3.6.3 Flashcards
What is the neuromuscular junction?
The synapse between a motor neurone and a muscle fibre cell.
What is the key to understanding how a myofibril contracts?
Understanding how a sarcomere contracts.
What remains the same length during contraction and relaxation of a muscle fibre?
Actin and myosin filaments.
What changes during the contraction and relaxation of a muscle fibre?
The pattern of light and dark bands of a sarcomere.
What theory suggests that actin and myosin filaments slide past one another?
The sliding filament theory.
What forms when muscle contracts?
Crossbridges between actin filaments and myosin heads.
What prevents crossbridges from forming when muscle is relaxed?
Tropomyosin covers myosin binding sites on actin molecules.
What role does troponin play in muscle contraction?
Troponin binds to tropomyosin and calcium ions, altering tropomyosin’s position.
What triggers the release of calcium ions in muscle fibres?
A nerve impulse arriving at the synapse.
What happens when calcium ions bind to troponin?
Tropomyosin moves away from the myosin binding site on actin.
What enzyme is located in each myosin head?
ATPase.
What is released when ATP is hydrolyzed during muscle contraction?
ADP and inorganic phosphate (P_i).
What happens to the myosin head when an actinomyosin crossbridge forms?
The myosin head tilts, pulling the actin molecule over the myosin.
What is the result of repeated cycles of forming and releasing actinomyosin crossbridges?
Continued contraction of the muscle.
What is required to actively transport calcium ions into the endoplasmic reticulum?
Energy released from the hydrolysis of ATP.
