VERTEBRAE—Small bones called vertebrae form your spine. Your spine supports your head and trunk, makes your body flexible and protects your spinal cord. There are five types of vertebrae:

• Seven small, flexible cervical vertebrae support your
  skull and neck.
• Your chest cavity is formed by 24 ribs extending from 12 thoracic vertebrae.
• The five lumbar vertebrae are the largest and carry most of your body weight.
• Five fused vertebrae below your lumbar vertebrae form the sacrum.
• Fused vertebrae form the coccyx, or tailbone.

DISCS—Between your vertebrae are shock absorbers called discs. Discs have a
strong outer casing with a pliable jelly-like substance inside.
SPINAL CORD—Your spinal cord, along with your brain, forms your central
nervous system. It’s about 18 inches long and a half-inch thick. It runs through a
canal in your vertebrae.
NERVES—About 31 pairs of nerves branch out from your spinal cord and travel
throughout your body. These nerves carry commands to your organs and muscles and
relay messages about touch, temperature and pain.
MUSCLES—Some 400 muscles work together to keep your spine steady, maintain
your posture and help you move.
TENDONS—More than 1,000 tendons connect your muscles to your bones.
LIGAMENTS—Bands of tissue between your bones support your back and keep it
from moving more than it should.

Your back supports you in everything you do. Your role is to support your back by using good posture, exercise and body mechanics to keep it strong, flexible and balanced.