The back is an intricate structure of bones, muscles, and other tissues that forms the posterior pa...
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The back is an intricate structure of bones, muscles, and other tissues that forms the posterior part of the body's trunk, from the neck to the hipbones and pelvis. The bones that form the core of the back structure are called the spine or spinal column. This stack of more than 30 bones, vertebrae, supports the upper body's weight and houses the spinal cord. The nervous system structure that carries signals which control the body's movements and convey its sensations. Each of the bones that make up the spinal column has a hole in the center, and when these bones are stacked, it creates a channel that surrounds and protects the spinal cord. The bones or vertebrae that make up the spinal column are not stacked directly on top of each other. There are spaces between them that are maintained by round, spongy pads of cartilage called intervertebral disks. Each intervertebral disk is made up of two components, the annulus fibrosus and the nucleus pulposus. The annulus fibrosus is the tough outer portion of the disk. The nucleus pulposus is the inner gel material surrounded by the annulus fibrosus. These disks and the space between the bones that they fill, give the lower back flexibility. The disks act much like shock absorbers throughout the spinal column to cushion the bones as the body moves. Bands of tissues called ligaments and tendons hold the vertebrae in place and attach the muscles of the back to the spinal column. Small nerves called roots enter and emerge from the spinal cord through spaces between the vertebrae. The spine has four regions. Starting from the top, there are seven cervical, or neck, vertebrae, labeled C1 through C7, twelve thoracic or upper back vertebrae, labeled T1 through T12, five lumbar vertebrae, designated L1 through L5 in the lower back, and finally, the sacrum and coccyx, a group of bones fused together at the base of the spine. Intervertebral disks are located between each vertebra from C2 through S1.