It is known that the human spine consists of thirty-four vertebrae, five of which belong to the lumbar region, seven to the cervical, twelve to the thoracic, five each to the sacral and coccygeal regions. Changes taking place with the earth's climate (in particular, its warming in the future) can contribute to the fact that the body and head of a person will be more elongated, the spine - thicker with the sacrum fused with the lumbar region. But these are hypothetical realities of future millennia.
Today, the human spinal column is a stable axis with a "cable-stayed" structure, which can be seen as a ship's mast resting on a pelvis with a "yard" at the level of the shoulder girdle. The structure of a typical vertebra in this system is somewhat different in different parts of the spine, but there are also important common features.
Most vertebrae have a "body" and "legs"
In particular, the largest size is the so-called vertebral body, which has a cylindrical shape.
The surface facing the back of the human body has a more complex structure. There are two articular processes extending from the posterior arch and dividing it into two parts. In front of each articular process there are "legs", and behind - two plates, to which the spinous process approaches. At the same time, transverse processes still extend from the vertebra as a whole at the level of the articular processes. This is how the structure of a vertebra in the human body looks like, which allows optimal attachment to muscle tissue.
The set of vertebrae allows for both static and dynamism
In the vertical plane, the components of the vertebra are anatomically balanced, which suggests the presence of three "pillars" in this bone structure. The first of them is formed by the articulating bodies of the vertebrae themselves (through the intervertebral discs), the second and third are located behind and are articular processes that are connected to each other through artroidal joints. The structure of the vertebra is such that their combination allows them to play a static role in the anterior “column” and a dynamic role in the posterior elements, which gives the spinal column the ability to bend and move as a whole. The movable element in this system consists of an intervertebral disc, an opening between the vertebrae, joints (interapophyseal), interspinous and yellow ligaments (according to the works of Schmorl). The interapophyseal joints play the role of pivot points here to minimize compression applied to the spinal axis.
What a vertebra looks like in different sections
If you study the structure of a vertebra at the level of its body, it can be noted that the shell of the body consists of an upper and lower plate, which are somewhat thinner in the center, since they contain cartilaginous plates in this place. The periphery of the vertebral body usually has an even greater thickness, since here, by the age of a person 14-15 years old, an epiphyseal plate is formed, which later merges with the vertebral body. If this process is disrupted, then Scheuermann's disease may occur.
The structure of the human vertebra, the photo of which is presented above, when viewed in a vertical-frontal section, shows that this element has a cortical thickening at the top and bottom. And in the center of the body itself there are bone-spongy trabeculae located vertically, in accordance with the axes of the forces applied to the spine, horizontally (to connect the side surfaces) and obliquely. Sections at other angles indicate that inside the vertebral body there is a fan attachment of fibers from the level of the two pedicles to the superior articular processes and the spinous process, as well as from the lower surface, through the level of the two pedicles of the vertebra, to the inferior spinous and articular process.
The vertebra collapses only under a huge load
This structure of the vertebra allows you to highlight the zones of maximum and minimumresistance to external loads. For example, an axial force of 6 centners causes a wedge-shaped compression fracture, since there is a triangular zone in the vertebra with minimal resistance. Under the influence of a force of 8 centners (800 kg), the vertebra is destroyed, as a rule, completely, the fixed parts of the spine become mobile, which leads to damage to the spinal cord.
Living cells in bone tissue
The chemical structure of a human vertebra and its complementary elements is based on a combination of mineral and organic substances, of which the first at a young age is approximately twice as much as the second.
Mineral components of almost all human bones are represented mainly by hydroxyapatite, and organic - collagen of the first type. Despite the fact that human bones seem "lifeless", many processes take place in them at the cellular level. For example, osteoblasts are obtained from advential cells, which synthesize the intercellular substance, then passing into osteocytes - cells that support metabolism (calcium transport to and from the bone), stabilize the organic and mineral composition of the bone. Also, osteoclasts “live” in the bone tissue, which help to utilize their spent bone tissue.
