Question

what are cross - bridges?
connections between the myosin heads and the actin filaments.
the connections between the actin filaments and the m - line.
the connections between the troponin and tropomyosin.
the connections between the myosin tails and the z - discs.
the connections between the actin filaments and the z - discs.

Explanation:

In muscle contraction, cross - bridges are formed when myosin heads bind to actin filaments. This interaction is crucial for the sliding filament theory of muscle contraction.

Answer:

Connections between the myosin heads and the actin filaments.