Muscles

Question 1

Describe the banding pattern in striated

Answer 1

• Lightest band is I band, actin only
• Darkest band is overlapping region, actin and myosin
• Medium shading is H zone/band is myosin only.

Question 2

Describe the sliding filament theory

Answer 2

• Attachment / cross bridges between actin and myosin heads;
• ‘Power stroke’ / movement of myosin heads / pulling of actin (over myosin);
• Detachment of myosin heads (requires ATP binding);
• (Energy from ATP) Myosin heads move back/to original position / ‘recovery stroke’;

Question 3

Describe the function of calcium ions in muscle contraction.

Answer 3

• Ca2+ Binding/changing shape/removing tropomyosin;
• Exposes actin binding sites;
• Myosin head attaches/cross-bridge formation;
• Activates ATP hydrolase;

Question 4

Nerve impulses arriving at the presynaptic membrane at the neuromuscular junction
result in shortening of sarcomeres. Describe how.

Answer 4

• Entry of calcium ions (presynaptic membrane);
• Vesicles fuse with membrane / exocytosis /release Ach (Acetylcholine);
• Neurotransmitter diffuses;
• Binds to receptors, postsynaptic / membrane / muscle membrane;
• Depolarisation / sodium ions enter;
• Release of calcium ions (from within the muscle);
• Removes tropomyosin / bind to troponin;
• Exposing binding sites on the actin;
• Actinomyosin cross bridge formation / myosin binds;
• Myosin head moves / pulls the actin along;
• Rachet mechanism / description /detach and reattach;
• ATP hydrolase activated;

Question 5

Explain the importance of ATP hydrolase during muscle contraction.

Answer 5

• Hydrolysis of ATP releasing energy;
• used to form / break actinomyosin cross-bridges;

Question 6

Muscle contraction requires ATP. What are the advantages of using aerobic rather than anaerobic respiration to provide ATP in a long-distance race?

Answer 6

• Aerobic respiration releases more energy /produces more ATP;
• Little/no lactate produced / does not accumulate;
• Avoids cramp / muscle fatigue;
• CO2 easily removed from the body / CO2 removed by breathing;

Question 7

A muscle fibre contracts when it is stimulated by a motor neurone. Describe how transmission occurs across the synapse between a motor neurone and a muscle fibre.

Answer 7

• Ca2+ channels / gates open;
• Ca2+ ions enter (pre-synaptic neurone);
• Vesicles move towards / fuse with presynaptic membrane;
• Release / exocytosis of transmitter substance / of acetylcholine;
• Diffusion (of transmitter) across gap / cleft;
• (Transmitter) binds to receptors in postsynaptic membrane;
• Na+ channels open / Na+ ions enter (postsynaptic side)

Question 8

After death, cross bridges between actin and myosin remain firmly bound resulting in rigor mortis. Explain what causes the cross bridges to remain firmly bound.

Answer 8

• respiration stops;
• no ATP produced;
• ATP required for separation of actin and myosin/cross bridges

Question 9

Describe the role of calcium ions in the contraction of a sarcomere.

Answer 9

• interact with/move/touch tropomyosin; (allow troponin as alternative)
• to reveal binding sites on actin; (not active sites)
• allowing myosin (heads) to bind/touch actin / actinomyosin formed;
• activate ATP hydrolase / energy released from ATP;

Question 10

Describe slow twitch muscle fibres

Answer 10

• have lots of mitochondria/ (slow fibres) respire aerobically;
• More myoglobin

Question 11

Describe fast twitch muscle fibres

Answer 11

• used for rapid/brief/powerful/strong contractions;
• Phosphocreatine used up rapidly during contraction/to make ATP;
• Anaerobic respiration involved;
• ATP used to reform phosphocreatine;
• Lots of phosphocreatine in fast twitch fibres;
• No myoglobin

Question 12

Describe the role of phosphocreatine

Answer 12

• Provides (energy and) phosphate / phosphorylates;
• To make ATP from ADP & Pi;