Functions of the Spinal Column
- The spinal column supports the body and the skull; helps in standing upright; maintains the balance of the body.
- Permits flexible movement; helps in head and neck movements. It also allows the body to stretch, bend, lean and rotate.
- Protects the spinal cord as well as the internal organs like lungs, heart, etc., which are inside the rib cage.
- Provides base for attachment of muscles, ligaments and tendons.
- The bone marrow inside the bones of the spinal column produces red blood cells and stores minerals.
- Connects the upper body to the lower body.
- The inter-vertebral discs acts like a shock absorber in the body.
The spinal column, also called the spine or the vertebral column, is situated in the dorsal side of the human body. It starts from the base of the skull and extends to the pelvic region. This flexible structure provides support to the body and also helps in three-dimensional movements.
Structure of the Spinal Column
The spinal column consists of many small cylindrical bones called vertebrae, arranged in a vertical manner. Each individual vertebra is separated from its neighbor by a cushion of cartilage called intervertebral disc (or intervertebral fibrocartilage). The vertebrae are stacked in such a manner that the roundish hole in successive articulated vertebra jointly takes the shape of a tunnel. This is called the spinal canal, which houses the spinal cord. The spinal cord, enclosed within the spinal column, is a long, thin bundle of nerve fibers that extends from the brain and runs through the spinal canal. It is surrounded by a fluid called cerebrospinal fluid, which protects the nerves. These nerves carry messages from the brain to different parts of the body and vice versa.
Normally, the spinal column is made up of 33 vertebrae. Each vertebra consists of an anterior portion with a bony arch, which encloses the vertebral foramen (the large hole at the center), a posterior portion with a spinous process (can be felt through the skin in cervical and lumbar regions), and two transverse processes (one on each side). Muscles and ligaments are attached to the various projections in the vertebrae.
The vertebral column, spinal cord, and nervous system have specific and important functions.
The vertebral column serves five main functions:
- Protects the spinal cord
- Provides balance and stability for the body
- Offers attachment points for the ribs, pelvic bones, and many muscles
- Allows for flexibility and mobility
- Supports the structure and weight of the body in various activities
The spinal cord is housed in and protected by the vertebral column. The spinal cord performs two main functions:
- Connects the peripheral nervous system to the brain
- Coordinates simple reflexes, such as sending a signal to pull your hand away from a hot object
The peripheral nervous system includes the nerves used for communication to and from the brain, spinal cord, and all other parts of the body, including the internal organs, muscles, skin, and blood vessels. There are 31 pairs of spinal nerves along the spinal cord that carry signals from the body to the brain.
Five Regions of the Spinal Column
A newborn baby’s spinal column comprises all the 33 vertebrae. As he/she reaches adulthood, the five sacral vertebrae fuse together to form one single bone. The same happens to the four coccygeal vertebrae. Hence, a normal adult human being has 24 movable vertebrae, followed by two bony structures in the lower back region. Some individuals may have lesser/more number of vertebrae in one region, which is usually compensated for in any other region, except the sacrum and coccyx. But, the number of cervical vertebrae remain the same.
The spinal column starts with the cervical segment in the neck and ends with the coccygeal segment in the lower back. Size of the vertebrae increases from top to bottom; the largest being the lumbar one. The 33 vertebrae in the spinal column are divided into five regions, which are described below.
Cervical (neck) vertebrae – C1 to C7: There are seven cervical vertebrae in the spinal column. Among the 24 movable vertebrae, the cervical vertebrae are the smallest in size. The main function of the cervical vertebrae is to support the skull. The first and second cervical vertebrae, known as ‘atlas’ and ‘axis’ respectively, are shaped in such a manner, so as to execute that function. The atlas is joined to the occipital bone at the base of the skull. This joint enables the upward and backward movement of the skull. The axis has got a tooth-like projection, which fits into the atlas. This joint enables the movement of the neck. The cervical vertebrae have small bifid spinous processes.
Thoracic (upper back) vertebrae – T1 to T12: The second region consists of 12 thoracic vertebrae. These vertebrae possess long spinous processes and relatively large vertebral foramen. The transverse processes of these vertebrae articulate with the rib bones. This feature restricts the movement of the thoracic vertebrae to some extent.
Lumbar (lower back) vertebrae – L1 to L5: The five lumbar vertebrae forms the third region of the spinal column. Compared to other vertebrae, the lumbar vertebrae are the larger ones. They have large spinous and transverse processes. The lumbar vertebrae also possess small accessory processes, which helps in its attachment with the back muscles.
Sacral vertebrae (fused) – S1 to S5: In an adult, the five sacral vertebrae fuse together to form a single bone called sacrum. It does not contain any intervertebral disc. The sacrum articulates with the last lumbar vertebra above and the coccyx below. It also has joints with the iliac bones (part of hip bone) on both sides.
Fused coccygeal vertebrae (tailbone): The four coccygeal vertebrae fuses to form a single bone (coccyx), which is the last segment of the spinal column. Like the sacrum, this region also lacks intervertebral disc. It articulates with sacrum through a fibrocartilaginous joint.
Curves of the Spinal Column
A side view of the spinal column shows four curves corresponding to the different regions. These curves, called cervical curve, thoracic curve, lumbar curve and pelvic/sacral curve, help humans to stand upright and maintain the proper balance of the body. While the thoracic curve is the least prominent one, the lumbar curve is more marked in females. Both thoracic and pelvic curves are called the primary curves, as they are present in the fetal stage itself. The lumbar and cervical curves are secondary ones, because they develop after birth. The cervical curve is developed when the infant starts holding his/her head erect. The lumbar curve is developed when the child begins to walk.