The tendons attach the muscles to the bones. The ligaments attach bones to other bones. The fascia are layers of clear wrappings around the muscles and their inner core and serve to keep their contents secure. The interconnections and interdependencies between these systems make diagnosis of many physical problems challenging and difficult. Where the problem presents itself is often not the source of the problem, in effect, pain is referred from another source.
Muscles have origins and insertion points.
Muscles will perform either a flexing or extensor function allowing the actions necessary to extend, abduct, adduct, retract, etc. In effect, these muscle allow the various joints of the body to move or articulate. Muscles do not perform motor or sensory functions unless energized by nerves originating in the spine. Problems can arise from muscle strains and tears, tendinitis where the muscles attach to the bones, or if nerves emanating from the spine and feeding the body's muscles are compressed, impinged, or avulsed. Additionally, the body has bursas and cartilage which absorb shocks between bones and muscles and bones and bones.