Understanding the Human Spine: Structure and Function

The human spine, a critical structural component of the body, provides support and protection to the spinal cord. Composed of a series of bones, ligaments, and intervertebral discs, it plays a pivotal role in maintaining an individual's posture and enabling a wide range of body movements. Here, we delve into the length, shape, and vertebrae of the human spine and explore the importance of intervertebral discs in spinal function.

1. Length and Shape of the Human Spine

The spine serves as the central support structure that connects various parts of the skeleton, including the head, chest, pelvis, shoulders, arms, and legs, keeping the body upright and facilitating mobility. Despite its bony composition, the spine exhibits remarkable flexibility due to its elastic ligaments and intervertebral discs.

The length of an individual's spine is closely linked to their height. On average, the spine measures approximately 71cm in men and 61cm in women. This vital structure bears the weight of the head, trunk, and arms, allowing for multidirectional movement. The spine's flexibility varies along its length, with the neck region being the most agile. Moreover, the natural S-shaped curvature of the spine provides stability, balance, shock absorption during walking, and protection against bone fractures.

2. How Many Vertebrae Does the Human Spine Have?

The human spine typically consists of 32 to 34 vertebrae, organized into five distinct segments:

• Cervical Segment (C1-C7): This segment includes seven cervical vertebrae, characterized by small, wide vertebral bodies with pedicles attached laterally to the vertebral bodies.
• Thoracic Segment (T1-T12): Comprising 12 thoracic vertebrae, this segment features downward-slanting long spinous processes and transverse processes that articulate with the ribs at the costovertebral joints.
• Lumbar Segment (L1-L5): The lumbar segment encompasses five lumbar vertebrae, known for their large, horizontal vertebral bodies, thick vertebral pedicles, and rectangular spinous processes.

• Sacral Segment (S1-S5): These five sacral vertebrae fuse to form the sacrum, connecting the pelvis through the sacroiliac joints.
• Coccyx: Composed of three to five fused vertebrae, the coccyx takes on a triangular shape, also known as the tailbone.

3. Intervertebral Discs Between Vertebrae

Between the vertebrae, except for the skull and the first cervical vertebra, the first and second cervical vertebrae, and the sacrum and the coccyx, there are 23 to 24 elastic intervertebral discs. These discs are biconvex lens-shaped, 3-9mm thick, highly elastic, and composed of cartilaginous and fibrous layers. The central nucleus pulposus, surrounded by fibrous layers, occupies the posterior two-thirds of the disc.

These discs collectively contribute to a quarter of the spine's height and play a pivotal role in maintaining spine flexibility, enabling upper body rotation, and absorbing the forces generated during activities like running and jumping. Throughout the day, spinal discs experience compression and decompression, causing the spine to vary in length, typically shorter by 1.5 to 2cm at the day's end. As individuals age, the spinal discs lose elasticity, become thinner, and lead to a reduction in overall height.

4. Nerve Transmission in the Spinal Canal

The spinal canal is formed by overlapping spinal foramen. Notably, the cervical and lumbar segments of the medullary canal are wider than the thoracic segment. The root canal assumes a triangular shape, except for the circular thoracic segment. The width of the spinal canal is determined by the distance between the pedicle bases on X-ray film, and the anteroposterior width is determined by the distance between the vertebral body face and the lower articular process's front.

At the junction of two vertebrae, except for C1, C2, sacrum, and coccyx, spaces are formed where spinal nerves exit the spinal canal. These spinal nerves carry signals between the brain and the body's muscles and internal organs. Additionally, they transmit sensory information such as touch, pressure, temperature, and pain from the body to the brain through the spinal cord. Together with the brain, the spinal cord forms the central nervous system.

In conclusion, the human spine, with its unique structure and multiple functions, serves as the backbone of the body, connecting and supporting various body parts and facilitating a wide range of movements. Understanding the spine's components, including its vertebrae and intervertebral discs, is crucial in appreciating its significance in our daily lives.