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Anatomy and Physiology of the Spine

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The spinal column — also known as the spine or backbone — protects the delicate nerve tissue of the spinal cord.

The Spine

  • More than two dozen bones stacked upon one another form the spine.
  • The bone closest to the head is called the atlas because it carries the weight of the skull.
  • Individual bones are grouped together and include — from top to bottom:
    • Seven neck bones (C, for cervical)
    • 12 chest-level bones (T, for thoracic​)
    • Five lower back bones (L, for lumbar)
    • Four fused bones forming the sacrum (S)
    • The tailbone (coccyx)

The Vertebrae

  • Each bony unit of the spine is called a vertebra; vertebrae is the plural form of the word.
  • A vertebra is made up of the body and the arch. The arch aligns and form the spinal canal when the vertebrae are stacked.
  • There are “cushions” between each vertebra; these intervertebral disks are made up of cartilage, collagen fibers, and water.
  • Ligaments hold the vertebrae and the intervertebral disks together.

Damage to the vertebrae

  • Vertebrae can be crushed by force pushing on it and making a fracture; it is the same mechanism that happens when someone breaks an arm or a leg.
  • Vertebrae can also be damaged when the ligaments that hold them together break; this makes the stacked vertebrae fall out of alignment.

Both falling out of alignment and breaks can injure the spinal cord. Injuries can range from a bruised spinal cord or, in a worst-case scenario, a crushed and interrupted spinal cord.

Spinal Cord

The spinal cord is composed of many nerve fibers that run from the base of the brain to the small of the back. It is the most important way for the brain to communicate with the rest of the body.

Spinal nerves:

  • Exit from the spinal cord to send and receive signals from muscles, skin, and other organs.
  • The nerves exit the bony canal through passageways, called foramen, between the vertebrae.
  • Nerves exiting near the:
    • Neck and upper back send and receive signals from the arms
    • Chest area are in charge of internal organs
    • Lower back control the legs and the genital area

The spinal cord runs within the spinal canal.

  • The spinal cord and the spinal canal are of equal lengths before birth.
  • The spinal cord stops growing earlier than the spinal canal that covers it.
  • In an adult, the spinal cord ends in the spinal canal in the small of the back, around the level of the second lumbar vertebrae (L2).
  • The rest of the spinal canal only contains spinal nerves and not the spinal cord itself.
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