VERTEBRAL COLUMN

• The vertebral column (VC) protects the spinal cord and forms the supporting girder of the vertebrate body. To it are attached the head, ribs, limbs and zillions of muscles and ligaments. The 3 primary components of the VC are:

1. Bones (vertebrae)

2. Fibrocartilages (disks)

3. Ligaments

• 7 spine-tingling features of the VC as a total unit:

1. The length of the VC is approximately 2/5 of the total body height.

2. The intervertebral disks make up approximately 1/4 of the total vertebral height.

3. The VC demonstrates 5 regional specializations. These regions and their percentage lengths are:

A. Cervical (20%)

B. Thoracic (39%)

C. Lumbar (23%)

D. Sacral (15%)

E. Coccygeal (3%)

4. In normal posture the VC forms a beautiful sigmoidal curvature.

5. The vertebral bodies gradually increase in thickness from C1 - S1.

6. The spinous processes tend to slope downward from C3 - T10/11 and become more perpendicular from T12 - L5.

7. Laterally, the presacral vertebrae display relatively large intervertebral foramina for the exit of spinal nerves.

• In the fetus, the VC is "C-shaped". This represents the primary (original) curvature. Secondary curves develop when the infant begins to raise and balance its head (shortly after birth) and to walk (approximately 1 year). Thus, in the adult, there are 2 primary and 2 secondary curves:

1. Primary Curves

A. Thoracic

B. Sacrococcygeal

2. Secondary Curves

A. Cervical

B. Lumbar

• Each of the presacral vertebrae is characterized by the following 5 components:

1. Body (or Centrum) - support of body weight

2. Vertebral Arch = pedicle + lamina - protection of the spinal cord within the vertebral canal

3. Transverse Processes - levers for the attachment of muscles and ribs

4. Spinous Process - lever for the attachment of muscles and ligaments

5. Articular Processes (sup. and inf.) - for intervertebral articulation

• 4 distinguishing features of the cervical vertebrae:

1. The bodies are relatively small, somewhat rectangular and lipped.

2. The transverse processes present a large transverse foramen traversed by the vertebral artery.

3. The spinous processes are typically short and bifid.

4. The articular processes face chiefly up (sup.) and down (inf.).

• 6 unique features of the atlas (C1):

1. Lacks a body

2. Has an anterior arch (with a post. facet for the dens) and tubercle

3. Has a posterior arch and tubercle

4. Has 2 lateral masses between the arches which support the art. processes

5. Has elongated sup. art. facets (for articulation with the occipital condyles) and more circular inf. art. facets (for articulation with the axis)

6. Presents paired grooves for the vertebral arteries.

• The single most unique feature of the axis:

1. Possesses a dens (= odontoid process) which actually represents the body of the atlas!

• The single most unique feature of C7:

1. Its non-bifid spinous process is very long and easily palpable for which reason it is called the vertebrae prominens.

• 4 distinguishing features of the thoracic vertebrae:

1. The bodies are medium-sized, heart-shaped and presents costal facets.

2. The transverse processes are somewhat cylindrical and knobbed and present facets for articulation with rib tubercles.

3. The spinous processes are long, prismatic and sloping.

4. The articular processes face chiefly backwards (sup.) and forwards (inf.).

• 2 interesting features of T12:

1. Its spinous process doesn't slope downward but is more perpendicular for which reason it is called the anticlinal vertebra.

2. Its superior articular facets are of the thoracic type while its inferior articular facets are of the lumbar type for which reason it should be called the transitional vertebra (but for some arcane reason it is called the "diaphragmatic vertebra" - perhaps because the aortic hiatus of the diaphragm lies in front of it!?).

• 4 distinguishing features of the lumbar vertebrae:

1. The body is large and kidney-shaped.

2. The transverse processes are spiked and spatular-shaped and possess accessory and mammillary processes (which in fact are the true transverse processes!).

3. The spinous processes are large, broad and hatchet shaped.

4. The articular processes face chiefly inward (sup.) and outward (inf.).

• 8 very interesting features of the sacrum:

1. The 5 fetal sacral vertebrae are fused into a single adult sacrum.

2. Because of this fusion, the laterally placed intervertebral foramina are split into 2 sets of 4 anterior (for ventral primary rami) and 4 posterior (for dorsal primary rami) sacral foramina.

3. The fused transverse processes are expanded into the enlarged alae and lateral masses.

4. The spinous processes are fused into an irregular median sacral crest.

5. The fused articular processes are now incorporated into the intermediate and lateral sacral crests.

6. The vertebral canal continues as the sacral canal.

7. The median sacral crest is frequently bifurcated leading to a sacral hiatus which normally ends in paired sacral cornua.

8. The promontory is the forward projecting anterior margin of the upper surface of the body of S1.

• 3 things to know about the coccygeal vertebrae:

1. They represent the caudal vertebrae of tailed vertebrates.

2. They vary in number from 1-4 and represent various degrees of fusion.

3. When fused they are said to resemble the beak of the cuckoo bird (family - Cuculidae).

• 5+ features and facts about the intervertebral disks:

1. They function primarily as weight bearing adapters and shock absorbers.

2. They make up approximately 1/4 of the length of the total spinal column.

3. They are formed of fibrocartilage and are classified as symphyses (intervertebral joint type).

4. Each disk has 2 parts:

A. An annulus fibrosus consisting of concentric lamellae of fibrocartilage

B. A central gelatinous nucleus pulposus which represents segments of the embryonic notochord. It is this central pulpy nucleus that is extruded through the anulus fibrosus in a herniated disk.

5. The vertebral bodies and intervertebral disks are firmly bound by 2 important ligaments:

A. Anterior longitudinal ligament - which also helps to prevent hyperextension of the VC.

B. Posterior longitudinal ligament - which also helps to prevent hyperflexion of the VC as well as posteromedian protrusion of the nucleus pulposus.

*Anatomical Oddity: There is no disk between the atlas (C1) and the axis (C2).

• 5 other ligaments you should learn to love:

1. Supraspinous ligaments - connecting the tips of the spinous processes except in the cervical region where it caps and blends with the ligamentum nuchae.

2. Ligamentum nuchae - a thick, median fibrous septum that separates the bilateral neck muscles. It is quadrilateral in shape and fills the space between the spinous processes and the basiocciput of the skull as far as the external occipital protuberance.

3. Interspinous ligaments - found between adjacent spines and best developed in the lumbar region.

4. Intertransverse ligaments - found between adjacent transverse processes and significant only in the lumbar region.

5. Ligamenta flava - bilateral (separated by a dorsal median cleft) elastic ligaments that connect adjacent laminae.

• The 5 movements of the VC:

1. Flexion = forward bending

2. Extension = backward bending

3. Lateral flexion = lateral bending

4. Rotation = vertical twisting

5. Circumduction = a synchronized combination of flexion, lateral flexion and extension