Spinal segments - structure and functions of the spine

The spine and its function

The human spine consists of, among other things, 24 small movable bones called vertebrae, which are stacked on top of each other. Between them are gel cushions called discs, which are designed to absorb pressure and keep the bones from rubbing against each other. The entire structure of the spine is linked by groups of ligaments and tendons that connect the muscles to the bones. Each vertebra has an opening in the center, which, with the anatomical arrangement of the vertebrae stacked on top of each other, creates a protective tunnel in the lumen of which the spinal cord and its nerve roots run.

A healthy spine, when viewed from the side, has a curvature resembling the letter “S,” which allows for an even distribution of weight. This is important because the spine is the central support structure for the entire body. These curvatures absorb body shocks and protect the spine from injury. The spine connects the different parts of the musculoskeletal system, helping you sit, stand, walk, twist and bend.

What elements does the spine consist of?

• Vertebrae: the spine is made up of 33 vertebrae, 24 of which are mobile, and the rest are fused vertebrae, forming the sacrum and coccyx. Each vertebra consists of two basic parts: the cylindrical shaft, which acts as a support, which is adapted to carry a lot of weight, and the thinner arch equipped with seven appendages, which are the sites of attachment of intervertebral ligaments and spinal muscles, also provide sufficiently stable movement between vertebrae.
• Intervertebral discs: are flat, round cushions between the vertebrae (there is one disc between each vertebra and the next) that act as shock absorbers for the spine. Each vertebra has a soft, gelatinous center called a nucleus pulposus and a strong outer fibrous ring. Intervertebral discs connect the vertebral bodies, transfer weight and provide mobility to the spine.
• Spinal cord: is a column of nerves passing through the spinal canal that extends from the skull to the lower back. From this bundle, thirty-one pairs of nerves branch out through the spinal openings, performing a very important role - they carry information between the brain and muscles.
• Soft tissues: these have an important stabilizing function - ligaments connect the vertebrae to keep the spine in position, muscles support the back and help it move, and tendons connect muscles to bones and aid movement.

What are the sections of the spine?

The spine consists of 5 sections, which in anatomy are denoted by letters, and the individual vertebrae of these spinal sections by numbers.

• Cervical segment - is made up of 7 cervical vertebrae (C1-C7),
• Thoracic segment - is built from 12 thoracic vertebrae (Thoracic Th1-Th12),
• Lumbar segment - is built from 5 lumbar vertebrae (lumbar L1-L5),
• Sacral segment - is built from 5 sacral vertebrae fused together (sacra S1-S5),
• Cervical (caudal) segment - is built from 4-5 fused cervical vertebrae (coccyx Co1-Co4/Co5).

Cervical section of the spine

The cervical section of the spine is made up of seven vertebrae, which differ in structure. The first of the cervical vertebrae, C1 - the pinnacle - is known as the atlas. This name refers to the mythical titan supporting the world on his shoulders. In human anatomy it is similar, the first cervical vertebra supports the head. Its characteristic feature is the absence of a shaft, and its shape resembles a ring with an anterior and posterior arch.

Second in order is the C2 vertebra called the pivot vertebra, with a prominent upward extension of the vertebral body, which is responsible for turning the head. The seventh C7 vertebra, called the protruding vertebra, is also distinctive in its appearance. Its shaft is larger than the other cervical vertebrae, and can be clearly seen when tilting the head forward. The structure of this last cervical vertebra is similar to the thoracic vertebrae, so it serves a transitional function between the cervical and thoracic parts of the spine.

The cervical section of the spine is subject to various types of pain. Very often it is associated with the type of work performed, with prolonged staying in a static position and lack of physical activity. Pain syndrome of the cervical spine can occur in the form of: pain, tenderness, increased muscle tension, stiffness and even immobilization. Long-term strains can lead to cervical discopathy, which accounts for almost half of all causes of pain in this part of the spine.

