The Spine: Form & Function

Genny Kapuler

Dharma is from the Sanskrit root dhr meaning to uphold, support, sustain. As B. K. S. Iyengar writes in Light on Pranayama, it is “the code of conduct that sustains the soul and produces virtue”. At Estes Park in 2005, Mr. Iyengar said, “That which has fallen, that which is falling, that which may fall, dharma holds it up.” In the body, the spine is like the dharma – it is that which keeps us from falling, that which holds us up.

The vertebral column or backbone is a long curved pillar, composed of segments called vertebrae, connected by ligaments and fibrocartilaginous discs. The function of the spine is weight bearing, to protect and allow movement in the spinal cord and internal organs of the torso and pelvis.

There is an axial line running from the heavens to the molten lava center of the earth. It is the pull of gravity. It is the plumb line in carpentry and architecture. In the body it runs from the crown of the head touching at C3 in the center of the cervical curve, runs through the center of the ribcage, touches just behind the navel at L3, and then runs through the soft tissue of the pelvis, either between the sitbones while sitting, or between the feet while standing. The spine supports this axial line.

The bulky part of each vertebra is its anterior part, called the body. The most posterior part is a bony projection called the spinous process, whence arose the terms spine and spinal column. The transverse processes protrude out to the sides, and serve as places for muscular attachments. The articular processes, superior at the top of the vertebra and inferior at the bottom, interlock with the vertebrae above and below. These articular facets function to prevent undesirable movements between adjoining vertebrae. The shape of the spine is pyramidal. Going down the spine, the vertebrae and corresponding discs increase in size in all dimensions, as do the articular facets.

The spine is divided into four sections named for the regions of the body: the cervical, thoracic, lumbar, and sacral. These sections correspond with the four curves in the spine. The infant is born with the spine in a C curve. The first months are spent developing the forward curve of the neck. Creeping around on the belly and crawling on all fours, the infant comes to sitting and then standing, creating a forward curve in the lumbar that echoes the forward curve of the neck. Walking is the height of the developmental motor process. Children have 33 vertebrae and adults have 26. Between puberty and about the age of 25 the five sacral vertebrae fuse to form the sacrum and the four coccygeal vertebrae fuse to form the tailbone.

The atlas is the first vertebra, located a little below the level of the floor of the nose. A ring of bone supporting the head, it is named for the Greek god who holds up the world. The atlas has no body and no spinous process so the head has great range of movement. It has very wide transverse processes for the muscle attachments of the head and neck. However, after a slight flexion or extension, the movement of the skull goes into the neck. In yoga, we have to make sure to connect the head into the spine so that in movement, whether forward or backward or side to side, the head does not fall, but stays connected and supported by the spine.

The word cervical is from cervix, the Latin word for neck. The cervical spine has seven vertebrae; most mammals have seven cervical vertebrae in their necks, even giraffes. The movement of the cervical spine is in all directions: flexion, extension, side bending and rotation. This freedom of motion is due to the horizontal shape of the vertebral facets. Facets are the joint surfaces of the articular processes, where the vertebrae fit together.

Thoracic is from thorax, the Latin and Greek words for breastplate. The 12 thoracic vertebrae have movement in all planes but the movement is less than in the cervical spine. Because there are 12, the accumulative movement is considerable. As we go up the thoracic curve the rotation increases with the most rotation in the upper ribs and thoracic vertebrae.

There are five lumbar vertebrae. Lumbar is from the Latin word for loins. In the lumbar region, the movements of flexion and extension are fullest, but due to the interlocking joints of the lumbar vertebral facets, rotation is prevented. There is very little rotation between the lumbar vertebrae, especially in standing. Rotation would put too much torsion on the discs.

Sacrum is the Latin word for sacred bone. The sacrum is made up of five vertebral bodies united by four ossified vertebral discs. The first sacral body has a prominent, oval, upper surface with a distinct forward tilt. The body of the first coccygeal vertebrae is united to the lower end of the sacrum by a fibrocartilaginous disc making this another moveable joint. So we can actually wag our tails like a dog or a cat.

Movements between the individual vertebrae take place at the discs and at the joints between the paired articular processes of the vertebral arches. Movements at the discs are greatest where the discs are thickest, and movements at the articular processes are greatest where the joint surfaces are largest. Also, weight borne by the individual vertebrae increases progressively as the series descends.

Discs are one fifth to one third as thick as the neighboring vertebral bodies. Discs are made up of concentric rings of fibrocartilage and a central mass of pulpy tissue which represents the remains of the notochord, the original fetal beginnings of the spine. Discs act as shock absorbers, and bulge when under pressure. Discs are relieved of pressure when we are supine. Being the non-rigid part of the vertebral column, they give it flexibility. When we move, different parts of the discs are under compression.

As yogis we take the form of the combination of our genetics and the way we have used and developed our bodies, and begin to focus on the cultivation of inner sensory awareness and alignment, through asana and pranayama. When we balance the spine – front/back, side/side, and up/down – we are also creating a harmonious support for the heart and the vessels of the circulatory system, the lungs, and the diaphragm. This lifted order in the thorax allows the iliopsoas muscles to support the abdomen and the connecting legs below.

In utero the spine develops before the limbs that develop as limb buds on the sides of the fetus. These buds flower into arms and legs. In asana we use these developmental pathways to organize the spine by the conscious use of the arms and legs and by drawing them back into the spine for support along the same threads that were originally spun out.

Muscularly, the support of the front of the spine is from muscles which reach from the skull down to about the third thoracic vertebrae. Then the support comes up from the legs in the form of the iliopsoas muscles which reach up to T12. From T3 down to T12 the support is from the heart, lungs, and thoracic diaphragm.

At the back of the spine, the erector spinae muscles interweave in four layers to support the vertebrae and connect the pelvis to the ribcage to the head. The duet of the erector spinae and the iliopsoas creates balance in movement.

There are 33 spinal nerves exiting from the spine out through openings between the vertebrae called foramina. If we lose the space between the vertebrae, either through disc degeneration or too much stress in the spinal muscles, the resulting reduction in the spinal foramina can put pressure in the exiting nerves.

To close, take a moment to apply this information directly into your body-mind: sitting on your sitbones, move your tailbone in and lengthen your spine up to behind your nose. Close your eyes, and see your spine in your mind’s eye. Direct more and more prana into your spine until you are fully lengthened and can sense the living vitality within each vertebra. Focus more precisely on the movement upward of the vertebrae and discs, and anchor your sitbones down as a counter-support. Balance your head on the top of your spine by lengthening the back of the skull and drawing a line from the upper palate to the back of the skull. Take a few quiet, observed breaths.

Genny Kapuler, Junior Intermediate III, began studying experiential anatomy, now called embodied anatomy, with Bonnie Bainbridge Cohen in 1975. She then became certified in Body-Mind Centering, and after that in the Alexander Technique. Genny teaches workshops and classes in anatomy at the Iyengar Yoga Institute of New York, her own studio and yoga studios internationally. She has studied many times with the Iyengars, both in India and in the United States, and was a student of Mary Dunn for over 20 years.

References: The Thinking Body, by Mabel Elsworth Todd. Primary Anatomy by John V. Basmajian.