Joints and movement
- muscles bring about movement at a joint - muscles can only pull they cannot push so two muscles are needed to move a bone back and forth. - a pair of muscles like these are called antagonistic. - a muscle that contracts to cause extension of a joint is called an extensor - a flexor contracts to reverse the movement - the hip, knee and ankle joints are examples of synovial joints - the bones that move in the joint are separated by a cavity filled with synovial fluid. - the bones are held in position by ligaments that control and restrict movement. -tendons attach muscles to the bones - cartilage protects bones within joints.
- synovial fluid: acts as lubricant - synovial membrane: secretes synovial fluid - ligament: joins bone to bone and is strong and flexible - muscle - fibrous capsule: encloses joints - pad of cartilage: gives additional protection - cartilage: absorbs synovial fluid and acts as shock absorber - bone - tendon: joins muscle to bone At a joint there is:
Joints and movement continued
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How do muscles work?
- muscle is made up of bundles of muscle fibres, each fibre is a single muscle cell - each muscle cell is multinucleate (has more than one nucleus) this is because a single nucleus could not effectively control the metabolism of such a long cell. - Tendons connect muscle to bone - the muscle is made up of bundles of muscle fibres. these are bound together by connective tissue. - each muscle fibre is a single muscle cell surrounded by a cell surface membrane. - Inside the muscle fibre is the cytoplasm containing mitochondria and the other organelles found in a cell. - Within each muscle fibre there are also numerous myofibrils, each is composed of repeated contractile units called sarcomeres.
- when the muscle contracts the dark band overlaps the intermediate band shortening the length of the muscle and the sarcomere. - there only myosin filaments occur there is a intermediate-coloured band. -...