Why is the spine
The spinal column refers to the bones that bear the weight of the body. The spinal cord is the nerve system that runs along the spinal column. The brain transmits electric signals along the spinal cord in order to control our bodies. This page contains physiological information on the spine.
There are three main functions of the spinal column:
To house and protect the spinal cord and its associated nerves.
To support the frame of the body in an upright position.
To provide motion throughout the body.
Consisting of thirty-three bones called vertebrae, the spine runs from the base of the skull down to the pelvis. Apart from the top two vertebrae, the anatomy of each individual bone is essentially the same, differing only in size and shape.
The vertebrae are held together by a combination of ligaments and muscles that allow flexibility and are separated by cartilage discs that act as shock absorbers. Two joints at the back of each bone allow for maximum movement, and pairs of spinal nerves exit holes at each level of the spine, sending the brain’s electric information to and from the various parts of the body.
A healthy spine is straight when viewed from the front. When viewed side-on, a fully-grown spine has three obvious curves that form an “S” shape. The neck and lower back curve slightly inwards (concave) and the upper back curves out (convex).
The thirty-three vertebrae are divided into five separate regions, each with different specific functions. The regions are:
Cervical (neck) – Seven vertebrae, which in descending order are named C1 to C7.
Thoracic (upper to mid back) – Twelve vertebrae, T1 to T12.
Lumbar (lower back) – Five vertebrae, L1 to L5.
Sacrum (pelvis area) – Five fused vertebrae, S1 to S5.
Coccyx (tailbone) – The four fused vertebrae of the tailbone.
Only the top twenty-four vertebrae can move, with the fused bones of the bottom two regions providing structural support.
This section looks at the five regions in turn:
Cervical The cervical spine, or the neck, supports the full weight of the skull and has the greatest range of movement.
Essential to this flexibility are the specialist roles played by the top two vertebrae, known as the Atlas (C1) and the Axis (C2) respectively. Shaped unlike any of the other vertebrae, the two bones are pivots: the Atlas connects to the skull and allows up and down nodding movements whilst the Axis enables a side-to-side shaking of the head motion.
Thoracic Contrasting with the cervical region, the twelve bones of the thoracic region of the spine have very limited movement.
With larger vertebrae than those in the neck, the main function of the thoracic region is to connect to the ribcage, which in turn protects the internal organs.
Lumbar The vertebrae in the lumbar region of the spine are larger, wider and broader still than those in the two regions above it. It is tremendously strong, carries most of the body’s weight and absorbs the stress from lifting and carrying.
There is a greater range of motion possible in the lumbar region than there is in the thoracic region, however not as much as in the cervical region.
Sacrum Immediately beneath the 24 individual vertebrae, there are the five fused bones of the sacrum. This is a triangular shaped ‘bone’ situated behind the pelvis. Its purpose is to connect the spine to the hip bones (known as the iliac).
Coccyx The final part of the spine is the coccyx - four fused bones often referred to as the tailbone. This is an important attachment for various ligaments and tendons throughout the pelvis area.
Housed inside the spine is the single most important structure that links the brain to the body - the spinal cord.
It is a slim, white, cylindrical cord consisting of millions of nerve fibres and is approximately the diameter of a human finger. It is surrounded by a protective, cushioning liquid called Cerebral Spinal Fluid (CSF) which prevents the vertebrae from damaging the cord.
It begins immediately below the brain stem and on average, descends 43cm to the first lumbar vertebrae (L1). At this point it ends at a region called the conus medullaris before blending into a mass group of nerves at the base of the spine called the cauda equinas.
The spinal cord makes up a relatively small part of the Central Nervous System (a mere 2%), but its significance cannot be understated:
It is the brain’s connecting road to the body, down which it sends and receives all of its electrical information. If this becomes damaged, it can have devastating effects.
Thirty one pairs of spinal nerves, also known as nerve roots, branch off from the spinal cord, pass through holes in the vertebrae before branching out yet again to control all the different parts of the body as part of the Peripheral Nervous System. Nerves relaying information from the brain to the body are called Motor Neurones and nerves carrying information in the other direction are known as Sensory Neurones.
Depending on the location of where spinal nerves branch out from the spinal cord, different parts of the body are controlled. Following the same logic as the vertebrae categorisation, these are divided into four regions:
Cervical nerves: Although there are only seven vertebrae in the neck, there are eight pairs of spinal nerves numbered C1 to C8. These enable breathing in addition to providing movement and feeling to the head, neck, shoulders, arms and hands.
Thoracic nerves: Twelve pairs of spinal nerves (T1 to T12) in the upper back that connect muscles in the back, chest and upper abdomen.
Lumbar nerves: Five pairs of spinal nerves (L1 to L5) supplying the lower back and regions of the thighs and legs.
Sacral nerves: Five pairs of spinal nerves (S1 to S5) that supply the buttocks, the bladder, bowel, the sexual region and some of the legs and feet.
The spinal cord plays a vital role in practically every part of the body and it can be damaged in many different ways, often with far-reaching consequences. Find out more about the types of spinal injury.