Synovial joints are those joints which have a gap between bones, rather than direct joining. If a joint isn’t synovial it is either fibrous (joined by dense connective tissue rich in collagen) or cartilaginous (joined by cartilage).
The bones may be held together by ligaments, beyond which the joint capsule with its protective fluid secreted by the synovial membrane lies. The synovial membrane and synovial fluid act to lubricate the joint. The fluid contains nutrients, and can act as a shock absorbent.
The capsule itself is well innervated, but lacks a blood supply. Nutrients and other molecules can travel by diffusion, although very slowly. A quicker route is fluid movement (convection) during exercise.
Hyaline cartilage caps the bone ends, and acts as a protective surface during movement and stress on the bones. Unlike the cartilage in cartilaginous joints (e.g. ribs), this cartilage doesn’t connect the bones together. The cartilage surface is smooth, so if they touch they slide over each other.