Coccyx "moves" more often in ladies
The structure of a human vertebra is conceived by nature so that “with the least expenditure of material, it has great strength, lightness, while reducing the influence of tremors and shocks” (Lesgaft Pyotr Frantsevich). Since the loads on different parts of the spine are different, the individual elements of this skeletal system differ from each other. For example, in the coccyx there are three to five vestigial vertebrae, of which only the first upper one has some signs of a classic vertebra - a small body and a coccygeal hump on the back surface (on both sides). In this department, such a feature as “coccygeal horns” is noted - the remains of the upper articular processes connected by ligaments to the sacral horns. It is noteworthy that in men the coccyx is often fixedly attached to the sacrum, while in women it is mobile, it can deviate back during the birth process.
Sacral foramen has custom sizes
In the sacral spine, the elements are also connected motionlessly. Here, four or five vertebrae have fused into a monolithic triangular bone with the apex pointing down. The sacrum is the base of the entire mobile spine, which also has its own small amplitude of movement - up to 5 mm in the young years of a person. It has two upper articular processes that are turned back and slightly to the sides. In front, the sacrum is concave, in the back it is equipped with a sacral and articular crest, where there is an opening in the sacral canal, the dimensions of which vary greatly from person to person.
The structure of the lumbar vertebra differs from other similar elements in the massiveness of the "body". From the first to the fourth element in the lower back, the vertebrae increase in size, andthe fifth, last, takes part in the formation of an additional joint for connection with the upper part of the sacrum. The fifth, lower vertebra in the lower back, has not a classic cylindrical, but a wedge-shaped body. It is worth noting that in the lumbar region, the articular processes at the top of the vertebrae are concave and point down and towards the middle.
There are pits on the thoracic vertebrae
What is interesting about such an element of the skeleton as the thoracic vertebra? The structure here has such a feature - the presence on the "body" of pits and half-pits for attaching ribs. In addition, the vertebrae in the thoracic part are larger than the cervical ones, but smaller than the lumbar ones, the height of the “bodies” increases gradually from the first vertebra to the twelfth.
It is also worth considering that the articular processes are located frontally, and the transverse processes are directed backward and laterally. A notable feature of this part of the skeleton is that the spinous processes are inclined downward and overlap each other as in a tile. Each thoracic vertebra, the structure of which is shown in the figure, along with vertebrae from other departments, is involved in such functions: creating support for the body, cushioning, protection. It contributes to the implementation of motor functions, takes part in metabolic and hematopoietic processes.
Among the cervical vertebrae are Axis and Atlas
The structure of the cervical vertebrae is so different from the structure of these elements in other parts of the spine that two of them are even given individual names. The first is Atlas, the vertebra to which the human skull is attached. It does not have a "body", instead of which there are two lateral "masses",connected by an anterior and posterior arch with tubercles of the same name. The lateral masses of Atlanta are equipped with upper and lower articular surfaces, and on the back surface at the anterior arch there is a hole for connection with the second vertebra - Axis. Interestingly, between the first vertebra and the skull, there is no intervertebral disc, which usually carries a shock-absorbing function.
Axis in its structure has a "tooth", which enters the fossa on Atlanta, as well as the lower articular process and the spinous process (unlike Atlanta). The structure of the cervical vertebrae from the third to the sixth is classical with a well-defined "sleepy" tubercle on the transverse process at the sixth vertebra. The carotid artery is often pressed against this tubercle when bleeding is to be stopped. The seventh vertebra in the cervical part has a long (non-bifurcated) process (spinous), therefore it is called a protruding vertebra, since he alth workers are guided by it when counting the vertebrae during the examination of the patient. The structural features of the cervical vertebrae are such that these elements have holes in the transverse processes, forming a bone channel through which large blood vessels pass to the brain, feeding the most important organ in the human body.
