11.2 – Muscles and Movement
11.2.1 – State the roles of bones, ligaments, muscles, tendons and nerves in human movement
Bones – Act as anchors for the muscles, and levers to control the movement of muscles, support and protect body parts
Ligaments – Connect bone to bone to prevent them from becoming dislocated. They are made up of strong fibres.
Muscles – Contract to allow for movement. Skeletal muscles attach to the bones, and are found in pairs called antagonistic pairs.
Tendons – Attach muscles to bones, made up of connective tissue
Nerves – Bundles of nerve cells that send messages through the body to specific places. They stimulate the contraction of muscles and altogether, the CNS coordinates movement
Combined, these different parts allow for the body to move at the joints. The movable joints in the body are called synovial joints because there is synovial fluid between the bones to keep them lubricated
11.2.2 – Label a diagram, of the human elbow joint, including cartilage, synovial fluid, joint capsule, named bones and antagonistic muscles (biceps and triceps)
Biceps – the flexor muscle attached to the radius, bends the elbow as the triceps relaxes
Triceps – extensor muscle attached to ulna, straightens the elbow
Humerus – attachment for muscles to form a system of levers
Radius – transmits force from the biceps through the forearm
Ulna – bone that transmits force from triceps through forearms
Capsule – seals the joint, contains synovial fluid, but does not restrict movement
Synovial Fluid – lubricates the join, reduces friction, nourishes the cartilage
Synovial Membrane – Secretes synovial fluid
Tendon – attaches muscle to bone
Cartilage – the flexible covers ends of bones to reduce friction between bones
Ligaments – Hold all the bones in their correct positions
11.2.4 – Compare the movements of the hip joint and the knee joint
11.2.5 – Describe the structure of striated muscle fibres, including the myofibrilswith light with light and dark bands, mitochondria, the sarcoplasmic reticulum, nuclei and the sarcolemma
Each muscle is made up of bundles of muscle fibres. Each fibre is then made up of even smaller structures, called myofibrils. The myofibrils are sarcomeres attached end to end, which contain light and dark bands, causing the myofibril to appears striped. In between the myofibrils, there are mitochondria to provide the energy for muscle contraction. The sarcoplasmic reticulum surrounds each myofibril.
11.2.6 – Draw and label a diagram to show the structure of a sarcomere, including Z lines, actin filaments, myosin filaments with heads, and the resultant light and dark bands
11.2.7 – Explain how skeletal muscle contracts, including the release of calcium ions from the sarcoplasmic reticulum, the formation of cross-bridges, the sliding of actin and myosin filaments, and the use of ATP to break cross-bridges and re-set myosin heads
A nerve impulse is sent and reaches the neuromuscular junction, causing the neurotransmitter acetylcholine to be released into the synapse. This triggers the depolarisation of the sarcolemma, which is the plasma membrane on the muscle fibre. As a result, calcium ions are released from the sarcoplasmic reticulum as bind to troponin.
Troponin displaces tropomyosin, which exposes binding sites for myosin to form crossbridges with thin actin filaments. The actin is pulled to the midline. ATP is then hydrolysed at the myosin head, causing it to detach from the actin binding site, then reattach further along the filament. The entire cycle repeats.
11.2.8 – Analyse electron micrographs to find the state of contraction of muscle fibres
Look for the narrower light ands, which will show that the muscle has contracted