The basics of spinal anatomy at Camp4 Human Performance
This blog post is designed to educate patients about spinal anatomy at Camp4 Human Performance. In future posts I will discuss biomechanics and the loading patterns of each segment of the spinal column. Those posts will make much more sense with an initial exposure to basic spinal anatomy. At Camp4, we are all about educating our patients so they can make informed decisions why chiropractic and functional movement rehabilitation is a good choice to stay healthy. For additional questions about our therapies or clinic hours call the clinic or simply ask a question online.
To get started, lets breakdown all the bones of the human skeleton, in order to narrow down which ones belong to the vertebral column. The vertebral column (aka spinal column) are synonymous, and in this post I will use them interchangeably. Out of 206 bones in your body, only 80 of those compose the spinal column.
There are 80 bones in the axial skeleton (which comprises the skull and spinal column)
28 in the skull
26 in vertebral column including the sarum (tailbone) and coccyx
24 (1 on each side) ribs attached to the middle, or thoracic, section of the spinal column
1 sternum which holds the ribs in place on the front side
1 hyoid bone near your throat
126 bones in the appendicular skeleton (arms, legs, fingers & toes)
60 in the upper extremity
2 clavicles (collar bones)
2 scapulae (shoulder blades)
60 in the lower extremity
2 in the pelvic girdle
There are 6 primary functions of the spinal column:
- To protect and control transmission of the spinal cord and nerves.
- Stabilization, by serving as an attachment point for muscles and ligaments.
- As a support and weight bearing structure for the head and body.
- To create shape and position of the body.
- To control movement and flexibility throughout all 6 ranges of motion.
- As a primary shock absorbing structure.
Of the 26 vertebral bodies, 24 are considered true and 2 are considered false. True segments consist of those that are freely moveable in an adult, and false vertebrae are those which are not freely moveable. An example of this is the sacrum and coccyx, which are not fused in children.
There are three regions of the spinal column which are True.
7 Cervical vertebrae (neck region) that creates a curve which is concave to the back and convex to the front, also known as a lordosis.
12 Thoracic vertebrae (upper and mid back) that creates an opposite curve which is concave to the front and convex to the back, known as a kyphosis.
5 Lumbar vertebrae (low back) with a curve similar to the cervical region.
There are an additional two fused regions in the lower most portion of the spine which are considered false.
1 fused sacrum made up of 5 segments
1 fused coccyx made up of 4 segments
Both of these segments create a joint, the sacrococcygeal joint with a concavity towards the front of your body similar to that in the thoracic spine.
In sum, the adult spine is composed of 26 segments (24 true + 2 false) and a child’s spine is composed of 33 (24 + 5 + 4). Complete bone fusion doesn’t happen until between we are between 18-25 years of age.
Between each of the vertebral bodies you have a wedge shaped structure called the intervertebral (between) disc, which is designed to transmit and restrict forces in each part of your spine. This creates a joint classified as a syndesmosis, which means it is a joint composed primarily of fibrocartilage, and is not a synovial joint. The exact structure and shape of each disc varies depending on the segment of your spine. This will be covered in greater depth in later posts given the important role they play in spinal biomechanics.
Both above and below, each vertebral body has two joints (articulations) with its adjacent vertebrae. The 2 superior (above) articulate with the inferior processes of the vertebrae above, and 2 inferior (below) which do the opposite. Including the intervertebral disc joint, each spinal vertebrae has 5 joints that control its motion. Exceptions to this are at the very top of your neck, the first two vertebrae, and in the mid back where the ribs create additional joints.
Each vertebral body has two processes, which project off the backside called pedicles. Pedicles are the connection point between the body of the vertebrae and the posterior, or neural arch. The neural arch consists of lamina, transverse processes, and a spinous process. The details of these names are less important than the understanding that this space houses the spinal cord. Since the discs create space, the arch-like structure of the pedicle above and below, creates a space between vertebral bodies called the intervertebral foramen. This is where the spinal nerves (peripheral spinal nerves) exit and enter the spinal cord for communication with the peripheral tissues.
You have a total of 33 peripheral nerves that exit your spinal cord, and each segment (cervical, thoracic, lumbar, etc.) of your spinal cord has these branches. The peripheral nerves in the cervical region exit the spinal canal above the vertebral body of the same number and once you reach the first thoracic vertebrae they exit below the vertebral body of the same number. The other peripheral nerves come from the cranial nerves and the splanchnic nerves which are part of your autonomic nervous system which also will be covered in a later post.
