Hey, this is Stan Prokopenko with Proko. It's time for our last two back muscles, the trapezius
and rhomboideus.
Trapezius
From the front it looks like a trapezoid shape, which is how it got the name trapezius. From
the back, however, it looks more like a kite or a spinning top.
Remember learning about the shoulder girdle way back in the bone lessons?
I hope so, because you'll need to be familiar with the scapula and clavicle for today's
lesson.
As you can see, the trapezius originates along the path of spine and inserts along the top
of the shoulder girdle. That means it attaches to the spine of the scapula, the acromion
process, and the clavicles. You can probably guess what it does, right?
Exactly! The trapezius moves the shoulders for things like shrugging or, well, anything
with your shoulders, really.
The trapezius doesn't just raise your shoulders. It anchors above and below the shoulder blades,
so it pulls the scapula closer to the spine and helps lower it too.
A good indicator of the function is the direction of the muscle fibers. As you can see, the
fibers of the trapezius pull in many different directions.
It's a pretty complicated muscle. Let's simplify it a bit by splitting it into a diamond shaped
tendon in the middle and 3 distinct portions around it - upper, middle, and lower portions.
Let's look at them in-depth.
Upper Portion
The upper portion is that trapezoid shape visible from the front of the body. It originates
from the base of the skull, along the nuchal ligament and the 7th cervical vertebra, which
is that bony landmark on the back of your neck. However, the muscle fibers don't reach
all the way to the midline. They attach to a flat, diamond-shaped tendon which is centered
around the 7th cervical vertebra. The upper portion of the trapezius attaches to the top
half of this diamond shape.
The fibers flow downward and laterally to insert on the lateral third of the clavicles,
as well as the acromion process. Sometimes the upper portion will also insert to a small
part of the spine of the scapula.
You can see here how the fibers twist around to insert on the clavicle in the front. And
again in a front view.
The function of the upper portion is to elevate the scapula. But, if the scapulas are fixed,
then the trapezius moves the head. When one side flexes, it tilts the head side ways.
When both sides flex together, they flex the neck to bring the head back.
Middle Portion
The middle portion continues where the upper portion left off. It originates along the
spine from T1 to T5, and reaches across the back to insert on the top plane of the spine
of scapula. The muscle fibers attach to the bottom half of that diamond-shaped tendon.
On a muscular or lean person the insertion along the scapula is quite dramatic...
Well, maybe not THAT dramatic. The muscle ends abruptly, so it bulges out above the insertion and clearly
outlines the spine of the scapula. It's one of the most recognizable features of the trapezius.
The muscle fibers of the middle portion are pulling more horizontally, from the spine
out to the scapula. So, when this portion is flexed it retracts the scapula inward,
pulling it toward the spine.
Lower Portion
The lower portion is the "tail" of the trapezius. It originates along the spine from T6 to T12,
which is the lowest thoracic vertebra. The fibers go upward laterally to insert on the
spine of the scapula again, but this time along the bottom edge.
There's a triangular tendon here that wraps over the supraspinatus. The muscle fibers
attach in an arc, so on the surface the muscle has a sharp C curve here. It almost looks
like someone removed a chunk with an ice cream scoop.
There's another triangular tendon at the bottom of the tail. Notice the "w" shape at the bottom
of the tail? Each side of the trapezius will have it's own tail, since it's the muscle
part that bulges on the surface. Even though the tendon attaches all the way at T12, visually
on the surface, it will appear to end earlier.
When flexed, this lower portion will pull the scapula downward, to lower the shoulder.
Rhomboid
Like the trapezius, the rhomboideus aka "rhomboid" is named after its shape. Unlike the trapezius,
the rhomboid is very simple. Woohoo! It's layered under the trapezius, so its form is
softened. However, the rhomboid is thick enough that it shows through on the surface, so we
definitely need to study it. Let's take a look.
It originates on the spine, from the 4th or 5th thoracic to the 7th cervical and also
on the nuchal ligament for the distance of one more vertebra. It reaches downward diagonally
to insert on the medial edge of the scapula. You can see its rhombus-like shape.
So, notice how its direction of pull in this area is perpendicular of the trapezius. The
trapezius pulls this way, and the rhomboid pulls this way. This crossing of the muscles
can create some complexity on the surface and changes the way it looks depending in
the articulation of the pose. But knowing how to track the muscles from origin to insertion
will help us dissect what we're seeing.
The rhomboid works with the upper portion of the trapezius to elevate the scapula, for
the shrugging motion. It also medially rotates the scapula and hugs it tight against the
rib cage. Not that kind of hugging. But mainly, the rhomboid retracts the scapula pulling
it back toward the spine. That's a lot of responsibility for a muscle most people don't
know about. Maybe that's why rhomboids can get really thick. Man, my rhomboids are so
swole.
We'll learn about the forms in the next lesson, as I show you how to draw the upper back.
See you next time!
So, we have a premium section for students that want to learn more. The premium section
has extended lessons with more information about the topic. It also has additional drawing
demonstrations. If you do the assignments for each lesson, these demos serve as the
answers for the assignment, so you can check your work. There’s an ebook version of each
lesson that you can download as a PDF. Print them out or keep them on your device so you
can quickly review the lessons. And finally the Premium section has 3d models that you
can spin around, study, and draw from any angle. If you don’t want your drawings to
look like this, go to proko.com/anatomy.
If you like this video, don’t be all selfish, share it with your friends! And if you want
to be updated about new videos click this button or go to proko.com/subscribe.