Spine

Spine Anatomy

The spine, also called the back bone, is made up of vertebral bones with cushioning intervertebral discs between them.  The spine is designed to give us stability and smooth movement, as well as providing a corridor of protection for the delicate spinal cord.   It is supported by muscles, tendons and ligaments, and innervated by nerves that branch out from the centrally placed spinal cord.

Having a well-functioning healthy back is essential for our mobility and ability to participate in various activities. Understanding the anatomy of the spine enhances your ability to discuss conditions of the spine and treatment options with your doctor.

Vertebra

The spine is made up of bony segments called vertebrae, and fibrous tissue called intervertebral discs.   The vertebrae and discs form a column from your head to your pelvis providing symmetry and movement to the body.  

This spinal column is made up of approximately 33 vertebral bones stacked one on top of the other from the base of the skull to the pelvis. Twenty-four of these vertebrae articulate with each other, while the last nine are fused together. Each vertebra is made up of several parts:

Vertebral body

This is the main part of the vertebra. It supports most of the load while standing and provides a platform for the attachment of the intervertebral discs.

Pedicles

These are two cylinder-shaped projections originating from the back of the vertebral body, connecting the front and back of the vertebra.

Lamina

Lamina are a pair of flat arched bones that form the roof of the spinal canal and provide support and protection to the spinal cord at the back.

Spinous processes

These are the bony projections that arise at right angles to the midline of the lamina. These projections can be felt when touching the back.

Transverse processes

These are bony protrusions located at the junction of the pedicle and lamina. They provide a place for the attachment of the back muscles.

Spinal canal

This is the tunnel formed at the center of the vertebra for the passage of the spinal cord.  

Facet joints

These are paired articular processes found at the vertebral arch. Each vertebra consists of two pair of facet joints: one pair called superior facets articulates with the vertebra above and the other pair, inferior facets articulates to the vertebra below.

Intervertebral discs

The intervertebral discs are flat, rounded soft tissue structures situated between two vertebral bodies of the spine.

The discs are composed of a tough, fibrous outer ring called the annulus fibrous and a soft, inner core called the nucleus pulposus. Intervertebral discs function as shock absorbers for the spine.  

Aging and injury can cause degeneration of these discs and cause painful rubbing of the vertebral bones.

Vertebral column

The vertebrae are arranged one on top of the other to form the spine. The spine is categorized into 5 spinal segments: cervical, thoracic, lumbar, sacral and coccyx.

Cervical

The cervical spine is called the neck. It begins at the base of the skull and is comprised of seven vertebrae numbered C1 to C7. The neck supports the weight of the head and allows the greatest range of motion due to two specially shaped vertebrae, the ring-shaped atlas and the peg-shaped axis, which are the first two vertebrae.

Thoracic

The thoracic spine is made up of twelve thoracic vertebrae, which are numbered T1 to T12. They start from the upper chest and extend to the middle back, communicating with the ribs in the front of the chest to protect the heart and lungs.

Lumbar

The Lumbar spine is made up of five lumbar vertebras numbered L1 to L5. These are situated in the lower back region and are larger in size. The major function of the lumbar vertebrae is to carry the weight of the body, and absorb the stress of lifting and carrying heavy objects.

Sacrum

The sacrum is a single bone, formed by the fusion of five sacral vertebras together. It connects the spine to the hip bones.

Coccyx

Also, called the tailbone, the coccyx is formed from the fusion of four bones and provides attachment for muscles and ligaments of the pelvic floor.

Spinal curves

The side view of an adult spine resembles a natural S-shaped curve. The curves provide strength and support to the spine, maintain balance and absorb shock. Any abnormality in the spinal alignment is called a spinal deformity.

Muscles

The most important spinal muscles include the extensors, flexors and oblique muscles, which work to stabilize the spine and allow the spine to move.

The extensor muscles are attached to the back of the spine and help us to stand and lift objects.

The flexor muscles originate from the front of the spine and include the muscles of the abdomen. These help in forward movement and lifting and controlling the arch of the lower back.

The oblique muscles are found at the sides of the body and help in the side-ways rotation of the back.

Any weakness or strain in the back muscles can cause incredible strain on the spine.

Ligaments

Spinal ligaments are strong fibrous bands that stabilize and hold the vertebrae in place. The major ligaments are the ligamentum flavum, anterior longitudinal ligament, and posterior longitudinal ligament. The anterior and posterior longitudinal ligaments are continuous bands that run from the top to the bottom of the spinal column along the vertebral bodies, and the ligamentum flavum attach one lamina to the other.

These ligaments function to maintain the alignment of the vertebrae.

Spinal cord

The spinal cord originates from the brain and extends through the base of the skull to the lower back through the spinal canal. It is covered by three membranes called meninges. Spaces between these membranes are filled with cerebrospinal fluid.

There are 31 pairs of spinal nerves that originate from the spinal cord. These nerves carry all the information from the body to the brain, controlling sensation and movement.

Any damage or injury to the spinal cord can cause loss of sensation or function to the part of the body that the nerves supply.

 

Click on the topics below to find out more from the orthopaedic connection website of American Academy of Orthopaedic Surgeons.