I learned a lot about the human spine this summer in the Experiential Anatomy online class led by the highly talented teaching team of Judith Hansen Lasater, Mary Richards and Lizzie Lasater. First of all, in fairness to Mary Richards, I need to get the nomenclature correct! As she noted, the vertebral column is a column or chain of vertebral bodies, whereas the spine is an anatomical term relating to a bony feature or ridge on various bones. Vertebra is singular; vertebrae is plural. There are some 33 bones in the vertebral column, most which move independently but several that are fused together and move as a unit.
The vertebral bones are arranged by size and shape, these being influenced by the curve in their respective part of the spine, and all of these attributes influences the function of that part of the spinal column. In order to bear more weight the bones get bigger from top to bottom of the column. In addition, the cervical vertebrae have less stability and more mobility, and progressing down the spinal column the lowest portion has more stability with less mobility.
Worship the normal curves
is the mantra that began the study of the vertebral column, giving new meaning to the age old exhortation to sit (or stand) up straight. Years ago I was able to memorize the number of vertebrae in each area according to meal times: 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae (breakfast at 7, lunch at 12, dinner at 5). I guess the snack is the sacrum, with 5 vertebrae fused into 1 bone, and the coccyx (aka tailbone) that consists of anywhere between 3 to 5 vertebrae.
The cervical curve is the neck area, and has as its first two vertebrae C1, the Atlas (named for the Greek God who held the heavens on his head), and C2, the Axis, which is responsible for head turning. The thoracic curve’s 12 vertebrae all attach to two ribs each, one on either side. The lumbar, or low back vertebrae are the most massive of all the vertebrae; think about how much weight they must bear, hence the need for their size. As noted in a prior post, there is maximum pressure on the vertebral discs when sitting, medium when standing and the least amount of pressure when lying down. Turns out this is why we are a tad taller in the morning.
Ever play with a slinky? If not, that’s a picture of one at the left. It is a spiraling column of wire that can “walk” down stairs and any movement in it reverberates throughout the entire slinky. This is similar to our backbone, which is a kinetic chain – “a connected chain of moving parts” where movement gets transferred up and down the spine.
The trio summed up the vertebral column as the central organizing axis – a giant, curved, coiled antenna receiving signals from the whole body. This axis connects to the hip axis, which is the central axis of movement. The part that connects these two axes is the sacrum, part of the vertebral column at the lumbrosacral joint (the joint between the last lumbar vertebra and the first sacral segment) and part of the pelvis at the sacroliliac joint (between the lowest part of the scarum and the iliac bone in the pelvis.)
My next post will explore each part of the vertebral column in a bit more detail.