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Release of Calcium Ions into the Sarcoplasm

The depolarisation of the sarcolemma is spread throughout the muscle fibre by the T-tubules which are in contact with the sarcoplasmic reticulum (SR). The SR actively absorbs calcium ions from the sarcoplasm.Depolarisation of the SR stimulates calcium ion channels to open. Calcium ions diffuse out of the SR and into the sarcoplasm down their concentration gradient. The calcium ions bind to the troponin complex causing it to change shape and expose the myosin binding sites on the actin filaments.

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Specification: AQA Biology (7402), A-level, 3.6.3 Skeletal muscles are stimulated to contract by nerves and act as. Topic: Muscles.

Key terms in this lesson

glycolysis: The first stage of respiration, occurring in the cytoplasm, in which glucose is split into two molecules of pyruvate with a net yield of 2 ATP and reduced NAD.
pyruvate: The three-carbon end product of glycolysis, which enters the mitochondrion for the link reaction in the presence of oxygen or is reduced to lactate or ethanol in its absence.
anaerobic respiration: Respiration that occurs without oxygen, in which pyruvate is reduced to ethanol (in plants and yeast) or lactate (in mammals) to regenerate NAD so that glycolysis can continue.

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