Unit III – The Spine

 
 

Objectives

 At the completion of this unit the student will be able to:

1.      Discuss the major functions of the spine.

2.      Identify the bony components of the spine.

3.      Identify the key parts of a typical vertebrae.

4.      Name all movements of the trunk.

5.      Locate on a picture the major muscles of the spine.

6.      Name the primary functions of the spine muscles or muscle groups.

7.      Discuss the relationship of the posterior and anterior spine muscle to postural support.

8.      Apply knowledge of anatomy to the important movement concept of head-tail connectivity.

 

 

Introduction

Units III -V will address the trunk, which is made up of the spine, the rib cage and breathing apparatus, and the pelvis.

It is important to remember that though we will be dealing with the anatomy of these components separately, they all function as a unit to provide motion and stability that resonates from the midline of the body.

As Peggy Hackney reminds the dancer in her book, Making Connections

“The concept that head and tail are in a constant and always changing interactive relationship is often the single most important realization that a student of movement can have. Such a realization provides the automatic in-road to patterning the whole body from a central core of active involvement. All movement, from simple to complex, is aided by awareness of relationship through the spine.” (pg. 87, Making Connections, Gordon & Breach Publisher, Amsterdam, 1998)

To fully understand this concept of head-tail connectivity the dancer must understand the anatomy of the trunk. Let’s begin now with the spine!  

 

Functions of the Spine

The spine, or vertebral column, forms the skeleton for the back. It is the central feature of the trunk. The spine bends and rotates in many directions, and forms a strong, but flexible support for the trunk. There are 23 intervertebral articulations (connections between bones) that allow the spine to perform multiple actions simultaneously. The spine has ligaments that limit motion and muscles that attach to provide motion. The delicate spinal cord is housed within the spinal canal of the bony spine and provides the nerve connections throughout the body.

The spine serves the important functions of:

  1.  Active movement of the trunk

  2.   Support for the body and respiratory function

  3.   Protection of the spinal cord and nerve structures

 The finely integrated system of muscles, nerves, ligaments, and fascia provide an anchor for important body functions like respiration, as well as postural support for the body – especially in positions against gravity.

Structure of the Spine

The main bony component of the spine is the vertebral column. It is composed of 5 sections:

Cervical – 7 cervical vertebra at the superior (top) portion of the spine

Thoracic – 12 vertebra form the middle portion of the spine; attach to 12 pairs of ribs

Lumbar – 5 vertebra that are the lower portion of the spine and primary weight bearers

Sacrum – 5 fused bones that make up the triangular bone at the base of the spine

Coccyx – 3-4 small bones that make up the tail bone at the lower tip of the spine

 

 

These vertebra are named according to the section and number:

 Example – the 7th cervical vertebra is called C7. The 2nd lumbar vertebra is L2.  

 

Structure of a Vertebra

The exact structure of vertebrae in each sections of the spine differs slightly to reflect the function of that area of the spine. However, each vertebrae has the same anatomical structures. Each vertebrae consists of 2 main parts:

Bony Structures:

  • The Body – the large anterior section

  • The Vertebral Arch – the posterior section

 

The Vertebral Arch has two sections: 

  • Pedicles – small bony pieces that connect the arch to the body of the vertebra

  • Lamina – these join posteriorly to form the spinous process

**The tip of the spinous process is visible when viewing an individual from behind. The spinous processes are the small pointed bony structures that run down the middle of the back.   

There are several facets, or flat places, on a vertebra that serve to connect or articulate with other vertebra, ligaments, or muscles:

      Articular Facets – located between the pedicles and lamina. They are both superior and inferior on the vertebra

      Transverse Processes – facets that project laterally

Vertebral Foramen – This  is the opening between the body of the vertebra and the vertebral arch. When the vertebra are stacked this forms the vertebral canal in which the spinal cord is housed.  

Structure of the Intervertebral Disc:

Each vertebra attaches to the other by a combination of 3 joints:

Two small joints on the posterior of the vertebra, the articular facets, connect the vertebral arch components and form the intervertebral foramen. The anterior joint between the bodies of the vertebra is called the Intervertebral Disc.

disc is shown in blue between the vertebral bodies

The Intervertebral Disc is designed for weightbearing and provides strength for the spine. It is a partially gelatinous structure. The internal portion of the disc is called the nucleus pulposus and is the more gelatin-like component.

