Spinal Regions & Vertebrae

Lesson Overview

In this lesson, we introduce the anatomy of the spine.

Objective

Become proficient in the anatomy of the spine including each of the five regions, the spinal curves and the vertebrae.

Description

Name the regions of the spinal column, the number of vertebrae in each region, and how vertebrae are labeled/numbered. Explain where we experience the most movement in the spine, and why. Describe the shape of each spinal curve. Understand the primary and secondary curves and why they are given those names. Describe vertebra and the joints related to vertebrae.

Overview of the Spine

  • The spine is also known as the spinal column, vertebral column or the backbone.
  • The spinal column is made up of 33 specialized bones called vertebrae.
  • Because the vertebrae of the sacrum and coccyx eventually fuse, there are, in effect, 24 vertebrae plus the sacrum and coccyx.
  • The spine has four “normal curves,” a term used by anatomists to underscore their importance.
  • Spinal curves are affected by genetics and postural habits.

Spinal Regions

Overview

The spine is described as having 5 regions:

  1. Cervical Spine
  2. Thoracic Spine
  3. Lumbar Spine
  4. Sacrum
  5. Coccyx

About the Regions

  • To see the spinal curves, the spine is viewed from the side.
  • The sacrum is the base of the spine and the back of the pelvis.
  • There are four curves in a healthy spine: cervical lordotic curve, thoracic kyphotic curve, lumbar lordotic curve and sacrum & coccyx kyphotic curve.
  • The vertebrae are numbered from the top down: C1 to C7, T1 to T12, L1 to L5, and S1 to S5.
  • The junctions where the curves of the spine change direction allow the most movement: C7 – T1, T12 – L1, and L5 – S1. For this reason, these points of transition are the most vulnerable to injury.

Cervical Spine

  • 7 vertebrae: C1 – C7
  • Lordotic: convex, curving in toward body
  • Most flexible part of spine and therefore often overused

Thoracic Spine

  • 12 vertebrae: T1 – T12
  • Kyphotic: curves away from body
  • If the curve exceeds 50 degrees, medical sources consider it abnormal and call it kyphosis
  • Generally can twist fairly easily but not bend forward and back as well

Lumbar Spine

  • 5 vertebrae: L1 – L5
  • Lordotic: convex, curving in toward body
  • Hyperlodosis is excessive curve
  • Generally can bend forward and back well but more challenging to twist
  • Tight hip flexors can tip pelvis forward, creating excessive low back curve

Sacrum

  • 5 fused vertebrae: S1 – S5
  • Kyphotic: curves away from body
  • The sacrum is the base of the spine and the back of the pelvis

The sacrum is a curved, bumpy bone that angles in toward the body at about 30 degrees, beginning at L5/S1; it does not point straight down. – Mary Richards link

Coccyx

  • 3 to 5 fused vertebrae with a tip that typically points straight down
  • Unlike rest of spine, it is dense bone only and does not house spinal cord

Coccyxes vary as much as noses – yours may be twice the size as your neighbour’s, or half the size. It may be a different shape and may point a different way. – The Normal Coccyx  

How Spinal Curves Develop

  • The thoracic and sacral curves — the kyphotic spinal curves — are developed in utero, and are therefore called primary curves.
  • The cervical and lumbar curves develop later and are called secondary curves.
  • The secondary curves are less stable and therefore more prone to issues.
  • The cervical curve develops during the birthing process and while learning to hold up the weight of the head, forming fully by around nine months of age.
  • The lumbar curve is the last curve to develop over time, fully forming by about age ten.
  • While the primary curves are supported by surrounding bones, the cervical and lumbar spine are “freestanding sections of the spine” which are therefore more impacted by the surrounding myofascia.
  • For a quick and clear primer on the evolutionary process of spinal development, see this 7-minute video where Leslie Kaminoff describes the environmental and functional purposes of the spines from sea creatures to mammals.

Development Over Time

In utero, the entire spine is in a primary [kyphotic] curve. It changes shape for the first time when the head negotiates the hairpin curve of the birth canal and the neck experiences its secondary (lordotic) curve for the very first time… The cervical curve continues to develop after you learn to hold up the weight of your head at about three to four months and fully forms at around nine months, when you learn to sit upright… At 12 to 18 months, as you begin to walk, the lumbar spine straightens out from its primary, kyphotic curve. By 3 years of age, the lumbar spine starts to become concave forward (lordotic), although this won’t be outwardly visible until 6 to 8 years of age. It is only after the age of 10 that the lumbar curve fully assumes its adult shape. – Leslie Kaminoff 

Secondary Curves are Less Stable

Because the secondary curves are developed and are the opposite of the curve of the column found in utero, they are less stable. It is much more common for yoga students to have problems with either the cervical or lumbar region than the thoracic or sacral, in part because of this lessened stability. – Judith Lasater 

Secondary Curves More Dependent on Muscles

All the primary curves are more or less maintained by the shape of the surrounding bones. The cranium is interlocked to itself, the thoracic curve is maintained by the ribs and sternum complex, the sacrococcygeal curve by the hip bones and pelvic ligaments and the heel by the shape of the foot bones. All the secondary curves, however, are more dependent on the balance of muscles, first to create and then to maintain their position: thus the cervical and lumbars, being the freestanding sections of the spine, depend more heavily on the guy-wires of the surrounding myofascia for their stability and positioning. – Thomas W. Myers 

Teaching Awareness

Here is a simple and effective exercise to help students become aware of the spinal curves.

