biology presentation for the skeleton
Length: 667 words (1.9 double-spaced pages)
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The skeleton of a human foetus is formed from tough but flexible cartilage that acts as a blueprint for bone construction. During ossification ( the changing of cartilage to bone) which begins before birth, the cartilage is broken down and the resulting space is filled by bone building mineral salts and protein fibres secreted by bone cells.
Humans have a bony endoskeleton made up of 206 bones, although we are born with up to 300, but many of these fuse during childhood. slide 2 The skeleton is divided into two parts ; the axial and the appendiculur.
The axial skeleton consists of the skull, backbone and rib cage which forms the upright axis of the body. It helps to protect the brain, spinal cord and organs in the chest.
The appendicular skeleton consists of the upper and lower limbs and the pectoral (shoulder) and pelvis and girdles. The human pelvis is adapted for an upright stance. the lower limbs support the upper body and enable walking and other locomotory movements to take place, where as the upper limbs are used for manipulation.
Just read off screen
Slide four – acetate 2
Muscles are used to move your bones. Most muscles are joined at both ends to bones. They are joined to bones by non elastic tendons. Bones are held in place by strong fibres called ligaments.
Slide five – acetate 3
Joints are formed when two or more bones come together. Most joints allow bones to move. The amount of movement depends on the type of joint. The elbow joint is a hinge joint. Joints that allow movement are called synovial joints. A synovial joint s adapted to enable a joint to move easily. They contain cartilage, ligaments, bones, synovial fluid and a synovial membrane.
The bones provide the solid base on which the tendons and ligaments are fixed. They are very resistant to being compressed, bent and stretched.
The cartilage is the smooth layer which covers the ends of the bones and which stops the bones rubbing together. It has high tensile strength, but it is not rigid. Can compressed and is able to act as a shock absorber.
The ligaments are strong fibres that hold bones firmly together. they form a protective cover around the joint. Are very strong and sufficiently elastic to allow movement when the bones in the joint move, so reducing the chance of dislocating a joint.
The synovial fluid is an oily liquid secreted by the synovial membrane. The fluid makes the surface of the cartilage slippery. It helps the joint move with as little friction as possible, by acting as a lubricant.
The synovial membrane secretes the synovial fluid and also acts as a waterproof seal for the joint,
Tendons attach muscles to bones. Tendons are very strong but have little elasticity and do not stretch, so that the muscle can pull on the bone.
Slide 7 – acetate 4
Sprain – if we wrench a joint we may tear a ligament or tendon. A sprained ankle may be caused by suddenly twisting the foot inwards.
Fracture – a broken bone is called a fracture. This can be a crack in the bone or a complete break. An x-ray will show any breaks. The bones are held in place by plaster so that the bones “knit” together again.
A simple fracture is when a bone is completely broken. The broken end of the bone does not penetrate the skin.
A greenstick fracture is when the bone is not completely broken and there is no penetration of the skin. Common in children, because their bones contain less calcium salts than the bones of adults.
A compound fracture is when the bone is completely broken. The broken bone end of the bone penetrates the skin.
A complicated fracture is when the broken ends of the bone tear into blood vessels or nerves.
Slide 8 – no acetate
Answers; 1 b) 206
3 c) ligaments