             Imagine jello that has been in the refrigerator too long!  

It is surrounded by a fibrous structure with criss-crossing layers that provide strength. This outer layer is called the annulus fibrosis.

Together the components allow the disc to have the ability to change shape with spine movement, and act as a shock absorber between the vertebra.

Ligaments:

 

Two important accompanying structures about the spine that contribute to mobility control and add stability to the spine are the Anterior and Posterior Longitudinal Ligaments. They are long ligaments that run the length of the spine in front and in back and serve as “check” strips for motion.
Try this now: Imagine you are standing straight and place a long piece of tape from the top of your chest to your navel, on the surface of your skin. After it is secured tightly backward bend. As the tape tightens it “checks” your backward bending by pulling when it reaches its tension limit. The longitudinal ligaments of the spine serve this same purpose and work together to protect the intervertebral disc from punching out between the vertebral bones.

Relevance to Dancers:  

Sometimes when the disc punches out, in spite of this protection, the result is a “slipped disc”. The appropriate medical name for this condition is a “herniated nucleus pulposis” or  a “herniated disc”. Male dancers should be especially aware of the risk for this injury. One common mechanism that causes a ruptured disc is lifting with a load. When a male dancer repeatedly lifts another dancer, and may do this in incorrect ways that put the back at risk for increased stresses, the result can be injury to the disc. It is important to maintain stable postures of the trunk and have strong support muscles to protect the disc.

  Now that you know the main structural components of  the spine, let’s look now at the movements of the spine and the muscles that make those movements happen.

 

Motions of the Spine

There are 4 primary motions of the spine:

 

  Flexion – forward bending of the spine that occurs in the sagittal plane.

 

Extension  - backward bending of the spine that occurs in the sagittal plane.
Side Bending – the right or left bending of the spine that occurs in the frontal plane.
Rotation – the turning of the spine to the right or to the left on the central axis of the body. There is more rotation in the cervical and thoracic spine, than in the lumbar region.

Relevance to the Dancer:

  Movements in the spine usually occur in multiple directions at the same time. Think of a dance phrase in which you move into forward bending but sidebend right and rotate to the right in your trunk at the same time. The stable nature of the bones, ligaments, and muscles allows us to put multi-directional stresses on the spine and move through space.

 

Muscles of the Spine  

 

Posterior muscles of the spine

Most of the body weight is anterior to the vertebral column. For this reason, there are many strong muscles on the posterior aspect of the spine to support and move the vertebral column and support it upright against gravity.

There are 2 primary groups of muscles in the back:

  • Extrinsic back muscles and Intermediate back muscles form one group.

  • Deep or Intrinsic back muscles form the second group.

Extrinsic Back Muscles – These are the superficial and intermediate muscles that produce and control limb and respiratory movements. 

Superficial the superficial muscle layer is shown on right–  Latissimus Dorsi, Levator Scapulae, Rhomboids. The Trapezius is below.

These connect the limbs to the trunk and control limb movement.

Intermediate the deeper layers are shown on left – Serratus Posterior

These are superficial respiratory muscles and will be discussed with respiration in Unit IV

 

_____________________________

Deep or Intrinsic Back Muscles – These are the deeper muscles that act to maintain postural control and actually move the vertebral column

These muscles are also layered from superficial to deep layers with the more superficial groups running in 3 long columns. These 3 muscle groups run the length of the spine and collectively are called the Erector Spinae Muscles. The Erector Spinae Muscles are the primary muscles that actively extend the spine.

The intrinsic back muscles are divided into the superficial and deeper layers

 

 The following are the most superficial group as seen above with muscles to the left of the spine:

  •  Iliocostalis – the lateral most column

  •  Longissimus – the middle column

  •  Spinalis – the medial most column; lines up by spinous processes

These muscles at connected superficially by a broad tendon that  attaches to the ilia and the sacrum called the Thoracolumbar Fascia.

