Neck Muscles Anatomy – Posterior Triangle, Prevertebral and Lateral Muscles


This is a tutorial on the posterior triangle
of the neck. So the posterior triangle is bounded at the back by the anterior border
of the trapezius muscle. Anteriorly, it’s bounded by the posterior margin of the sternocleidomastoid
muscle (so this muscle here). And at the base, you’ve got the middle third of the clavicle.
And at the apex of the posterior triangle, you’ve got this bit of bone behind the mastoid
process, so this part of the occipital bone. So again there are several muscles which run
through the posterior triangle and I’m going to run you through these. Just to start off with, we’ve got the scalene
muscles, which quite annoyingly aren’t on this model. These originate on the transverse
processes of the cervical vertebra and they insert onto the first and second ribs. So
you’ve got three scalene muscles. You’ve got anterior, middle and posterior scalene muscles.
I’ll just flick over to a diagram to show you these, but they originate on the transverse
processes of the cervical vertebrae and run down through the posterior triangle to insert
onto the upper and second ribs. So here we have the diagram of the scalene
muscles. So you’ve got the anterior, the middle and the posterior scalene muscle. They originate
on the transverse processes of the cervical vertebra and they insert onto the ribs. So
the anterior scalene inserts on the upper surface of the first rib anteriorly and you’ve
got the middle scalene muscle which inserts a little bit posteriorly, just posterior to
the groove for the subclavian artery on the upper surface of the first rib. And then you’ve
got the posterior scalene which inserts onto the second rib, again, on the upper surface. So you can see by the origin and insertion
of these muscles that these will elevate the ribs. When they contract, they’ll draw the
ribs upwards. Unfortunately, they’re not shown on this model,
but you can just visualize that they would run through the posterior triangle here. So the next muscle is the splenius capitis.
This muscle inserts onto the back of the skull just behind the mastoid process and it actually
inserts on the mastoid process as well, but it’s not shown on here. I’ll just remove the
trapezius muscle, so you can see the origin. The splenius capitis originates on the spinous
processes of the vertebra, the spinous processes of C7 to T4 and it inserts onto the back of
the skull on the mastoid process and just below the superior nuchal line on the occipital
bone. Obviously, you’ve got one on either side. What this muscle does is it draws the head
backwards when it contracts. It brings the head backwards if they’re both contracting
at the same time. If one contracts, then it will rotate the head around, but if both contract,
it will draw the head backwards. So that’s the splenius capitis. Also running through the posterior triangle,
we’ve got the levator scapulae. This muscle as the name suggests elevates the scapula.
It originates on the upper surface of the scapula, the medial border of the scapula
(the upper medial border) and it inserts onto the transverse processes of the cervical vertebra.
It actually has four insertion points. It inserts onto the transverse process of C1
to C4. What this muscle does is it elevates the scapula. That’s the levator scapula. So the next muscle is the omohyoid muscle.
This is one of the strap muscles. If you watch the tutorial on the anterior triangle, the
muscles of the anterior triangle, you’ll have seen that the omohyoid inserts onto the hyoid
bone lateral to the sternohyoid and it has two bellies. It’s got an inferior and superior
belly. So the superior belly runs in the anterior triangle and the inferior belly runs in the
posterior triangle. So it’s the inferior belly that actually runs
in the posterior triangle. It has a tendon which inserts it onto the clavicle and then
it continues as the superior belly to attach to the hyoid bone. So that’s the omohyoid
muscle and it originates on the upper border of the scapula. It starts off here, winds
through the posterior triangle into the anterior triangle and attaches to the hyoid bone. So just to show you a quick diagram of that,
you’ve got the origin of the omohyoid on the upper border of the scapula and you’ve got
the inferior belly running through the posterior triangle. You’ve got this intermediate tendon,
which actually attaches to the clavicle and then you’ve got the superior belly of the
omohyoid, which inserts on the hyoid. What this muscle does is it draws the hyoid
bone down. It depresses the hyoid. So those are the muscles of the posterior
triangle of the neck. While we’re here, you can see these muscles
here which lie in front of the vertebra. These muscles are the prevertebral muscles. I’m
going to just quickly show you the prevertebral and lateral muscles of the neck. These are muscles which lie anterior to the
vertebral bodies and then you’ve got some lateral muscles which I’ll show you. I’ll
just flick over to a different view. So here, I’ve taken away the strap muscles,
the esophagus, the trachea and we’re just looking anteriorly at the vertebra. We can
see the prevertebral muscles sitting on top of them. So the prevertebral muscles flex the neck
and flex the head. The lateral muscles flex the head laterally. The prevertebral muscles,
you’ve got the longus colli and you’ve got the longus capitis. The longus capitis inserts onto the inferior
surfaces of the occipital bone, so the basilar part of the occipital bone just immediately
inferior to the foramen magnum. That’s the longus capitis insertion point. They originate
on the transverse processes of the cervical vertebra, so vertebra C3 to C6. So this is
the longus capitis originating on the transverse processes of C3 to C6 and inserting onto the
basilar part of the occipital bone immediately anterior to the foramen magnum. I’ll just
highlight that and you can see that. That’s the longus capitis. So again, you can visualize the function of
this muscle. Because they originate on the transverse process and insert here, when they
contract, they bring the head downwards. So they flex the head. That’s the longus capitis
which flexes the head. That’s one of the prevertebral muscles. And then you’ve got this muscle here, which
is the longus colli muscle. What this muscle does is that it flexes the neck anteriorly. This muscle has three parts. It’s got a superior,
inferior, oblique part and a vertical part. It has various origins and insertions on the
anterior parts of the vertebral body and the transverse processes of the vertebra. So what
it does is that it flexes the neck anteriorly and laterally and it gives slight rotation
to the opposite side. And then next, you’ve got the rectus capitis
muscles. These muscles, I’ll try and get a good view of them. It’s this muscle here.
You’ve got the rectus capitis anterior and you’ve got the rectus capitis lateralis. So
here, you can see, this vertebra here is the atlas bone, the first cervical vertebra. The
rectus capitis anterior originates on the upper surface of the transverse process of
the atlas bone and inserts onto the basilar part of the occipital bone. It flexes the
head at the atlanto occipital joint. You’ll see the word ‘rectus’ used a lot in
anatomy. It’s just Latin for ‘straight’. It’s a straight muscle. You’ve got the rectus abdominis
muscles and you’ve got the rectus muscles of the eye. ‘Capitis’ means ‘of the head’.
So its straight muscle of the head and it’s the anterior one because it lies anteriorly
on the atlas bone. So then you’ve got the rectus capitis lateralis
because it lies laterally. So this muscle is shown out of place on this model, but it
actually lies on the superior surface of the transverse process of the atlas and inserts
onto the occipital bone. What this muscle does is it flexes the head laterally on the
same side. So that’s the rectus capitis lateralis. There you go! That’s the prevertebral and
lateral muscles. You’ve got the rectus capitis muscles, so the rectus capitis lateralis,
you’ve got the rectus capitis anterior. And then you’ve got the prevertebral muscles.
You’ve got the longus capitis and the longus colli.