You are taller in the morning than you are at night due to the daily compression of the discs between your vertebrae. Gravity also causes these discs to compress so that after the age of 40 you will get slightly shorter each year. In zero gravity these discs expand, meaning astronauts who spend any length of time in outer space start to grow taller.
The thoracic and pelvic curves are called primary curves because they are formed in the foetus. The cervical and lumbar curves are termed secondary curves because they take shape after birth. The cervical curve develops when a child holds up its head and can sit upright while the lumbar curve develops when a child begins to walk.
While most people might think of the spine as straight, when viewed side-on it has several curves. These correspond to the different sections of the column – the cervical, thoracic, lumbar, and pelvic.
Once you reach adulthood, the five sacral vertebrae fuse to form one bone, and the four vertebrae of the coccyx fuse to form one bone.
Without a spine your upper body would be jelly and your brain wouldn’t be able to transmit messages to your limbs.
The spine acts as the central pillar of your body. It supports your trunk and is part of a framework that protects your organs. It’s also a strong, bony protector of the spiral cord in much the same way that the bony shell of the skull protects the brain.
Your spine is composed of a series of vertebrae that are stacked one upon the other, becoming progressively bigger from top to bottom as the weight they support increases. Most people have 33 vertebrae in total, although some people might have 32 or 34.
There are four regions of the spine. The main purpose of the cervical spine, which is made up of the 7 vertebrae in your neck, is to support the head. This part of the spine has the greatest range of motion, which allows the head to turn.
Next is the thoracic spine in your trunk, which has 12 vertebrae, with one rib attached to each side. This assembly forms the thoracic cage, which protects the internal organs contained in the chest. Because of the rigidity of the thoracic cage, this part of the spine is less mobile than the cervical and lumber regions.
The lumbar (lower back) region has 5 vertebrae. These vertebrae are larger than the thoracic and cervical vertebrae because of the weight they carry. The lumbar vertebrae sit on the top of the sacrum, which is basically a single unit formed by 5 fused vertebrae. Likewise the coccyx or tailbone at the end of the spine is made from four fused vertebrae.
The stacked vertebrae are designed to support weight and resist compression. Though they all have a drum shaped front section called the body, each individual vertebrae has different features that are unique to its region of the spine.
Towards the rear of the vertebrae, a bony arch called the lamina envelopes the spinal canal, which contains the spinal cord and nerve roots. Ligaments and muscles attach to the bony offshoots from elements called spinal processes, which emerge from the vertebrae bodies. The lumpy parts or the spine that you can feel by rubbing your hand down the middle of your back are called the spinous processes.
Between the vertebrae are sandwiched little cushions (or discs) made up of fibrocartilage, which act like the spine’s shock absorbers. Ligaments help to hold the vertebrae tightly together and have a little give to allow some movement – but not too much – so as to maintain the integrity of the spinal canal.
Together, the discs, ligaments and muscles help the vertebrae to stay correctly aligned – and all 3 protect the spinal cord from injury. Between the vertebrae there are also openings either side of the spinal canal called foramina, which allow nerve roots a way out of the spinal canal to supply particular parts of the body. The spinal cord is surrounded by spinal fluid, as well as layers of protection that include the dura mater, a thick leathery covering that encloses the delicate nerve fibres. The spinal cord runs from the base of the brain through the cervical and thoracic regions, ending in the lumbar region where it fans out into nerve roots.
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