A muscle is made up of many muscle cells - also known as muscle fibers - which are long, multinucleated cells and are composed of cylindrical organelles called myofibrils. These are arranged into basic units known as sarcomeres, formed from overlapping actin and myosin filaments. Many muscle fibers are bundled together into fascicles, which themselves are enclosed together inside a sheet of connective tissue to form the muscle itself.

Bone is a form of connective tissue composed of various types of cells. The three major cell types are:

• Osteoblasts - bone-forming cells.
• Osteocytes - mature bone cells which control bone maintenance.
• Osteoclasts - responsible for bone breakdown in order to regulate its volume.

A bundle of axons in the peripheral nervous system which carry information via electrochemical nerve impulses. There are three types of nerve, depending on which way the information is being carried:

• Afferent nerves - carry information from sensory neurons to the central nervous system - eg. cutaneous nerves.
• Efferent nerves - carry information from the central nervous system to their target muscle via motorneurons.
• Mixed nerves - contain both afferent and efferent axons, conducting both ways.

A tendon connects muscle to bone, whereas a ligament connects two bones to one another.

A sprain is an injury in a ligament due to overstretching, resulting in a possible tear.

A strain is a similar injury, however it applies to muscles rather than ligaments.