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    intervertebral disk

    vertebrae and disks
    Vertebrae and intervertebral disks. The annulus fibrosus of the disks is shown in purple and the nucleus pulposus in blue
    intervertebral disk
    Section through an intervertebral disk
    A flat, circular, plate-like structure containing cartilage which lines the joints between adjacent vertebrae in the spinal column. Each intervertebral disk consists of a hard outer layer which surrounds keeps intact a soft gelatinous interior. The outer layer is a fibrocartilaginous ring called the annulus fibrosus. The inner core, known as the nucleus pulposus, acts as a shock absorber to cushion the vertebrae during movements of the spine, and so minimizes jarring when walking, running, or jumping.

    In older people, the intervertebral disks may wear out, becoming less supple and more susceptible to damage from injury. One of the most common forms of damage is a slipped disk, also known as a herniated disk or disk prolapse, in which part of the disk's soft center bulges out through a weak area in the hard outer layer. This may compress a spinal nerve root and produce symptoms, such as mucle weakness and/or pain in the back and leg.


    Why we get shorter during the day and in old age

    The jelly-like core – the nucleus pulposus – contains a lot of water. During the day, the weight of the upper body, pressing down on the spinal column, squeezes water out of the inner parts of the intervertebral disks. This flattens out the disks and results in us getting slightly shorter as the day wears on. The amount of water in the vertebral disks also decreases as we get older, which is one of the main reasons we tend to be shorter in our sixties and seventies than in our twenties.


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