle has several origins from the third thoracic to fifth cervical vertebrae.
We’re moving now to the insertion points for the longus colli. And the insertions for this muscle are the upper cervical vertebrae, the transverse processes of the fifth and sixth cervical vertebrae, and the anterior tubercle of the atlas.
Now, let’s take a look at the innervation that is seen here, highlighted in green, for the longus capitis and the longus colli. What you need to know is that these muscles are innervated by branches of the cervical plexus.
We like to have a quick word on the different functions associated to these muscles. The main task of these two muscles is bending forward the skull—what is known to be as ventral flexion—and furthermore, they cause lateral flexion of the cervical column and the atlanto occipital joint through unilateral contraction. This means that one part of the muscle will contract. Then, it will help lateral flexion to the same side of the contraction, to that we call usually as ipsilateral movement.
We’re now ready to move on to the last muscle on our list that is seen here, highlighted in green. From the very first list that we saw on this tutorial, this is the platysma. And this is a bit special, a bit of a special muscle that makes it even more interesting to learn it.
The platysma is a paired, flat, superficial neck muscle that is considered to be part of the facial muscles. What makes it special is that unlike other muscles, it is directly connected to the skin. It completely covers both front sides of your neck. And due to direct insertion to the skin, it can change facial expression along with the other facial muscles.
But if we have to look into origin point for this muscle, it arises from the fascia covering the upper parts of the pectoralis major muscle and also the deltoid muscle.
And when it comes to an insertion point for this muscle, its fibers cross the clavicle and proceed obliquely upward and medially along the side of the neck towards the skin of the lower jaw.
The platysma is also innervated by this nerve that you see here, highlighted, the facial nerve, like we also see in other facial muscles being innervated by, then, the facial nerve. And you can see that the platysma is innervated by the lower branches of the facial nerve, the cervical branches of the facial nerve.
In terms of the functions associated to the platysma, a contraction of this muscle leads to depression of the lower jaw, bottom lip, and corners of the mouth as well.
It also tenses and shortens the skin of the neck, and is responsible for mimic expression of shrieking and threatening an enemy for example.
Since we just explored one of the facial muscles, I would like to end this tutorial with this image that you see now on the screen.
We’re now looking at an image from a book by Charles Darwin, The Expression of Emotions in Man and Animals published in 1872. And it explores genetically determined aspects of behavior.
It was published 13 years after On the Origin of Species, and in this book, Darwin seeks to trace the animal origins of human characteristics such pursing of the lips in concentration and the tightening of muscles around the eyes in anger and efforts of memory.
Darwin sought out the opinions of some eminent British psychiatrists of the time in the preparation for this book, which forms Darwin’s main contribution to psychology.
Just before I finish this tutorial, I wanted to leave you with a little bit of trivia and extra knowledge.