1.

In skeletal muscle A. Contraction occurs when its pacemaker cells depolarize sufficiently to reach the threshold for firing. B. Calcium is taken up by the sarcotubular system when it contracts. C. Actin and myosin filaments shorten when it contracts. D. The sarcomeres shorten during contraction. E. Contraction strength is related to initial length of the muscle fibres.

Answer»

A. False Skeletal muscle has no pacemaker cells and shows no spontaneous activity. 

B. False Calcium is released from intracellular stores when it contracts. 

C. False The filaments do not shorten but slide together over one another. 

D. True There is greater overlap of the actin and myosin fibrils. 

E. True Moderate stretch increases contraction strength as in the heart.



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