As time passes the forces on the disc can make its jelly / gelatin portion wear out and lose height. A point of interest is that the force on our discs throughout the day causes us to lose height! Whilst astronauts, in weightless conditions, increase their height since the lack of gravity keeps discs from being compressed; the separation between vertebrae is therefore increased.
There are no nerves in the nucleus; they are located in the most external layers of the fibrous ring. This explains why wear and tear on the discs may not be painful as there are no nerves to receive and transmit pain. The function of the intervertebral disc can be summarised as:
1 To separate the vertebrae
2 To allow for movement of the spine
3 To act as shock absorbers
Vertebrae are linked together by ligaments, muscles and tendons which also insert into or attach onto the spinal processes to allow movement.
Ligaments are fibrous tissue that connects bones to other bones, they:
1 Possess varying amounts of elastic tough fibrous tissue which help support the spine.
2 Pass across the articulating surfaces of the facet joints and between the vertebrae
3 Help to prevent unwanted or excessive movements
As they are elastic, ligaments can be damaged if they are over-stretched. With sudden and excessive movements a ligament can be weakened, torn or snapped.
The word muscle comes from the latin meaning little mouse! It is a contractile tissue of the body and its function is to produce force and movement. Muscles:
1 Sit over the ligaments
2 Are attached to the bones by tendons
3 Control body movements
4 Act in pairs, as one muscle tightens (contracts) the other relaxes to allow movement.
· Postural muscles hold up the body against the influence of gravity.
· Other important muscles involved in the function of the spine are the abdominal muscles
· Muscles require energy to work efficiently
Muscle work can be either static or dynamic.
Static muscle work is when a muscle is in constant contraction without producing any movement. This could be, for example, when holding a tray or when maintaining your foot on an accelerator pedal when driving.
When muscles work statically blood flow is restricted, oxygen supply is reduced, leading to a build up of waste products, muscle pain and fatigue then occur. If repeated frequently this can lead to deterioration and degeneration of soft tissues and joints. Static muscle work cannot be maintained for long periods.
Dynamic muscle work involves a muscle alternately contracting and relaxing such as when polishing a surface or waving a hand. This type of work allows a fresh supply of blood and oxygen to reach the muscle and also allows waste products to be removed.
A tendon (or sinew) is a tough band of fibrous connective tissue that connects muscle to bone, or muscle to muscle and is designed to withstand tension. Tendons are similar to ligaments except that ligaments join one bone to another. Tendons and muscles work together and can only exert a pulling force.
Facet joints are:
1 Small, sliding joints at the back of each vertebrae
2 Each vertebrae is joined to the next by facet joints
3 The facet joints are designed to allow for movement of the spine together with the discs
4 Help prevent the spine moving beyond its normal range of movements and so putting too much pressure on the discs