Topic 11.2 Muscles and Movement

Question 1

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

Answer 1

Bones

• provide hard framework to support body
• magnify force provided by muscle contraction
• acts as levers for body movement
• allows protection of vulnerable softer tissue and organs
• forms blood cells in bone marrow
• allows storage of minerals, esp. calcium and phosphorus

Ligaments

• tough, band-like structures
• connect bone to bone
• strengthen joint
• prevents dislocation

Muscles

• provide effort/force necessary for movement by contracting
  
  • occur as antagonistic pairs

Tendons

• cords of dense connective tissue
• connect skeletal muscles to bones

Nerves

• proprioreceptors in ligaments and muscles allow constant monitoring of position of joint parts
• help prevent over-extension of joints and its parts
• coordinates and stimulates muscle contraction

Question 2

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).

Answer 2

• tendons connecting muscle to bone
• ligaments connecting bone to bone

Question 3

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

Answer 3

• Cartilage: reduces friction between bones and absorbs compression
• Synovial fluid: lubricates to reduce friction, provides nutrients to cells of cartilage
• Joint (synovial) capsule: surrounds joint, encloses synovial cavity (preventing fluid from escaping) and unites connecting bones
• Tendons: attach muscle to bone
• Ligaments: attach bone to bone
• Biceps muscle: contracts to bring about flexion (bending) of arm
• Triceps muscle: contracts to bring about extension (straightening) of the arm
• Humerus: acts as lever that allows anchorage of muscles of elbow
• Radius: acts as a lever for biceps muscle
• Ulna: acts as a lever for triceps muscle

Question 4

11.2.4 Compare the movements of the hip joint and the knee joint.

Answer 4

Similarities

• both involved in movement of leg
• both are synovial joints

Type of joint

Hip joint: ball and socket

Knee joint: hinge

Range of motion

Hip joint: freely movable; 360°, multiple planes possible

Knee joint: freely movable; one plane possible

Bones

Hip joint: pelvis and femur

Knee joint: femur and tibia

Question 5

11.2.5 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

• Sarcolemma is the membrane surrounding muscle fibre
  
  • has multiple tunnel-like extensions penetrating interior of cell
• Many nuclei lie in sarcolemma
  
  • fibres are long and were formed from many muscle cells fusing together, hence the fibres are multinucleated
• Many parallel tubular myofibrils running length of cell
  • divided into sections called sarcomeres, and made of two different myofilaments (proteins responsible for contraction)
  • Where thin (actin) and thick (myosin) filaments overlap, a dark band occurs, and this is flanked by light regions containing actin only
    
    • ​reason for banded appearance of striated muscle fibres
• Large number of mitochondria squeezed between myofibrils (because muscle contraction requires a lot of ATP)
• The internal membranous network is called the sacroplasmic reticulum, which surrounds muscle myofibrils
  
  • it is analogous to endoplasmic reticulum but is specialised for muscle contraction (it contains high levels of Ca²⁺ ions)

Question 6

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.

Answer 6

• Z lines mark ends of sarcomere
• A bands (dark bands) extend entire length of myosin filaments
  
  • H bands occur in middle of A bands - contains only myosin, no actin
  • M bands occur in middle of myosin (this protein holds myosin filaments together)
• I bands (light bands) contain only actin, no myosin
• myosin
  
  • myosin heads
• actin

Question 7

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.

Answer 7

Overview: actin myofilaments slide over myosin myofilaments during muscle contraction, making sarcomere shorter.

1. Action potential reaches terminal end of motor neuron. ACh released into synapse. Action potential initiated in muscle cell membrane.
   
   • i.e. motor neuron stimulates muscle fibre
2. Sarcoplasmic reticulum releases calcium
3. Calcium causes binding sites on actin to be revealed
4. ATP becomes ADP, causing myosin heads to change angle and become cocked
5. Myosin heads attach to new actin sites and form cross-bridges
6. ADP is released. Myosin heads move actin filaments towards centre, making sarcomere shorter
   
   • ​​called the power stroke
7. ATP binds to myosin causing cross-bridges to break
8. Step 4-7 repeat if calcium is still present
9. Calcium ions are reabsorbed into sarcoplasmic reticulum
10. Muscle fibre relaxes

Question 8

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

Answer 8