The collection of these can all be damaged by pressure which is extremely important to consider when it comes down to saddle fit, design and pressure distribution.
Pressure pushes circulation out of living tissue which can damage, bruise and kill cells as there is no longer a supply of oxygen and nutrients. If the area is damaged continuously then the area is replaced by scar tissue.
When nerves are damaged it may cause atrophy (muscles waste away), the horse will lose its healthy top line and develop hollows behind the scapular near the withers giving a hollow look.
The long back muscles work together with the skeletal structure to create movement in the back and other parts of the horse away from the spine. The muscles feel so soft that you would never imagine that they are layers upon layers of muscles which continue from the pelvis to the neck, under and over the scapula which are contracting and relaxing with every movement.
The back is strengthened from ligaments running along the top of the spinal processes similar to straps that help with storing and releasing energy to assist the musculature.