Actin and tropomyosin are part of thin filaments of skeletal muscle. Tubulin is present in microtubules. Myosin is muscle protein.

When Ca^{+ ions combine with troponin contraction of muscles initiates. During contraction the Z lines come closer together and the sarcomere becomes shorter. The length of A band remains constant. I bands shortens and H-band narrows.}

Ligaments are specialised connective tissues which connect bones together, hence if they are cut or broken the bone will be come unfixed.

Hinge joint: elbow joint, knee joint, ankle joint, interphalangeal joint.

Gliding joint: Intercarpal joint, intertarsal joint, sternoclavicular joint and joint between pre and postzygapophysis of adjacent vertebra.

Fibrous join: Joints of cranium -bones. Joints between teeth and jaw bones.

Cartilaginous joint: Joints between mammalian vertebrae and two innominate bones (pubic symphysis).

Floating ribs are 2- pairs (11^th and 12^th pair) which are not attached to sternum

The pelvic girdle is formed by two innominate bones consists of three separate bones ilium, ischium and the pubis.

Elbow joint is an example of hinge joint. The elbow is a hinge joint; it can open and close like a door. Hinge joint allows angular movement in one plane only, increasing or decreasing the angle between the bones e.g. elbow joint, knee joint etc.

Glenoid cavity is found in pectoral girdle.

Major causative factors of osteoporosis are imbalances of hormones like calcitonin of thyroid, parathormone of parathyroids, and sex hormones and deficiencies of calcium and vitamin D.