Why must skeletal muscles work in antagonistic pairs to move a joint?
Muscles can only contract.
One muscle contracts to pull the bone while the opposing muscle relaxes; the reverse movement requires the opposite muscle to contract.
What type of tissue forms the rigid framework that muscles pull against during movement?
Incompressible skeleton
Bones do not change shape when muscles contract, allowing force to be transmitted effectively.
What is the name of the long cylindrical muscle cell that contains many nuclei and myofibrils?
Muscle fibre
Skeletal muscle fibres are formed by fusion of myoblasts, giving them multiple nuclei.
What structure within a muscle fibre is composed of repeating contractile units arranged end-to-end?
Myofibril
Myofibrils contain repeating sarcomeres responsible for muscle contraction.
What protein forms the thin filaments in skeletal muscle that interact with myosin during contraction?
Actin
Actin filaments slide past myosin filaments during the sliding filament mechanism.
What protein forms the thick filaments whose heads bind to actin to generate force?
Myosin
Myosin heads form temporary cross-bridges with actin during contraction.
Fill in the blank:
During contraction, actin filaments slide over ______ filaments, shortening the sarcomere.
myosin
The filaments themselves do not shorten; instead they slide past each other.
Which ion released from the sarcoplasmic reticulum triggers the start of muscle contraction?
Calcium ions
Ca²⁺ binds to regulatory proteins, allowing myosin heads to attach to actin.
Which molecule directly provides the energy required for myosin heads to detach and re-cock during contraction?
ATP
ATP hydrolysis provides the energy for the power stroke cycle.
What high-energy molecule in muscle cells can rapidly regenerate ATP during short bursts of intense activity?
Phosphocreatine
Phosphocreatine transfers a phosphate group to ADP to quickly reform ATP.
True or False:
Tropomyosin normally blocks the binding sites on actin when a muscle is relaxed.
True
When calcium ions are released, tropomyosin moves away to expose the binding sites.
True or False:
Fast skeletal muscle fibres contract slowly but resist fatigue for long periods.
False
Fast fibres contract quickly and powerfully but fatigue more rapidly than slow fibres.
Which type of skeletal muscle fibre is adapted for endurance activities such as long-distance running?
Slow-twitch fibres
These fibres have many mitochondria, a rich blood supply and rely mainly on aerobic respiration.
Which type of skeletal muscle fibre is specialised for rapid, powerful contractions such as sprinting?
Fast-twitch fibres
These fibres generate high force quickly but fatigue relatively rapidly.
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