11.2 Muscles and Movement
1. State the roles of bones, ligaments, muscles, tendons and nerves in producing human movement.
- Bones provide rigid framework against which muscles attach and against which leverage can be produced, changing the size or direction of forces generated by muscles.
- Ligaments connect bone to bone, restricting movement at joints and helping to prevent dislocation.
- Muscles attach to bones via tendons, and when muscles contract, they create the forces that move bones; using leverage, small muscle contractions can produce large bone movements
- Tendons attach muscles to bone.
- Nerves provide a communication network along which messages can be sent signaling muscles to contract at a precise time and extent, so that movement is coordinated.
2. Label a diagram of the human elbow joint including cartilage, synovial fluid, joint capsule, named bones and named antagonistic muscles (biceps and triceps).
3. Outline the functions of the structures of the human elbow joint named in 11.2.2.
- Cartilage: reduces friction between bones where they meet
- Synovial fluid: lubricates joint to reduce friction
- Joint capsule: seals the joint and holds in the synovial fluid
- Humerus: upper arm bone: attachment of biceps and triceps
- Ulna & radius: forearm bones: attachment of biceps and triceps
- Biceps: attaches from humerus to ulna & radius
- Triceps: attaches from humerus to ulna
- Antagonism: biceps and triceps attach across elbow joint; while triceps contracts to to extend arm, biceps relaxes; conversely, while treceps relax and the biceps contract, flexing the arm
4. Compare the movements of the hip joint and the knee joint.
- Knee: hinge joint
- allows considerable movement in one plane
- but constrains movement from other two planes
- flexion bends the leg
- extension straightens the leg
- Hip: ball and socket joint
- allows movemnt in three planes
- protraction /retraction: forward and backwards
- abduction/adduction: sideways in and out
- rotation: circular movement
- allows movemnt in three planes
5. Describe the structure of striated muscle fibers, including the myofibrils with light and dark bands, mitochondria, the sarcoplasmic reticulum, nuclei and the sarcolemma.
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.
7. Explain how skeletal muscle contracts, including the release of calcium ions from the sacroplasmic 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.
Actin:
- thin filaments (myofibrils) extending from sarcomere ends (Z lines) toward center (M line)
- thick filaments (myofibrils) extending from sarcomere center (M line) toward ends (A band = length of myosin)
- released from sarcoplasmic reticulum in response to neural depolarization
- Ca2+ ions attach to troponin binding sites
- troponin = protein bound to actin filaments
- tropomyosin = fibrous protein spiraling around actin
- binding of Ca2+ ions to troponin binding sites moves tropomyosin to expose cross-bridge binding sites
- exposed cross-bridge binding sites allows myosin heads to attach to actin forming cross-bridges needed for sarcomere contraction
- myosin filaments overlap with actin filaments
- mysosin arms attach to actin, forming cross-bridges
- movements of myosin arms ratchet along actin, contracting sarcomere
- myosin breaks attachment, reattaches to actin, and repeats ratcheting contraction of sarcomere
- ATP phosphorylation of myosin heads provides energy for ratcheting power stroke of muscle contraction
8. Analyze electron micrographs to find the state of contraction of muscles fibers.
