Organisation of the Neck

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This is a tutorial on the organization of the neck. I’m going to talk a little bit about the anatomical triangles of the neck, the anterior and posterior triangles. And then I’ll go on to talk about the fascial compartments. I’ll also talk a little bit about the different structures that pass through the anatomical triangles, but I’ll go on to more detail on other tutorials on this.

We’re looking at an anterior view of the neck. You can see this thin muscles here. This is the platysma muscle. This is contained in the superficial fascia of the neck.   I’ll get rid of these and show you the different triangles.

 

If I just zoom a little bit more, I got rid of the platysma muscle, which lies in the superficial fascia and then you can see this big muscle here, which runs from the mastoid process down to attach onto the sternum and also onto the clavicle.   It’s got two attachments, a sternal and a clavicular attachment, then it’s also attached to the mastoid process up here.   This is the sternocleidomastoid muscle named because of its attachments.

 

The anterior triangle of the neck is defined by few boundaries – the inferior border of the mandible forms the superior border of the triangle, the midline forms the medial border and the anterior border of the sternocleidomastoid muscle forms the lateral border of the triangle.   The triangle is this here, the midline, inferior surface of the mandible.

 

You’ve got the inferior surface of the mandible forming the superior border. You’ve got the anterior border of the sternocleidomastoid forming the lateral border and the midline of the neck which runs right down here forms the medial border.   That’s the anterior triangle of the neck.

 

As you can see here, there are several structures which run in the anterior triangle of the neck. I won’t go into huge detail on what these are, but I’ll just quickly go through them.

 

You can see this bone here. This is the hyoid bone. This bone is important because it forms the attachment for many muscles which make up the floor of the mouth and it provides attachments for the tongue muscles and it’s involved in swallowing.   This is the hyoid bone here.

 

Muscles above it are called the suprahyoid muscles and these run in the anterior triangle. And you’ve got these muscles below the hyoid bone, so these are the infrahyoid muscles. These infrahyoid muscles are also called strap muscles because of their appearance. I guess they look like a strap, so these are the strap muscles.

 

Below the strap muscles, we’ve got the thyroid gland. We’ve got the larynx here and the trachea. We’ve also got the parathyroid glands behind the thyroid.

 

And then also, you’ve got these vessels, which obviously run in the anterior triangle. You’ve got the common carotid and its branches, so the external and internal carotid. You’ve got the internal jugular vein running through the anterior triangle. And then you’ve also got nerves.   For instance, the vagus nerve and recurrent laryngeal nerves run through the anterior triangle.

 

That’s the anterior triangle. Just to recap, it’s formed by the anterior border of the sternocleidomastoid, the inferior margin of the mandible and the midline of the neck.

 

The posterior triangle lies just behind the anterior triangle. It’s formed by the posterior border of the sternocleidomastoid, the middle portion of the clavicle and the anterior border of the trapezius muscle, this big muscle at the back (the big, powerful muscle there).

 

The apex of the posterior triangle is this bit of occipital bone just behind the mastoid process here. You can see the triangle formed by the anterior margin of the trapezius, the middle portion of the clavicle and then the posterior border of the sternocleidomastoid with its apex just behind the mastoid process.

 

Again, the posterior triangle of the neck contains a lot of important structures. I’m not going to go through all of them, but just a few… We’ve got the levator scapula, which elevates the scapula, runs through the posterior triangle. You’ve got scalene muscles which attach to the ribs and originates on the transverse process of the cervical vertebra. They’re not shown in here, but they’re accessory muscles of respiration.

 

And then you’ve got vessels.   You can see the subclavian vein and artery running through the posterior triangle. You’ve got the external jugular and the vertebral veins running through the posterior triangle. And then you’ve got this plexus of nerves, the brachial plexus, you’ve got the accessory nerve, which innervates the trapezius. Several structures run in the posterior triangle.

 

I’ve mentioned before a little bit about the fascial compartments of the neck. The structures in the neck are organized into packages within layers of fascia. Fascia is this tough fibrous connective tissue, which wraps around the different structures and compartmentalizes it.

 

The different structures are contained in different layers of fascia. You’ve got superficial fascia and then you’ve got the deep fascia.   The superficial fascia contains the platysma muscle, which was that muscle I removed at the start, which was that thin strap, sheet-like muscle. And then you’ve got the deep fascia, which there are several different layers. You’ve got the investing layer, you’ve got the carotid sheath, the pre-tracheal fascia and the prevertebral fascia. I’ll just quickly show you a diagram to explain that.

 

I’ve got this diagram here. Sorry about the resolution, but it does explain the fascial  compartments. We’re looking at a cross-section of the neck. This is anterior and this is posterior. The superficial fascia isn’t included on this diagram. This is just the deep fascia of the neck.   The superficial fascia would run outside of this and the platysma would be contained here anteriorly in the superficial fascia.

 

We’ve got the investing fascia, which encloses the entire neck. You can see how it splits to surround the trapezius muscle posteriorly and anteriorly, it splits to encapsulate the sternocleidomastoid muscle.

 

And then you’ve got these others fascial compartments.   Here, the fascia is all in green. We’re looking at the green areas. This fascia here is the pre-tracheal fascia and it encloses the viscera of the neck. It encloses the trachea, the thyroid gland. It actually encloses the esophagus, which isn’t shown on this diagram.

 

Just anterior to the pre-tracheal fascia, you can see these little oval shapes. These represent the strap muscles, the infrahyoid muscles. Then you’ve got this little circular fascia. This is the carotid sheath. This encloses the jugular vein, the carotid artery and the vagus nerve.   This neurovascular bundle has its own sheath, the carotid sheath.

 

And then you’ve got the prevertebral fascia, which actually runs all the way back to enclose the vertebral column and the muscles associated with it.   You’ve got the prevertebral muscles, the anterior, middle and posterior scalene muscles and the deep muscles of the back which are enclosed by the prevertebral fascia.

 

Just to quickly recap. You’ve got superficial and deep fascia. Superficial fascia runs outside the deep fascia and encloses the platysma muscle. And then the deep fascia has four compartments.

 

You’ve got the investing layers, which surrounds the entire neck and encapsulates the trapezius muscle and the sternocleidomastoid muscle. You’ve got the carotid sheath, which contains the common carotid artery, the internal jugular vein and the vagus nerve. You’ve got the pre-tracheal fascia, which encloses the larynx, trachea, thyroid gland and esophagus (the viscera of the neck). And you’ve got the prevertebral fascia around the cervical vertebrae and the associated deep muscles, scalene muscles and prevertebral muscles.

 

That’s the organization of the neck.