Anatomy of the Spine

Anatomy of the Spine

The spine is an important part of your body’s structural support system.  It maintains upright posture, enables flexible motion, and protects your spinal cord, nerve roots, and many vital internal organs.  The four regions of the spine are listed from top to bottom:

Cervical, neck 7 vertebrae; C1-C7 It protects the brain stem, supports the skull, and enables a wide range of neck and head movement.
Thoracic, mid back 12 vertebrae; T1-T12 Ribs attach to the thoracic vertebrae; limits movement, protects vital organs.
Lumbar, low back 5 vertebrae; L1-L5 It carries most of the body’s weight.
Sacral, sacrum 5 bones; S1-S5 fused into a triangular shape Tailbone (coccyx) is below the sacrum.

Spinal Curves

Viewed from the front, a healthy spine is straight up and down. Viewed from the side, a spine has four distinct curves.  Curves are described as being either kyphotic or lordotic.

Curve Name Direction Spinal Location
Kyphotic Outward Thoracic and sacral
Lordotic Inward Cervical and lumbar

Bony Structures

Spinal bony structures are made of cortical bone (outer shell), cancellous bone (inner latticework-like), and bone marrow (produces blood).

  • Body: Viewed from above, the body appears oval. From the side, the body is thicker at the ends and thinner in the middle.
  • Pedicles:  Two short processes protrude from the back of a vertebral body.
  • Processes:  Spinal processes are finger-like projections.  The three types are: articular (joint), transverse (crosswise) and spinous (lever-like).   They serve as connection points for ligaments and tendons.
  • Laminae:  Two flat bony plates extend from the pedicles on either side and join at the middle.
  • Intervertebral Foramen: At the left and right sides, and between (inter) the upper and lower vertebrae nerve passageways are naturally created.  Nerve roots branch out from the spinal canal through foramen (sometimes termed neuroforamen).
  • Facet Joints: Located at the back of the spine, two facet joints help connect two vertebral bodies, enable the spine to bend forward and backward, and twist.  These joints restrict excessive forward (hyperflexion) and backward (hyperextension) movement.

Discs and Endplates

  • Intervertebral Discs:  A disc is made of fibrocartilage.  The outer ring (annulus fibrosus*) encases a gel-like matter (nucleus pulposus).  Discs absorb and distribute biomechanical forces, resist compressive forces, and are important to spinal stability.  Disc height separates two vertebral bodies and helps create neuroforamen; nerve passageways.

*The annulus fibrosus consists of elastic collagen fibers. Collagen is made up of fibrous bundles of protein bound together by a proteoglycan gel. The fibers are oriented at different angles, similar to the construction of a radial tire.

  • Endplates:  The top (superior) and bottom (inferior) of each vertebral body is coated with anendplate.  Endplates are complex cartilaginous structures that blend into the intervertebral disc and help support the disc.

Spinal Cord

The spinal cord is protected by bone and suspended in cerebrospinal fluid.  The cord is slender and cylinder-shaped; it’s approximately the diameter of a little finger.  The spinal cord begins below the brain stem and ends near the first lumbar vertebra (L1).  Thereafter, the cord becomes the cauda equina; nerves resembling a horse’s tail.

Ligaments

Ligaments are fibrous connective tissue that attach to bone.  Ligaments connect two or more bones together and help stabilize joints.  Spinal ligaments create a natural brace effect that stabilizes the spine and helps prevent injury.  Ligaments add to joint stability at rest and during movement.

Tendons and Muscles

Tendons attach bone to muscle.  Fascia, strong sheath-like connective tissue, encases individual or groups of muscle.  Tendons are an extension of fascia.  Spinal muscle stabilizes the spine and powers flexion, extension, and rotation.

Rehabilitation Medicine Center of New York knows spinal anatomy is a complex subject.  We want to help you understand why you have back pain and/or neck pain.  We look forward to answering your questions so you can make important decisions about your treatment!