Question

the cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. what is a cross bridge?
atp bound to a myosin head
a myosin head bound to actin
troponin bound to tropomyosin
calcium bound to troponin

Explanation:

In muscle contraction, a cross - bridge is formed when a myosin head binds to actin. This binding is a key step in the cross - bridge cycle that leads to muscle contraction. ATP bound to myosin head is in a different state of the cycle before binding to actin. Troponin - tropomyosin interaction and calcium - troponin binding are regulatory steps related to cross - bridge formation but not the definition of a cross - bridge itself.

Answer:

A myosin head bound to actin