Thoracic section of the spine

The thoracic section of the spine consists of 12 vertebrae located at the level of the thorax. The thoracic vertebrae have a much more massive structure and longer spinous processes than the cervical vertebrae located above. Their vertebral bodies are wedge-shaped and increase gradually downward, with the anterior part lower than the posterior. As a result, the thoracic segment of the spine forms a kyphosis - a thoracic curvature. The thoracic vertebrae, due to their structure and connections with the ribs and the sternum, form the thoracic cage, which protects important internal organs such as the heart and lungs.

Compared to other parts of the spine, the thoracic section is the least mobile, mainly due to the presence of ribs. Therefore, injuries to the thoracic spine are quite rare, but pain in this area, can be very troublesome. The pain can be the result of a postural defect, being overweight which places an additional burden on the spine (including large breasts), unnatural posture at work or excessive training loads. Pain in the thoracic spine may be accompanied by other symptoms such as pain in the sternum area suggestive of heart disease, numbness and pain in the arms or legs.

If you have thoracic spine pain, it's a good idea to see an experienced physical therapist for kinesiotherapy. Exercises that strengthen the muscles of the spine can also be helpful in combating pain. In the long run, performing them regularly will eliminate pain and have a positive effect on correct posture.

The lumbar section of the spine

The lumbar section of the spine consists of five vertebrae, which, compared to other spinal vertebrae, are much larger and thicker - more like blocks. They have a strong arch which provides an attachment site for the numerous muscles of the back. The great massiveness of the lumbar vertebrae is due to their function - they provide stability to the spine and help support the weight of the upper body. The lumbar spine curves inward, forming a C-shaped lordotic curvature.
Because the lumbar vertebrae are the most stressed in the spine, they experience a lot of pressure and strain during daily physical activities, so this section is the site of frequent pain. Pain in the lumbar region can result from: overload and trauma, injury, inflammation, degenerative changes or even anatomical anomalies.

Among the most common causes that trigger lumbar spine pain are abnormalities in the intervertebral discs. They are subjected to heavy loads, especially in sports, being prone to micro-injuries and even the formation of intervertebral disc herniation. A common cause of pain in the lumbar spine is degenerative changes, the formation of which is a long-term process. These changes lead to damage to the intervertebral disc and cartilage of the intervertebral joints.

Sacral section of the spine

The sacral segment of the spine consists of 5 sacral vertebrae fused together to form the sacrum. It has several important functions in the body - it forms the backbone of the spine and acts as a support for the lumbar vertebrae. In conjunction with the pelvic bones, it provides stability and allows the body's weight to be transferred to the lower limbs. It protects the spinal nerves and internal organs located in the pelvis, such as the intestines and reproductive organs.

Because of its rigid structure, the sacral segment of the spine limits mobility in the lumbar region to prevent excessive movement and potential damage. Numerous muscles of the pelvis and lower back attach to the surface of the sacral segment. They are responsible for stabilizing the pelvis and movements associated with the lower extremities. The sacrum is rarely the cause of pain and is often mistakenly associated with sacral pain. Pain in this region is most often associated with the sacroiliac joint.

The nodal section of the spine

The lowest part of the spine is the nodal segment. It is made up of 4-5 nodal vertebrae fused together to form the so-called coccyx. It has important functions in the anatomical structure, ligaments, tendons and muscles are attached to it. The cuneiform segment of the spine is slightly protruding outward, making it unfortunately prone to injury, such as in falls on the back or buttocks. Treatment usually involves minimizing pain during the period of spontaneous fusion of the tailbone.

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Bibliography:

• OrthoInfo - "Spine Basics" - Contributed and/or Updated by Daniel K. Park, MD, FAAOS; Peer-Reviewed by Stuart J. Fischer, MD, FAAOS - 2020
• National Library of Medicine - Anatomy, Back, Vertebral Column - Charisma DeSai; Vamsi Reddy; Amit Agarwal - 2022
• Spine-Health - Spinal Anatomy and Back Pain - Dr. Thomas Scioscia - 2017