Muscles

Question 1

What is the lightest band in striated muscle and what does it contain?

Answer 1

The I band; contains actin only.

Question 2

What is the darkest band and what does it contain?

Answer 2

The overlapping region; contains actin and myosin.

Question 3

What is the medium shaded band and what does it contain?

Answer 3

The H zone/band; contains myosin only.

Question 4

What forms between actin and myosin heads during contraction?

Answer 4

Attachment or cross bridges.

Question 5

What happens during the power stroke?

Answer 5

Myosin heads move and pull actin over myosin.

Question 6

What causes the myosin heads to detach?

Answer 6

ATP binding.

Question 7

What happens to the myosin heads after detachment?

Answer 7

Myosin heads move back to original position (recovery stroke) using energy from ATP.

Question 8

What is the first action of Ca²⁺ ions in muscle contraction?

Answer 8

Bind to/change shape of tropomyosin or remove tropomyosin.

Question 9

What does removing tropomyosin do?

Answer 9

Exposes actin binding sites.

Question 10

What happens after actin binding sites are exposed?

Answer 10

Myosin head attaches and forms cross-bridge.

Question 11

What else do calcium ions activate in muscle contraction?

Answer 11

ATP hydrolase enzyme.

Question 12

What happens when nerve impulses arrive at the presynaptic membrane?

Answer 12

Calcium ions enter the presynaptic membrane.

Question 13

What happens after calcium ions enter the presynaptic membrane?

Answer 13

Vesicles fuse with membrane and release acetylcholine (Ach) by exocytosis.

Question 14

Where does acetylcholine diffuse to?

Answer 14

Across the synaptic cleft to the postsynaptic (muscle) membrane.

Question 15

What happens when acetylcholine binds to receptors on the postsynaptic membrane?

Answer 15

Depolarisation occurs and sodium ions enter.

Question 16

What happens inside the muscle after depolarisation?

Answer 16

Release of calcium ions from within the muscle.

Question 17

What do calcium ions do in the muscle?

Answer 17

Bind to troponin and remove tropomyosin.

Question 18

What happens once actin binding sites are exposed?

Answer 18

Actinomyosin cross-bridge forms as myosin binds.

Question 19

What is the role of the myosin head in contraction?

Answer 19

Moves/pulls actin along via ratchet mechanism (detach and reattach).

Question 20

What does ATP hydrolase do?

Answer 20

Hydrolyses ATP to release energy.

Question 21

How is this energy used?

Answer 21

To form and break actinomyosin cross-bridges.

Question 22

Why is aerobic respiration better for long-distance races?

Answer 22

Releases more energy and produces more ATP.

Question 23

What does aerobic respiration produce less of?

Answer 23

Little or no lactate.

Question 24

Why is less lactate beneficial?

Answer 24

Avoids cramp and muscle fatigue.

Question 25

How is CO₂ removed in aerobic respiration?

Answer 25

Easily removed by breathing.

Question 26

What opens in the presynaptic neurone when stimulated?

Answer 26

Calcium ion channels/gates.

Question 27

What happens when Ca²⁺ ions enter the presynaptic neurone?

Answer 27

Vesicles move and fuse with presynaptic membrane.

Question 28

What is released from the vesicles?

Answer 28

Acetylcholine (transmitter substance) by exocytosis.

Question 29

Where does acetylcholine diffuse?

Answer 29

Across the synaptic cleft/gap.

Question 30

What happens when acetylcholine binds to postsynaptic receptors?

Answer 30

Sodium ion channels open, and Na⁺ ions enter.

Question 31

Why do cross bridges remain firmly bound after death?

Answer 31

Respiration stops and no ATP is produced.

Question 32

Why does the lack of ATP cause cross bridges to stay bound?

Answer 32

ATP is required to separate actin and myosin cross bridges.

Question 33

What do calcium ions do to tropomyosin?

Answer 33

Interact with/move tropomyosin.

Question 34

What is revealed after tropomyosin moves?

Answer 34

Binding sites on actin.

Question 35

What happens at the binding sites?

Answer 35

Myosin heads bind to actin (actinomyosin formed).

Question 36

What enzyme do calcium ions activate?

Answer 36

ATP hydrolase.

Question 37

What is a key feature of slow twitch fibres?

Answer 37

Have lots of mitochondria and respire aerobically.

Question 38

What pigment do slow twitch fibres have more of?

Answer 38

Myoglobin.

Question 39

What are fast twitch fibres used for?

Answer 39

Rapid, brief, powerful contractions.

Question 40

What energy source do they use rapidly during contraction?

Answer 40

Phosphocreatine.

Question 41

Which type of respiration is involved?

Answer 41

Anaerobic respiration.

Question 42

What is phosphocreatine used for after contraction?

Answer 42

To reform ATP.

Question 43

What is a key characteristic of fast twitch fibres regarding phosphocreatine?

Answer 43

Have lots of phosphocreatine.

Question 44

What pigment do fast twitch fibres lack?

Answer 44

No myoglobin.

Question 45

What does phosphocreatine provide?

Answer 45

Energy and phosphate.

Question 46

What does this phosphate do?

Answer 46

Phosphorylates ADP to make ATP.