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!
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