Spine – anatomical structure:
The human spine consists of 33-34 vertebrae, stacked one upon another to provide a mobile axis for the head and trunk. The spine is situated in the dorsal part of the body. Its vertebrae form the bony border through which the spinal cord descends. The entire spine is divided into the following regions (beginning with the uppermost one):
- cervical - consisting of 7 vertebrae
- thoracic - consisting of 12 vertebrae
- lumbar - consisting of 5 vertebrae
- sacral (sacral bone) - consisting of 5 vertebrae
- coccygeal (tailbone) - consisting of 4-5 vertebrae
The structure of all vertebrae is similar, but vertebrae in each section of the spine have certain characteristics that distinguish them from vertebrae in the other sections. Each vertebra comprises two basic parts, i.e. a vertebral body and a vertebral arch. The vertebral body is the strong and thick anterior part of the vertebra, whereas the vertebral arch is a weaker and thinner structure at the back of the vertebra. The vertebral body and the vertebral arch surround the vertebral foramen. Each vertebra has seven projections called processes that extend from the vertebral arch:
- unpaired posterior spinous process
- paired superior and inferior articular processes extending upwards and downwards
- paired transverse processes extending laterally
A correctly developed spine has physiological curvatures that optimize its function. The cervical spine forms a forward curve (called a lordotic curvature). The thoracic vertebrae exhibit a backward curve (a kyphotic curvature), whereas the lumbar spine forms a lumbar lordotic curvature. The last curvature, sacral curvature, is formed by the sacral bone.
| Atlas | Atlas |
| Kręg obrotowy | Axial vertebra |
| Kręg wystający VII | Prominent vertebra |
| Otwory międzykręgowe | Intervertebral foramens |
| Wzgórek kości krzyżowej | Promontory of the sacral bone |
Most vertebrae have intervertebral discs between them, which enable the spine to move in different directions. An intervertebral disc is composed of an outer part, i.e. the annulus fibrosus, and an inner part, i.e. the nucleus pulposus. In a healthy spine, the main constituent of the nucleus pulposus is water (about 80%); therefore its operation is subject to the laws of thermodynamics. The nucleus pulposus plays an important role during flexing movements in the spine. When the spine moves in one direction, the nucleus pulposus moves in the opposite direction. For example, when the spine bends forwards, the nucleus pulposus moves backwards. It behaves analogically when we bend backwards or laterally. The intervertebral disk serves as a specific cushion and shock absorber for the entire spine.
| krążek międzykręgowy | intervertebral disc |
| jądro miażdżyste | nucleus pulposus |
| pierścień włóknisty | annulus fibrosus |
| więzadło poprzeczne przednie | anterior transverse ligament |
| więzadło podłużne tylne | posterior longitudinal ligament |
| nerw rdzeniowy | spinal nerve |
The functions of the spine:
The location and structure of the spine enable it to play an important role in our body. The main functions of the human spine include:
- protection of the spinal cord
- providing support for the body
- functioning as a motor organ
These functions are vital for the ability to perform a wide range of daily activities.
Cervical spine:
The cervical spine consists of 7 vertebrae. The most characteristic vertebrae in this section are:
- the first vertebra - atlas (atlantal vertebra)
- the second vertebra - axis vertebra
- the seventh vertebra
The first two vertebrae are essential for our mobility. The atlas bears the weight of the head and, together with occipital condyles, forms the upper joint of the head. This joint allows the head to move forwards and backwards. It is the only vertebra in the spine that has no vertebral body or a spinous process. The axis vertebra and the atlas form the lower joint of the head, allowing it to rotate and move in lateral directions. The axis vertebra has an unusual anatomical structure, with a vertebral body considerably longer in its upper part. This different structure of the first two vertebrae ensures significant mobility of the cervical spine.
The seventh vertebra has an easily palpable spinous process, as it is more prominent than in the other vertebrae.
Thoracic spine:
The thoracic spine consists of 12 vertebrae. Unlike the other vertebrae, thoracic vertebra attach to the ribs, with which they form costovertebral joints. Vertebrae on the thoracic level possess strong and massive bodies and vertebral arches. In comparison with the cervical section, the mobility of this region is significantly reduced. The structure of the two last thoracic vertebrae (i.e. 11 and 12) resembles that of the lumbar vertebrae.
Lumbar spine:
The lumbar spine consists of 5 vertebrae. Both lumbar and thoracic vertebrae are quite large in comparison with the cervical vertebrae. The lumbar spine exhibits greater mobility than the thoracic spine. The movements of the lumbar spine often accompany the movements of the shoulder and hip joints.
Sacral spine:
The sacral spine consists of 5 vertebrae, which fuse together as we grow up (usually at the age of about 20 years), forming one sacral bone. The sacral bone constitutes the back part of the pelvis.
Coccyx (Tailbone):
The coccyx is composed of 4–5 rudimentary vertebrae with clearly preserved vertebral bodies. Similarly to the sacral bone in children, vertebrae in this section, which are initially separate, become fused into a single bone.
Sources: 1. Bochenek A.; Reicher M.; Anatomy of Man, Volume I; PZWL Warsaw 1999.
2. Putz R.; Pabst R.: Atlas of Human Anatomy - Sobotta; Urban & Partner Wrocław 1997.
