All About the Spine: Anatomy and Movements

by Shari
Recently in my classes and private sessions I have been receiving a lot of questions about the spine and exactly how it moves in different yoga poses. I thought I would do a blog post to summarize basic spinal anatomy and what the yoga practitioner needs to consider when practicing. I also think it is important for us to learn about spinal movements because so we can begin to understand why one movement feels good to do while another movement either hurts or just doesn’t “go anywhere.” Many of our teachers are very skilled in the instructions they give us, but, for me, I always think that it is important to understand the why (I have never been very good about blindly following orders).
Let’s start with the anatomy of the spine. The spine is composed of separate vertebra, which are separate into five regions of the spine. The cervical spine is the neck area and there are seven cervical vertebrae. The thoracic region is the area that begins at the level of the collarbones (clavicle) and extends all the way down to the waist. The thoracic vertebrae connect to the ribs, and there are 12 thoracic vertebrae and 12 paired ribs. The lumbar region begins at the bottom of the rib cage and extends into the pelvis. There are five lumbar vertebrae and the last vertebra sits on top of the sacrum. The sacrum consists of five vertebrae fused into a single bone (the five are initially un-fused at birth, but begin to fuse in our late teens). It is joined on two sides to the pelvis and sits deep within the pelvic basin. At the bottom of the sacrum, we find the coccyx, which is composed of three vestigial vertebrae—our “tail” of bygone days.
It is important when learning about the spine to view it from multiple angles, including isideways, front facing and back facing. When you view it from these three angles, you can begin to appreciate the beauty and complexity of the spine. Some of the things that you may notice immediately when looking at pictures or, better yet, a three-dimensional model, of the human spine is that the various regions look different. The cervical vertebrae are petite and small in size, the thoracic vertebrae are bigger, with longer and more angled spinous processes, and the lumbar vertebrae are much more massive and substantial.
Also, it is apparent that the spine is not a rod but has four basic curves. The cervical region curves inward (concave), the thoracic spine curves outward (convex), the lumbar spine curves inward (concave), and the sacral region curves outward (convex). The shape of the spinal curves are important for transferring the load/weight, and maintaining those curves with weight-bearing forces keeps the spine healthy with minimal deterioration of joint surfaces. The cue that sometimes we hear in yoga class to keep our spine “straight” is a misnomer, because naturally the spine is curved! We don’t want to take the curves away but we do want to balance where the movement occurs.
Another point to consider is that the shape of the spine will change when we move through a range of motion in our daily lives as well as in our asana practice. Whenever we sit, stand, walk, reach, lie, and so on, we are changing spinal position. Sometimes the adjustments are small and imperceptible, and other times they are much more global. Going from sitting to standing changes the spinal curves in small degrees, while going into a deep forward bend or backbend changes the curves more dramatically. The muscles that attach to the spine are forever working to keep the spine stable in whatever position we are in.
There are three specific movements that the spine moves through. When we bend forward and curve the spine (reversing the lordosis of the cervical and lumbar region and exaggerating the curve of the thoracic region) this is called flexion. We cause spinal flexion in forward bends whether in a chair or seated on the floor. The degree of forward bend is generally limited by our leg and back flexibility. Some very common forward bends that require different degrees of flexion could be Seated Forward Bend (Paschimotanasana) and Plow pose (Halasana), which you could think of as an upside down from of Seated Forward Bend.
Why do I say there are different degrees of flexion? Well, for someone who is very tight in their legs or in their back muscles, just the act of sitting in Staff pose (Dandasana) with a lift under their pelvis is very challenging. Their natural inclination might be to sit in a rounded back or flexed spine position to start and then when they bend forward even more this becomes an unhealthy forward bend because there isn’t good distribution of the change in the spinal curve.
For the tighter student, learning to sit with their spine in neutral curves is the way to begin practice for spinal safety. The student who has a lot of flexibility in their hamstrings may have tight back muscles so when they bend forward there is no change in their spinal curves—both examples are extremes.
The key to healthy forward bends whether in Paschimotanasana or Halasana is for there to be “ease” in the bend.  The same principles apply to standing forward bends like Pyramid pose (Parsvotanasana). Props like chairs, bolsters, and blocks allow you to find the shape of the pose without the struggle to get into a pose you aren’t ready for.
The opposite movement to flexion is called extension. In extension, the curves of the cervical and lumbar region are deepened and the curve in the thoracic region is lessened. We extend our spines in classic backbends like Upward Bow pose (Urdva  Danurasana) Upward-Facing Dog pose (Urdva Mukha Svanasana), and Camel pose (Ustrasana).
Of course, our spines can also twist, as when we turn to look behind us in a car. We twist our spines in seated twists, such Bhajrajasana, or Marichyasana, and in standing poses, such as Triangle pose (Trikonasana) and  Revolved Triangle pose (Parivrtta Trikonasana). And in certain poses we combine both flexion and twisting as in Parivrtta Janu Sirsasana. Poses with both extension and twisting are less common, but one is example is the One-Legged Downward-Facing Dog pose with a twist (the pose that looks like a dog peeing).
The key concept to protecting your spine in all your poses is understanding where we want to encourage the movement and how to distribute the movement so not causing excessive motion  at one vertebral level . Another key concept is not to use momentum to push through “resistance.” When we are overly aggressive in attempting to gain motion this is where injury will surely occur.
So let’s break down this concept of spinal motion a bit more. If we understand that different parts of our spine move more in certain movements, does this mean that certain asanas will affect different parts of the spine differently?  Yes, absolutely!  The cervical and lumbar regions are concave when the spine is at rest and when we move into a backbend these areas become more concave in relation to the curve reversal of the thoracic region. Because the thoracic region is stabilized anteriorly by the rib cage and posteriorly by the long spinous process, there is relatively less curve reversal from convex to concave in this region. And we move into a forward bend, the rounding of the thoracic curve increases into more of a convex shape. The opposite occurs in the cervical and lumbar spines; they start in relative concavity and as the forward bend moves throughout the spine, their shape changes from concave to relatively convex.
In twists, it is important to try to encourage full spinal involvement, but understand that the majority of the twist will occur in the thoracic region, followed by the cervical region and lastly the lumbar region. There is very limited rotation of the lumbar vertebra due to their specific structural construction.
When you practice, try to picture how your spine changes shape from the starting position into the position of the asana and then back to your start position. This is your experiential anatomy lesson of flexion (forward bending) and extension (backward bending), and twists. Also, please try not to allow your spine to round or flex whenever doing twists.. The key to healthy twists is to keep the spine long, with a good conscious control of maintaining the curves as you twist. This is often erroneously called keeping the spine “straight”, but now you know better when you hear this cue from a teacher!