muscles

Question 1

Describe the banding pattern in striated muscle

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

Ca2+ released from sarcoplasmic reticulum into sarcoplasm
ca2+ bind to tropomyosin
changes the 3 structure causing tropomyosin to expose the tropomyosin head binding sites on the actin filament
tropomyosin heads bind to actin binding sites forming cross bridges
tropomyosin head nods pulling the actin filament a short distance
adp and pi are released from myosin head by ATP hydrolase

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 slow twitch muscle fibres

Answer 9

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

Question 10

Describe fast twitch muscle fibres

Answer 10

• 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 11

Describe the role of phosphocreatine

Answer 11

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