From Savasana, notice the parts of the spine in contact with the earth:

  • Upper back
  • Sacrum
  • These are the kyphotic curves

Then take note of the parts of the spine that are off the floor:

  • Neck
  • Low back
  • These are the lordotic curves

A Different Take

For an opinion that might be considered contrary to the more common perspective, see the NPR article, Lost Posture: Why Some Indigenous Cultures May Not Have Back Pain. In this article, the focus is on a “J” shaped spine rather than an “S” shaped one

Vertebrae & Intervertebral Joints

Basic Anatomy

  • The spine is made up of 33 irregular, specialized bones called vertebrae.
  • The vertebrae vary in size and shape according to their location and associated function but follow a similar structural pattern.
  • “The vertebrae are bound together by two long, thick ligaments running the entire length of the spine as well as by smaller ligaments between each part of vertebrae.” (Larry Payne PhD)
  • All animals with spinal columns are known as vertebrates.

Individual Structure

  1. Each vertebra is labeled as having a “body” or “centrum” which is the thick oval bone forming the front of the vertebra.
  2. The “vertebral arch” is the name for the posterior portion of each vertebra.
  3. The opening in the vertebra for the spinal cord is called the “vertebral foramen.” (“Foramen” means a natural opening or passage, especially through a bone.)
  4. There is another opening called the “intervertebral foramen” which is the passage for the spinal nerve to exit the from the vertebral column. (source)
  5. The bony projections from the vertebra are called “spinous processes.They provide attachment points for muscles and ligaments. (The atlas and coccygeal vertebrae do not have spinous processes.)
  6. Spinous processes are the ridges that can be felt along the back of the spine.
  7. “The shape and orientation of the articular processes vary in different regions of the vertebral column and play a major role in determining the type and range of motion available in each region.”

Variations by Region

There are several different types of vertebrae, classified by their position. Cervical vertebrae form the upper part of the spinal column, with two special cervical vertebrae, the atlas and the axis, connecting the spine to the skull. Next come the thoracic vertebrae, which include points of attachment for the ribs, followed by the lumbar spine, which includes the broadest and largest bones to support the body weight. The sacral and caudal vertebrae follow, and in humans, these are fused into structures known as the sacrum and tailbone, respectively. – wiseGEEK 

Intervertebral Discs & Joints

  • Each moveable segment of the vertebral column (except C1/C2) is separated by “intervertebral discs” and “articulating facet joints.” 
  • Discs are spongy material that serve to absorb shock.
  • “The intervertebral discs are fibrocartilaginous cushions serving as the spine’s shock absorbing system, which protect the vertebrae, brain, and other structures (i.e. nerves). The discs allow some vertebral motion: extension and flexion. Individual disc movement is very limited – however considerable motion is possible when several discs combine forces.”
  • There are joints between the bodies of vertebrae and joints between vertebral arches.
  • Intervertebral joints include both synovial and cartilaginous joints. 

The Effect of Gravity on Intervertebral Discs

Did you know that astronauts get taller in space? According to NASA studies, when the spine is not exposed to the pull of Earth’s gravity, the intervertebral discs expand and as a result the spine gets a bit longer… Once the astronauts return to Earth, their height returns to normal after a few months adapting to the Earth’s gravitational pull. In fact, you can test the effect of gravitational pull yourself if you measure your height before you go to bed and then again right after you wake up. The difference can be as much as 2 centimeters, which is attributed to the fact that intervertebral discs get compressed and dehydrated during the day (because of the gravitational pull and mechanical forces from both movement andsitting). During the night’s sleep the discs get rehydrated again – as a result you wake up taller. – Olga Kabel

Movement

  • While the vertebrae protect the spinal cord, they are also designed for movement.
  • “The spine is made up of vertebrae and their joints, each of which can move in six different directions. That’s a lot of movable parts, increasing the odds of something going wrong.” (Larry Payne PhD)
  • Intervertebral joints “allow for limited mobility between individual vertebrae but great stability to protect the spinal cord. Mobility of the spinal column comes from combining the limited movement of individual intervertebral joints as a whole.” (Ray Long MD)

Discs & Facet Joints

The discs create space between the vertebral bodies, allowing range of motion. The facet joints are bony connections between each vertebral body that guide direction of movement. They become more vertically oriented as you travel down the vertebral column. Generally, the more vertically oriented the facet joint is, the less range of motion you have in side-bending and rotation. Facet joints have a specific orientation in each region of the vertebral column. [Certival – almost horizontal for increased mobility. Thoracic – almost vertical for increased rotation. Lumbar – vertical for increased flexion and extension and limited side-bending and rotation.] – Mary Richards