B2 High-Intermediate 912 Folder Collection
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The spine is literally the backbone of the body. It holds the torso together and moves
it around.
Hey there, I'm Stan Prokopenko, you're watching Proko.
We're going to start our study of the skeleton with the spine. The spine is the connection
between the 3 major masses: the head, ribcage and pelvis. And it's wedged between 2 butt
cheeks.
When constructing the figure, it's common to start with these 3 masses, before adding
the limbs. Remember how in the figure drawing course we used the bean and Robo bean to quickly
establish the torso? The bean was a simple way of establishing the gesture of the torso
using simple shapes. The robo bean added more structure to the bean to describe its orientation
in space.
Melissa: I can't even see the spine. Why do we study it?
Here's the deal with the spine. It places the rib cage, the pelvis, and the skull wherever
they happen to be, and they can't go anywhere the spine doesn't let them. They inherit the
spine's limitations. If we want to construct a torso in any pose, we need to understand
the spine. Let's do it.
Big Structure of the Spine
The spine is strong enough to support the weight of the upper body, yet flexible enough
to move. It's composed of 24 individual vertebrae - hard bones that give the spine its strength.
The vertebrae have flexible cartilaginous discs between them, that allow the spine to
move as a single line. Each plane moves only a little, but they add up to a lot. Like string
of beads. Every little movement contributes to a graceful curve.
There are 4 sections to the spine. The cervical section of the neck consists of 7 vertebrae.
The Thoracic section of the ribcage has 12 vertebrae, one for each rib. The Lumbar section
of the lower back has 5 vertebrae. The fourth section is technically considered as 2 separate
sections, but I'm going to combine them - the sacrum and coccyx, which is the tailbone.
The sections give the spine a 4-arch curve. If the spine were a straight line, it would
be strong, but rigid. This 4 arch curve gives better flexibility for shock absorption and
aids in balance. And it's the framework for the posture of the body.
The cervical curve is the least curvy - it's almost a straight line. But, it does have
a very subtle forward curve. The thoracic curve is longest, and more curvy than the
cervical section. It curves backward and aligns with the shape of the ribcage. The lumbar
section curves forward and is even more curvey. The Sacral curve is the most curvey of all
the sections. So, as you can see the curves get progressively curvier as they go down
the spine.
Common Structure of the Vertebrae
The vertebrae of each section have slightly different structures, some for strength, some
for flexibility. However all the vertebrae, share the same common components.
Each has a thick disk-like Body, which connects to the neighboring vertebra with a squishy
little pillow, forming the main joint of the spine.
On the back of the body is a u-shaped Arch, creating a hole through which the spinal cord
runs. This locks the fragile spinal cord inside and provides protection.
On this arch are a few processes; little spikes that stick out like the needles on a porcupine.
A Spinous Process points out posteriorly. The subcutaneous tip is the only part of the
vertebrae that makes an appearance on the surface body.
The shape and angle of the spinous process changes as we move down the spine. Cervical
spinous process fans out like a lobster tail. Thoracic is a long spike. Lumbar is like the
blade of an axe. But these shapes are not observable on the surface. We can only observe
that the thoracic are pointy and the lumbar are longer. The first 6 cervical aren't visible
at all. Those are deeper in the neck, cover by the nuchal ligament. The first visible
vertebra is 7th Cervical, which is considered a major landmark of the body. This is the
most pronounced and clearly visible vertebra along the spine, seen right in the the middle
of this diamond shape between the trapezius muscles. Also, the middle vertebrae of the
thoracic section are usually not visible, even during forward lean, when the back muscles
are stretched. But, this varies. Sometimes you'll see all the thoracic and lumbar vertebrae.
Motion
What the spine does, affects the entire torso.
The thoracic section leans back, and the sacral leans forward. Since the rib cage and pelvis
attach to the spine, they inherit this lean. So this, is the default position. Not this.
From there each section has it's own range of motion.
The lumbar section has the largest and strongest vertebrae of the spine. It takes on the responsibility
of holding all the weight of the upper body. It also takes care of lateral bending, flexion
and extension. Especially flexion. When you bend down to touch your toes, most of that
bending happens at the lumbar region.
The lumbar region is able to bending side to side, mostly at the top 3 lumbar vertebrae
because the bottom two are connected to the sacrum by ligaments.
Rotation is restricted in the lumbar region..
The thoracic vertebrae are not as large and strong as the lumbar, so you'd think they
have more flexibility. But, you'd be wrong. The interlocking structure of the vertebrae
and the fact that they are attached to the ribcage, keep the thoracic section relatively
still. Flexion, extension and lateral bending are very minimal. However, the thoracic section
is able to rotate. Rotation is the main motion of the thoracic section.
The cervical spine is the thinnest and most delicate, so this allows for more flexibility
in the neck. Rotation along all 3 axes is possible. Flexion, extension, lateral bending
and rotation.
The first 2 vertebrae of the cervical section are unique. The Atlas and Axis. The axis has
a vertical cylindrical process inserting into atlas. Can you guess what kind of joint that
creates? [pause] You guessed it! A pivot joint. As we'll see in a few minutes, this allows
the head to rotate left and right.
50% of cervical rotation is at the joint where the atlas meets the axis. 50% of cervical
flexion and extension is at the joint where the altas meets the skull. So, the head can
rotate side to side and up and down without much help from the rest of the neck, but the
head can't bend laterally. The neck does that. Instead of drawing this, you would draw this.
Let's review. The cervical section is somewhat separate from the rest of the spine. It moves
the head around and has a lot of freedom to move in all directions. The thoracic and lumbar
sections are more limited and have to work together. Thoracic takes care of most rotation
and lumbar takes care of flexion, extension and lateral bending.
Drawing the spine
Ok all that information is great and all.. But how do we actually draw this stuff. How
does this apply to drawing the figure? I'll show you in the next video. Keep your eyes
out for that.
That's it, thanks for watching! If you're posting your drawings, use hashtag #proko
and don't forget to follow me on Facebook and Instagram. Also check out the Anatomy
for Artists group on Facebook at facebook.com/groups/anatomy4artists! If you like this video, share it with your
friends, and if you want to be updated about new videos click here to subscribe to the
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Anatomy of the Spine - for Artists

912 Folder Collection
vulvul published on September 27, 2015
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