The Musculoskeletal System.docx

The Musculoskeletal System The skeleton is the framework of the human body. At birth, it consists of 270 bines, but this number reduces to 206 by adulthood, as some bones fuse together. The skeleton is split into two parts: - Axial skeleton: Runs down the centre of the body, and consists of the skul...

The Musculoskeletal System The skeleton is the framework of the human body. At birth, it consists of 270 bines, but this number reduces to 206 by adulthood, as some bones fuse together. The skeleton is split into two parts: - Axial skeleton: Runs down the centre of the body, and consists of the skull, vertebrae, ribs, and the sternum - Appendicular skeleton: Runs along the sides of the body, and consists of pectoral and girdles and their attached limbs (7) The Spine The spine consists of 33 bones in humas, made up of the following subsections: - Cervical: Forms the neck and consists of seven vertebrae. The first bone is called the Atlas - Thoracic: The next 12 vertebrae hold the ribs that protect the organs in the thoracic cavity. The first seven ribs are called True Ribs as they connect directly to the sternum. The next three are called False Ribs and connect indirectly to the sternum. The final two are called Floating Ribs because they do not connect to the sternum - Lumbar: These five vertebrae form the lower back - Sacrum: The five vertebrae of the sacrum are fused and connect the spinal column to pelvic girdle - Coccyx: These are tail bones, and in humans there are four of them fused together Functions of Bones - Support: The bones of the skeleton form a solid framework inside the organisms, this is called the endoskeleton. The skeleton on the outside of the organism is called the exoskeleton. The skeleton acts as a place for the attachment of muscles and organs, and it produces the basic outline of the organism - Protection: The skull protects the brain, the ribs protect the lungs and heart, the vertebrae protect the spinal cord and, the pelvic girdle protects the reproductive organs - Movement: The bones act as levers and the joints act as pivots, while the muscles provide the force required to produce movement - Blood cells: Produced in the bone marrow from stem cells - Storage: Some fat is stored in yellow bone marrow found in the cavity of long bones Cartilage - Contains a flexible fibrous protein called collagen. Collagen fibres are embedded in a matrix of calcium and phosphorus salts. - It covers the tips of bones where they meet in joints and so reduces friction. It also acts as a shock absorber. Intervertebral discs Cartilage is found in between the bones of the vertebral column. These are called intervertebral discs. They act as shock absorbers and reduce friction as the spine moves. These discs have a jelly-like interior Ligaments Ligaments connect bone to bone at joints. Their primary job is to prevent the dislocation of the two bones by limiting the degree of movement between them. The Synovial membrane produces the synovial fluid which lubricates joints Tendons Tendons connect muscle to bone. Examples include the Achilles tendon, which joins the calf muscle to the heel of the foot. Long Bone Anatomy (8) - Periosteum: Layer of connective tissue providing a fibrous coating - Compact bone: Made of bone cells (osteoblasts) embedded in a matrix. Calcium salts e.g., calcium phosphate, give bone its strength while protein gives bone its flexibility. Found mostly in shaft (diaphysis) of a bone and as a layer around the ends of bones. - Spongy bone: Like compact bone that contains numerous hollows to minimise weight. Spaces are filled with red bone marrow that produces blood cells. - Hollow centre (medullary cavity): Contains inactive yellow bone marrow. Stores fat. This bone marrow can convert to red bone marrow if the body requires an increase in blood cell formation. Bone Growth (9) - Embryonic cartilage begins to be replaced with bone around the eight week of development in the uterus - Osteoblasts are bone cells responsible for ossification (conversion of cartilage into bone) - They produce collagen and then calcium phosphate forms around the collagen fibres. The osteoblasts become trapped in this calcium phosphate and become dormant bone cells - The increase in the length of a bone is due to a growth plate found between the epiphysis and the diaphysis - In this, plate cartilage is continually formed and turned into bone. - The growth plate ceases to function at adulthood - People in need of growth must receive injections before the cartilage discs have disappeared. Joints Synovial fluid is a thick, slippery liquid that is produced by the synovial membrane. It acts as a lubricant, minimising wear and tear by reducing friction. It also acts as a shock absorber, cushioning the bones during movement (10) Joints are formed where two bones meet. There are three types of joint: - Immovable (fused): Bones are in contact e.g., skull, pelvis - Slightly movable: allow a small amount of movement e.g., spinal column - Movable: Hinge, allows a large amount of movement e.g., knee Ball and socket, allow movement in all planes e.g., hips Skeletal Muscle Skeletal muscle is attached to bone and is under our conscious control. Also called striated muscle. It is described as contractile because it can only shorten, and has to be pulled back to its original length by another muscle acting in the opposite direction before it can be used again. Antagonistic Muscle Pairs of muscles that act against each other to produce movement in opposite directions, e.g., biceps and triceps of the upper arm which flex and extend the forearm. The biceps at the front of the upper arm contracts, becoming shorter and thicker, to flex the arm and as this happens the movement stretches the relaxed triceps muscle at the back of the upper arm. The triceps muscle contracts to straighten the arm, and this movement pulls the relaxed biceps muscle back to its original length and thinness Bone Disorders – Arthritis - A disease of the joints. It is very painful and can cause disfiguration and function loss of the affected joints. Causes include injury, age, autoimmune disease, and heredity. Prevention is helped by maintaining a healthy weight, taking plenty of exercise, and avoiding activities that cause joint damage. Treatments include painkillers and non-steroidal anti-inflammatory drugs. There is no cure.