Muscles and Movement

Question 0

Label a diagram of the human elbow joint, including cartilage, synovial fluid, joint capsule, named bones, and antagonistic muscles (biceps and triceps)

Answer 0

• humerus
• radius
• ulna
• tendon

Question 1

State the roles of bones, ligaments, muscles, tendons, and nerves in human movement.

Answer 1

1. Bones: anchorage for muscles, act as levers, support body, protect internal organs
2. Ligaments: connect bone to bone, restrict movement at joints, prevent dislocation
3. Muscles: contract to move bones, skeletal muscle occurs in antagonistic pairs (one extends, other flexes, ie. biceps/triceps)
4. Tendons: attach muscle to bone, allow bone movement
5. Nerves: stimulate muscles to contract at precise time/extent so movement is coordinated

Question 2

Outline the functions of the structures in the human elbow joint named in 11.2.2

Answer 2

1. Biceps: flexor muscle, bends arm at elbow
2. Triceps: extensor muscle, straightens arm
3. Humerus: provides anchorage for muscles
4. Radius: transmits forces from biceps through forearm
5. Ulna: transmits forces from triceps through forearm
6. Capsule: seals joint
7. Synovial Fluid: lubricates joint to reduce friction
8. Cartilage: layer of smooth/tough tissue over ends of bones to reduce friction
9. Tendon: attaches muscle to bone

Question 3

Compare the movements of the hip joint and the knee joint

Answer 3

Both:
- held by ligaments to prevent dislocation
- need muscles to provide force for movement
- synovial joints, lubricate + reduce friction
- ends covered in cartilage, reduce friction + absorb shock
Knee:
- hinge joint
- movement in 1 plane; bending (flexion), straightening (extension)
- greater range of motion when flexed
Hip:
- ball and socket joint
- movement in 3 planes; protraction/retraction (forward, back), abduction/adduction (sideways, back), rotation
- greater range of motion than knee

Question 4

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.

Answer 4

• Thin actin filaments - helix shapes
• Thick myosin filaments - thick rounded shapes with myosin heads
• Sarcomere between 2 Z-lines
• Dark band in centre, light band around Z line

Question 5

Describe the structure of striated muscle fibres, including the myofibrils with light and dark bands, mitochondria, the sarcoplasmic reticulum, nuclei, and the sarcolemma

Answer 5

Striated (skeletal) muscle is a collection of large multinucleated muscle cells/fibres; contracts by sliding filaments (myofibrils)

1. Myofibrils: cylindrical, parallel, elongated bundles of contractile/elastic proteins
   - repeating units (sarcomeres) which have light/dark bands
   - light/dark bands extend around all myofibrils in muscle fibre (gives striated appearance)
2. Mitochondria: provide energy (ATP) for muscle contraction
3. Sarcoplasmic Reticulum: modified ER that wraps around each myofibril
4. Nuclei: muscle cells/fibres can have many nuclei
5. Sarcolemma: plasma membrane, surrounds each muscle fibre

Question 6

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 reset myosin heads

Answer 6

• Actin: protein makes up thin myofibrils; has binding sites on filaments for myosin; normally blocked
• Myosin: motor protein makes up thick myofibrils; bind to actin filaments; convert chemical energy (ATP) into mechanical energy (motion)
• Ca 2+ ions: actively transported by sarcoplasmic reticulum from cytosol to inside SR; lead to exposing binding sites on actin
• Cross-bridges: link actin + myosin to create force that moves actin; sliding filament model
• ATP: binds to myosin to provide energy needed to move actin

Sliding Filament

1. Relaxed muscle, actin binding sites blocked by tropomyosin (protein), myosin can’t bind and is in low energy state
2. ATP binds to myosin heads, hydrolizes forming ADP+Pi (inorganic phosphate), myosin in high energy state, heads cock and extend
3. Action potential releases Ca2+ from SR into muscle cell cytosol
4. Ca2+ exposes binding sites on actin
5. Myosin heads attach to binding sites forming cross-bridges
6. ADP+P released, myosin Xbridge changes shape and bends back (power stroke) to low energy state
7. Actin slide past myosin toward centre of sarcomere
8. Length of sarcomere decreases, Z lines move closer together
9. More ATP attaches, myosin heads release and attach further down
   10: (repeat 5-8) Actin pulled toward centre, iff ATP + Ca2+ are in cytosol
10. Ca2+ pumped back to SR, contraction ends, actin blocked, muscle relaxes

Question 7

Analyse electron micrographs to find the state of contraction of muscle fibres.

Answer 7

• muscles can be fully relaxed, slightly contracted, moderately contracted, and fully contracted.