Topic 11.2 Movement Bone and Muscle

Bones Bones and muscles work together to move the body – Bone and exoskeleton provide framework PartFunction BonesSupport body, attachment LigamentsProvide stability at joint; attach bone to bone TendonsAttach muscle to bone for movement NervesSend impulses to muscles for relaxation & contraction

Skeletal muscle are antagonistic Work in pairs When one relaxes the other contracts Example, biceps and triceps

Elbow Joint Joints are where two bones meet Joints allow movement in different directions Synovial joints: have synovial fluid to prevent friction Elbow and knee are hinged synovial joint Ball and socket joints (shoulder and hip) Pivot joint (head) Gliding joint (wrist)

Elbow joint

Parts & functions StructureFunction CartilageReduces friction and cushions ends of bones Synovial fluidLubricates & prevents friction between ends of bones Joint capsuleSeals the joint space & provides stability BicepsFlexor muscle, pulls the arm upward when contracted TricepsExtensor muscle pulls the arm downward when contracted HumerusLong upper arm bone RadiusShorter of the two bones in the forearm UlnaLonger of the two bones in the forearm

Muscle Types Three types of muscle tissue – Skeletal or striated – Cardiac – smooth

Skeletal muscle Composed of myofibrils (actin & myosin) Arranged in unique ways for distinct functions Sliding over each other Basic unit of a muscle contraction is called a sarcomere

Each muscle cell can contain thousands of sarcomeres Each sarcomere is made of a myofibril – Myofibril contains actin and myosin – Actin is the thin filament – Myosin is the thick filament

Stacked myofibrils are found within each cell surrounded by the muscle cell membrane called the sarcolemma – Contains T tubules (transverse) – Reach deep into the cell – Increase surface area of sarcolemma

Skeletal muscle can be very long so it is multinucleated Also contain a special endoplasmic reticulum called the sarcoplasmic reticulum – Stores and releases calcium as needed to initiate a muscle contraction Packed with mitochondria for energy

Sarcomere Functional unit of muscle cells Composed of many repeating sarcomeres Composed of sliding filaments PartFunction Z linesBorders of the sarcomere H zoneRegion where only myosin is located A bandRegion where myosin overlaps with action (dark band) I bandRegions where only actin is located (light band)

Contraction of skeletal Muscle Initiated by and action potential from the nervous system Steps are as follows: 1. action potential arrives at terminal button releasing a neurotransmitter (acetylcholine) 2. Neurotransmitter released into synapse 3. Neurotransmitter is attached to receptors on sodium gated channels on sarcolemma (depolarization)

4. Action potential spreads through T-tubules of sarcolemma releasing calcium from sarcoplasmic reticulum 5. calcium attached to troponin (protein) causes tropomyosin to shift, exposing myosin binding sites 6. each myosin head binds an ATP and splits the ATP into ADP + Pi (inorganic phosphate) causing the myosin head to bend outwards 7. Each myosin head forms a cross-bridge with actin & releases the Pi. Release of Pi causes myosin heads to bend inward and slide the actin over the myosin (shortening sarcomere)

8. Each myosin head binds a new ATP to break the cross-bridge 9. The cycle repeats until no more action potentials are sent and calcium is pumped back into the sarcoplasmic reticulum

Sliding filament Theory

Electron Micrograph of Skeletal Muscle