The spine, also called the backbone, is made up of vertebral bones with cushioning intervertebral discs between them. The spine plays a crucial role in providing structural support and smooth movement, as well as providing a corridor of protection for the delicate spinal cord, which is a key part of the central nervous system. It is supported by many muscles, tendons, and ligaments, and innervated by nerves that branch out from the centrally placed spinal cord. The spinal cord runs through the spinal canal, and nerve roots exit through the intervertebral foramen to innervate the peripheral nervous system.
Having a well-functioning healthy spine is essential for our mobility and ability to participate in various activities, as the spine supports body weight and protects the spinal cord. Understanding the anatomy of spine enhances your ability to discuss conditions of the spine such as spinal stenosis, spinal cord injury, and degenerative changes, and treatment options, including spine surgery, 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. The spine is a complex structure that supports spine health and protects the spinal cord, which ends at the lower lumbar region.
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 vertebrae fuse to form the sacrum and coccyx. 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, provides a platform for the attachment of the intervertebral discs, and plays a critical role in shock absorption.
Pedicles: These are two cylinder-shaped projections originating from the back of the vertebral body, connecting the front and back of the vertebra, and forming part of the vertebral arch that houses the spinal canal.
Lamina: Lamina is 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, which is housed within the spinal canal and ends at the lower lumbar region in early adulthood.
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 and play a role in muscle attachment and leverage for movement.
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, including intrinsic back muscles that aid in spinal movement and posture.
Spinal Canal: This is the tunnel formed at the center of the vertebra for the passage of the spinal cord, which extends from the brain to L1-L2 in adults and ends at the lower lumbar region. The spinal cord housed within the spinal canal is about half an inch thick and protected by the vertebral arch.
Facet Joints: These are paired articular processes found at the vertebral arch. Each vertebra consists of two pairs of facet joints; one pair called superior facets articulates with the vertebra above and the other pair, inferior facets articulates with the vertebra below. Facet joints guide movement and provide stability to the spine, allowing for controlled motion between vertebrae.
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 fibrosus and a soft, gel-like center called the nucleus pulposus. Intervertebral discs function as shock absorbers for the spine and help absorb shock during movement. There are 23 intervertebral discs in the human spine. Aging and injury can cause degeneration of these discs and cause painful rubbing of the vertebral bones, potentially leading to spinal disc herniation or spinal stenosis.
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. The cervical spine also plays a role in protecting the spinal cord and spinal nerves branch out from this region to innervate the upper limbs and other bones in the area.
- 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, which are vital internal organs. The thoracic spine has natural curvature called thoracic kyphosis that helps balance the body and absorb forces during movement. Nerves branch from this section to innervate the chest and abdominal wall.
- 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. This region also marks where the spinal cord ends, and the cauda equina begins, which is clinically important for procedures like lumbar puncture.
- Sacrum: The sacrum is a triangular bone located as a single bone, formed by the fusion of five sacral vertebras together. It connects the spine to the hip bones and plays a key role in supporting the lower limbs and core muscles.
- Coccyx: Also called the tailbone, the coccyx is formed from the fusion of four small bones and provides attachment for muscles and ligaments to the pelvic floor, aiding in stability and support of the lower extremities.
Spinal Curves: The side view of an adult spine resembles a natural S-shaped curve, which includes cervical lordosis, thoracic kyphosis, and lumbar lordosis. 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. Any weakness or strain in the back muscles can cause incredible strain on the spine.
- 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 control the arch of the lower back.
- The oblique muscles are found at the sides of the body and help in the sideways rotation of the back.
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 with the vertebral bodies, and the ligamentum flavum attaches one lamina to the other. These ligaments function to maintain the alignment of the vertebrae, supporting the spinal anatomy and aiding in the stability of the spine's natural curves: cervical lordosis, thoracic kyphosis, and lumbar lordosis. The ligaments work in conjunction with the erector spinae muscles and other intrinsic back muscles to maintain posture and facilitate movement.
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. Many people in the U.S. have chronic spine pain, and conditions such as osteoarthritis, spinal stenosis, and spinal disc herniation can lead to pain, numbness, and weakness.
The spine is a complex anatomical structure made up of bones, joints, tendons, ligaments, muscles, nerves, and the spinal cord. This strong spinal column, consisting of 33 vertebrae including the five vertebrae of the lumbar region and the fused sacrum and coccyx, provides the basic structure, support, and flexibility to the human body.
Understanding this complex anatomy of spine highlights the importance of seeking specialized care form an experienced specialist. At the MIS Spine Institute, our surgeon’s goal is to accurately diagnose these structural issues and deliver targeted, minimally invasive spine surgery or conservative therapies to protect your neural health, alleviate chronic discomfort, and safely restore your mobility.
