1.3 Skeletal System

Question 1 (1.1)

a) State three appropriate functions of the skeletal system.

The skeleton supports the main frame of the body. This helps support the softer tissues and provides points for muscles to attach. The skeleton also protects internal organs and reduces their risk of injury. Assisting the body to be able to move the muscles that are attached to the bone and when they contract the bones move with them.

b) Explain the function as it relates to muscle attachment and locomotion.

Muscle cells contract when actin (a globular protein structure) and myosin (a motor protein) slide past each other. This changes the shape of the cells and length. These types of muscle are attached to the skeleton by tendons and are under voluntary control.

These contractions cause the limbs to move and a posture. Each muscle fibre has many smaller fibres together these is called myofibrils. The myofibrils have even small structures inside them these are called actin and myosin fillaments. The filaments slide in and out to form the contractions of the muscles. However, for the muscle as a whole to contract, the actin and myosin filaments must overlap, this causes the sarcomere to shorten. This then triggers the reaction by the release of calcium ions in the presence of troponin and tropomyosin proteins. Releasing of calcium, provides an energy source adenosine triphosphate (ATP), this facilitates the interaction of myosin and actin at the molecular level. When looking at this at a high magnification level it is shows small bridges, these are known as myosin cross bridges. The thick filaments extend over to the thin filaments. These cross bridges continuously attach, rotate, detach, and reattach which results in the sliding of the filaments, shortening of the sarcomere, and the result we see to be a muscle contraction. There are four stages that demonstrate this theory. The first stage the myosin travels to hydrolyse ATP and this then becomes reorientated and energised as ADP. The second stage in this cycle is that myosin binds together with actin this forms bridges ADPT continues. The third stage the myosin head rotate inwards from the

These bones are made out of connective tissue rather than cartilage.

The steps in intramembranous ossification happen is first the development of the centre of the bone followed by calcification, formation of the trabeculae and lastly the development of the periosteum.

Endochondral ossification starts with points in the cartilage known as "primary ossification centres." They mostly appear during fetal development, but a few short bones can begin their primary ossification after being born. They are responsible for the formation of the diaphyses of long bones, short bones, and certain parts of irregular bones as well.

Secondary stages of ossification happens after birth, and forms the epiphyses (end part) of long bones and also the irregular and flat bones. The diaphysis and both epiphyses of a long bone are separated this is by a growing area of cartilage also known as the epiphyseal plate. These bones continue to grow until the point the child reaches maturity of the skeleton by the age of about 18 to 25 years. All of the cartilage is replaced by bone, fusing the diaphysis and both epiphyses together making a