Muscles and movement

Question 1

What does ‘antagonistic pair of muscles’ mean?

Answer 1

• Muscles work in pairs of flexors and extensors
• The agonist contracts whilst the antagonist is relaxed

Question 2

What are the structures of ligaments and tendons?

Answer 2

• Ligament joins bone to bones
• Tendons join muscle to bone

Question 3

Describe the structure of the skeletal muscle

Answer 3

• Muscle cells are fused together to form bundles of parallel muscle fibres called myofibrils
• Myofibrils are made up of contractile proteins (actin and myosin)

Question 4

Describe the structure of the cell membrane in a muscle fibre

Answer 4

• Cell membrane is called the sarcolemma
• Bits of the sarcolemma folds inwards and stick into the sarcoplasm forming T tubules (they spread electrical impulses)

Question 5

What is function of the sarcoplasmic reticulum?

Answer 5

• Store and release calcium ions needed for muscle contraction

Question 6

What does Z, A, M, I, H band signify in a myofibril?

Answer 6

Z band= boundary between sarcomeres
A band= where myosin and actin overlaps
M band= attachment for myosin
I band= only actin present
H band= only myosin present

Question 7

Explain the role of Ca2+ ions in muscle contraction

Answer 7

1. Action potential moves through T-tubules in the sarcoplasm and Ca2+ channels in sarcoplasmic reticulum opens
2. Ca2+ binds to troponin triggering a change in shape and position of tropomyosin
3. This exposes binding site on actin filaments so cross-bridges can form

Question 8

Outline the ‘sliding filament theory’

Answer 8

1. Myosin head and ADP + Pi binds to the exposed binding sites forming cross-bridges connecting the two filaments
2. As the myosin head ‘nods’ its head changes shape and it loses ADP, pulling actin over myosin
3. ATP attaches to myosin head causing it to detach from actin
4. ATPase hydrolyses ATP to ADP + Pi so the myosin head can return to to its original position

Question 9

How does sliding filament action cause a myofibril to shorten?

Answer 9

• Actin filaments are pulled towards each other therefore the distance between adjacent sarcomeres shorten

Question 10

What happens during muscle relaxation?

Answer 10

1. Ca2+ is actively transported back into the sarcoplasmic reticulum
2. Tropomyosin once again blocks actin binding site

Question 11

What is the fixed joint and what is an example of it?

Answer 11

• Joints that allow little or no movement
• Pelvis/skull

Question 12

What is the pivot joint and what is an example of it?

Answer 12

• One bone rotates in a ring of a bone that doesn’t move
• Neck/forearm

Question 13

What is the ball and socket joint and what is an example of it?

Answer 13

• A rounded end that fits into a cuplike cavity
• Shoulder/hips

Question 14

What is the hinge joint and what is an example of it?

Answer 14

• Back and forth like motions
• Elbows/knees

Question 15

What is the gliding joint and what is an example of it?

Answer 15

• One part of the bone slides over the other
• Ankle/spine

Question 16

What are fast-twitch fibres?

Answer 16

• The myosin head bind and unbind from the binding site 5 times faster than slow-twitch fibres
• The rapid contraction-relaxation means they need large amount of Ca2+

Question 17

What do fast-twitch fibres rely on?

Answer 17

• Anaerobic respiration for ATP supply
• Suited to short bursts of high intensive activity

Question 18

What is the structure of fast-twitch fibres?

Answer 18

• Fewer capillaries
• Low amounts of myoglobin are present

Question 19

What are slow-twitch fibres?

Answer 19

• Contract more slowly for sustained activities and rely on aerobic respiration

Question 20

What is the structure of slow-twitch fibres?

Answer 20

• Denser network of capillaries
• High amounts of myoglobin, mitchondria and haemoglobin