Other important structures in regards to spinal anatomy at Camp4 Human Performance are the 9 cardinal ligaments of the vertebral column. There is one that runs on the front and back of the vertebral column called the anterior and posterior longitudinal ligament. Others which go between each spinous process connecting them all called the interspinous and supraspinous ligament. Similarly, there are ligaments that connect each transverse process and also lamina together called the intertransverse and ligamentum flavum. These ligaments are designed to serve as muscle attachments, restrict and control motion, share spinal loading mechanics, and facilitate cell-to-cell communication.
“The spinal column itself makes up approximately 40% of your total body weight”
Now lets talk about the histogenesis and properties of bone.
One important thing for people to understand is that the cellular constituents and chemical reactions necessary for bone formation are the same for all bones in the body, and they are continuously changing throughout your life. Bone is always formed by replacing some pre-existing material, more specifically cartilage, in a few different ways.
There are two primary means by which this happens, termed histogenesis. One of the ways in which vertebral bodies are formed is termed enchondral ossification. In this bone formation model, cartilage is present and causes growth and formation at the ends of bone by the continuous cell division of cells called chondrocytes. This cell division is also accompanied by secretion of an extracellular matrix, which can thicken, forming chondroblasts that cause an apposition of the matrix to make bones thicker and longer. Bone is a dense form of connective tissue which means there is a high proportion of extracellular material in relation to cells.
“Enchondral ossification is also responsible for the healing process of bone fractures”.
One very important thing to note is that bone is a living and growing organ, it is not dead inanimate tissue.
– highly dynamic and metabolically active
– hard, yet light weight and resilient to tension and compression
– constantly remodeling (understress = atrophy, overstress = hypertrophy)
– highly vascular
– innervated by nerve fibers that run with nutrient arteries
– protect and support muscles
– perform hemopoiesis (production of blood cells and platelets)
– store salts (Ca+, P) in its matrix
– mechanical basis for movement
– fibers – highly organized collagen fibers (mostly) and elastic fibers (minimal) which give bone strength and resiliency
– Organic salts – hydroxyapatite crystals (primarily calcium phosphate and calcium bicarbonate) and ground substance ( glycosaminoglycans, chondroitin sulfate, deratan sulfate, and hyaluronic acid)
Bone has three primary layers
- an outer cortical layer which is 80% of the skeletal mass and serves as a protective outer shell
- an inner trabecular layer which is the other 20% of the skeletal mass but 80% of the bone surface making. The trabecular layer is less dense and more elastic and rigid and makes up most of the bone tissue in the spine.
- An outermost periosteal layer which is specialized connective tissue which surrounds the compact bone layer except at the articulating (joint) surfaces. This layer has a rich nervous and vascular supply and provides the interface for tendon and ligament attachments.
Three types of bone cells
– Osteoblasts which are bone forming cells that synthesize bones by making osteoids and producing alkaline phosphatase which is an enzyme that helps mineralize Ca+ and P precipitate from blood. They also manufacture matrix collagen.
– Osteoclasts, derived from marrow are bone remodeling cells. These cells resorb bone by digesting the old mineral matrix. They secrete enzymes (acid phosphatase) responsible for this process. These cells also contain estrogen, vitamin D and calcitonin receptors, which inhibit resorption.
– Osteocytes are the mature bone cells and the most numerous of the three. Osteocytes are really osteoblast cells trapped in the bony matrix and are responsible for maintaining the regulation of activity. They contain mechanoreceptors which are responsible for reulating the bons response to stress.
Wolff’s law (1892)
– Bone will transform to stressors and is constantly remodeling and growing! Since bone is a living structure, it adapts itself to its surroundings and demands placed on it. Stressed bone remodels and becomes stronger to resist the stress. Removal of stress leads to resorption where it is not needed. As an example, the weight bearing bones of the lower limb are stronger due to them being under more stress. Bones under stress become larger, heavier, and more dense.
** peak bone mass varies between individuals and density peaks at approximately 25 years of age**
In the vertebrae of the spine, the trabecular pattern inside the cortex looks like a scaffolding with the vertical collagen fibers being more predominate. The horizontal struts simply support the vertical beams which carry the primary load. A prolonged increase in axial load results in an increase in trabeculae (mostly vertical).
Factors which affect the shape and strength of bones
– Genetic factors – gender and genetics
– Hormonal status
– Poor nutrition – vitamins & minerals, too much alcohol or drug use, cigarettes and tobacco, carbonated beverages, too much grains or salt
– Lack of mechanical constraints – weightless environment, disuse and lack of compressive forces, sedentary lifestyles, and paralysis
– Metabolic factors – calcium, phosphorous, vitamins a, c, and d, and hormones from the pituitary.
Important clinical notes about bones:
– Bones can heal and remodel
– Bones can be painful
– Bones bleed when they fracture
– Change with age
Now you understand spinal anatomy at Camp4 Human Performance, call today to schedule an appointment and see how we can improve your function (801) 878-7356