Question Video: Describing the Primary Role of Calcium Ions in Muscle Contraction | Nagwa Question Video: Describing the Primary Role of Calcium Ions in Muscle Contraction | Nagwa

Question Video: Describing the Primary Role of Calcium Ions in Muscle Contraction Biology • Third Year of Secondary School

In the sliding filament theory of muscle contraction, what is the primary role of calcium ions?

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Video Transcript

In the sliding filament theory of muscle contraction, what is the primary role of calcium ions?

To answer this question, we need to learn some more information about the sliding filament theory of muscle contraction and the role of calcium ions in this process.

When a muscle fiber is relaxed, a protein filament called tropomyosin, shown here in blue, coils around a thin protein filament called actin, shown here in orange. Tropomyosin blocks sections of the actin filament that contain binding sites for the globular heads of another protein filament called myosin, shown here in pink.

When the muscle fiber is stimulated by an electrical impulse from a neuron, calcium ions are released from a specialized organelle in the muscle fiber called the sarcoplasmic reticulum. These calcium ions bind to tropomyosin, changing its shape. This moves tropomyosin away from the myosin binding sites on the actin filament, exposing them. The movement of tropomyosin away from the myosin binding sites allows the myosin heads to temporarily bind to the actin filament, which will eventually result in contraction of the muscle fiber.

Now we know the correct answer to this question. The primary role of calcium ions in the sliding filament theory is to bind to tropomyosin, changing its shape and moving it away from myosin binding sites.

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