Imagine this fascia is like the packing tape you find on a box. It is strong with small longitudinal fibers that are difficult to tear.

 

 
The following are the deeper layer intrinsic muscles of the back as seen below:

These muscles are the small and shorter muscles that connect the vertebra. They connect from the transverse processes of one vertebra to the spinous processes of the neighboring vertebra. These muscles work together to extend and rotate the spine. There are 3 layers of these muscles:

  •   Semispinalis – superficial

  •   Multifidi – deeper

  •   Rotatores – the deepest layer

 You cannot put your fingers on these muscles through the skin. They are located very deep and below other more superficial muscles.

 

 

 

Let’s Review and picture the layers of muscles before we begin to talk about specific spine muscles:

 In diagram above the layers are illustrated and shown superficial to deep from the posterior surface::

Skin & Fascia - most superficial and overlays the other structures; beneath this layer are the layers of muscles:

  • green line is superficial layer: Superficial Back Muscles- trapezius, lattissimus, levator scapulae, rhomboids

  • blue line is superficial intrinsic layer:  Superficial Intrinsic Muscles- iliocostalis, longissimus, spinalis

  • white line is deep intrinsic layer:  Deep Intrinsic Muscles - semispinalis, multifidus, rotatores

 

Another deep muscle that impacts spine movement is the Quadratus Lumborum. It is located between the lowest typical rib and the top of the ilia. This muscle functions to hike your hip. Stand on the floor with weight evenly on both feet. Hike your right hip toward you head. The quadratus lumborum on the right side must do a shortening contraction to produce this movement.

 

Quadratus Lumborum  
Remember these muscles groups function primarily to extend or rotate the spine. Let’s consider now the muscles that are located anterior to the vertebral column and function to flex the spine.

 

Anterior Muscles of the Spine

The abdominal muscles together form the anterior portion of the muscle support for the spine. They are also an integral part of core support and abdominal wall support for respiration. The abdominal muscles as a group bring the trunk into a flexed position, or forward bending. There are four main groups of abdominal muscles:

1)      Rectus Abdominis – This is the central-most muscle which has striations across it. If the individual is well developed and has low body fat, you can see the rectus abdominis under the skin and see the striations. This is most often visible in men. (see illustration just below right)

 

External Obliques

 Internal Obliques

2) & 3)  External Oblique and Internal Oblique – these muscles lie more laterally on the chest and are angled from outside to middle from above, and from outside to middle from below. They form a shape like an "x" across the abdomen. They attach from the ribs above down to the top of the pelvis below. When these muscles contract together they flex the spine. When there is contraction of one side they flex and rotate the spine to the opposite side. (see picture below right)

Weakness of the oblique muscles results in decreased breathing efficiency and decreases the support of the intestinal organs. The obliques act like a girdle to support the gut area.

                  
When the abdominal obliques perform this action from a sit-up position on your back there is rotational motion that brings the shoulder  toward the opposite knee.
4) Transverse Abdominis – this is the deepest abdominal muscle. It is located between the ribs and the top of the pelvis beneath the other abdominal muscles. It forms a horizontal band across the gut area. It functions as a girdle also to compress the abdominal area. This muscle is thought to play an important role in stabilization of the trunk. It is a deep holding muscle that when activated allows movement of the limbs around a stable spine and pelvis.
Transverse Abdominis
 

The abdominals will be discussed in more detail as they relate to respiration in the next unit.

 

Muscle Integration about the Spine – Postural Support

 

The posterior and anterior muscles that surround the bony spinal column have been discussed. The anterior muscles function to bend the spine forward, while the posterior muscles work to backward bend the spine. It is important to remember, however, that these muscle groups function together in a dynamic, isometric fashion to provide postural support for the trunk, especially against gravity. The back extensors and flexors maintain a constant tension and support the trunk in space. This central support from the muscles provides adequate stability of the trunk that allows the extremities to move around a stable core. If there is an imbalance in the muscular structures of the trunk instabilities can result. 

This concludes Unit III.

Another important component of trunk and core support is the respiratory component of the trunk. This will be discussed in Unit IV.  Return to Blackboard to proceed to Unit IV.